4>, upward lalillching: Sliding starts on the bearings when the inclinar.ion of the reaction R with respect to the vertical is:
a II
(r
+
p)V
2. II
H
Vtan(e~cf»
. For small values of the angles: H=(r
p)V
Because p varies with environmental condi tions (cleanness of the plates in particular), the launching equipment and the pier will be de sjgned for H = rV. The downward movement of the bridge is controlled by a restraining jacking force:
(h)
FIGURE 7.69. Reactions on piers during launching. upward launching. (b) downward launching.
(a)
F = N(tan ()
tan 4»
or F
N(r - p)
For the same reasons as above. the safe value of F is equal to Sr. 3. I} < 4>, upward launching: As above, the hori zontalload applied to the pier is: I-I
(r
+
p)V
4. 8 < 4>, downward launchiug: In this case the horizontal load on the pier is applied in the di rection of the movement with a value of: H=(r-p)V
Because of the possible variation in the angle of friction, it is safer to provide a braking sys tem to control the movement of the bridge. Pier Cap Detailing The pier caps must be care fully detailed in order to provide room for the fol lowing devices:
Temporary sliding bearings Vertical jacks to lift the bridge after launching to install the permanent bearings Horizontal guiding devices during launching
352
Incrementally Launched Bridges
Adjusting jacks for correction of the relative dis placements bel\~) piers and deck /
Moreover, to {educe the pier bending moments induced by launching, the sliding bearings are often eccentric. However, it is possible to reduce or balance this horizontal force b\ installing ties an chored in the ground. If the piers are verv high, the horizontal force can be eliminated bv using jacking equipment directh' installed on the piers.
Demolition of a Structure by Incremental Launching
7.10
\\'e close this chapter with an unusual application showing the interesting potential of incremental lallnching. An overpass structure over the A-I !l1otorwa\' non h o/' Paris needed to he demolished {()I' replacement by another structure as part of a highway relocation program. The limited head room hetween the existing bridge soffit and the clearance diagram. IOget her with the considerable Iraflic on 1he major I1lOlOrw<\v providing pcrrna nenl access from Paris to Charles de Gaulle Air port, made all conventional methods of demolition extremely diITicult and unadapted. A very simple scheme was devised whereby the deck was launched awa\, from the traffic onto the approach embankment to be conventionallv de molished at leisure. The dimensions of the bridge
-
LAUHQlING
--
and the principle of the method are shown in Fig ure 7.70. The 900-ton st.ruct.ure had a width of 26 ft and the following spans: 46, 46 ft. The existing reinforcing did not provide th'e nec essary strength to resist superstructure dead load during launching. Therefore, a rear launching-out tail 26 ft long was installed at the end opposite the direction of launching, while exterior post-ten sioning tendons were placed above the deck \0 strengthen the structure. The bridge was lifted off its hearings 7 in. to in stall sliding bearings and lateral guiding devices in preparation for the operation. The whole opera tion was performed in weeks as fol\ows: Design and preparation of the contract Mobilization and purchase of equipment Launching
References I. \",'illi Baur, "Bridge Erection b\ Launching b Fast, Safe, and Efhcienr," Cillit ElIgilll'l'1'illg-ASCE, Vol. 47, :\0. 3, ;"1arch 19i7
REAR NOSE {TAil
--- --
II
_-+ . . . . . -'4'-"6~'_ _+-
LATERAl. ;UIDE5
900 t
TOTAL W£lGIlT
PROCEDURE
2}
lI!'T
TOTAL BRIO(O[
PLACE ROLL~RS
SCHEDULE
7~
0\1"'1 PIERS
_ DESIGN
_ Moe.
3)
IN$,ALL
APPROACI4
CONCRE,E
4)
!'ILL AND
8,
TOTAL
51('2 WEEKS
CONTRACT:
'2
2
PURCHASES
_ LAUNCHING
BEAM~
PLACt[ PROVI510.. Al..
A REAR .. ost:
'26
FT.
PIT
,RAFFIC IN,f:RRUP'TlOH : AND
(10
P.M. TO
LONQ
FIGURE 7.70,
g
Traffic was interrupted for onl\' fOllr nights be tween 101'.\1. and 6 ."o.:V1. The operation turned out to he a complete success in ~pitc of its originality.
+-----'4""b"-'---+-t _ _"",55"-'_ _-+__-""5,,,,,5_'
1/
2 2
Bridge over A-I, launching out.
6
,...M.)
4
1,i!(OI-!.'T!I
353
References 2. Anon., "First I ncrementally Launched Post-Ten sioned Box Girder Bridge to Be Built in the enited States," Bridge Report, ifec;;mb~r 1976, Post-Ten sioning Illstitute, Phoenix, Ariz. 3. Arvid Grant, "Incremental Launching of Concrete Structures," Journal oj thl' A //Iaican COllcrl'te Institute, Vol. 72, :'\0.8, August 1975. .t. Anon., "Val Restel Viaduct for the Provincial Road :'\0. 89 :-.lear Rovereto, Trenro," Pre.I'/rl'ssf'd Concrele Structures ill Italy 1970/197.J., ;\ssociazione Italian
5. Anoll., "Segmental Box Girder Bridges \fake the Hig Time in C.S.," Engiuntiflg Sl'w\-Rurml, \larch 2, 197H.
6. Anon., "Wabash River Bridge, Covington, Indiana," Portland Cement Association, Bridge Report, SR201.01E, 1978, Skokie, Ill. 7. M. Maddison, "Crossing the Cutting willl Segmenrs ar Sonning," Concrele, The Journal of Ihe Comrl'te S()cil'ly (London), Vol. 12, :'\0. 2, Februarv 197H. 8. K. H. Best, R. H. Kingston, and \1. J. Whatley, "lll cremental Launching at Shepherds House Bridge," Proceeding-r, Insiliululli oj Civil Ellg/llnn, Vol. ()4, Part I, February 1978.
8
ConcTete Segmental Arches,
Rigid FTatnes, and l~russ BTidges
8.1 8 ')
8.3 8.4
8.5
INTRODUCTION SEGMENTAL PRECAST BRIDGES OVER THE
MARNE RIVER, FRANCE
CARACAS VIADUCTS, VENEZUELA GLADESVILLE BRIDGE, AUSTRALIA ARCHES BUILT IN CANTILEVER 8.5.1 Review of Concept~ Summary of Structures with Temporary Stays 8.5.2 Neckarburg Bridge, Germany 8.5.3 Niesenbach Bridge, Austria 8.5.4 Kirk Bridges, Yugoslavia
8.1
Introduction
All arch hridge, in a pnlpcr setting, is an eleganl and graccful structurc with acsthetic appcal. IIl ... tiJl(tin.-h', a lannan relales to all arch hridge as a forlll Ihat follows ils function. Long before pre sl ressed concrete was devcloped as a tech Ilolog\', COlHTcte arches were lIsed for long spans, taking advantage of the compressivc stress induced bv gravitatiollal forces into a ctIned member Illuch as earlicr gClJcrations of huilders had done with Ill;tSOlJn' arches. Three bridges designed and built ·bv Eugene Fre\'ssinel het ween 1907 aml 19 lOin central Frallce were 10 become a major landmark in the dc\'cloplllcI1I of concrele struci ures. I n the Veur
8.6
RIGID·FRAME BRIDGES
8.7
8.6.1 Saint Michel Bridge in Toulouse. France 8.6.2 Briesle Maas Bridge. Netherlands 8.6.3 Bonhomme Bridge, France 8.6.4 Motorway Overpasses in the Middle East TRuSS BRIDGES 8.7.1 Retrospect on Concepts for Concrete Truss Bridges 8.7.2 MangfalJ Bridge, Austria 8.7.3 Rip Bridge, Australia 8.7.4 Concept for a Cro~sing of the English Channel REFERENCES
,JI(I,I a Iriu'lIIjlh. Oil Ihl' riKlil b(III1i, (I hill {)lwrlou/iIlIK lli(' hridK(' ,lilt was ottlljlir't/ liv Sf'l'f·ral
Load If,llillK
Ihow(JJu/ stH·r/alon 11,110 had lalil'lI (ht'lr plate alrNu'.)' al dawlI 10 11'{1Ith llif' failurl' o/the liridW' !,ret/ictcd Ii) (J lowl //f'Uls/m/H" ,101d 10 sOllie /II/haN))' (olll/H·lilor. Thesl' hopI'S WIT!' d(,(l'iZ'nl, (!lui wc Iwd a COli Ii IIUOU5 Iml!' of
/iNn'v ,,[mill rolln,l tra;'diIlK till' bridK(' bark and Jorth quilf ullabl!' 10 prodllte (/l)vlhillK //lure tho II Ilu· rompuled {'{wi" rlff/I'(lio/l.1.
Belweell 1907 and 1911, howe\'er. fears de veloped in Frevssinel's mind. II seemed thai the hand rails, which had been properly aligned al the lime of Ihe load lest, were showing some convexity IOwaI'd Ihe sky £II the Ilodes of Ihe crown hinges. By the spring of 1911 the crown had moved down ward as much as 5 in. (0.13 m), and corre spondingly the springings had raised appreciably. Without telling an~'one, Freyssinet mobilized a team of four devoted men and placed hydraulic rams at the arch crowllS to raise the bridge spans to their original profile; he then replaced the hinge by a rigid concrete connection between the two abutting half-arches. This near-disaster was the
Introduction
- -
--- - FIGURE 8.1.
first consefluence seen in a 'itructure of a phenom enon t heretofore com pletel v ignored: long-term concrete creep. Other beautiful concrete arches were also con structed in the same period. The Villeneuve Bridge over the Lot River in southwestern France, Figure H.2, is an interesting example. The twin arch ribs are of plain concrete with a clear span of 316 ft (96 m) and a rise of 47 ft 4 in. (14.5 Ill). Each rib has a solid sectioll 10ft m) wide ~Ind 4 ft 9 ill. (1.45 m) deep built in at both ellds illto the con crete abutments. The reinforced concrete deck rests upon the arch ribs through a series of thin spalldrel columns, faced with red brick. Construction began shortlv before World War I and was interrupted for four year'i, fortunately not before the concrete arch ribs could be GIst on a wooden falsework, Figure H.3. Inllllediateh' upon completion, hydraulic rams were used at the midspan section to lift the concrete arches off the Ldsework and acti\'ely create the compressive stress in them, a techniqlle from Fre\ssillet's fertile mind that already contained the germ of the idea of pre stressing.
ct
FIGURE 8.2.
355
Villeneuve Bridge m'er the Lot River.
\'curdlc Bridgc. The bridge was completed in 1919 and kept the world's record for long-span concrete .'itructllre.'i for several years. The photograph appearing in Figure 8.2 was taken bv olle of the authors in the summer of 1980; it shows that beautiful structure in a rell1arkable state after sixty vears of contillu ous operation under constallt urban traffic. Another Freyssinet design, the TOlllleills Bridge over the Garonne Ri\'er, was built at the sallle time, ~\I1d he considered it to be one of his nicest bridge structures, Figure 8.4. The Plougastel Bridge in Brittal1\, Figure I.:~8, reached for longer spans with concrete arches. For t he first time a box section was emploved, calling on an ingenious method of construction in which ,I wooden falsework was floated into position and re used se\Tral tillles for the \'arious arch ribs. Di mensions of the structure and t\'pical details of the arches are shown in Figure 8.5, which is a bcsilllile of a document published in 1930. The three arches ha\'e a span length 01611 ft (186.40 m) and GIlTV a single-track railroad ;lI1d a two-lane highwa\'. The reinforced concrete trussed double deck ,ICcoIllIllodates the train track Oil its lower level and the highway on the upper. ;\Tear the arch crown in each span, the train passes through the arch rib. The arch ribs were onlv slightlv reinforced and the quantity of steel was 39 Ib/\'d:l (2:~ kg/Ill:I), in spite of the relati\'ely thin walls used for the box section. The three arch ribs were constructed one after the other on a temporary wooden arch built on shore and Aoated into position for each of the three concrete arches, Figures 8.6 and 8.7. This wooden arch was 490 ft (ISO \11) long and weighed 550 tons (500 mtl, including the two reinforced concrete end sections, which allowed the thrust created by the concrete arch ribs to be transferred
1.>0
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CIVIL
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Fin,1
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ail::;
Fin·:\
Fill, 2. Dem.] cli:val.Jon
. \ Il
ell
flfj
Filr·~j rhl
.1.
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clef
FIGURE 8.3.
ViIlCIlClI\'L'
Tdrtiel1p
rill
tablw['
Segmental Precast Bridges Over the Marne River, France
FIGURE 8.4. Tonneins Bridge over the Garonne River, France.
to the arch spnl1gll1gs completed earlier on the foundation caissons. Two barges and a temporarv steel tie slightlv above the water level, with the help of the large tidal range, allowed the tral!sfer of this faisework from the construction area to the three positions of use and its final return after completion of the con crete structure. As this outstanding ulldertaking neared COIII pletion in 1930 after live veal'S of uninterrupted effort, Frevssinet expressed his thoughts as fol lows: In B riitan.v light is lihe a fail)' who cunsta Iltf.y plays at
cOl'aillg nature with [many! changing coats, now of Ifad, nuw ofsifl'l'T or o//Jear/s, or of something immllte . rial and radiant. Toward the fe'ming 0/ the load testing of lhe bridge. she had spread her most sumptuous treasures on the roadstead and each line 11' lhe work, changl'd into a lung rosary unreal light, added another tOl/ch of beaut)' to till' mar vellous whole, proving in this way tltat the Fair.v of the Roadstead had already adopted the child that men had im/J()sed Oil her and had known how to weave for him garments magnijiant enough to hide all the imperji'ctiolls of the worh.
8.2
Segmental Precast Bridges over the Marne River, France
Located some 30 miles (50 km) east of Paris, the Luzancy Bridge represents probably the first ap plication of truly segmental construction as we
357
know it today. It incorporated so many innovations in a single structure that it would not be out of place in today's modern bridge technology. The single-span structure, Figure 8.8, is a double-hinged arch with a distance between hinges of 180 ft (55 m) and a very tight clearance diagram for river navigation that allowed only 4 ft 3 in. (1.30 m) below the finished grade of the roadway. Consequently, not only is the bridge structure very shallow, 4.16 ft (1.27 m), at midspan, but the rise to-span ratio of the arch is unusual: 1123. The bridge consists of three parallel box sections made up of pre~ast segments 8 ft (2.44 m) long, con nected after placement in the structure by precast slab sections at both top and bottom Hanges, Figure 8.9. The bridge is prestressed in three directions: The 4 in. (0.10 m) webs are vertically prestressed resist shear.
to
The longitudinal box girders are then prestressed to connect the precast segments and resist bending. The negative-moment prestressing tendons at the top flange level over the arch springings are lo cated in grooves provided at the top surface of the precast segment upper flange and are ultimateh embedded in a 2 in. (50 mm) concrete topping. This dense, high-quality concrete pavement pro vides the sole protection for the high-tensile steel wires and also sen'es as the sole roadway wearing course. In spite of the excellent behavior of this structure after more than 34 years of operation, it would probably be difficult to envisage duplicating it todav. Transverse cOllllection between the box girders and the connecting slabs is achieved by prestress Ing.
There was no cOllventional reinforcing steel in the bridge superstructure except in local areas. such as the Freyssinet concrete hinges at the arch springings. The erection was just as remarkable as the conception of the bridge. Each box girder con sisted of 22 segments, which were cast in a central yard at the rate of one a dav (little progress has been achieved after thirty years). Afterward thev were carefully aligned on concrete blocks to take the profile of the finished structure with proper provision for camber. The tin. (20 mm) wide joints were dry packed to allow segment assembly by pre stressing. In fact, the 22 segments of each box girder were assembled at this stage in three units: two side units made up of three segments each. and the center unit incorporating the remaining 16
<:;0
CJl 00
LE GENIE CIVIL
ONT
,EN
ETO
AETvlE, SUR
EL ORN, PRES DE PL 0
GAS
'ad.. tUl M¥I
"'I'r'M,/In"IN/iV!
~;(T.,t:"--
.FIGURE 8.5. Plougastcl Bridge. dimensiolls of the st rurt II Ie alld details or the arches. a facsilllile of a docllmcllt puhli~h('d ill I!1:30.
L (
NIS
)
Segmental Precast Bridges Over the Marne River, France
FIGURE 8.7. FIGURE 8.6.
359
Plougastel Bridge, wooden falsework.
Plougastel Bridge, wooden falsework.
segments with a length of 170 it (52 rn) and a maximum weight of 134 tons (122 mt). All three units were assembled on the bridge centerline im mediately behind one abutment, while the delta shaped sections representing the arch springings were GIst ill place over the abutment in their final location in the structure. A special aerial cableway made up of two steel towers resting on both batiks and properly an chored to the rear, a svstem of suspended winches,
ane! a unique elliptical drum aHowed the transfer of the precast girder units from their assembly po-
.j
, ~.:1,~.j".J
,
FIGURE 8.8.
LuzaIlCV Bridge.
foulre median/] - Dem! coupe dans (axe
Oemt· coupe
a /a
FIGURE 8.9.
eM
Dem!· coupe
a 211 "'00
de la eli
Luzancy Bridge, concrete dimensions.
360
Concrete Segmental Arches, Rigid Frames, and Truss Bridges
51110n on the banks to their final location in ~< structure. In spite of a seemingly involved concept, the operations were carried out safely and rapidly; a center beam was placed in only eight hours and a complete arch including all preparatory and finishing operations was assembled in 120 hours, Figure 8.] O. Another interesting feature of this structure was the incorporation at both arch springings of Freys sinet fiat jacks and reinforced concrete wedges between the arch inclined legs and the abutment sills, to adjust and control the arch thrust and the bending moments at midspan. FIGURE 8.12. One of the five Marne River Bridges: 'The bridge was opened to traffic in May 1946 Esbly, Anet, Changis. Trilbardou, and lJssv. after successfullY proving its structural adequacy Figure 8.12, at the following locations: Esblv, Anet, through a comprehensive series of static and Changis, Trilbardou, and Ussy. All five bridges d\namic load tests, following a custom still in use have the geometric dimensions shown in Figure today in several European countries. Figure 8.11 8.13: gives a view of the finished structure. This first precast segmental arch bridge was fol Distance between hinges: 243 it (74 m)
lowed a few years later bv a series of five other Rise of the central axis at the crown over the abut
structures, all of the same type and in the same ment hinge: 16.3 ft (4.96 m)
geographical area, the valley of the Yfarne River, Depth at crown: 2.82 ft (0.86 111) Deck width: 27.5 ft (8.40 m) The deck structure is made up of six precast gir ders, each consisting of: Two precast spnngmgs
delta-shaped
sections
at
the
Thirty-two precast' segments 6.8 ft (2.07 111) long and weighing from 2 to 4.2 tom (1,8 to 3.8 mI).
FIGURE 8.10.
Luzanc" Bridge, erection of central
section.
FIGURE 8.ll.
rise.
Luzaney Bridge, view showing flat arch
The same design and construction principles used at the Luzancy Bridge were repeated for this series of five bridges, except for some improve ments commensurate to the experience gained from the first structure and taking into account the importance of the project. Precasting of the 960 segments was achieved in a factory completely en closed and using the most modern concrete man ufacturing techniques of that period. Each segment was fabricated in two stages in heavy steel forms. Top and bottom flanges were cast first, with high-strength steel stirrups em bedded in both units. After strength was achieved, a set of steel forms equipped with jacks was placed between the flanges, which were jacked apart to stress the web pretensioned stirrups. Then the web was cast between the flanges. There was no need for any conventional reinforcing steel in the pre cast segments. The concrete was vibrated with high-frequency external vibrators, then compressed for maximum
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361
362
Concrete Segmental Arches, Rigid Frames, and Truss Bridges
compaction and steam cured for a fast reuse of the forms. The equivalent 28-day cylinder strength was in excess of 6500 psi. l\:ear the precast factory, an assembly yard al lowed the segments to be carefully aligned and as sembled by temporary prestressing into sections, which were transferred into barges to be floated to the various bridge sites. Each longitudinal girder was thus made up of six sections:
The two delta springing sections Two illtermediate five-segment sections Two center ten-segment senions Halldling or these various sections was perforl1led In the Llizalln cahle-way properl\' rearranged for the purpose. The stahility oj the side scctiol!s, at both ends, was ohtaillcd 1)\ temporan' calltilcHT cables
The qu,llltities of malerials for the superslI'uc ture were ven low, considering the span length alld the slenderlless or the stnlcture:
FIGURE 8.15.
Marne River Bridges. ereclioll of cell
tral se('lioll.
Precast ronCl-ete: :lS:I y<1'I (2iO m:') Reinforcillg' steel: 13.2 tOllS (12 ml) Prestressing steel: 13.2 tOllS (12 mt) For a deck area of 6540 it 2, the quantities per square foot were:
FIGURE 8.16. t ral sen ion .
\larne Ri\'er Bridges, erection of C(,I1
Precast concrete: 1.46 ft 31ft 2 Reinforcing steel: 4.0 Ib/ft 2 Prestressing steel: 4.0 Ib/ft 2
FIGURE 8.14. Ii 011.
1\larne River Bridges, erened end sec
As in the Luzancy Bridge, the high-density con crete placed over the exposed longitudinal pre stressing tendons was also used for the roadway
Caracas Viaducts, Venezuela
\larne Ri\'er Bridges, cOllJpleted struc
FIGURE 8.17. ture.
we;lrillg course. The behavior of these bridges has been excellent for thirty years,
8.3
Caracas Viaducts, Venezuela
In Venezuela in 1952 a highway was being con structed between Caracas and La GlIaira airport. Alignmem of' this highwav necessitated crossing a gorge at thrt'e locatiolls :vith relativel\ large bridges. These structures were designed and con structed LInder the direction or Eugene Frevssinet. I ,·\lthollgh the three bridges aI'e similar in ap pearance, Figures 8.18 and 8,19, thev vary In
FIGURE 8.18.
Caracas Viadtlcts, Bridge I. TABLE 8.1.
Bridge
363
Caracas Viaducts. Bridg('s '2 and :1.
length as shown in Table 8.1. ~ Preliminary investi gations indicated that adequate soillllaterial would probably be found irregularly at great depths. Construction of abutments to resist large bending moments under these conditiolls would be difficult if not impossible. The decision was therefore lIlade that the abutments would resist olllv the centered thrust or the arches alld that the hending moments applied to the abutment would be reduced, as far as practical, to zero. This required that hinges be located as Ileal' as possible to the points of origin of the ;ll\:hes. Because of consideration of long-term creep deformation Oil bllckling of tlte arch and possible conscq lIences of abut llIent displacemcnt as might be caused bv an earthquake, the decision was made to eliminate a crown hinge, thlls result ing ill t\,'O hinged arches,' Although rhe bridges v
Caracas Viaduct Arches
Total Length
Hciuht lrom Bed "of Gorge
10 U It C)08.0 111) IBO It (25:~ m) 700 ft (2I3 ...t m)
230 It (70.1 Ill) 2..t0 It (73.2 lll) 170 It (51.0 tIl)
\lain Span 190 It (151.H Ill) 4:70 ft (14:5.7 111) 4;"):3 It (131:\.1 Ill)
364
Concrete Segmental Arches, Rigid Frames, and Truss Bridges
",
I , Piers of the access \ltaduct. hIOged a! the h:(l!
Caracas S.1e
FIGURE 8.20. Caracas Viaducts, cleYUlioll of Bridge 1, from reference 1 (courtesv of Ciyil Enginecring-ASCE). An elevation of Bridge 1, Figure 8,20, shows the principal dimensions and foundations of the arch. The three hridges have identical cross sections, Figure 8.2l. The poured-in-place concrete deck topping varies in thickness from 2 in. (50 mm) at the edges to in. (190 mm) at the center to pro \'ide a trallsverse slope of l.57c for drainage. Each deck span, except at the crown, consists of eight precast prestressed I girders. Variations in span lengt h of the deck girders are accommodated by adding or rcmoving standard form units. 1dentical transvcrsely prestressed precast stay-in-place deck slahs span transversely between the deck girders. Continuity of the deck girders is accomplished by longitudinal tendons placed in a groove in the top of the top flange of the girders. 2 Approach piers alld spandrel columns over the arches consist of three I-shaped columns of a standard cross section shown in Figure 8.21. A five-segment precast cap beam on the columIls re
ceives the eight deck I girders. A perspective of the deck over the piers is shown in Figure 8,22. The precast deck girders, cap beams, and slab are sup ported on the cast-in-place piers, and the whole as sembly is prestressed vertically, transversely, aI1d longitudinally. The center span consists of three parallel double-hinged arch ribs 27 ft 6 in, (8,4 m) on center, Figure 8,21. Each arch rib is a box with a width of 10 ft 6 in. (3.2 m) and a slightly varying depth fmm 9 ft 6 in, (2,9 m) to lOft (3,05 m) at the supporting points of the deck. To provide in creased capacity to resist end moments developed by horizontal loads, the width of the ribs is in creased to 17 ft (5.18 m) at the spring lines. The 5 in. by 5 in. (127 mn) x 127 mm) fillets provided at each inside corner of the box are to reduce the concentration of torsion stresses. Thickness of the bottom flange of the box rib was kept to a minimum to reduce weight on the falsework. The
~ standard cross section through arch
:"1",
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~>o'~ i I ~"t,~ * - - 1 0 ' 6 11 - - ,
Cross section of pier A-A
FIGURE 8.21. Caracas Viaducts, typical cross section, from reference 1 (courtesy of Civil Engineering-ASCE).
Caracas Viaducts, Venezuela
365
FIGURE 8.22. Caracas Viaducts. perspective of deck over piers, from reference 1 (courtesy of Civil Engineering-ASCE).
thicker top flange provides the box rib with the re quired area and moment of inertia for resisting t hrllst and live-load llIoments. Design of these structures considered a design wind pressure of 50 psf (2.4 k~/m~). The arch ribs carry part of the wind pressure to which they are directly subjected: the remainder is transmitted to the deck structure bv bending of the spandrel col umns and the connection of the arch rib to the deck at the crown. The arches were assumed to be transverselv fixed in the foundations, the end mo ment developed in the springings resulting in a slight transverse displacement of the pressure line.~
Thus, the deck structure was chosen as the prin cipal member to resist wind loads, requiring the exclusion of all Joints in the deck from abutment to abutment. The condition of deck continuitv leel to the attachment of the deck to the arch on both sides of the arch crown. This was aCCO!1l plished by prestressing the continuous cables provided over the top flange of the girders and anchoring them into the arch. Six girders were connected to the arch in this manner; the two intermediate girders that 'do not rest directly on the arch were lengthened to the crown, Figure 8.21. 2 During construction, an open joint was provided at the crown. In this joint Freyssinet Hat jacks staggered with concrete wedges were inserted, acting as a hinge for the arches to adjust the pres sure line during different phases of construction. Expansion and contraction of the deck due to temperature, creep. and shrinkage take place over
an approximate length of IDOO ft (305 m), de~ veloping approximatelv symmetrically on both sides of the arch crown. Free movement 0[' the deck structure over the pilasters was accommo dated bv providing two concrete rockers over each transverse wall of a pilaster. The rockers consisted of a 3 ft 6 in. (1.07 m) high continuous wall throughout the width or the bridge with a continu ous Frf'vssinet-tvpe concrete hinge at both the top and bottom. Approach piers were fixed in the deck at the top and hinged at their footings. Because of their height, these piers have sufficient flexibility to allow movement of the deck without developing appreciable bending moments, the exception being the short stiff piers next to the abutment, which were hingetl both top and bottom. 2 We shall describe the construction procedure for the superstructure of Bridge I, which was also used for the other two bridges. Because the cable way did not have the capacity to transport the deck girders across the canvon, precasting operations were established at both ends of the bridge. During construction of the foundations, precasting opera tions were started at both sites at either end of the bridge. When the foundations for the approach piers were completed, the cableway transported and po sitioned the precast Fre\'ssinet pier hinges to their respective locations, where they were grouted to their respective foundations. Pouring of the piers then commenced, lIsing special steel forms at tached to the hinge blocks. Two sets of forms were used in leap-frog fashion to maintain a pouring
366
Concrete SegmentalArches, /ligtdFrames, ano Truss Bridges
rate of 5 ft (1.52 m) per cia\. Because olthe hinge al I he base of each pier column, Ihe piers required Icmporarv support unlillhe deck girders could he placed. The firsl 25 ft (7.62 Ill) lift of each column in each pier was supported bv a light sleel scar folding Ihal surmunded each colul11 n; the scaf foldings, in \Urn, were braced logel her. Succeed ing 25 ft (7.62 111) lifts were braced 10 the previous lift hy light timher trusses. :\s t lie colul11ns in the piers rose, steel reinforcement was placed; at the sallie tiI1le, holes for vertical prestressing tendons were cast in the concrete by the insertion of H in. t:1H III 111) steel tuhes, which were withdrawn H hours after concrete placemellt. L' pon completion of t he three colu m ns of an ap proach pier, precast segments of the cap beam were placed atop the columns and prestressed HTticallv to them ,IS indicated ill Figure 8.22. The \1\0 intermediate cap beam seglllents were placed 1)\ the cablcw,1\ and lemporarily held ill position hI' steel brackets. Four prestressing tendolls were then placed through t he cap beaJll segmcnts and the fOllr \crtical I i ill. (:~H llllll) joillls between the segmcnts wcre packed with a rich mortar. At'ter eight to ten hOlils the longitudillal tendom in the cap healll \\'('re strcssed and allchored to cOlllplete a pier bent. which was then reach \0 receive the deck girders and slabs. The 1:17 It (41.75 111) high pilasters at each end or the arch are four-celled hollow boxes 20 b\' HO ft (6.1 x 24.4 111) in plan with all walls 41 in. (120.65 111111) thick. They were ("011 stmeted in lifts with special steel forl11s that were Icap-frogged. Ten \'Crtical prestressing tendons
the cantile\'er method, this formwork being placed by the merhead cablew;n alld held in place b\ a system of cable stalS.-;Phus, the arch rib was essen tially constructed to the quarter-point s. The -center half-span formwork was constructed as a light wooden trussed arch assembled at the bottom of the camOI1 and winched into position from the ends of the quarter-span cantileyers. The timber falsework t russ was wedged against the concrete arch ribs already erected. It acted as an arch under the weight of the bottom flange concrete, t1'an5 mitt ing it s t hrust.to the cantile\'cred arch sections pre\iously erected. Later the timber falsework acted compositeh \"it h t he hardened bottom flange concrete to support the webs and top flange of the hollow box arch rihs when t hey were placed.' The following discussion describes the erection sequellce or the cellter-spall arch ribs.:! The fIrst falscwork unit ill the quarter-span (or each arch rih consisted of a tilllber platforlll ;) I ft (9.45 Ill) ill length with" width of 27 f't Hill. (H.43 Ill) at the spring lille and a widt h of 17 It 2 in. (5.23 m) at the opposite end, Figure H.~g (Phase I). This platform was C0I1S\J1IC\cd of g x lOin. (76.2 x 254 111m) tim hers 011 edge at 10~ in. (267 mill) centers covered OIl Ihe uppel' face with tin. (12.7 III Ill) thick plywood. It provided the form for the bO\lolTt of the arch rib. For the first section or the quarter span, three of these units (one for each rib) were placed In the cablewa\', supported by cable staYs A and B. and their position adjusted by hydraulic jacks at Ihe ends of the anchor cable stays. ~ext tOllr precast Freyssinet hinge blocks were posi tiolled ,It the spring line and assembled into one hinge block hy prestressing thelll together. Forms were then erected 011 the ralsework for the webs of t he arch rib, ami placement of concrete com menced, Figure 8.23 (Phase As the weight of each increment of concrete came onto t he forms, the cable stays elongated and the geometry of the arch-rib soffit had to be carefully adjusted bv the hydraulic jacks. C pOll completion of the cOllcreting for the first section of the quarter-span, falsework section 2 was attached to it and supported by two more cable stavs, C amI D. After geometry adjustment, con creting continued, Figures 8.23 (Phase 3) and 8.24. As a result of the position of the cable stays and the concreting sequence, angular deformations were possible between falsework sections I and 2. Thereforc, a temporary concrete hinge was placed in the lower flange of the arch rib, which would allow angular deformation but transmit the thrust to maintain equilibrium. When the concreting of
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FIGURE 8.23. Caracas Viaducts, erection and construction sequcnce. from reference Ci\'il Engineering-A5CE).
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Concrete Segmental Arches, Rigid Frames, and Truss Bridges .~
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the second portion of arch rib was completed and adjustment made, the temporary hinge was blocked and the two sections were prestressed t()~etl!eL In the same manner. temporan' hin~es were lIsed lor the remaining sectiolls of the quaner-span arch rib am! at each end of the cen Iral half-span arch sectioll, The firsl Iwo secliollS of arch rib thus became a COI1liIlUOUS member supporled at the ouler end by cable SlaYS, and during conslruction of the resl of the arch its ~eo!l!etric posilion was adjusted by cable slay l), The next operalion was Ihe erection of the third lalsework ullit consisting of a Irusswork. Its weight was slIch that it could not be accommodated by the cahleway. Therefore, it was assembled al the bot tom of the canyon below its position in the arch. The OllIeI' end was lifted by the cab!ewa\' and the inner end by a winch located at the end of the pre viollsly concreled section of the al·ch. Stay cables E passing over Ihe pilaster were attached, and the bottom flange of the new arch rib section was cast, Figures 8.23 (Phase 4) and 8.25. In like manner the next section of trussed falsework was positioned and supported by cable stav F. l\"ext, concrete lor the bottom flange of the rib was placed, including small concrete brackets
which protruded below the bottom flange totake the Ihrust of the 267 fl (81.4 m) central falsework after its positioning, Figure 8.23 (Phase 5). In Ihe last phase of the quarter-span concreting, the vertical webs were fOnlled and concreted, as well as a few narrow strips across the top to provide stiffness to the arch-rib members, which at this slage had a C-shaped cross section, Figure 8.23 (Phase 6). The anchor stay cables were again ad justed 10 bring the 125 ft (38 m) quarter-span into its proper position. The central 267 ft (81.4 m) falsework span had been assembled at the bottom of the canvon below its final position in the arch, Figure 8.26. The ends of the timber falsework arches were lied logether by sleel cables acting as lies to keep the arch falsework rigid. The whole central falsework was hoisted inlo positioll by winches localed at the ends of Ihe cll1tile\'erecl quarter-span unils, Figure 8.27. Ollce the cenlral falsework was ill place and tl\e location of the crown exactly positioned, cement mortar was packed in the g-ap bet ween the ends 01 Ihe cenlral falsework and Ihe quarter-span falsework, and eXIra-flat sand boxes were em bedded in the joint for subsequent slripping of the celllral falsework. After two days, the steel tie cables on the central falsework were released and the winches support-
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FIGURE 8.27.
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ing the section were loosened. At this point the cOlllbination of the central trussed falsework and the cOllcreted quarter-span units acted as a com pletc arch frOlll abutment to abutmellt. :'\ cxt, t he bottom Aa nges of the arch ribs were cOllcreted, in a previousl\' arrallged sequence, IIp to the crown Oil each side, and temporary crown hillge blocks were placed. The other temporal'\' hinge~ hctweell clements of the quarter span were hlocked alld the cable stays up to stay D removed. The cOlllbillation of timber falsework and partly huilt concrete arch ribs contillued to be held in po sition Iw sta\'s D, E, and F, with a temporar\' hinge at F onlv. Thc vert ical webs of the arch ribs over the cen tral sectioll were then concreted lip to the crown Ilillge; cable st,l\' D was released; crown concrete was cOlllpleted; the remaining construction joints were tied with prestressing tendons; and the last cable stays E alld F were released. At this point the
concrete arch ribs, less the top Aange over the center 260 ft (79.25 m) section, carried themsehes as well as the dead load of the entire falsework. I\:ext, the cement joints at the ends of the falsework were destroyed, sand boxes emptied, and, after the steel cable ties had been retightened, the central section of falsework was lowered, Fig ure 8.28. Falsework elements in the quarter-spans were lowered by hand winches. Spandrel columns were constructed next. Then, following a carefull, \\'orked out sequellce, the top flanges of arch ribs over the central section were concreted. Upon completion of the arch ribs the deck beams and slabs were placed, ill the manner previoush' described for the approach viaducts, in a s\'ll1metrical and simultaneous manlier on both sidcs of the crown ...\fter the deck had bcen pre st ressed transverseh', it was prest ressed longit udi lIall, ill the same lllallncr as the approach \'iaducts. Finishcd Viaduct I is shown in Figure 8.29. . In 1973, twellt\'-one \,ears after the construction of the~e arches, t he\' were reevaluated to see how they \\'Oldd IIOW be desiglled and cOllstructed. Fig ures tl.30 alld 8.31 compare the actual project COII structed ill 1952 with the structure as it wmIld have been designcd in 1970 (two boxes) and in 1973 (single box). The three-arch-rib and eight-bealll su perst ruct u re would be replaced by a variable depth box section (cantilever construction using precast segments) supported on slip-formed piers. The arch remains an appealing and aesthetic structure and might still prove to be competitive; but perhaps the construction technique suggested in the :'\ecbrburg Bridgc (Section 8.5.2) might be lllore appropriate today, either cast in place or precast.
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Caracas Viaducts, finished Viaduct 1.
371
Gladesville Bridge, Australia
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Gladesville Bridge, Australia
This precast segmental arch bridge, cOlllpleted in 19G4, spans the Parramatta River between Glades ville and DrunI111()\'lle and selTes a large seuioll of the northern ~Irea of the Snlnev Metropolis, Fig ure H.:12. A fter award of con tract the cont ractors submit ted ,Ill alternative desi.!.{ll. Thev proposed that the arch be built 011 fixed falsework. whereas in the original design part of I he arch was to be built on floating falsework and lOwed illto positioll. The original design called for an arch span of 910 ft (277.4 III). The alternate design increased the dear SP;llI of the arch to 1000 ft (305 m) and eliminated the necessitv for deep-water excavation for the arch foundations on the Gladesville, or nonhern, side of the river.! Total bridge length between 'lbulinents is 1901 ft 6. in. (579.6 m). The 1000 ft (305 111) clear span arch consists of four arch ribs, Figure 8.33, sup ported on massive concrete blocks. known as "thrust blocks," founded on sandstone on each side of the river. Roadwav width is 7'-2 ft (22111) with 6 ft (l.8 m) wide sidewalks on each side. The roadway has a grade of 6~:t at each end, and the grades are lonl1~cted In' a vertical curve 300 it (91.4 m) in length over the center portion of the structure. The arch has a maximum clearance. at the crown,
of 134 ft (40.8 111) above the water and not less than 1'-20 ft (36.6 Ill) above water level for a width of 20(] ft (61 Ill) in the center of the river. COllstruction of the bridgc involvcd t hc follow ing main opcrations 4 : I. Excavation for fOllndation of: a. Arch Il1mst blocks 011 each ~idc of the rivcr at the shoreline and partly below wat.er. b. Abutments at the ends of the bridge. c. Shore pier columns of the approach spans on eaLh sidc of the river. <) Concreting of the arch thrust blocks, the abutments and columns. 3. Driving of falsework piles in the river amI erection of steel falsework to support the hol low COllcrete blocks and diaphragms forming each of the four arch ribs. 4. Casting of the box-section segl1lents of the arch and diaphragms and the erection of the fOllr arch ribs one at a time. 5. Jacking each rib to raise and lift it off the falsework. 6. Casting of concrete deck beams on each side of [he river. 7. Erection of the deck beams to form the road wav over the arch. 8. Paving of the concrete roadwav and final com pletion of the structure.
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Caracas Viaducts, comparison of cross sections.
Gladesville Bridge, Australia
FIGURE 8.32. reference 4.
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Gladcs\'ille Bridg-e, aerial view, from
The roadway deck is supported on pairs of pre stressed concrete columlls, Figure 8.33. The wall thickness is 2 ft (0.6 m), except ill the tal! colullllls above the arch foulldation where the wall thickness is increased Iw 6 in. (152 ll11l1). At the top of each pair of colullln~ there is a reinforced COllcrete cap beam to support the deck giJ:!lers. During construction it was necessarv to provide blsework to support the box segments ami dia phragms tlmt make lip cadi of the four arch ribs in the arch. The falsework was made up of steel tubuh\r columns 011 steel tubular pile trestles car ning spans of steel beams 60 ft (18.3 Ill) long and a steel tl'lISS spall of 220 ft (67 Ill) over a navigation opening in the Gbdesville (Ilonhel'll) half of the
FIGURE 8.34. Gladesville Bridge, arch rib Ctlscwork and positioning of arch rib SCg:I11CIH, from refcrcllceL
falsework. These falsework units were tied to gether and anchored at each end to the thrust blocks, Figure 8.3-L Piling was taken down to rock ill the river bed. Steel columns, braced together, forllled a tower extending transverseh the full width of the bridge at the center of the falsev·/Ork. rranwerse lIlell1
FIGURE 8.33. Gladesville Bridge, schematic of four arch ribs, col umns. and deck. from reference 4.
374
Concrete Segmental Arches, Rigid Frames, and Truss Bridges
hel'S, extending the full width of the bridge. above the waterline connected the pile trestles, Figure R.34. The balance of the falsework was of sufficient width to support one arch rib. Upon completion of erection of an arch rib, the falsework was moved transversely on rails on the transverse members of the pile tr~stle to a position to enable erection of the adjacent arch rib, until all arch ribs were erected. Equipment installed 011 the central tower lifted the arch box segments and diaphragms from water level and positioned them. The tower also sened as a lateral bent to stabilize the individual arch ribs alter they were self-supporting alld until thn were tied t oget her. 4 The hollow-box segments and diaphragms were cast;) lIliles (4.8 kl1l) dowllstream h'om the bridge site. The casting \anl was laid out to accommodate the lllallilfacture of one arch rib at a time. Each arch rib consists of 108 box segments amI 19 dia phragms. Each arch-rib box segment is 20 rt (6 m) wide, with depths decreasing from 23 ft (7 Ill) at the thrust block to 14 It (4,3 Ill) at t he crown of the arch. measlIred at right angles to the axis of the arch. The lengt h 01 t he box segments a long the arch varies from 7 It 9 in, (2.:~6 111) to 9 It :) ill. (:1.1-12 III). After the box ullits were llI
FIGURE 8.35. Glades\ille Bridge. C'OInpleled liHIl' arcli rihs. frolll reference ..t.
8.5
Arches Built in Cantilever
Cntil the appearance of the concrete cable-stay bridge starting in 1962 (see Chapter 9), long-span concrete bridges were t he domain or the arch type 01 structure. Clitil 1977, with lhe (()mplelion 01 the Brotonne Cable-Stay Bridge ill France with a span of 1050 It (320 m), the record length for a concrete hridge had alwavs been held by an arch tq)e bridge. When the Kirk Bridges in Yugoslavia were completed in 1980, the larger arch with a span of 1280 ft (390 Ill) once again regained for the arch the record of longest concrete span.
FIGURE 8.36. bridge.
Glades\'ille Bricl!J;e, vicw of compleled
Arches Built in Cantilever
375
Here is a brief chronology of record concrete arch spans up to 1964:
1930, Plougastel Bridge, France: three spallS of 611.5 ft (186.40 m) 1939, Rio Esla, Spain: 631 ft (192.4 111) span 1943, Sando, Sweden: 866 ft (264 m) span 1963, Arrabida. Portugal: 886 ft (270 m) span 1964, 19uacu, River Parana, Brazil: 951 ft (290 111) span 1964, Gladesville, Sydney, Australia: 1000 It (305 m) span The concrete arch bridge does not enjov the favor it once did. \Iodern methods of bridge con struction utilizillg prestressing, cable stays, and segmental construction have all but eliminated it from contention as a economical bridge type. However, with the application of these modern methods to the older form, and givell the proper site conditions, concrete arches may regain some of their lost popularity.
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8.5.1 REVIEW OF CO.\'CEPT; SU.H.\URY OF STRUCTLRES WITH TEJliJOR."IR'( STAYS
The use of temporary staYs to facilitate the con struction of arch bridges begall. perhaps, with the Plollgastel Bridge. Tem porarv prest ress tendons were used to provide stabilitv to the short arch cantilever sections emanating from the arch foull dations (see Figure 8.5). Prestressing telldolls \'.;ere used to support the falsework of the Rio Esla Bridge and were incorporated into the structure, However. the l)1ore novel Illethod, which is the birth of today's technology, was emploved in the construction of the Saint Clair Viaduct at Lvon, France, by ),1. Esquillan. The stabilitv of precast segments was obtained bv the use of temporary stays. In the construction of the Caracas Viaduct, Freyssinet extended this concept bv using tempo rary stays to support the falsework and construct a mu<;h longer cantilever section of the arch. This same stay system was then used to accommodate the forces produced by lifting the center arch sec tion falsework (see Section 8.3). This concept was partially recaptured for the construction of the Iguacu Bridge in Brazil, where the falsework of the central portion of the arch was supported by tem poraI;y stays. The first arch bridge to be constructed using the concept of supporting segmental sections of the
FIGURE 8.37. COllcrCIC arches built in calli ilc\cr v,il II teillporar\' slavs. (0) With SlaVS alld pvlOIlS. (ii) With slays . .' palldrel COIUIIlIlS, alld P\"IOllS. (I") Wil h spalldrel col 1l1l1llS. lie diagonals and ,ta\s.
arch bv temporary sta\"S is the Sibellik Bridge in Yugoslavia. Falsework for an approxilllate lellgth of 88.6 ft (27 Ill) was supported on Bailev trusses. which were in turn supported bv temporary suys. Figure 8.37b, consisting of a combination of cables and structural steel rolled shapes. This arch was constructed in nine sections. f(Hlr on each side and the central closure sectiolJ. A llIodificatiotl of this concept was used for a secotld Yugoslav bridg'e at Pag with a 634 ft (193.2 111) span constructed ill seven sections. A further modiflcatiotl was used for the Van Staden Bridge in Somh Africa, Figure 8.37a, with a span of 656 ft (200 m). A somewhat different concept is wher'e, with the assistance of spandrel columns, the stays act as temporary diagonals during construction, Figure 8.37c. In this manner, the structure is built as a variable-depth Pratt truss. This concept was used for the Kirk Bridges in Yugoslavia. 111 some in stances these temporary diagonal stays may be in corporated into permanent diagonals such that in the final configuration the structure is a truss and not an arch (see Section 8.7.3). In summarizing the construction methods using temporary cable stavs. we find two basic categories:
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FIGURE 8.38. (Opposite) :-':eckarburg Bridge. erec tion scheme and sections. from referellce 5. (a) LOIl gitudinal section. (h) Erection scheme. (e) Cross section.
Where the arch is supported directly by the tempo rarv stavs Where the temporary slavs act as diagonals of a Pratt truss during construction Characteristics of the arch bridges using this con cept of temporary stays during construction are presented in Table 8.2. 8.5.2
.YECKARBLRG BRIDGE. GERHLVY
This unique and contemporary arch-supported structure, some 50 miles (80 kl1l) southwest of Stuttgart, crosses the Neckar River near Rottweil, Germany. It is a part of the federal expressway :\-81 from Stuttgart to the west of Bodensee with a connection to Zurich, Switzerland. The original scheme proposed bv German au thorities cOllsisted of a steel girder structure sup ported on tall piers. Designer-contractor Ed. Zub lin. Stuttgart, developed an alternative design consistillg of twin concrete arches to support the roadway. The proposal was to construct the arches segmentallv b~ the cantilever method and con strllct the twin single-cell trapezoidal box girders for the roadway by the incremental launching lechni
FIGURE 8.39. i\;eckarburg Bridge, completed arch (courtesy of Willhelm Zellner).
FIGURE 8'.40. :-':eckarburg Bridge, arch just belm'e closure (COl! rtesv of \Villhell11 Zellner).
structure is constructed as two independent paral lel slructures with a 1.8 ft (0.54 m) gap in the me dian. Roadway spans are 98 ft (30 m) in the ap proach sections and 72.6 ft (22.14 m) over the arch. Each independent arch rib is a two-cell box. The arch ribs were constructed in symmetrical halves, Figure 8.40. The curved form work was 43 ft (13. I 111) long, the first 23.3 ft (7.1 Ill) of the form clamped to the previously constructed arch seg ment and the remaining 19.7 ft (6 m) remained to cast the next segment incremellt. The first 2:3.3 ft (7.1 m) of arch segment at the arch foundation was constructed by' conventional forming methods. There are 14 segments on each side of an arch rib and a closure segment at the crown of each arch. The exterior dimensions of each two-cell arch rib are 21.3 ft (6.5 m) wide by 9.8 ft (:3.0 m) deep. Ex terior webs vary in thickness from 10 to 11 in. (260 .to 280 mm). and the interior web is 6.3 in. (160 mm) thick. The arch rib was cast in two operatiolls -fi rst the bottom Hange and seconcl the webs and top Hanges.;' Piers supported by the arch or independent foundations are of a constant section and slip formed by conventional methods. Sliding bearings are used at the abutments and the short stiff piers 1 and 13. The remaining piers are hinged to the superstructure deck such that the elastic piers can follow the superstructure movement. 5.6 During construction, as each half-rib was can tilevered out from its foundation, it was supported by a temporary system of Dvwidag bar stays, Fig ures 8.38, 8.41, and 8.42. After completion of the arch, the temporary stavs were removed, except those required to stabilize the arch during the in cremental launching of the superstructure deck. Dywidag bar stavs were anchored either to a pier foundation or to Dywidag rock anchors in the side of the vaIley.5
1.>0 -.J
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supporting Ihe
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Characteristics of Ardl Bridges Constructed with Cable Stays
1% I,on
(:OI1f"tl'lH tl()ll
Yf';tr of
TABLE 8.2
(,0[,
Ih(' IWO
"pt'illgings 01 (he arch
Ilillged ;)1
Fi"'d
Fixed
hall")"), of hr' .II " .. lie jatk~
i'os... ihihly of cor the thru'\t at Ihe cnnnt hy a JT( linf.{
;J(
lhe no'\'\.'n h) " hattery of 11y~ .il a,,)i, .lacks
n'( ling the thrllsl
Pot;sibliJtyof
Sialic A, "It Scheme
1092 It (:1:l2,H
III)
10'.. of deck is R
(orillHltal (utva
Remarks
~ 7.
-
1:
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--
...,..
~
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r;
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.", :::c C,;:! -::-::: :::
r.
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:5.,:":_
::
~
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~
379
380
Concrete Segmental Arches, Rigid Frames, and Truss Bridges
'"..
FIGURE 8.41. ~eckarburg Bridge, temporal): Dywi dag bar stays supporting cantilevered arch rib (cour tesY of Willhelm Zellner).
FIGURE 8.43.
Neckarburg Bridge. launching of deck
girder.
FIGURE 8.44. :":eckarburg
Bridge,
dose-up
01
launching nose.
FIGURE 8.42. :":eckarburg Bridge, temporary Dywi dag bar stays supporting cantilevered arch rib (cour tes\' of' Willhelm Zellner).
The trapezoidal box girders of the superstruc ture deck were constructed behind the Singen abunnent and incrementally launched "downhill" toward the Stuttgart abutment, Figure 8.43. A close-up of the launching nose is shown in Figure 8.44. Overall girder width is 48.8 ft (14.9 m) with a constant depth of 7.5 it (2.3 m). Girder segments were cast in lengths of 65.6 fl (20 m). The lift and push combination of hydraulic jacks (see Chapter 7) launched the girder in lOin. (0.25 m) incre ments. To maintain deformations of the arch and
piers. resulting from the horizontal forces of the incremental launching operations. within allowable limits, the tops of the piers were tied back to the abutments and the arch was tied back bv the tem porary stays used during the arch construction. An inno\'ation introduced bv Zublin on this project was the use of bearings for the incremental launching that remained as permanent bearings. Prior procedure had employed a system of' tempo rary bearings for the incremental launching and then a transfer to permanent bearings. s 8.5.3
NIESENBACK BRIDGE, AUSTRIA
This is a two-rib arch structure utilizing the free cantilever construction method for each half-arch, Figure 8.45. The arch has a span of 394 ft (120 m) with a rise of 123 ft (37.5 m). Each arch rib is a two-cell box with exterior dimensions of 16.4 ft (5 m) wide by 8.2 ft (2.5 m) deep. The roadway con sists of a concrete slab and girder system with an overall width of 57.7 ft (17.6 m). Although the lon gitudinal axis of the arch is in a straight line, the
381
Arches Built in Cantilet'er Final structure
Structure during construction Hllfspylon
17.60 9.90 lSJO
FIGURE 8.45.
:-;iesenback Bridge. ele\3.tion. plan. and cross section. from reference 7.
roadway it supports has a centerline radius. in plan. of l092 it (332.8 m). The curved roadway structure has spans of 65.6 ft (20 m) over the arch and is supported by two 3.3 ft (1.0 m) square piers, one on each arch rib. At the arch foundations, roadway support is by a wall pier with dimensions of 4.6 ft (l.4 m) by 33.8 ft (10.3 m).
'
Each two-cell box arch rib is constructed r.·v the cantilever method. using a 41 ft (l2.5 m. long traveling form. The form clamps to the prec--::ding construction such that a 19,7 ft (6.0 m) se~~.ment can be cast. A crew of seven men was able to ':ast a segment on a weekly cycle. To keep moments in the cantilevering arcC1 to a minimum during construction, the cantik-,ered
Concrete Segmental Arches, Rigid Frames, and Truss Bridges
382
portion of the arch was supported by a S\'stem of Dvwidag bar stays, Figure 8.45. Stay stresses are monitored at each stage of construction to main tain a nearly moment-free condition in the arch. Dywidag bal's used in the stays were 1 in. (26.5 111m) diameter and were used because they were easily coupled and could be reused. 7
8.5.4
KIRK BRIDGES, rUGOSLAVIA
These structures connect the mainland with the Island of Kirk in the Adriatic Sea. In between is a small rocky olllcropping known as St. Mark, such that from the mainland 10 SI. i\1ark is the world's longest concrete arch with a span of 1280 ft (390 m) and from SI. Mark to Kirk is the seventh longest concrete arch with a span of 800 ft (244 Ill), Figures lAO amI H.4G. Because the distallce between the shores of the mainland and St. Mark is 1509 ft (460 m), the arch support is partially founded in the sea, Figure 8.17. The arch reaction of approximately 15,400 LOllS (14,000 mt) is accoIllmodated by the inclined pier in the sea, which takes 9900 tons (9000 mt) to the rock, while the nearly horizontal box structure
:I ·
8.6
Rigid-Frame Bridges
Another bridge type thai lends itself to the con temporary segmental concept is the rigid-frame bridge. Cnfortunately, segmental construction has not often heen applied to this type of structure. The reason is probably that the segmental concept is associated with the conventional girder type bridge, and designers have gin:n little considera tion to applying this method 10 the rigid-frame bridge. Hopefully, the few examples that follow will stimulate thinking about this t)'pe of structure.
-t~Jl_'Q--+ :
!
~ I"
. I
above sea level takes the other reaction component of 6600 tons (6000 mt). A system of temporary stays was used to s.upport the arch as it was progressively cantilevered out from the springings, Figure 8.48. These temporary stays were used as the top chord and diagonals of a temporary variable-depth Pratt truss during con struction, Figures 8.48 and 8.49. The arch rib con sists of a three-cell rectangular precast box, which was cast in segment lengths of 16.4 ft (5 m) and assembled with <;:ast-in-place joints, Figure 8.48. A view of the completed arch with spandrel columns is given in Figure 8.50.
..
"1',1
--+ co
.
+
LW
--1
Section 1
Section 2
KERK
_~
ELEVATION
FIGURE 8.46.
I
2t' OO"--_--l:.:.:72~
Kirk Bridges, ele\'ation and sections.
Jeo
I
300 I
1
L:::; I
i
! - 6.
~O
T -1<;1.00
.000
I
U, I
J J. 50
FIGURE 8.47.
Kirk Bridge. foundation detail. 383
384
Concrete Segmental Arches, Rigfd Frames, and Truss Bridges
FIGURE 8.48: tion.
.-........... •
~~
..
-1"
Kirk Bridge, erection of first arch sec-
_"'0: _
'"
--......:.~--",
FIGURE 8.49.
FIGURE 8.50.
Kirk Bridge, completed arch.
'_
.
Kirk Bridge. erection approaching
(TOWll.
FIGURE 8.51. SainI l\1ichael Bridge. \iew of the pleted structure.
COITI
Ja;n'
FIGURE 8.52. Saint Michael Bridge, partial longitudinal sectioll.
8.6.1
SAI.\'"/' ,H/CHEL BRIf)GE IN TOULOUSE, FRANCE
This beautiful structure, Figure 8.5 L appears as a sliccession of arches with inclined legs, crossing the two branches of the Garonne River in the southern city of Toulouse, France. Typical dimensions of a rigid frame are presented in Figures 8.52 and 8.53. Because the bridge replaced an obsolete struc ture resting on masonry piers, it was possible to
construct the inclined legs on suspended scaffold ing using temporary ties anchored to the masonry piers before they were demolished, Figure 8.54. The longitudinal girders were cast in place be tween the legs to complete the rigid frame. Over each pier an expansion joint with laminated bear ings is provided in the roadway slab, Figure 8.54. Another view of the finished bridge is pre sented in Figure 8.55.
I
I
13:'1'"
FIGURE 8.53.
Saint :Vlichael Bridge, typical section.
Neopr~n~
b
\
.I
FIGURE 8.54.
Saint :Vlichael Bridge, constructioll sequence at tvpical pier.
FIGURE 8.55. Saim \'[ichael Bridge. finished struc ture. 385
386 (1.6.2
Concrete Segmental Arches,
Rigi~
BRIESLE MAAS BRIDGE, NETHERLAl'lDS
The Briesle Maas Bridge near Rotterdam, com pleted in 1969, is a distinctive structure with its V-shaped piers, Figure 8.56. This bridge, crossing the Meuse River, is situated in an area reserved for pleasure boating and recreational purposes. It was therefore considered essential to maintain a high degree of bridge aesthetics. Although the design is perhaps not the most economical, it was chosen to meet t he aesthetic req uirements. The three-span superstructure consists of a 369 f'l \ 112.5 m) center span with end spans of 264 ft (!-iO.5 111). Trans\'erselv, the superstructure consists of three precast singie-cell boxes, joined at iheir flange tips by a longitudinal closure pour and transverselv prestressed, Figure 8.57. The hollow inclined legs of the V piers are structurally con llccted to the deck strllcture by post-tensioning, and the V pier is snpported at its base through neo prene hearing pads on the pile cap foundation. Fig nres H.5H and !-i.59. 'rhe superstructure, with the exception of a few cast-in-place closure joints, is CO III posed of precast segments. Shear forces, mainly concentrated in the webs, Ilormally are transferred to piers or columns by a diaphragm. Prefabrication prevented this solution
Frames, and Truss Bridges
in this project, however, as the additional weight in the pier segments would have increased intolera bly. Shear stresses were maintained at an accept able le\'el by increased web thickness and by u-iaxial prestressing. At the moment that the midspan closure pour of the center span is consummated, the bending mo ment at this joint is zero. With time this moment increases, as a result of creep, to a significant per centage of what would occur if the bridge were built as a continuous structure on falsework. 'Pre stressing to accommodate both conditions cannot be gi\'ell maximum eccentricit\·, and it becomes both difficult to execute and expemive. A consid erable amount of prestressing was saved b\' eliminating the condition of zero stress at closure and therefore preventillg creep. This was accol1I plished by inducing an upward reaction under segmelli s 7 and 72. Figme H.59, ancr joi I1t closure. Simultaneously with the increase of these reactio;1 forces, prestressing tendons in the central span were stressed. Upon completion of the end spans the illduced forces were released automatically by prestressing the end spans. Segmellts were produced at an existillg castillg vanl 68 miles (1 IO kill) from the bridge site. A long-line precasling bed (see Figure 11.37) was
I
~
~i
~
.._1
CROSS
FIGURE 8.57.
•123 EZl CJ
SECTION
Briesle Maas Bridge, Irans\'el'se cross section.
LONGITUDINAL SECTION WITH CABLE PROFILE
FIGURE 8.58.
Briesle Maas Bridge, longitudinal section with tendon profile.
ospholl
prtrtrtuod
ConOllt~
prtslrtilled
CXltlcntt: (ill
rltnf{\f't.Wd
conerell
(p!af!t;.}
liholi
Rigid-Frame Bridges
387
_D_
A B
C D E
Steel frame Jacks Rubber beanng pads Joints Counter weight
F= G=
Joint Temporary SUflPort H"" Scaffol di ng J = Joint
FIGURE 8.59.
Briesle \la;ls Bridge, erectioll sequence.
lIsed witl! a Ie!l(.ith equal to a half-spall-that is, Olle cantilevcr. Three sets of sC(.illlent forllls were elllploved to cast a total of 2:H segll1ents, avcragill(.i 7R reuses. Seg-ments were transported to the bridge site b\' barge. The variolls stages of erection are indicated in Figure R.59..\ special structural steel frame was used to position the inclined precast hollow-box legs of t he piers a nd to su ppon the seven precast road W;IV girder sCgll1ClltS hefore cast ing the joillts at t he corners of the delta pier portion of the structure. This frame was also utilizcd to balance the pier during- erection of the remainder of the roadway g-irder seglllcnts amI to adjust, by means of jacks, thc loads ill the inclincd legs of the pier during various stages of erection. CpOIl cO!l1pletion of the balanced cantilever erection about both piers, tcmporarv supports were placed under segments 7 and 72 (the extreme end seglllcnts of the partiall\ completed end spans) so that thc temjJoran' steel frames under the piers could be remmec/o At this point"both hahes of the stnicture were in an unstable equilibrium condition, therefore, counterweights were placed over the supported segments, Figure 8.59, to prevent the half-structures from toppling over. Jacks atop the temporar\" suppOrts were used to adjust the position of the bridge halves with respect to olle another and to induce the upward vertical reaction forces previollslv discussed. Also, dif ferences in elevation between the three box girders
were adjusted by these jacks. Arter castinJ4 Ihc center-span closure joint and stressinJ4 in the center spall, the remaining segments in the end spans were placed Oil falsework, FiJ4llre H.GO; do SUI'C Joints were cast: and longitudinal and tran~ verse prest ressing was completed. All segments in the balanced call!ilever portion of the structure were placed In a !loating crane. Because of the crane's small reach, it could not place the last five segments need cd to complete the end Spall. Therefore, it placed thcm on a 'illlail doll v installed 011 top of the falsework, which would roll them into their final positions. To ~I\()id dismantling the falsework after cOll1pleting (Jilt' girder and reinstallillJ4 it under the lIext, II was constructed so that it could bc lowered ~lI1d m()\cd transverselv into position, Figure R.60. A close-up of tlte piers of the flnished ~!rllC!lln> is shown in Figure 8.61. 8.6.3
BOXflO.H.HE BRIDGE. FR.·/SCE
The Bonhomme Bridge over the 81;1\'et River ill Brittany, France, was designed and built between 1972 and 1974, Figure 8.62. This three-spall slant-leg portal-frame bridge has a center span of 481 ft (146.7 111) and end spans of223 ft (6i.95m), Figure 8.63. The span between the foundations of the slant legs is 611 ft (186.25111). A tubular steel framewOI'k was used to support the slant legs tem porarilv until closure at midspan, Figures 8.64 and
Concrete Segmental Arches, Rigid.frames, and Truss Bridges
388
FIGURE 8.60. span.
Briesle :V{aas Bridge, erection falsework for hlst fi\'e segments ill the end
8.65. This structure was huilt h:' the cast-in-place balanced cantilever method. For adjusting the geometry of the bridge, flat jacks were placed under the legs and at midspan. A detail of the ;tCUustillg jacks placed on top of thl:; temporary support is shown in Figure 8.66. Flat jacks and sand boxes were used both to adjust the geometry of the bridge before closure was achieved at midspan and later to release the energy stored in the legs of t he temporary supports, which were loaded with the full weight of the bridge. FIGURE 8.61. \' piers.
Briesle Maas Bridge, close-up \'iew of
FIGURE 8.62.
Bonhomme Bridge over Blavet Ri\'er.
~ORIENT ~
~
______________________________
~2~8~2~,~60~
KERVIGNAC,.. ________________________________ ~~
____~6~7~,9~5~____~______________~1~~~6~,7~O~________________T-______~6~7~,9~5~__~~
FIGURE 8.63.
Bonhomme Bridge, eie\'ation.
FIGURE 8.64.
Bonhomme Bridge. construction stages .
.. +
••
++.~ • +
G RANI T E
FIGURE 8.65.
••••
+ + •
+
Bonbomme Bridge, temporary support. 389
390
Concrete Segmental Arches, Rigid Frames, and Truss Bridges
The scheme is a ven satisfactory one in terms of both the aesthetics of the finished structure and simplicity of construction. However, it may be used only when site conditions allow the foundations of the temporary supports to be established safely at a reasonable cost. Figure 8.67 shows the temporary supports during the balanced cantilever construc tion of the bridge.
8.6.4
FIGURE 8.65.
(Continued)
MOTORWA}' OVERPASSES iiI,' THE MIDDLE EAST
The use of precast segmental construction for the Alpine Motorways in southern France was de scribed in Section :~.15. It was shown how mass production could be applied to the construction of a large number of similar overpasses. This experience was repeated recentlv in a mid dle eastern country for the cOllstruction of 17 overpass structures over an existing freeway, Fig ure R.6R, To minimize disturbance of freeway trafflc, it was fdt that a three-span rigid-frame structure with inclined legs would be an attractive solution. Dimensions are shown in Figures R.69 and 8.70. The total deck length of 252 ft 3 in. (77 m) is di vided into 32 precast segments for each of the twin box girders. Deck wjdth of the overpasses is either 36 ft (II m) or 46 ft (14 m). The same box section is used for all structures, and the cast-in-place lon gitudinal closure strip varies as required. The slant legs are precast in the same plant where the deck segments are produced. The typi cal erection sequence is shown in Figure 8.71. A temporary bent founded at the edge line of the new freeway is used to place and adjust the precast legs on either side of the bridge. Segments are placed in balanced cantilever from the special seg ment located atop the slant legs. A light temporary bent in the short side spans is used to reduce the bending moment in the slant legs during construc tion. After completion of the cleck and removal of all temporary supports, the structure is in effect a two-hinged arch with vertical restraints at both ends. The bridges were analyzed for earthquake and large thermal variation loads (seasonal varia tion of 120°F and temperature gradient between top and bottom flange of 18°F). Figure 8.72 shows a detailed view of the inclined legs and the temporary support during construc tion.
ra iO! II
FIGURE 8.66. Bonhomme Bridge, details of bearing of concrete can tilever on temporary support.
1
1
10----1 I
I
I
I
I 1 1
-+-----1 I
1 1
I I
,
10 rOI I
'
AND 'SAND
BOX
1
I
4-_._ _ _ _ 11
!
~
IOi L ____
J'
391
392
FIGURE 8.67.
Concrete Segmental Arches, Rigid Frames, and Truss Bridges
BOllhomme Bridge, during call1ile\'er
cOIlSlnIC{ion.
Plain
19'-0"
FIGURE 8.68.
\1otorw;1\ O\'el'jl
19'-0"
FIGURE 8.70. Motorwav O\'erpass Frames, cross sec tioll and elevation of inclined legs.
new.
8.7.1 RETROSPECT ON CONCEPTS FOR CONCRETE TIWSS BRIDGES
8.7
Truss Bridges
As with rigid frames, segmental construction has seldom been applied to truss bridges. Once again the designer must realize that the principles of segmental construction, together with imagination, can be applied to bridge structures other than the mllventionaJ girder bridge.
Trusses were used in all long-span cantilever steel bridges, and it was logical to conceive of the appli cation of this type of structure to prestressed con crete. An interesting example of such an approach is presented in Figure 8.73, in which an origi nal sketch made in 1948 by Eugene Freyssinet for the design of a precast prestressed concrete truss is reproduced. The studies were applied to two specific exam pIes:
149.3
FIGURE 8.69.
Mowrway Overpass Frames, longitudinal section.
Truss Bridges
393
(a) '-_ _ _ _ _ _---.l
(b)
L _ _ _ _~_..::;
(c) '---:::_ _ _ _ _ _-.-::J
(d)
~
____ ...._ _ _ _. J
~Iororwa\' O\'erpass Frames, erection sequence, Stage L (b) Stage 2, (e) Stage ,~. (il) Stage 4.
FIGURE 8.71. (tI)
A bridge over the Hanach River near Algiers. Algeria, with a clear span of 400 ft (123 m), Figures 8.14 and 8.75. A major crossing of the Rhine River at Pfaffen dorf, Germany, with a main span of 600 ft (180 m)
FIGURE 8.72. Motorway Overpass Frames, detail of inclined leg and temporary support.
These studies were very encouraging from the viewpoints of both economy of materials and simplicity of construction. The deck was to be en tirely precast, with members assembled by pre stressing. Construction would proceed in balanced cantilever from the main piers until reaching midspan closure, where adjustment of the deck geometry and loads in the members was provided by jacks.
...'-'"
!J:)
A --=
,
J.. B
for a cOllcept
(t~J.OJ
_ _ ELEVATION
,ketch of E.
:.;<'~~--=r;.~""",
\.:~
e
40,00
1%
L? 'A
51
12300
Concept
:sc=-
f'IGURE 8.74.
,e
vrSlSIO>' SI $1
or prcstrc"cd
or a
truss
~ iz
1.l:"_"""""'''''F~T',",''r'''Y-'T ",.-rT_:r_r-r_T""r:--r'-J'7-.r'!""'T-,--,,....,.,"~,--r~:r-"-r-"---T
:\~,
FIGURE 8.73. COllcrete truss (1 \HH).
-->
/'
precast
t.O.(JQ
~~-
JI'jJ\
ir-~,
395
Truss Bridges 112 COUPE B_ B
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FIGURE 8.75. Concept of a truss bridge.
The use of I girders at 7 ft (2 m) spacing for the precast deck would not be considered today as the optimum design. One of the authors, who was in volved in the studies with E. Fr-eyssinet, remembers also that many technological problems such as the connection details between diagonals ,and chords were not completely solved. Neither of these two designs reached the con struction stage, and the concept was rapidly for gotten before its potential could be objectively as certained. Oddly enough, the designers of steel structures followed a similar path. Abandoning prematurely the concept of truss structures, which had allowed st,lch outstanding structures as the Firth of Forth Bridge to be built all over the world, they turned to web girder structures and closed box sections with all the critical problems they entailed, such as elas tic stability. Perhaps it is time to reassess some major design approaches in both steel and concrete for very long spans. 8.7.2
anced cantilever, as construction started at one abutment and proceeded to the opposite abutment by progressive placement. Temporary interme diate piers were used as required to reduce the cantilever stresses. Figure 8.77 shows an interior view. The lower flange is used as a walkway for pedestrians and for bicycles. The railing in the center surrounds an opening in the bottom flange where stress condi tions do not require the concrete area. Figure 8.78 is an interior view looking through one of the floor openings, and Figure 8.79 is another interior view. 8.7.3
RIP BRIDGE, AUSTRALIA
The recently completed Rip Bridge, Figure 8.80, north of Sydney, Australia, has a center span of
lHANGFALL BRIDGE; AUSTRIA
The Mangfallbrucke in Austria, Figure 8.76, on the autobahn between Munich and Salzburg was constructed in 1959. This structure is perhaps best described as a large box girder with the webs being a trusswork. Total length is 945 ft (288 m) from abutment to abutment; the center span is 354 ft (108 m) with side spans of 295.5 ft (90 m). It was constructed as cast-in-place segmental using the free cantilever method. However, it was not bal
FIGURE 8.76.
Mangfallbrucke, general view.
396
Concrete Segmental Arches, Rigid Frames, and Truss Bridges
I
~
FIGURE 8.77. Iruss\\'orL
Mangfalllwiicke, illterior "lew showing FIGURE 8.80.
FIGURE 8.78. MangfalJbriicke, interior "iew looking through 1I00r opening.
FIGURE 8.79.
:'-.1angfallbriicke, general interior view,
Rip Bridge, general \·iew.
600 ft (182.88 m). The identical cantilever trusses, which sit symmetrically on either side of the cross ing, reach out 240 ft (i3.56 m) toward each other to support a 122 ft (3i 01) drop-in simple span at their extremities, Figure 8.81. The erection scheme is illustrated in Figure 8.82. Note that cable stays were used as diagonal mem bers during construction to support the arch seg ments. Temporary falsework bents were used at each panel point of the truss on the landward side of the main piers. Precast concrete elements were delivered from a precasting plant some 80 miles (130 km) from the site. Each panel of the lower chords of the truss was assembled from five precast I-shaped elements with a 1 ft (0.3 m) longitudinal pour strip between the flange tips. Similarly, the upper chord was as sem bled from five rectangular two-cell precast members. Erection of one of the lower chord members is shown in Figure 8.83. The exterior two I-shaped lower chord members are supported by the diagonal stays, while the interior three ele ments of the lower chord are supported by a trans verse beam arrangement from the exterior two during construction. Each diagonal member was assembled from lon gitudinally split halves, which, when brought to gether, encase the diagonal prestress tendon stays, incorporating them into the structure by concrete poured in place between the two halves. The upper chord or deck members are erected after the verti cal members along with temporary falsework to support the deck panels, while the cast-in-place concrete is placed between the deck elements and transversely prestressed.
Truss Bridges
397
6
c·c
a·a
A·A 1
FIGURE 8.81.
Rip Bridge, eic\;uiol1 and cross sections.
Prestress cable to support lower member
r In-situ panel
. rAbutment
FIGURE 8.83.
Rip Bridge, erectioll of lower chord .
The deck performs as a prestressed concrete tension member. As construction proceeds, addi tional prestress is progressively added to ensure that the deck remains in compression. H.7.-ILocation of
1F=~~~#~=';?'ii'''=;F~~~~~~), flat jack temporary
hinges for shape correction
CO.VCEPT FOR.i CROSSlXC OF THE
ENGLISH CHANNEL
Certain projects rOt, crossings, such as of the Eng lish Channel between France and Great Britain. the Straits of Messina, and even the Straits of Gi braltar. have exerted a powerful fascination on the minds of the great engineers of this century. FIGURE 8.82.
Rip Bridge. erection sequence,
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References
Eugene Frevssinet was no exception, and he spent the last vears of his long professional career studying the crossing of the English Channel with a series of 2000 ft (612 m) long prestressed concrete spans. The many worthwhile ideas contained in this COIKept are not likely to be developed soon, or even bv the lUrn of the centurv. Figure 8.84 presents all elevation of a typical 2000 ft (612 Ill) span, which was contemplated as a prestressed concrete composite truss. :'1ajor mem bers of the truss were not of conventional pre stressed concrete, because such high stresses had to be accepted to keep the weight of the span within acceptable limits. A new material to be used for that purpose had occupied Freyssinet's mind for several years and had even beel! laboratorv t.ested for confirmation of the concept. \Vhen a concrete member is cOlllpletely confined in an envelope that creates perlllanently biaxial transverse compressive stress, it will resist safelv much higher stress than if subjected to a lTlonoaxiai stress or reillforced COII ventionall\' with ulltensioned transverse reinforc ing (such as spirals in a circular column). From a tecllllolo){ical point of view, the perrna llent active restraint creating tt1e biaxialt ransverse compressio:1 is easilv achieved in a Illelllber that h
'
399
to sustain several times as much longit udinal COIll pressive stress as a reinforced concrete member without excessive strains, provided it is initiaIlv loaded to ofTset the initial strain. Such a project and such a material could not be developed in a short period of time, They are mentioned here at the close of this chapter as a conceptual heritage, which it is onr dutv to make fUllctional.
References I. E. Frc;"ssinet, "Larsest Concrete Spans of the Americas-Three '.follllllletltal Bridses Built ill Venezuela," Ci<'il EII,l..,riIlPl'rill[;-tlSCE. '.larch 195:1, ;2, Jean
.\Iuller, "Largest Concrete Spans of the Americas-How the Three Bridges Werc De signed," Citlil E II!-,riIlPl'rillg-ASCE, '.farch I ()5:l,
:3. Rober! Sham
"J.
":\ew Brid~e over Panamatta Rilcr at (;I;H!es\'ille," ,Hllill ROi/d" Journal of the lkpartlllcill of \bill Roads, :\ew SOllth Wales, DeccmiJer 19(i4.
.\11011"
5. :\11011., "'!"albrijcke ROllwcil-:\cckarhul'){," ZlIhlill Rlllld\rllfl1l,
Hefr 7/H. DezcHlllcr 1971), StUtl,l-iart,
Ct'l'm
6. ",\rcl1 Slipforlller ShUll", (;rollfld Support In Crm'i Valle<' FII.!.,rillI'Prwi.( .\'fIl'.I-UI'(IJTlI, JUIIC I. 197H. 7, ,\110IL, ":\iesenhachbriickc, Bog-en illl Freit'll Vm h;IlI:' ;\ustria 1~170-74, FIt' COlll-{re;,s HI7,!, :\('\\ York.
i
L
9
Concrete Segmental Cable-Stayed Bridges
9.1
INTRODUCTION
9.2 9.3 9.4 9.5 9.6
9.1.1 Historical Review 9.1.2 Advantages of Concrete Cable-Stayed Bridges 9.1.3 Structural Style and Arrangement LAKE MARACAIBO BRIDGE, VENEZUELA WADI KUF BRIDGE, LIBYA CHACO/CORRIENTES BRIDGE, ARGENTINA MAINBRUCKE. GERMANY TIEL BRIDGE. NETHERLANDS
9.1
Introduction
The concept of supporting a beam 01' bridge bv in clined cable sta\,s is not new, and the historical evolution of this type of structure has been dis cussed in the Iiterature. 1- li Although the modern renaissance of cable-stayed bridges is said to have begun in 1955, with steel as the favored material, in the last 1>\'0 decades a number of cable-stayed bridges have been constructed using a reinfOI'ced or prestressed concrete deck system. In recent years several concrete cable-stayed bridges have been built in the long-span range. In 'at least four current projects, alternative designs in concrete and steel have been prepared for competitive bid ding. Cable-stayed bridges are extending the com petitive span range of concrete bridge construction 10 dimensions that had previously been considered impossible and reserved for structural steel. To date, approximately 21 concrete cable-stayed bridges have been constructed, and others are either in design or under construction. A tabular summary of concrete cable-stayed bridges is pre sented in Tables 9.1 and 9.2. 400
9.7 9.8 9.9 9.10
PASCO-KENNEWICK BRIDGE, U.S.A. BROTONNE BRIDGE. FRANCE DANUBE CANAL BRIDGE. AUSTRIA NOTABLE EXAMPLES OF CONCEPTS 9.10.1 9.10.2 9.10.3
Proposed Great Belt Bridge, Denmark Proposed Dame Point Bridge, U.S.A. Proposed Ruck-A-Chuck), Bridge. U.S.A.
REFERENCES
9.1.1
Hl-5TOR1CAL REVIEW
Since the beginni ng of the cable-st
401
Introduction TABLE 9.1.
Location
Type
Guadalete River, Spain Yakima River. Wash., C.S.A. Venezuela Kiev, U.S.S.R. Obourg, Belgium Genoa. Italy Rome, Italy Denmark Denmark Pretoria, S. Africa Geelong, Australia Perth, Australia Libya Londonderry, :-.i. Ireland Hoechst, West Germany Parana River, Argentina Tiel, Holland Barranquilla. Columbia Vienna, Austria Taiwan ;\.'ormandy, France Province Poetenza, Italy State of Wash .. C .S.A. Chertsey. England Auburn, California, C .S..-\. Jacksonville, Florida. U.S.A. Eas't Humington, W.Va., U.S.A. Weirton, W,Va., C.S.A.
Aqueduct Highway Highway Highway Pedestrian Highway Highway Highway & rail Highway & rail Pipe Pedestrian Pedestrian Highway Highwav Highway & rail Highway Highway Highway Highway Highway Highway Highwav Highwav Rail Highway Highway Highway Highway
Bridge Tempul Benton City Lake Maracaibo Dnieper River Canal du Centre Polcevera Viaduct Magliana Danish Great Belr' Danish Great Belt" Pretoria II Barwon River 12 Moum Street 13 Wadi Kuf 14 Richard Foyle
2 3 4 5 6 7 8 9 10
15 16 17 18 19 20 21 22 2:) 24 25 26 27 28
~Iainbriicke
Chaco/Corrientes River Waal Bananquilla Danube Canal Kwang Fu Pont de Brotonne Carpineto Pasco-Kennewick ~I-25 Overpass Ruck-A-Chuck)", Dame Point" East Huntington" Weirton-Steubenville"
Concrete Cable-Stayed Bridges-General Data Spans (ftyl
66-198-66 [email protected]@57.5 525-5@771-525 216.5-472-216.5 2@220 282-664-689-460 476-176 multispans 1132 multispans 1148 2@93 180-270-180 [email protected] 320-925-320 230-689 485.6-308 537 -803.8-5:)7 312-876-312 228-459-228 182.7-390-182.7 220-440-440-220 471-1050-471 100-594- 100 406.5-981-406.5 [email protected] 1:>00 650-1300-650 158-300-900-608 820-688
Year Completed
1925 1957 1962 1963 1966 1967 1967 Delayed by funding Delayed by funding
1968 1969 1969 1971 Project abandoned
1972 1973 1974 1974 1974 1977 19i1 1977 1978 1978 Design completed Design completed C nder construction In design
a Design by White Young and Partners. "Design by Clrich Finsterwalder. "Alternative design with structural steel. I ft = 0.305 m.
The stays were introduced to replace two piers that were found to be too difficult to construct in deep water. Thus, the stays were introduced to provide !ntermediate support in the main span. OnJuly 5,1957, a stayed structure crossing the Yakima River at Benton City, Washington, was opened to traffic. Designed by Homer M. Hadley, the structure has a total length of 400 ft (122 m) with a center span of 170 ft (51.9 m) flanked on each side by twO continuous spans of 57.5 ft (17.53 m) each. A 60 ft (18.3 m) central drop-in span of 33 in. (0.84 m) deep steel beams is supported by transverse concrete beams, supported in turn by structural steel wide-flange stays. Continuous lon gitudinal concrete beams comprise the remainder of the structure and receive support at their ex tremity, in the center span, from the transverse concrete beams and si:eel stays.4.8 In the more than half-century that has elapsed since.Torroja's Tempul Aqueduct. 21 cable-stayed bridges have been constructed (Table 9.1). Thir teen, or 62%, of these structures have been con
structed in the past decade. In the last five years nine have been completed, representing 43% of the total. Within the last three vears the span of 1000 ft (300 m) has been exceeded, and a current design contemplates a span of 1300 ft (400 m). It has taken almost a quarter-century to reach a span contemplated by Prof. Morandi in his original de sign concept for the Lake Maracaibo Bridge. Be that as it may, it is obvious from the statistics that in recent years the concrete cable-stayed bridge has been accepted as a viable structure.
9.1.2 ADVA.YT,1GES OF CONCRETE CABLE-STAYED BRIDGES
As engineers, we are aware that no particular con cept or bridge type can suit all environments, con siderations, problems, or site conditions. The selection of the proper type for a given site and set of circumstances must take into account many parameters. The choice of material, in addition to
Concrete Segmental Cable-Stayed Bridges
402
TABLE 9.2.
Bridge Telllp,,1 Cit\ :1 I.ake \Iar'acaibo t DlHcpl'l' River :) Canal till Ct'llllT Polec\!'r'a \. iad lIC! i \Iagliana ii Ibrllsir (;rcaf Bell" ~I Ibrllsh (;n'at Heir" 1O Pt ('loria II B~rn\ Oil Ri\ ('I 12 \Ioll!l! Street 1:\ \\adi I\.u! 1·1 ]{i\n I'ovlc I C, \Loi nbriHke It; l :han',!( ;Ollit-II tes Ii Rl\,'r Wa." Ii> B;'IT;u)(llIilla I ~l Dalllll)(' Callal 20 I;. hang I'll 21 1'0llt de Brotollll(' ;2~ ( :arpilll'io 2:\ t'asn)' l\.('nl)(·\\I(\-. 2,1 ;\!_:!c, ()verpa'" ') _:) Rtlc\-'-A-( :lllIcb ;2(i J),mte 1'01111 .) _f \-:;"t Illlntingroll :2H \\' "i rtoll,Slelll)('miJle 2
lklllOll
"
Stav Planes 2 2 2 2 2 2
Concrete Cable-Stayed Bridges-Dimensional Parameters
Stay :\0 Stavs Arrangement
:1 4 1
Radiating Radiating
2
Radiating Harp Radiating Fan
1(; 2 2 2
14.1
0.07
2 I :{ 2
2
139.4 95 65.6 I4H 111.5
(J.IH 0.20
315 41 43
1'11.H
0.27 0.44 0.16 0.42 0.19 0.52 0.3H 0.19 (l.11
52.Fl
() 15
2:11 94,75
0.22
~9
2 2 2 2
(ft)
Pvlon Heightto-Span Ratio'
Harp lIar], Radiating Radiating
177.5 :{60 172 J[J5
O.:~O
0.21 0.23
:> 2 2 2 2 :! " .)
2 2
Deck Width
(It)
Girder Depth ( rt) 6.9 3.~5
2 :1 2 2 2
Pylon Height All(lV'e Deck
2 21 IH .)
20 21 15116 24
Radiating
Lm Radiating Fan
220 il
0.16 0.22 0.:19
Harp Radiatitlg Radiating
:,02 279.4 :l33.2
0.2:1 0.:1J 0.41
57 5.H7 59 79 :11.7Y 46 15.8 6 15.75 42.5 9H 101.5 ~7
101 :17 '1l.H Gi G:1 ·11 ,~V 79,H 39 .,}4 105.75 41 103.5
16.4 4.H 1.94 15 9oH-13.2
2:1.5 2,95
3
2 11.5-23
1l.5
SpantoDepth Ratio'
Girdn Construction Type"
2H.7 52.3 46.7 9i'1.75 113 46 :{6 4ii 390 31 :{H.5 5HA 70 60
ell' Clp/pC d-i-, PC PC CII'/PC d-i-s CII'!pC d-i-s PC segments CI P segmeuts ell' Ul' ell' CI Pipe d-i-s PC seglllen ts
57
H.5 I 1.5 II.c) 10 9.2
70 76 -16 4"~.3-
12,5
H4
I 1.:, i 9 H,5 '1-6 5 !l.5
52 140 20 I '1:~ 260 IHO 96.5
ClP
UP PC/CIt' d-i-s PC and ell' CI I' segments PC and ell' PC PC and ell' ell' PC segmetlls ell' PC scgments ell' and PC Composite Composite
., Design Il\' Wilile Young and Partners.
/. ])csign b\ t 'Iri," I-ir"ler\\'aldel'.
. Sct' Tahk ~I.I lor malor 'pall dilllcllsions.
"(:II' ~ (,;lst-in-place. PC = precast. d·i-s = drop-in·span.
, Forlll Inver""lit paraholoid in space.
! Pel single-cell box.
I It = O.:HJ:, Ill.
material properties, depends on availability and Ihe prevailing economics al a particular time as well as Ihe specific localion of the site. The process of weighting and evaluating Ihese parameters for variolls tvpes of bridges under consi~eration is certailllv Illore an art than a science. III e,,;du:ttillg a concrete cable-stayed bridge, the designer should be aware of the following advan tages: I. The main girder can be very shallow with re spect 10 the span, Span-to-girder-depth ratios vary from 45 to 100. With proper ael'Odynamic streamlining and multistays the deck structure call be slilll, having span-to-depth ratios of 150 10400, and lIot convey a massive visual impres SIOIL
2. Concrete deck structures, b" virtue of their mass and because concrete has inherently favorable damping characteristics, are not as susceptible to aerodynamic vibrations, 3. The horizontal component of cable-stay force, which causes compression with bending in the deck structure, favors a concrete deck struc ture. The stay forces produce a prestress force in the concrete, and concrete is at its best in compression. 4. The amount of steel required in the stays is comparatively small. A proper choice of height of pylon with respect to span can yield all op timum solution. 9 5. Live-load deflections are small because of the Iive-Ioad-to-dead-Ioad ratio, and therefore
Introduction
403
concrete cable-stayed bridges are applicable to
railroad or mass-transit loadings.
6. Erection of the superstructure and cable stays is relatively easy with today's technology of prestressing, prefabrication, and segmental cantilever construction. 9.1.3
STRUCTURAL STrLE ASD ARRASGE,\lE.YT
Many of the concrete cable-stayed bridges have been designed by -"1orandi or have been strongly influenced by his style. Commencing with the Lake Maracaibo Bridge, of the 12 bridges constructed, excluding pedestrian and pipe bridges (see Table 9.1), six have been designed by -"{orandi, Figures 9.1 through 9.6. A third prize winner in the 1967 Danish Great Belt Bridge Competition was the Morandi-style design proposed by the English con sulting firm of White You ng and Partners, Figure 9.7. The Chaco/Corrientes Bridge, Figure 9.8, very much resembles the Morandi style.
FIGURE 9.3. Magliana Viaduct (courtesy of L'lndus tria Italiana del Cemento).
FIGURE 9.4. Wadi Kuf Bridge, general construction view (collrtesy of Prof. R. MOl'amli).
FIGURE 9.1. Lake :Vlaracaibo Bridge, general "iew, from !'eferen<:e 1 I (courtesy of Julius Berger-Bauboag Aktiengesellschaft).
FIGURE 9.2.
Polcevera Creek Bridge, general view.
FIGURE 9.5. Garrido).
Barrallquilla Bridge (courtesy of L. A.
404
Concrete Segmental Cable-Stayed Bridges
FIGURE 9.6. Carpineto Yiaducl (courtes\' of L'II1 ciuslria Italiana del Cemento).
FIGURE 9.7. Dallish Great Belt Bridge, anist's rend ering (courtesy of \'.'hite Young and Partners).
These structures, with the exception of the Ma gliana, Barranquilla, and Carpineto bridges, are typified by the A-frame pylon positioned in the plane of the stays and an auxiliary X frame- or in clined struts to support the deck structure at the pylon. Thev are staticallv determinate systems so as to preclude am' possible damage from differen tial settlements of the bridge piers and pylons or from light seismic shocks. A simple schematic of the structural scheme is shown in Figure 9.9, which consists of a series of independent balanced systems, each carried by an individual pier and pylon. These systems are then connected by drop-in girders, which are simple span girders spanning between independent sys tems. IO The cantilever girder is supported at two points (C and D) by a pier system and elasticany supported at two points (B and E) by the cable stays, thus producing a tbree-span girder with cantilevers on each side. The stays are supported bv a pylon ponal frame that is independent of the pier system supporting the girder. Another entry in the 1967 Danish Great Belt Competition by Ulrich Finsterwalder, of the Ger mall firm Dyckerhoff & Widmann, deviated from the Morandi style and was awarded a second prize. Finstcrwalder's design proposed a multiple-span, multistay system using Dywidag bars for the stays, Figure 9.10. The deck was envisioned as being con structed by the cast-in-place balanced cantilever
a
b
c
e
FIGURE 9.9. Schematic oj !'.iorancii-st,le structural scheme, from rei'erence 10 (cot! rtesv of the America n COllcrele I nstilUle).
FIGURE 9.8. Chaco/Corrientes Bridge, general view, from referellce 13 (courtesy of 'lJormer Gray).
FIGURE 9.10. Danish Great Belt Bridge, artist's rend ering (courtesy of Ulrich Finsterwalder).
Lake Maracaibo Bridge, Venezuela
segmental method, each segment being supported by a set of stavs. This concept was later to be con summated in the )'lain Bridge and in the design of the Dame Point Bridge. The choice of geometrical conflguration and number of stays in a cable-stayed bridge system is subject to a wide variety of considerations. If cable stays are few, they result in large stay forces, which require massive anchorage systems. A relatively deep girder is required to span the large distance between stays, producing span-to-depth ratios vary ing from 45 to 100 (see Table 9.2). Depending upon the location of the longitudinal main girders with respect to the cable-stay planes, large trans verse cross girders may be required to transfer the stay force to the main girder. A large number of cable stays, approaching a continuous supporting elastic media, simplifies the anchorage and distribution of forces to the girder and permits the use of a shallower girder, with span-to-depth ratio varving from 150 to 400 (see Table 9.2). The construction of the deck can be erected roadway-width by free cantilever methods from stay to slav without auxiliary methods or stays. If the depth of the r<..>adway girder can be kept at a minimulll. the deck becomes, more or less, the bottom chord of a large cantilevering truss; it needs almost no bending stiffness because the inclined stan; do not allow any large deAections under concentrated loads. 6 In the 55 years since Torroja's Tempul Aque duct the concrete cable-stayed bridge has evolved from basically a statically determinate structure with one stay on each side of the pylon to a highly indeterminate system with multistays. As demonstrated by the Danish Great Belt Bridge ·Competition. the Pasco-Kennewick Bridge, and the Pont de Brotonne, spans of approximately 1000 ft (300 m) are practical and have been ac complished. The practicality of spans of 1300 ft (400 m) is demonstrated by the Dame Point Bridge. and spans approaching 1600 ft (500 m) are considered technically feasible. Leonhardt 6 has projected that with an aerodynamically shaped cOI,nposire concrete and steel deck a span of 2300 ft (1500 m) can be achieved. With today's technology of prefabrication, prestressing, and segmental cantilever construction, it is obvious that cable staved bridges are extending the competitive span range of concrete bridges to dimensions that had previously been considered impossible and into a range that had previously been the domain of structural steel. This technological means exist; they only require implementation.
9.2
405
Lake Maracaibo Bridge, Venezuela
This bridge, Figure 9.1, has a total length of 5.4 miles (8.i km). Five main navigation openings COII sist of prestressed concrete cable-stayed structures with suspended spans totaling 77 I ft (235 m). The cantilever span is supported on four parallel X frames, while the cable stays are supported on two A frames with a portal member at the top. There is no connection anvwhere between the X and A frames, Figure 9.11. The continuous cantilever girder is a three-cell box girder 16.4 ft deep by 46.7 ft wide (5 ~ by 14.22 m). An axial prestress force is induced into the girder as a result of the horizontal component of cable force, thus, for the most part, only conventional reinforcement is required. Ad ditional prestress tendons are required for nega tive moment above the X-frame support and the transverse cable-stav anchorage beams. II The pier cap consists of the three-cell box girder with the X frames continued up into the girder to act as transverse diaphragms, Figures 9.12 and 9.13. After completion of the pier, service girders were raised into position to be used in the con struction of the cantilever arm. Owing to the addi tional moment, produced during this construction stage by the service girder and weight of the can tilever arm, additional concentric prestressing was required in the pier cap, Figure 9.13. To avoid overstressing of the X frames during this opera tion, temporary horizontal ties were installed and tensioned bv hydraulic jacks, Figures 9.13 and 9.14.
FIGURE 9.11.
Lake Maracaibo Bridge, pier cap with X frames, from reference 11 (courtesy of Julius Berger-Bauboag Aktiengesellschaft).
;.-1
FIGURE 9.12. reference 11
~Jlall IOwel ,md X-frallles, f rolll of Julius Berger-BalllJo
Lake Maracaibo Bridge, main
(colirtesY
f-.E-r"----------48,55
\
\
\ \ \ \ \
\ \ \
\ \ \
\
Service girder for cantilever arm
~
II
"" "" " "" ;~-,a.i:~7-:-7III
: \..J,/ I I
/
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/
'{/: \.:,/ ,I / '\. I /
. . _____
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FIGURE 9.13. Lake Maracaibo Bridge, pier cap of a main span and service girder, from reference II (counesy of Julius Berger-Bauboag Aktiengesell schaft). 406
Wadi Kuf Bridge, Libya
FIGURE 9.14. Lake ~laracaibo Bridge, brace mem hers bear agaillSl X frames after being tensioned by hy draulic jacks, from reference 11 (courtesy of Julius Berger-Bauboag Aktiengesellschaft).
In the construction of the cantilever arms, spe cial steel trusses (service girders) were used for formwork. Thev were mpported at one end by the completerl pier cap and at the other end by aux iliary piers and foundations, as shown in Figure 9.15. • The anchorages for the cable stays are located in a 73.8 ft (22.5 m) long prestressed inclined trans verse girder. The reinforcing cages for these members were fabricated on shore in a position corresponding to the inclination of the stays. They
407
FIGURE 9.15. Lake \[aracaibo Bridge, placing ser \ice gir
weighed 60 tons and contained 70 prestressing tendons, Figu re 9.16. The cable stavs are housed in thick-walled steel pipes, Figure 9.17, which were welded to steel plates at their extremities and were encased in the anchorage beam. A special steel spreader beam was used to erect the fabricated cage in its proper orientation. The suspended spans are com posed of four prest ressed T sections.
9.3
Wadi Kuf Bridge, Libya
The Wadi Kuf Bridge in Libya, designed by Prof. Morandi, consists of two independent balanced
FIGURE 9.16. Lake Maracaibo Bridge, fabrication of anchorage beam, from referellce 11 (courtesy of Julius Berger-Bauboag Aktiengesellschaft).
408
Concrete Segmental Cable-Stayed Bridges
9.4
FIGURE 9.17. Lake :Ylaracaibo Bridge, housing for cahle slavs, fmm reference 11 (courtesy of jUJillS Ikrgcr-Bauboag Akliengesellschaft).
cable-stay systems having their ends anchored to the abutment by a short hinge strut. The cable-stay systems are connected by a simply supported drop-in span, Figure 9.4. This structure consists of only three spans. The center span is 925 ft (2S0 m) long and the two end spans are each 320 ft (97.5111), for a total length of 1565 ft (475 111). The simply supported drop-in center portion of the main span consists of three double-T beams ISO ft (55 111) in length; each beam weighs approximately 220 tons (200 mt).12 The A-frame towers are 459 ft and 400 ft (140 and 122111) high and the roadway deck is 597 (1S2 Ill) above the lowest point of the valley beneath the Slrllct ure. 12 The su perstructure is a single-cell box gilder that varies from 13 ft (4.0 m) to 23 ft (7.0 111) at the pylons. The single-cell box is 24 ft (7.4 m) wide and with cantilever flanges forms a 42.7 ft (13 111) cleek. The contractor made good use of traveling forms to construct the box girder and deck, using the balanced cantilever technique to build on both sides of the pylons at the same time. Traveling forms were used because extreme height and difficult terrain made other conventional con struction methods impossible or too. costly. The deck was constructed by progressive cast-in-place segments, attached to the previously completed segments by means of temporary prestress ties and subsequent permanent post-tensioning Dywidag bars. The procedure adopted required temporary cable stays to support the cantilever arms during the construction sequence as the superstructure progressed in both directions from the pylon. When the superstructure extended sufficiently, the permanent stays were installed, and the structure was completed in the same manner.
ChacolCorrientes Bridge, Argentina
The Chaco/Corrientes Bridge (also referred to as the General Manuel Belgrano Bridge) crosses the Parana River between the provinces of Chaco and Corrientes in northeast Argentina and is an im portant link in one of the highways between Brazil and Argentina, Figure 9.8. It has a center naviga tion span of 803 ft lOin. (245 m), side spans of 537 ft (163.7 m), and a number of 271 ft (82.6 m) ap proach spans on both the Chaco and Corrientes sides of the riv<:;r. The vertical clearance in the main spans above flood level is 115 ft (35 m).13.14 The superstructure of this bridge consists of two cast-in-place concrete A-frame pylons, which sup port a deck of precast segmelllal post-tensioned concrete. The pylons are flanked by concrete struts, which reduce the unsupported length of the deck, Figure 9.18. Although the pier cap section of the deck (between inclined struts) is cast in place, the cantilever portion consists of precast segments. The drop-in spans are cast in place. The deck structure consists of two longitudinal hollow boxes 8 ft 2Y2 in. (2.5 m) wide and with a constant depth of II ft 6 in. (3.5 m), which support precast roadway deck elements, Figure 9.19. The precast girder elements were match-cast on the river bank in lengths of 13 ft I Y2 in. (4.0 m), with the exception of shorter units at the point of stay attachment, which contain an inclined transverse anchorage beam, Figure 9.20. Units were cast by the long-line method on a concrete foundation with the proper camber built in. Each ullit was cast with three alignment keys, one in each web and one in the LOp flange. The units were erected as balanced cantilevers with respect to the pylon to minimize erection stresses. After a unit was hoisted, an epoxy joint material was placed over all of the butting area; then the unit was placed against the already erected unit and tensionedY To eliminate the need for falsework, the inclined struts and pylon legs were supported by horizontal ties at successive levels as construction proceeded, Figure 9.21. The legs were poured in segments by cantilevering the formwork from previously con structed segments. When deck level was reached, the girder section between the extremities of the inclined ties was cast on formwork. To further stif fen the pylon structure, a slab was cast between box girders at the level of the girder bottom flanges. This slab is within the limits of the cast-in-place box girders and inclined struts and serves as an addi tional element to accept the horizontal thrust from the cable stays. The upper portion of the pylon was
Chaco/Corrientes Bridge, Argentina
157~
409
Precast segments
(10.00 m) 4 ft 1ij in. (1.50 m)
Precast construction
-+Cast·in·place
369 ft 1 in. (112.50 m)
-.;- Precast construction 369 ft 1 ih. (112,50 m)
_ 8 0 3 ft 10 in (245,00 m ) - + - - 5 3 7 ft 0 in. (163.70m)~
Center span Side span
FIGURE 9.18. Chaco/Corrientes Bridge. longitudinal geometry. from refer ence H (courtesy of Civil Engineering-ASCE). 8~ in,
9 It 2~
(2,80
In,
27 ft 3 in,
9 It 2i in.
8~ in,
(8,30 m)
(2.80m)
(22 em)
m)
Cast·in·place concretei 2% down '
2% down
-
I
I t. Bridge
8 ituminous pavement
Box girder
I
I
~ 8 It 2~ in,~ 11 (2.50 m)
ft 3~ in. (3.45 m)
I Symm. about t.
+'
~. 11 ft 5~ in, (3.50 m)
channel
".
:±==::::J
7~ in, to 1 ft 7~ in. t;
,
I
(20-50 em) J9~ in, to l1ij in. 11 ft 3~ in,~ 8 ft 2~ in. (25-30 em) (3.45 m) (2.50 m)
FIGURE 9.19. Chaco/Corrientes Bridge. deck cross section, from reference H (cOl1rtesv of Ci\il Engincering-ASCE).
FIGURE 9.20. Chaco/Corricllles Bridge. cable an chorage at girder, from refcrence 14 (courtesy of Civil Engineering-ASCE).
then completed, using horizontal struts to brace the legs until they were connected at the apex. Fig ure 9.21. 13• 14 The precast box girder units. with the exception of those at the cable-stay anchorage. were cast 13 ft 1V2 in. (4 m) in length by the long-line. match-cast procedure. The soffit bed of the casting form had the required camber built in. Alignment keys were cast into both webs and the top flange. Match cast ing and alignment keys were required to ensure a precise fit during erection. Each 44 ton (40 mt) unit was transported bv barge to the construction site and erected by a traveling crane operating on the erected portion of the deck. Since each box was lifted by a balance beam, four heavy vertical bolts had to be cast into the top flange of each box. The lifting crane at deck level allowed longitudinal
410
Concrete Segmental Cable-Stayed Bridges
-'2. Erect diaphragms between lines of boxes and post-tension. 3. Place temporary and permanent stays as erec tion proceeds. 4. Remove temporary stays. 5. Remove temporary post-tensioning in the can
tilever sections.
6. Place precast deck slabs between box girders. 7. Concrete the three 65 ft 8 in. (20 m) drop-in spans. 8. Place asphalt p~\'ement, curbs, and railings.
9,5
FIGURE 9.21. Ch;lr()/C()lTiellle~ Bridge. crefllOll sc qll('Il(C of p\lOIl. fmlll reference 14 (courtes\ of Ci,il b Igillecrillg-:\SCE),
1I1(l\CIl1Cllt of the suspellded box. Upon erection to the proper elevation, the unit was held to within 6 in. (150 llllll) of' the mating unit while epoX\' joi1lt 1l1ateriaJ was applied. Bearing surfaces of the unit w('re sand-blasted alld water-soaked before erec tioll, The water film was removed before erection and application of the epoxy joint material. The tra\eling deck crane held the unit in position against its mating unit until it could be post-ten sioned into position. The crane was slacked off without waiting for the joint material to cure. 13• 14 To minimize overturning forces and stresses in the pylon, it was necessarv to erect the precast box ullits by a balanced cantilever method on both sides of the centerline of the pvlon, The erection sched ule delltalldcd simultaneous erection at each pYlolJ, although the pylons are independent of each other. \\'hen four precast box units were erected ill the cantilever on each side of the pylon, temporary stays were installed from the 'top of the pylon to their respective connections at deck level. After installation of the temporary stays, cantilever erection proceeded to the positions of the perma nent stays, and the procedure was repeated to completion of the installation of the precast box units. 13 The erection sequence may be outlined as fol lows: 1. Erect precast boxes and post-tension succes sively.
Mainbrucke, Germany
The Main Bridge near Hoechst, a suburb of Frankfort, constructed in 1971 is a prestressed. cast-in-place. segmental, cable-stayed structure that connects the Fahwerke Hoechst's chemical in-. dustrial complex on both sides or the River Main in West Germany, Figure 9.22. It carries two three-lane roads separated by a railway track and pipelines. This structure, a successor to Finster walder's Danish Great Belt Bridge proposal, repre sents the first practical application of the Dywidag bar stay.l:; The hridge spans the river at a skew of 70° from the high northern bank to the southern bank, which is 23 ft (7 m) lower. The center navigation span is 486 ft (148.2,3 m) with a northern ap proach span of 86 ft (26.17m) and southern ap proach spans of 55, 84, 95, and 129 ft (16.91, 25.65, 29, and 39.35 m), Figure 9,23. Railroad track and pipelines are in the median between the two cantilever pylon shafts and are supported on an 8.7 ft (2.66 111) deep torsionally stiff box girder, Figure 9,24. The centerline of the
FIGURE 9.22.
Mainhriicke, [rom reference 16.
Mainbrucke, Germany
FIGURE 9.23.
Mainbrticke, elevation and plan, from reference 16.
aUERSCHNITl DER
S~ROM OFFNUNG
!;
I
I, :! I~
1
aUERSCHNITT DER VORLANDOFFNUNGEN
FIGURE 9.24.
:\lainbrticke, cross sections, from reference 16.
longitudinal webs of the box girder coincides with
the centerline of the indi\'idual cantilever pylons,
, and they are 26.25 ft (8 m) apart. Transverse cross
beams at 9.8 ft (3 m) centers form diaphragms for
the box and cantilevers, which extend 39 ft (11.95
m) on one side and 36 ft (II m) on the other side of
the central box to support the two roadways, Figure
9.25. The cross section of the towers consists of an an
choring web in the center, san9wiched by two flat
pl;,lte flange elements, Figure 9.26. In a transverse
elevation of the pylons, the width of the pylon in
creases from the top to just below the transverse
strut, where it decreases to accommodate clearance
requirements for both modes of traffic, Figure
9.26. The stay cables (Dywidag bars) are in pairs,
horizontal to each other in the main span and ver
tica~ in the side span, thus simplifying the anchor
age detail at the pylon. Figure 9.26. 16
FIGURE 9.25. \Iainbrticke, view of deck at pylon
(courtesy of Richard Heinen),
411
,1
I
I
412
Concrete Segmental Cable-Stayed Bridges ANSICHT' QUER '
VERANKERUNG DER SCHRXGSEILE 1M PYLON
FIGURE 9.26.
l\lainbnjcke, pYlon and cable configuration, from refer
ence 16.
COllstruction of the bridge superstructure was hy the cast-in-place segmental method. Figure 9.27. Segments in the river span were 20.7 ft (6.3 m) in length, corresponding to the spacing of the stays, Segments in the anchor span were 19ft (.5.8 Ill) ill lellgt 11. Segments in the allchor span were concreted before the corresponding segment in the river span to maintain stability. The pylon segments were associated with the superstruc ture segments. and each pylon segment was slip formed. Figure 9.28 shows the partially completed structure and the falsework necessary to install the stays. Each stay is composed of twenty-flve 16 mm (% in.) diameter Dywidag bars encased in a metal duct. which is grouted for corrosion protection similar to post-tensioned prestressed concrete con struction.
FIGURE 9.27. Mainbriicke, casting of deck segments (courtesy of D}'ckerhoff & Widmann).
9.6
Tiel Bridge, The Netherlands
The Tiel Bridge,17 Figures 9,29 and 9.30, crosses the Waal River, which, together with the Maas and the Rhine. flowing east to west, divides the
FIGURE 9.28. Mainbrucke, partially structure (courtesy of Richard Heinen).
completed
r.,;o
"'" -
!):;tu
i
NORD _NORTH
II¥!
VIAOUC O'ACCE5
-1W....-
APPUIS GLlS5ANTS SliOING BHRING5
-l aXl
-
6
r
._&».
~--,
APPUIS CAOUTCHOUC RUBi:lER BEARINGS
r~~~~
_"''D
_ _ _ ,JD)
_ _ ~~
FIGURE 9.29. Tiel
]I'd!l
APPUIS GLiSSANT5 SLIDING BEARINGS
APPROACH VIADUCT
10
~
__
OUVRAGE PRI NCIPAL
14
15
MAIN BRIDGE
~.=:
414
FIGURE 9.30.
CotlCrete Segmental Cable-Stayed Bridges
Tiel Bridge, main spam,
\;etherlands into northern and southern parts, struCl ure pr()\ides a needed t rafflc link be tween the town of Tiel and the south of the (OUI1 tn' and is a lIlajor north-south route, The structure has an overall length of 4656 ft (1419 111) and consists of a 2644 ft (806 Ill) curved viaduct on a 19,685 ft (6000 111) radius, which in cludes ten continuous 258 ft (i8,5 111) long spans alld a 200H ft (G12 Ill) straight main structure CO!1l prising three ~t,l\ed spans of 312,876, and :112 ft (95, 26i. and 95 Ill) and two 254 ft (ii.5 111) side spans. The cross section cOllsists of two pI'eGlst concrete boxes. each supporting two vehicular and one bicy de lane, The total width of the superstructure, which is R9 it (2i.2 Ill) in the access viaduct, Figure 9.:11. is elliarged to 103 ft (31,5 m) over the main ~tnl('lllI'e so a~ 10 accommodate the pdon sup porting the sta,'s, The structure crosses not only the "Vaal Ri,'er but also a flood plain, which is under water during the willter months. :'\avigation requirements dictate a horizontal de,lI'allee of 853 ft (260 m) and a verti cal clearance of30 ft (9.1 m).
Thi~
FIGURE 9.31.
Tiel Bridge, approach ,'iaduCL
The ten-span 2648 ft (806 m) long access viaduct is continuous over iL~ entire length. The super structure is supported on the piers by sliding teflon bearings, except at the three center j)iers where it is supported on neoprene bearings, hav ing a thickness such that they fix the viaduct at these piers. Expansion joints are located at piers 1 and II. The superstructure in the access viaduct consists of two precast rectangular boxes of a con stant depth of 11.5 ft (3.5 m) and width of 21 ft 8 in. (6.6 111). The top flange including cantile\ler O\'erhangs has a width of 44 ft (13.44 m). The l)Verall width of the approach viaduct deck is 89 n 3 in. (2i.2 111), including a longitudinal pour strip. The viaduct was constructed by the precast bal anced cantilever met hod with cast-in-place closure pours at the midspans. To accommodate the can tilever compressive stresses in the hottom flange ()\er the piers, the thie Kness of 1 he ilOll om flange is . linearly increased from a minimum of 8 in, (200 1ll!1l) to 24 in. (600 111m) over a length of 33 ft (10 m) on each side of the pier. Each pier segment cOJltains a diaphragm. Because of the potential flooding of the river from A, pril through December a nci the consequent loss or damage of fabework and loss of time, it was decided to build the access viaduct utilizing precast segments in the balanced or "free" cantilever con su'uction. The segments could be cast during flooding and placed in storage. Erection of the segments, which WOUld take less time than the casting, could be accomplished after the Hood had subsided. The precast segments, weighing 132 tons (120 mt), were cast in I11m'able forms on a casting bed baving the length of one span (by the long-line method, see Section 11.6.2). Segments were Slored by and parallel to the casting bed and handled by a 130 ft (40 m) span gantry crane, Figure 9.32. They were transported to the site (access viaduct abut ment) by means of a 132 ton (120 I1lt) capacity trolley and then placed in the structure by the same gantry crane used in the precasting yard for han dling, Figure 9.33. The trolley was used to trans port the segments because the gantry was usually engaged in the precasting yard or in placing seg ments in the viaduct. The gantry crane was such that it spanned over the twin boxes in the super structure and 'the trolleyway used to transport the segments. Segment joints are of the epoxy-bonded type (see Section 11.5). Cantilever imbalance is accom modated by a temporary support adjacent to the pier, Figure 9.33. Five temporary prestress bars
Tiel Bridge, The Netherlands
415
FIGtJRE 9.32. Pn~castillg plant. (1) Casting hed, (~) re-bar srorage, (C) segment storage, (cl) {oncrete hdtch plant, (5) office, (6) gamry crane, (7) hridge approach.
are used as provisional prestressing to hold the segments in position until permanent prestress tendons can be threaded into the ducts and stressed. The sVlTlmetrical box girder main structure consists of a 254 ft (7i.5 m) 'Side span, a 312 it (95 m) side stayed span, and a 331 ft (101 111) section of staved center span cantilevering toward the center of the bridge. The center section between the staved cantilever ends is made up of four 213 ft (65 m) suspended lightweight concrete girders. Two alternatives were considered for the cable stay pylons: a single p\'lon located on the 1011 gitudinal centerline of the bridge or a ponal-type pylon. To simplify the project, the portal-type pylon was selected. The portal pylon is fixed to the .pier and passes freely through the superstructure. Figure 9.34. The superstructure is fixed at the pylon piers except l'or rotation. It is allowed to move longitudinally at succeeding piers. Two alternatives were also considered for the stay system: a multiple stay system supporting the deck almost continuously and a system consisting of a few large staY's. As prestressed concrete stays had been selected, the second solution became somewhat mandatorY" Construction of prestressed
FIGURE 9.33.
FIGURE 9.34.
Free pas.sage of pYlol1 t 11 Hlllgil deck.
concrete stays is a costly operation requiring extell sive high scaft'olding, Figure 9.35; thus it is advan tageous to reduce the number of stays. The short stays of the bridge have a slope of I: 1 and the long stavs a slope of I :2. Their points of anchorage to the deck are respectively at 156ft (47.5 111) and 312 ft (95 m) OIl both sides of a pvlon. The long stays have a cross section of 3 by 3.:; ft (0.9 by 1.0 m) and are prestressed bv 36 tendons Oil the bank side and bv 40 tendons on the river side, because of the larger load on that side, Figure 9.36a. The effect of the different loads on the stays introduces a flexural moment into the pylon. The short stays have a cross section of 2.13 by 3.3 ft (0.65 by 1.0 m) and are prestressed by 16 tendons
Placing of segme!l!s bv gal1lry crane.
Concrete Segmental
416
Ca~le-Stayed
Bridges
Three loading conditions were considered for the stays from a statics point of view:
FIGURE 9.35. Fabcwork for sta\' construction.
the hank side and 20 tendons on the river side, Figure 9.36b. The concrete of the stays has a 2H-day stl-ength 01 approximately 8700 psi (60 ,\IPa). Its function is llot only to protect the tendons, hut also to increase the rigidity of the stays, which is four times that of the tendoJ]s alone. 011
(a)
Short stays 20/16 cables
(b)
FIGURE 9.36.
1
Cross section of stays.
1. For the self-weight of the stays and dead toad of the superstructure, the deck is considered as supported on nonyielding supports. which are the stay anchorage points, and the load in the stays results from the reactions at these points. 2. For design live load, the deck is considered as supported on yielding supports, the rigidity of which is determined by the rigidity of the pre stressed stays. . 3. The prestress of the stavs was calculated with a safety factor against cracking of 1.1 for dead load and 1.3 for live load, without allowing an~ tension in the concrete. The ultimate load safety Elctor is 1.8. For the load condition be tween cracking and collapse the stay rigidity is reduced to the rigidity of the tendons alone .. Their excessive elongation, in case they yielded, would lead to an excessive deflection of the box girder and a premature collapse be fore the proposed safety limit. Therefore, it was necessary to reduce the initial stress of the tendons to 40 to 45o/c of their ultimate strength in order to keep them in the elastic range up to ultimate load determined by the safety factor of the structure as a whole. The sag of the long stay is 2.3 ft (0.70 m) in a length of 328ft (l00 m) under dead load. Under live load the sag is reduced to 1.8 ft (0.55 m). The cross section of the staYs at their extremities is in creased slightly to resist bending stresses. These stresses were calculated by the method of finite dif ferences. In the longitudinal direction the girders are prestressed primarily by the horizontal components of the stay forces. The unstayed end spans are pre stressed with 54 tendons. In the other spans addi tional prestressing is provided by 10 tendons that overlap each other at the supports. These tendons were required until such time as the stay forces were applied and, at completion, to provide safety against cracking and collapse. The deck slab is pre stressed transversely by tendons spaced at 12 to 17 in. (0.30 to 0.44 m). The suspended 213 ft (65 m) span is composed of four precast lightweight concrete girders with a 6500 psi (45 MPa) concrete. The cast-in-place deck slab is increased from a thickness of 9.8 in. (250 mm) in the box girders to 12.6 in. (320 mm), owing to the smaller restraint of the slab in the one web girders.
Tiel Bridge, The Netherlands
The following restraints and conditions were considered in the determination of the construc tion procedure for the main spans of the structure: I. The exclusion of falsework from the river be cause of navigation requirements.
2. The potential for flooding. 3. The presence of the precasting plant on the north bank. 4. The possibility of adjusting the attachment points of the stay to the deck.
417
"'''' .41
!--~=
II
12
PHASE 2
12A
13
~
!~~_~~=I=
I I I I 475~ 72.50
4750
4750
PHflSES DE CONSTRUCTiON DE
L' OUVRAGE PRINCIPAL
Construction was executed in increments limited by the attachment points of' the stays to the deck. The stays were prestressed progressively, by in
creasing the number of stressed tendons as the load in the stays increased. However, during cer tain construction phases when the load in the stays decreased, some of the tendons were detensioned or slacked otT. Using the north side (access viaduct side) as an example, the construction was divided into the following phases, Figure 9.37: PIlil ,I I' 1:
C()n~I/'l1cti()n
o/thl' mller .lImns-that i,l, the stay-supported side span and/lanking span
a. Superstructure from pier 11 to pier 12 and a 72 ft (22 m) cantilever into the next span b. Extension up to temporary support l2A c. Extension up to pier 13 with a 26 ft (8 m) cantilever into the center span; simultaneous construction of the pylon . Phase 2:
Construction of the first section Ol'er the river and the short forestay,
Phase 3:
Construction of the second section over the riNr and the long/oresta}.
The external spans on the north side were con structed on falsework during the dry season. Ctilizing the precast plant on the north side, pre cast segments 16.7 ft (5.10 m) long weighing 132 tons (120 mt) were assembled on the falsework. Segments were joined by tin. (5 mm) cast-in-place joints. Placing of the segments was carried out by the same gantry crane as for the access viaduct. On the south bank, where there was no precasting plant, the external spans were cast in place on false.work. The cantilever river spans were built on 157 ft (48 m) long steel falsework, consisting of four 10ft
MAIN BRIDGE CONSTRUCTiON PHASES
FIGURE 9.37.
~lain
bloidge construction phases.
(3 m) deep girders on 23 ft (7.10 m) centers. This falsework was suspended at one end by prestress ing strands from the top of the pylons. At the lower end. the temporary support strands were an chored in a cross beam that supported the steel falsework by four 350 ton (315 mt) jacks. The 3 ft (1.0 m) stroke of the jacks allowed adjustment of the level of the suspension points, and the jacks were used also to release the temporary prestress suspension strands when the final stays were in stalled. At the opposite end, the steel falsework was hinged. The horizontal force component on these hinges was transmitted directly to the completed part of the deck, and the vertical component was taken by 1 in. (26 mm) bars. In Phase 3, the temporary stays were deflected by means of 95 ft (29 m) booms. This provided the advantage of maintaining the angles at the lower connection equal to that of Phase 2 and keeping approximately the same force level in the tempo rary stay. The falsework used in Phases 2 and 3 was car ried on a barge; it was positioned by two derricks located on the completed part of the deck and by a floating crane. After the box girders were cast, the level of the falsework was adjusted, the last joint
418
Concrete Segmental Cable-Stayed Bridges
was cast, and the concrete was prestressed. The next steps were constructing the stays, prestressing them, releasing the temporary stays, and removing the blsework. In order to reduce creep and shrinkage, the stays were made of 17 ft (5.15 Ill) long segments with protruding reinforcement and 16 in. (0.4 m) cast-in-place joints. The building of the falsework for the stays and the handling of the precast segIllents were carried out with the hel p of a 16 [on (15 mt) tower crane 213 ft (65 m) high, running on the deck. The precast 213 ft (65 m) suspended span gird ers weighed 468 tons (425 mt) and were trans ported by barge.
9.7 Pasco-Kennewick Bridge, U.S.A. The hrst cable-stmed bridge with a segmental con crete superstructure to be constructed in the United States is the Pasco-Kennewick Intercity Bridge crossing the Columbia Rh'er in the state of \Nashingloll, Figure 9.3R. ConstruClioll began in August 1975 and was completed in May 1978. The overall length of this structure is 2503 ft (763 m). The center cable-stayed span is 981 ft (299 111), and the stayed flanking spans are 406.5 ft (124 m). The Pasco approach is a single span of 126 ft (38.4 m),
FIGURE 9.38. Pasco-Kennewick (courtesy of An'id Grallt).
Intercity
Bridge
-while the Kennewick approach is one span at 124 ft (37.8 m) and three spans at 148 ft (45.1 m).4.15.18.19 The girder is continuous without expansion joints from abutment to abutment, being fixed at the Pasco (north) end and having all expansion joint at the Kennewick (south) abutment. The con crete bridge girder is of uniform cross section, of constant 7 ft (2 m) depth along its entire length and 79 ft 10 in. (24.3 m) width. The shallow girder and the long main spans are necessarv in order to re duce roadway grades to a minimum, to provide the greatest possible na\igation clearance below, and to reduce the number of piers in the 70 ft (21.3 m) deep ri\·er. The bridge is not symmetrical. The Pasco pylon is approximately 6 ft (1.8 m) shorter than the Ken newick pylon, and the girder has a 2000 ft (610 m) vertical curve that is no[ symmetrical with the main span. Therefore, the cable-stay pairs are not of equal length, the longest being 506.43 ft (154 m).IH , There is no attachment 01 the girder at the py lons, except for vertical neoprene-teAon bearings to accommodate transverse loads. The girder is supported only by the stay cahles. There are, of course, vertical bearil1g~ al the approach piers and abutments. It is estimated that the natural fre quency of the girder, where it will respond to dynamic acceleration (i.e., earthquake), is 2 cycles per second. If the siluatjon occurs where the lon gitudinal acceleration exceeds this value, the ver tical restraint at the I:asco (north) abutment is de signed to fail in direct shear, thus changing the structure frequency to 0. I cycles per second, which renders the system illSensitive 10 dynamic excita tion. The three main spans were assembled from precast, prestressed concrete segments, while the approach spans were cast in place on falsework, Figures 9.39 and 9.40. Deck segments were precast about 2 miles (3.2 km) downstream from the bridge site. Each seg ment weighs about 300 tons (272 mt) and is 27 ft (8.2 m) long, Figure 9.41. The segment has an 8 in. (0.2 m) thick roadway slab, supported by 9 in. (0.22 m) thick transverse beams on 9 ft (2.7 m) centers, and is joined along the exterior girder edges by a triangular box which serves the function of cable anchorage stress distribution through the girder body, Figure 9.42.6 Each match-cast segment re quired approximately 145 yd3 (111m 3 ) of concrete, continuously placed in a previously adopted se quence within six hours. After initial curing in the forms, the girder segments were wet cured for two weeks in the storage yard, air cured for an ad ditional six months, prestressed transversely,
Brotonne Bridge, France
FIGURE 9.39. Pasco-KcIlnewick Intercitv Bridge. precast segmellts ill maill spans (courtesv of An'id Granl).
FIGURE 9.40. Pasco-Kennewick Intercity Bridge, ap proach spans cast in place on falsework (collrtesy of Waltcr Brvant, FHWA Region 10).
419
cleaned, repaired, completed, loaded on a barge, and transported to the structure site for illStalla tion in their final location. F01' possible unpredictcd developments a shimming process was held in re serve for mainta1l1111g the assembled girder geometry correctness, but it was not used. There are no shims in the segmentally assembled, epoxy-joined prestressed concrete girder.I.;·lH.l!> The sections were barged directly beneath their place in the bridge and hoisted into position, Figure 9.43. Fiftv-eight precast bridge girder segments were required for the project. The stays are arranged in two parallel planes with 72 stays in each plane-that is, 18 stays 011 each side of a pylon in each plane. Thev are held at each pvlon top, 180 ft (55 111) above the bridge roadwaY', in a steel weldment, Figure 9.44. Stay all chorages in the bridge deck are spaced at 27 ft (8.2 11l) to correspond with the segment length. The stays are composed on in. (6 mm) diameter parallel high-strenglh steel wires of the EER type. The prefabricated SlaVS, manufactured bY' The PreSCOll Corporation, arrived on the job site on reels, Fig ure 9.45, and contained from 73 to 283 wires, de pending upon their location in the structure. They were covered with a ~ in. 00 mm) thick poly ethylene pipe, and after installation and final adjustment were protected against corrosion by pressure-injected cement grout. cl'he outside di ameter of the pipe covering varies from 5 to 7 in. (0.12 to 0.17 m). Design stress level for the stays is 109 ksi (751.5 MPa). Stay anchorages
9.8
Pasco-Kennewick Intercity Bridge, precast segments in casting yard (courtesv of An'ill Grant). FIGURE 9.41.
Brotonne Bridge, France
The Pont de Brotonne, designed and built by Campenon Bernard of Paris, crosses the Seine River downstream from Rouen in France. Because of increased navigation traffic in the area, a second crossing over the Seine River was urgently needed between the two harbors of Le Havre and Rouen. The first one, the steel suspension bridge of Tan carville, was opened to traffic in 1959. The second, the Brotonne Bridge, the world's largest cable staved prestressed concrete bridge, was opened to traffic in June 1977. 20 A model of the structure is
I
22.50 m
CROSS -SECTION
OF
CONCRETE
BRIDGE sleeve cushion
I
4A
48 SECTION A - A SECTION. ELEVATION 8 - B FIGURE 9.42. Pasco-Kennewick Intercity Bridge, cross section alld allchorage of st
or
FIGURE 9.43. Pasco-Kennewick Intercity Bridge. erection of precast segments from barge (courtesy of Arvid Grant). 420
FIGURE 9.44. Pasco-Kennewick Intercity Bridge. pylon and stay attachment steel weldment at top (cour tesy of Arvid Grant).
Brotonne Bridge, France
FIGURE 9.45. Pasco-Kennewick prefahricatcd cahle stay on rcel.
Intercity
Bridge,
shown in Figure 9.46 and the general layout in Fig ures 9.47 and 9.4:8. The box girder carries four lanes and replaces ferry service between two major highways that run north and south of the Seine. Because large ships use this section of the river to approach the inland port of Rauen 22 miles (35 km) to the east, vertical navigation clearance is 164 ft (50 m) above water level, which results in a 6.5% grade for its longer approach. 15.21 Total length of structure IS 4194 ft (1,278.4 m), consisting of the main bridge and two approach viaducts. The main crossing has a span of 1050 ft (320 m). On the right bank, the transition between the main span and the ground is quite short be cause of a favorable topography where limestone strata slope upward to a relatively steep cliff. On the left bank, the terrain is flat and occupied by meadows. With an allowable maximum grade of 6.5% and a maximum height of fill of 50 ft (15 m), a nine-span viaduct was required to reach the main ·bridge. In a structural sense, the bridge is divided into two sections separated by an expansion joint at a point of contraflexure in the left-bank viaduct span adjacent to the cable-stayed side span, Figure 9.48. 20
FIGURE 9.46.
Model of the Pont de Brotonne.
FIGURE 9.47. Brotonne.
421
Artist's rendering of the Pont de
The prestressed segmental concrete deck con sists of a single-cell trapezoidal box girder with interior stiffening struts, Figures 9A9 and 9.50. In the approach spans. web thickness is increased from 8 in. (200 mm) to 16 in. (400 mm) near the piers, and the bottom flange thickness is increased to a maximum thickness of 17 in. (430 mm). The only portion of the segment that was precast is its sloping webs, Figure 9.51, which were precast at the site. The other portions of the cross section, including top and bottom flanges, interior stiffen ing struts, and cable-stay anchorages (in the main structure only), were cast in place. Each segment is 9.8 ft (3 m) long. Extensive use of prestressing was made in the deck to provide adequate strength to this light structure. To resist the extreme shear stresses it was decided to place vertical prestressing in the webs. Pretensioned units were stressed on a casting bed, Figure 9.52, and equipped with specially de signed button heads. thus producing a combina tion of pretensioning and anchorage plates. This system has the advantage of ensuring a perfect centering of the prestressing force together with a very rapid transfer of this force at both ends. In tensive rupture tests proved that an extremely high resistance to shear was created by this sys tenl. 20 Finally, prestressing was also used as follows, Figure 9.53: 20 1. Transversely in the top flange to provide flexural strength to the thin 8 in. (200 mm) slab. 2. In the inclined internal stiffeners, to accom modate tensile forces created by the transfer of loads from the box girder to the stays.
.c.. N)
Nl
! \
+.58,50._ ~5850
____ . __320,00
I
'
,')
464 40
.12'840
FIGURE 9.48.
Ccm'r;d
or Brolollllc
,
• 5,5,iQ., nOO~
(63') 19.20
t r s o 6.S0 15')(21')
1.60
(5')
ROADWAY
I
(18')
(13')
FIGURE 9,49.
FIGURE 9.50. Bridge.
Illtel'ior
vIew
of
deck,
b:..:lkhead
ROADWAY
( 18')
Cross sectioll of BroHlIIIH:
FIGURE 9.51.
cou?ler for
steel forms
(21 ')
(13')
Brotonnt'
tensi(;n~ ::"cc S
1.50 ( 5')
6.50
160 • (5') •
Brid~e.
Precast webs, Brownnc
";;ensioning jack
distributiun
be~~
36 mm d i~te.1~i~n-;:-od~
?lcju3table
adjustable brackets'
brackets
"Y',,!dag nut
Brid~c.
11~36 mm ,-,,""...- ..~~.
Dywidag "-
tension bar.
FIGURE 9.52.
Casting bed for pre tensioned webs.
423
424
Concrete Segmental Cable-Stayed Bridges
FIGURE 9.53.
Various prestressing systems in the box girder.
;). Transversely in the bottom flange, to coun teract tensile forces created by the stiffeners. 4. Longitudinally near the center of the main span, to allow for a reasonable margin of the order of 300 psi (2 MPa) of compressive stress in view of creep and secondary tensile stresses. Before erection of the superstructure, the bridge's 12 approach piers were slip-formed, nine on the left bank and three on the right. The pier shaf'ls have an octagonal curvilinear cross section inscribed inside a l3 by 29 ft (4.0 by 8.75 m) rec tangle, Figure 9.54. The same section was used for all the approach-span piers, whose height varied from 40 to 160 ft (12 to 49 m). The shape of the piers did not substantially increase costs but did in (Tease the aesthetic appeal of the piers. The piers bear through a reinforced concrete footing on four rectangular slurry trench walls used as piles with a maximum length of60 ft (18 m), Figure 5.17. The pylon pier shafts also have an octagonal curvilinear shape inscribed inside a 30 ft (9.2 m) square to produce equal bending resistance about both principal axes. They are supported on foun dation shafts having a diameter of 35 ft (10.86 m) with a maximum wall thickness of 6 ft 8 in. (2.03 111). The foundation shafts transfer the loads to a limestone stratum at a depth of 115 ft (35 m) below ground level. Foundation shafts were built inside a circular slurrv trench wall, which was used as a cofferdam for dewatering. 20 When slip-forming of the piers reached deck level, the piers were prestressed to their founda tion so as to stabilize them for erection of the deck segments. As the precast deck units were erected,
w
18
8
!Jeeticm A-A
FIGURE 9.54. spans.
Pier and
Section B-B foundation
of approach
Section C-C
Section D-D
120,oa
Longitudinal Section A-A
FIGURE 9.55.
Half center span and pylon.
__ 8..-l0 __ . _ _ _
connection between pylon and pier
FIGURE 9.56.
~
layout or neoprene bearings
Connection between pvlon, deck, and pier. 425
426
Concrete Segmental Cable-Stayed Bridges
the pylon was constructed by conventional methods. Two single-shaft pylons carry a svstem of 21 stays located on the longitudinal axis of the struc ture, Figure 9.55. The reinforced concrete pylons required limited cross-sectional dimensions to pre clude an unnecessary increase of the deck width while providing sufficient dimension to accommo date bending stresses from a transverse wind di l'cction. Total pvlon height above the deck is 231 ft (70.5 m). Construction of the pylon required leap frog forms with 10 ft (3 m) lifts. An interesting feature is the total fixity of the pylon with the box girder deck. Because the bending capacity of the pYlon pier and foundation had to be such as to ac commodate unsymmetrical loads due to the can tilever construction, a decision was made to take advantage of this requirement in the final structure to reduce the effect oflive load in the deck. There fore, the pylon was constructed integral with the deck at its base, both pylon and deck being sepa rated from the pier by a ring of neoprene bearings, Figure 9.56. 20
FIGURE 9.57.
Cable-Slay anchorage.
All deck loads are carried to the pylon piers by 21 stays on each pylon. Each stay consists of 39 to 60-0.6 in. (15 mm) strands encased in a steel pipe, which is grouted after final tensioning. Stay 1ength varies from 275 to 1115 ft (84 to 340 m). Anchor age spacing of the stavs at deck level is every 19.7 ft (6 m), even other segment, where the inclined stif feners in the deck segments converge, Figures 9.53 and 9.57. A special deck anchorage block was de signed to accommodate the variable number of strands in the stay as well as to allow full adjust ment of the temion in the stavs by a simple an choring nut, Figure 9.58. The anchorage of the stays is such that it is possible at any time during the life of the structure to either readjust the ten sion in the stay or replace it without interrupting traffic on the bridge. Permanellt jacks are incorpo rated into the anchorage, Figure 9.59, such that by tensioning the stav the
,;,J""
renr-
FIGURE 9.58. Jacking of stay.
-
427
Danube Canal Bridge, Austria
concrete
cover
FIGURE 9.59.
Permanent stay anchorag;e.
FIGpRE 9.60. \l
(3 m) beyond the end of the completed section were used to place new elements. The strucwre is shown at the start of main span construction in Figure 9.61, before closure of the main span in Figure 9.62. and completed in Figure 9.63. 20
FIGURE 9.61. reference 20:
Start of main span cOBstruction. from
FIGURE 9.62. erence 20.
Before closure of main span. from rd
FIGURE 9.63. Aerial view of the Brotonne Bridge. from reference 20.
9.9
Danube Canal Bridge, Austria
This structure is located on the West Motorway (Vienna Airport Motorway) and crosses the Danube Canal at a skew of 45°. It has a 390 ft (119 m) center span and 182.7 ft (55.7 m) side spans,
Concrete Segmental Cable-Stayed Bridges
428
I,
I 182.7 ft
390 ft
55.7 m
110m
FIGURE 9.64.
.,
d,
Construction of half-bridge on bank of
FIGURE 9.66.
·1·
55.7 m
·1
EIe\'ation of the Danube Canal Bridge.
Figure 9.64. It is unique because of its construction technique. Because construction was not allowed to interfere 'with navigation on the canal, the struc ture was built in two 360.8 ft (110m) halves on each ballk and parallel to the canal, Figure 9.65. Cpon completion the two halves were rotated into
FIGURE 9.65. c
182.7 ft
final position and a cast-in-place closure joint was made, Figures 9.66 through 9.69. In other words. each half was constructed as a one-time swing span. The bridge superstructure is a 51.8 ft (15.8 01) wide trapezoidal three-cell box girder, Figure 9.70. The central box was cast in 25 ft (7.6 m) long seg ments on falsework, Figure 9.71. After the precast inclined web segments were placed, Figure 9.72. the top slab was cast. Each half-structure has two cantilever pylons fixed in a heavily prestressed trapezoidal crosshead pmtruding under the deck with a two-point bear ing on the pier, Figure 9.73. At the cleek level the stays attach to steel brackets connected 10 pre stressed crossbeams, Figures 9.74 and 9.75. Each stay consists of eight cables, two horizontal by four vertical. At the top of the pylons each cable is seated in a cast-irol,l saddle. The cable saddles are stacked four high, Figure 9.76, and are fixed to each other as well as to those in the adjacent plane. The cables were first laid out on the deck. fixed to a saddle, and then lifted by a cralle for placement at the top of the pylon. The cables were then pulled
Plan of Danube Canal Bridge during construction and final state.
Danube Canal Bridge, Austria
FIGURE 9.67.
Danube Canal Bridge during rotation.
FIGURE 9.69. FIGURE 9.68.
429
Closure joint. Danube Canal Bridge.
Danube Canal Bridge during rotation.
FIGURE 9.70.
Cross section. Danube Canal Bridge.
at each extremity by a winch rope to their attach ment point at the deck level. During rotation of the two half-bridges, the dec k and pylon sat on a bearing consisting of five epoxy-glued circular steel plates. The top plate was coated with teflon, sitting in turn on a reinforced concrete block that sat on a sand box. After rota
tion the structure was lowered to permanent bearings by emptying the sand box. At the canal-bank end the deck had a concrete wall on its underside, bearing on a circular con crete sliding track, Figure 9.77. The bearing be tween the wall and the track was effected by two concrete blocks clad with steel plates, under which
430
Concrete Segmental Cable-Stayed Bridges
FIGURE 9.71. HI idge.
Comtl'uClioll
Oil
ballk. Danuhe Canal
Trapezoidal U'osshead. Danube Canal Bridge. FIGURE 9.72.
Precast \\cbs. Dallube Callal Bridge.
tclloll-coated neoprene pads were introduced during the rotation 1110vemel1l (similar to the in rrementallaullching method). The pivoting was ac complished by means of a jack pulling on a cable anchored in a block located near the sliding-track elld. After rotation the two haJ"es of the structure were connected by a cast-in-place closurejoint, and continuity tendons were placed and stressed. 22 The filial structure is shown in Figure 9.78.
9.10 9.10.1
Notable Examples of Concepts PROPOSED GREAT BELT BRIDGE, DENMARK
The competitIon for a suitable bridge design in Denmark produced many new concepts and ar chitectural styles. The design requirements spec ified three lanes for vehicular traffic in each direc tion and a single railway line in each direction.
FIGURE 9.74. Jacking of stays. Dallube Canal Bridge.
The rail traffic was based on speeds of 100 mph (161 km/hr).2:! Navigational requirements stipu lated that the bridge deck be 220 ft (67 m) above water level, and the clear width of the channel was to be 1130 ft (345 m). A third prize winner in this competition was the Morandi-style design proposed by the English con sulting firm of White Young and Partners, Figure
Notable Examples of Concepts
FIGURE 9.75. Bridge.
431
Cable-stav attachment. Danube Canal FIGURE 9.77. Circular concrete sliding track. Dan ube Canal Bridge.
FIGURE 9.78.
.-
, '11
,
FIGURE 9.76. Stav saddles at pylon. Danube Canal Bridge.
9.7. This design embodied the principles of a cable-stayed bridge combined with conventional approaches of girders and piers with normal spans. The principal feature of this bridge design is the three-plane alignment of cable stays. This feature may become more important in urban areas, where trends in the future may dictate multimodal trans portation requirements and an increase in the
Completed Danube Canal Bddge.
number of automobile traffic lanes. The deck COI1 sists of two parallel single-cell prestressed concrete box girder segments. Figure 9.79. The rail traffic is supported within the box on the bottom flange and the road traffic is carried on the surface of the top flange. The box girder contemplated a depth of 23.5 ft (7.2 m) and width of 27.75 ft (8.45 m) with the top flange cantilevered out 12 ft (3.7 m) on each side. The piers and towers were to be cast-in-place construction to support the deck segments, which were to be precast at various locations on shore and floated to the bridge site for erection. The maximum weight of a single box segment was es timated at 2200 tons (2000 mt). All segments of the superstructure were to be of reinforced and prestressed concrete. Up to this point in time, when the competition for this structLre was conducted, all the concrete cable-stayed bridges had been either designed by
Concrete Segmental Cable-Stayed Bridges
432 _
3.675 m
8.'\5 m
------.;.-~--
3.675 m----o-
Main longitudinal prestressing tendons
I
7.20 m
Vertical prestressing bars
FIGURE 9.i9. Danish Great Belt Bridge. section through deck beam at ex pansion and constructioll joint. frolll reference 23.
;'vloralldi (Lake Maracaibo, Wadi Kuf, and so on) or strongly influenced bv his style (Chaco/ Corrienles). They were typified, for the most part, bv the transverse A-frame pylon with auxilian X-frame support for the girder. However, an entry in the Danish Great Belt Competition by Ulrich Finsterwalder of the German firm of DyckerhofT & Widmann deviated from this style and wa~ awarded a second prize. Finsterwalder proposed a multiple span, multi stay system using Dywidag bars for the stays, Fig ure 9.10. This proposal contemplated a spacing
between pylons of 1148 it (350 m) and a spacing.of the stays at deck level of 32.8 It (10 111). P\"lon height above water level was 520 ft (158.5 m). 1n a transverse cross section the deck was 146 (44.5 m) wide with two centrally located vertical stay planes 39 ft 4 in. (12 m) a part to accommodate the two rail traffic lanes, and three automobile traffic lanes in each direction outboard orthe stay planes, Figure 9.80. The solid concrete deck had a thickness of 3 ft (0.9 m) in the transverse center portion, under the rail traffic, and tap~red to a 1.3 ft (0.4 m) thickness -1.;.158,50
:.12,50
form
I
F'"
~.--.~.--.l._-------- 350,00 -~·-----""'---175,OO --~
- - - ------------------ -r
~-
, ,!
JA:=~=~===~==~:::==::::;::::::::==~::::=====i::======.!i. c'i 0,40
Ij"": - - - - 15,25 ----."'!2,OO:...-lO,OO-----.i2,OO:..-~-- 15,25 _ 1...---------
------44,5O~·--·--------·
..--.--
FIGURE 9.80. Danish Great Belt Bridge, elevation and cross section (courtesy of DyckerhofJ & \\'idmann).
.:!:, 0,00
Notable Examples of Concepts
at the edges. The deck was to be constructed by the cast-in-place balanced cantilever segmental method, each segment being supported by a set of stays. 9.10.2
PROPOSED DA.'vlE POIST BRIDGE, U.S.A.
The proposed Dame Point Bridge over the St. Johns River in Jacksonville, Florida, as designed by the firm of Howard ;-';eedles Tammen & Bergendoff, is a cable-stayed structure with a con crete and a steel alternative. An artist's rendering of the concrete cable-stayed bridge alternative is shown in Figure 9.81. Navigation requirements dictate a 1250 ft (381 m) minimum horizontal opening and a vertical clearance of 152 ft (46.3 m) above mean high water at the centerline of the clear opening. The proposed concrete cable-stayed main structure will h;l\'e a 1300 ft (396 m) central
. --..,..;:,:..""
/
~~~:.
FIGURE 9.81. Dame Point Bridge. arris["s rendering of Ho\\'ard :\cedles LlIl1l11en & Bergendoff).
«Olll'lCSV
433
span with 650 ft (198 m) flanking spans. The layout of the main structure is shown in Figure 9.82.24 Structural arrangement of the bridge deck is shown in Figure 9.83. The bridge deck, which will carry three lanes of traffic in each direction, will span between longitudinal edge girders on each side. The longitudinal edge girder is in turn sup ported by a vertical plane of stays arranged in a harp configuration. The concrete deck and edge girders take local and overall bending from dead and live load in addition to the horizontal th rust from the stavs. 25 The stay cables are anchored in massive ver:tical concrete pylons, two at each main pier, which carry all loads to the foundations, Fig ure 9.84. In the center span, at each edge of the deck, the stays are in a single plane spaced 30 in. (0.76 m) vertically, Figures 9.84 and 9.85. Stays in the side spans, along each edge, are in two planes spaced 30 in. (0.76 m) transversely. Spacing of pairs of stays along the edge beam is approximately 30 It (9.1 111). Preliminary design contemplates 7 to 9 Dywida~ bars per stay, It in. (31.75 mm) in diameter, the number of bars per stay being a function of stre~s in the stay. The Dvwidag bars are to be encased in a metal duct. During erection the fabricated length of duct is left uncoupled. After final adjustment the lengths of duct are coupled and pressure grouted. Thus, the steel encasing tube will thell be composite for live load and secondary dead loa
llev. !5f
(396m
(198m)
1
2600 Main River Bridge ( 793m) FIGURE 9.82. Dame Point Bridge. concrete cable-staved alternative, from reference (courteS\' of Ho;,-ard :\eedles Tammen & BergendofO.
~l
105'-10" (323m)
43'-6"Roadway (06m)2'
43'-6" Roadway (133m)
(!33m)
Cables
C~llit
in
abies
plact' Declo.
i
~Pfecast
Cast- in-situ Beam
T Beam
FIGURE 9.83. Dame Point Bridge. structural arrangemellt of bridge deck. from reference :24 ("(Jurtes\ of HO\\'ard '\c(,dlcsLlllllllCIl &- lkrgcmio!f).
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SIDE VIEW
FRONT VIEW
FIGURE 9.84. Dame Point Bridge, pylon
""
~
u-.
HOw,"D
N:~o':~>":~~·::;~~·cR.G:~o.o::IHNTB
FIGURE 9.85. Dame Poillt illidge, snpnSlrnUllrt' of Ilowan/ :\ccdlcs LlIlIIlICIl & Bcrgelldofl).
(l()llne~V
ISOMETRIC VIEW OF ERECTION SEQUENCE
lal iOll,
\7
from
",
BECI~
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or
CAS.T'IIl~?LAC£
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sap
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(621;0) PR£CAS1 T BEAM
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1.0NSTRIJCT
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TOPf'IN4 [)UII::IIfG EACH (YClf.
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DAMES POINT BRIDGE
CAST~Itl-PlACE
CASTwl~'PLAtE
10,-- ERECT (6)RO) PFlECAST T firM.
lo6,~, [FlECl
JOI~TS
GIRDER SEGMENT
tS- REPEA; STEPS 10 THRU )'< TO STEP lOS
14- RfPlAT STEP 6
13·- REPEAT STEP 1
12- REnAT ST[P 9
I! -
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9- ERECT (4TH) PR£{AH T BCAM
r SEAM
(;A5T-IN~f>LACf
6- OiHT (3RD) PHECAlT
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CONSTRUCT n{>!(,Al
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IRGIN TYPICAL HQtJHlCt Of (ABtES. GIRDER ArlD CUNSTRLlCTIOll
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3- ERECT fiRST PRUAST T BEAM
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ll'rt'll'IlC(,
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PLATE 17
Concrete Segmental Cable-Stayed Bridges
436
balanced cantilever method. Two pairs of traveling forms are then used for sequential casting of 17.5 ft (5.3 m) lengths of edge girders on each side of the pylon. The bridge deck consists of single-T precast Hoor beams spanning between longitudi nal edge girders and a cast-in-place topping. The precast T's are pretensioned for erection loads. After erection the entire deck is post-tensioned to provide positive precompression between edge girders under all conditions of loading, Figure 9.85. 24 ,25 A hinge ex pansion joint is provided at the cen terline of the main span to allow for changes of superstructure length due to temperature, creep, and shrinkage. Similar joints are provided at the end piers, and link connections are used to prevent vertical movement of the superstructure.
0./ 0.")
1)IUW()S/~n
fa ·C'l(-.·}-UIL 'CAl' HW n(;/:', C.S ..·/.
The site for the proposed Ruck-A-Chucky Bridge designed In T. Y. Lin International, Figure 9.86, is approximateh' 10 miles (16 kl1l) north of the pro posed Auburn Dam and about 35 miles (56 kill) northeast of Sacramento, California, crossing the middle fork of the American River. The river at this location is about 30 ft (9 m) deep and 100 ft (30.5 m) wide: however, upon impounding of the water behind the proposed dam, the river will be come 450 It (137 m) deep and 1100 ft (335 m) wide. 2 (; In order to provide a 50 ft (15 m) vertical clear ance above high resenoir water level, a bridge length of 1300 ft (396 m) will be required between the hillsides, which rise at a 40° angle from the
horizontaL Two existing roads parallel the canyon faces; a straight bridge across the river would re quire extensive cuts into the rock faces of the can yon to provide the necessary turning radiu~ at the bridge approaches. This would be not only expen sive but would also be damaging to the environment. Conventional piers in the river provide prohibitive design constraints, not only because of the 450 ft (137 m) water depth, but also because of the seis micity of the area. The hydroseismic (seiche effect) forces provide a formidable design load. After extensive studies, the proposed final solu tion was that of a hanging arc, Figures 9.87 and 9.88. The geometric configuration of this structure is such that the stays are tensioned to control the stresses and strains, in order to balance all the dead load with zero deHection; the curved girder carries the traffic and absorbs the horizontal component of the stays as axial compression. The stays are an chored on the slope according to the design form~ tion to control the line of pressure in the girder. Thus, an ideal stress condition is achieved with almost no bending or torsional moments. After numerous studies and trade-olfs a final radius of cunature was selected at 1500 ft (457 m).26 Two alternative designs have been prepar,=d for this structure, one with a steel box girder and one with a lightweight concrete box girder. The con crete box girder, Figure 9.89, is fixed at the abut ments and has no hinges or expansion joints in the 1300 ft (396 m) spcin. Depth of this box girder is 8.5 ft (2.6 m), so as to provide vertical stiffness and to distribute live load and construction loads on the deck to a sufficient number of adjoining cables. Stay anchorage at the girder is at 30 ft (9 m) inter vals, based on construction and aesthetic consider ations. 26
FIGURE 9.86. Ruck-A-Chucky Bridge, artist's rend ering (courtesy of T. Y. Lin).
.10
c"o ....
lercn'llCl' ~ti .
FIGURE 9.87.
BRIDGE
RlIck-.\-Chuckv Hlidgc,
~~
of
12'9.691
CHOj1tD· LIN,rN
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Ruck-A-Chuch Bridge, cross section of concrete box girder alternative, from reference ::6.
10. R. Morandi, "Some Types of Tied Bridges ill Pre stressed Concrete," First International Symposium, I. A. Feige, "The Evolution of German Cable-Staved Concrete Bridge Design, ACI Publication SP::3, Bridges--An Overall Survey," Acier-Slahl-Sleel, :\0. Paper 23-25, American Concrete Institute, Detroit, 12, December 1966 (reprinted in AISC Engineering 1969. journal, july 1967). II. Anon., TIll" Brid!il' S/JIlnnmg I.rlkp .H{/mmilJl) 1/1 Vrn ezw11l. Wiesbaden, Berlin, Bauverlag (;m 1)I-L, 2. H. Thul, "Cable-Staved Bridges in Germany," Pro ceedings, Cunference on Structural Steelwork, I flstilutiun 196~\. of Civil Engineer>, Sl'ptember 26 to 28, 1966, London. I::. Anon., "Longest Concrete Cable-Stan~d Span Can tilevered over Tough Terrain," Enginfenng NPll',\ 3. W. Podolny, jr., and J. F. Fleming, "Historical De Record, julv 15, 1971. velopment of Cable-Staved Bridges," journal uj the Structural Divisiun, ASCE, Vol. 98, No. ST9, Sep 13. ::\. Gray, "Chaco/Corrientes Bridge in Argentina," tember 197::. JJ unicipal EngillCPrs journal, Pa per :\1). 380, Vol. 59. '4:, W. Podolny,jr., and]. B. Scalzi, "Construction and Fourth Quarter, 1973. Design of Cable-Stayed Bridges," john Wiley & 14. H. B. Rothman, and F K. Chang, "Ll)ngest Precast Sons, Inc., :--Jew York, 1976. Concrete Box-Girder Bridge in Western Hemi sphere," Civil Engineering, ASCE, March 1974. 5. ~L S. Troitsky, "Cable-Staved Bridges-Theory and Design," Crosby Lockwood Staples, London, 1977. 15. W. Podoiny, jr .. "Concrete Cable-Stayed Bridges," Transportation Research Record 665, Bridge En 6. F. Leonhardt, "Latest Developments of Cable gineering, Vol. 2, Proceedings, Transpurtatiun Research Stayed Bridges for Long Spans," Saetryk af Bygoningsstatiske ivfeddelelser, Vol. 45, No.4, 1974 Board Conference, September 25-27, 1978, St. Louis, Mo., National Academy of Sciences, Washington, Denmark). D.C. 7. 'E. Torroja, Philosophy of Structures, English version
References
by J. ]. Polivka and !¥filos Polivka, V niversity of California Press, Berkelev and Los Angeles, 1958. 8. H. M. Hadley, "Tied-Cantilever Bridge-Pioneer Structure in V.S.," Civil Engineering, ASCE, january 1958. 9. F. Leonhardt and W, Zellner, "Vergleiche zwischen Hzmgbrucken und Schragkabelbrucken fur Spann weiten tiber 600 Ill." Intemationnl dssociation j(n Bridge and Structural Engineering, Vol. 32, 1972.
16. H. Schambeck, "The Construction of the Main Bridge-Hoechst to the Design of the 365 m Span Rhein Bridge Dusseldorf-Flehe," Cable-Staved Bridges, Structural Engineering Series No.4, june 1978, Bridge Division, Federal Highway Adminis tration, Washington, D.C. 17. Anon., "Tiel Bridge," Frey'>sinet International, STUP Bulletin, March-April 1973. IR. A.l'vid Grant, "Pasco-Kennewick Bridge-The
440
Concrete Segmental Cable-Stayed Bridges Longest Cable-Stayed Bridge in !'\orth America." Ch'l} Ellginrrring, ASCE, \'o!. 47, :\'0. 8, August
1977. 19. Arvid Grant, "Intercity Bridge: A Concrete Ribbon on']' the Colu!I1bia River, Washingtoll," Cablc Staved Bridges, Structural Engineering Series No. 4, June 1978, Bridge Di\'ision, Federal Highway Administration. \\'ashington. D.C. 20. C. Lenglet, "Brotonne Bridge: Longest Prestressed Concrete Cable Stayed Bridge," Cable-Stayed Bridges, Structural Engineering Series !'\o. 4, June 1978, Bridge Division, Federal Highwa\' Adminis tration, \\'ashington, D.C.
21. Anon., "Cable-Staved Bridge Goes to a Record with Ihbrid Circlel Design." Lligill(,l'Iill{!, .\'('il',I-R('rou/, October 28. 1976. qq AIIOIl., "The Danube Callal Bridge (Austria),"
~
Frl'"),ssinet international, STUP Bullrtill, May-June, 1975. 23. Anon., "Morandi-Stde Design Allows Constant Sus pended Spans," COl/.witing Eligilll'l') (l,ondon), ~1arch 1967.
24. H. J. Graham, "Dame Point Bridge," Cable-Stayed
Bridges, Structural Engineering Series No.4, June
1978, Bridge Division, Federal Highway Adminis
tration, Washington, D.C. 25. Anon., "Dame Point Bridge," Design Report, How ard :\'eedles Tammen & Bergendoff, ;'\ovember 1976.
26. T. Y. Lin, Y. C. Yang, H. K. Lu, and C. M. Redfield, "Design of Ruck-A-Chucky Bridge," Cable-Stayed Bridges, Structural Engineering Series No.4. June 1978, Bridge Division, Fecleral Highw;1\ Adminis tration, Washington, D.C.
10
Segmental Railway Bridges
10.1
INTRODUCTION TO PARTICULAR ASPECTS OF RAILWA Y BRIDGES AND FIELD OF APPLICA· TlON
10.2
LA VOULTE BRIDGE OVER THE RHONE RIVER, FRANCE MORAND BRIDGE IN LYONS, FRANCE
10.3 lOA
10.5 10.6 10.i
CERGY PONTOISE BRIDGE NEAR PARIS, FRANCE MARNE LA VALLEE AND TORCY BRIDGES FOR THE NEW EXPRESS LINt NEAR PARIS, FRANCE CLICHY R.-\ILWAY BRIDGE l'iEAR PARIS, FRANCE OLIFANTS RIVER BRIDGE, SOUTH AFRICA
10.1 Introduction to Particular Aspects of Railway Bridges and Field of Application Construction of segmental post-tensioned bridges for railway structllres started in France in 1952 . with a bridge
10.8
INCREMENTALLY LAUNCHED RAILWAY BRIDGES FOR THE HlGH·SPEED LINE, PARIS TO LYONS, FRANCE 10.9 SEGMEl'iTAL RAILWAY BRIDGES Il'i JAPAN 10.10 SPECIAL DESIGN ASPECTS OF SEGMEl'iTAL RAILWAY BRIDGES 10.10.1 Magnitude of Vertical Loads 10.10.2 Horizontal Forces 10.10.3 Bearings 10.1 0.4 Stray Currents 10.10.5 Durability of the Structure 10.10.6 Conclusion 10.11 PROPOSED CONCEPTS FOR FUTURE SEGMEN· TAL RAILWAY BRIDGES
moderate proportion of the design load. Fatigue and durability of railway structures, therefore, are essential problems and need careful consideration, particularly in view of the fact that maintenance and repair of railway structures under permanent
FIGURE 10.1. La Voulte Bridge. new of the com pleted structure. 441
Segmental Rc;ilway Bridges
442
trafflc is a very critical operation that can lead to unacceptable disturbance in a railway network.
10.2
La Voulte Bridge over the Rhone River, France
This first segmental prestressed concrete railway bridge is a notable structure and a landmark in the development of prestressed concrete. Constructed in 1952, it carries one railway track over the Rhone River near la Voulte, 80 miles (128 km) south of Lyons, in the southeastern part of France. The structure has five spans, each 164 ft (50 m) long. Each pier is made up of two inclined legs. and each span is an independent frame supported by an inclined leg at each end. Between the inclined legs on each pier, the deck is supported by a small beam resting on simple bearings. Construction proceeded using the cantilever schellle, with poured-ill-place segments. The form travelers wcre supported by a temporary sted truss i>ridge, Figure 10.2. The cantilevers were built sYlllllletrically III ol1e span. the unbalanced moments being taken care of by temporary post-tcnsioning connecting t he two inclined legs ali(I the independent beam on one pier. The seg lllellts were 9 It (2.75 m) long. Tbe bending mo mellls 01 each completed frame were adjusted by jacks placed at midspan and by continuity post tellsionillg tendons. Figure 10.3,
10.3
Morand Bridge in Lyons, France
This structure is a combined highway and mass transit bridge over the Rhone River in Lyons,
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FIGURE 10.2. La Voulte Bridge, aerial view of [he deck under construction.
FIGURE 10.3. La Voulte Bridge. cantilever' deck con struction in progress.
France's third largest city. It is a three-span con tinIlous struclllre witll span lengths of 160, 292, and 160 ft (49,89, and 49 m), resting on two river piers and two end abutments, which allow the tran sition of highway and railway traffic on both banks. The deck is made lip of two parallel box girders carrying at the upper le\el three lanes of highway traffic including sidewalks. Inside each box girder is a railway track for the mass-transit system, Fig ure 10.4. . This final scheme proved to be significantly less expensive and more efficient in terms of the layout of the railway system. than did the initial proposal, which contemplated a submerged tunnel for the railway crossing and a separate bridge for the highway traffic. Dimensions of the structure in cross section are shown in Figure 10.5. The railway clearance of 13 it 5 in. (4.12 m), including ballast and rail, calls for a 15 fl (4.56 m) structural height in excess of the normal requirements for a maximum span length of 292 It (89 m). A constant-depth girder could thus be maintained throughout the river crossing except in the vicinity of the river piers. where short straight haunches allow the depth to be increased to 22 ft 7 in. (6.90 m). Over the piers a strong transverse diaphragm connects the two box girders, and the additional height over the pier allows the continuity of the diaphragm over the height of the haunch while the full clearance of the trains is maintained inside the box girders. The deck was built in balanced cantilever with 10 ft (3.0 m) long cast-in-place segments using one pair of travelers on a typical one-week cycle, Fig ures 10.6 and 10.7. Typical quantities of materials are as follows for the deck alone:
443
Morand Bridge in Lyons, France
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Deck area Concrete Reinforcing steel Prestressing steel (longitudinal and transverse)
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FIGURE 10.6. su perstructure.
Morand Bridge, construction of the
Both concrete and reinforcing steel quantities far exceed those required for a typical highway be cause of the very important increase of loads due to the railway lines in the box girders. The structure was completed and opened to traffic in 1977.
444
Segmental Railway Bridges
single box carries the twin tracks, with the depth varying between 13.6 ft (4.15 m) and 17.9 ft (5.45 m) for the maximum span length of 280 ft (85 m) as shown in Figures 10.9 and 10.10. The segmental deck was cast in place, with travelers working in the conventional balanced cantilever fashion.
10.5 Marne la Vallee and Torcy Bridges for the New Express Line near Paris, France The extension of the Paris mass-transit system in the highly populated southeastern suburbs was the occasion for building a long elevated segmental prestressed concrete railway structure in a sensitive urban environment, Figure 10.11. This structure, located in the city of Marne la Vallee, includes a bridge over the Marne River and a long viaduct carrying two parallel railway tracks. Near the tran: sition between the river bridge and the viaduct a passenger station is carried by the bridge structure. Three major considerations guided the choice of the structure:
FIGURE 10.7. \loralld Bridge, constructioll of supcntructlln'. :--';otc pier segment for second parallel box girder.
10.4
Cergy.Pontoise Bridge near Paris, France
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railway lille \\'as completed ill 1977 between
Paris alld the new satellite W\\'n oj Cergy.Pontoise. A major prestressed COllcrete structure carries this line onT sen'ral ohstacles, including an inter change between two expressways (A-~6 alld :\-14) alld two brallches of the Seine Ri\·er.
Maintain maximum clearance at ground level, not only to reduce the visual disturbance to the neighboring population, but also to allow all piers of the new structure to be fully compatible with the layout of all existing and future roads.
The treslle structures have a solid slab deck with spans varying between 65 ft (20 m) and 117 ft (35.60 m). T\'pical dimensions of the two main bridges over the Seine are shown in Figure 10.8. A
Elevation (a)
Typical cross section (b)
FIGURE 10.8. section.
Cergy-Pontoise Bridge, dimensions.
(a)
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Marne La Vallee and Torcy Bridges near Paris, France
445
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FIGURE 10.9. Cergv-Pontoise Bridge, cantilever con struction.
FIGURE 10.10. c1osurc.
Cergv-PoI1toise Bridge. mam span
Produce a structure that is aestheticallv pleasing when seen constantly from nearby.
Protect the neighbol'ing population from unac
ceptable noise aggression.
Basically, the structure is a single box of constant depth built of precast segments assembled by pre stress into a continuous beam; the beam rests upon vertical piers provided with an architectural shape and regularly distributed at distances of 90 ft (27 m) to 120 ft (36 m), Figure 10.12. Both parallel tracks are laid on the transversely prestressed deck slab of the box girder and on a crushed-Slone bed retained sidewavs bv three conlinuous reinforced concrete walls. A central noise barrier separates the two opposite tracks and pre vents the noise of a train riding one track to travel across to the other. At the edge of the concrete box girder. precast concrete panels manufactured with spe~ial white cement improve the appearance of the structure while providing the outside sound barriers. I
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FIGURE nUl. Marne la Vallee Bridge, aerial view of the completed structure.
FIGURE 10.12. :'/arne la Vallee Bridge. finished structure from ground level.
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In plan, the structure is laid out on a curve with a minimum radius of curvature of 1640 ft (500 Ill). Figure 10.11. Characteristic dimensions of the Marne la Vallee Viaduct are shown in Figures 10.13 and 10.14 and are summarized as follows:
L Bridge over the Marne River: a. Total length, 528 ft (161 mi.
b. Three-span continuous bridge with spans of 157, 246, and 125 ft (48, 75, and 38 m). c. Cross section: constant-depth box section with depth of 12.8 ft (3.90 m), web thick ness varying from 20 to 35 in. (0.50 to 0.90 m) and bottom flange thickness from 7 in. (0.18 m) at midspan to 51 in. (1.30 m) over the river piers. Length of precast segments 5.6 ft (1.71 m). d. Two river piers are founded on large diameter bored piles and support the su perstructure through special teflon bearings.
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Marne la Vallee Bridge, typical sections of deck and piers.
Marne la Vallee and Torey Bridges near Paris, France
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f. All bearings in the viaduct are standard laminated elastomeric pads. g. Piers are made of twin columns located under the webs of the box girder and con nected at ground level by a common foot ing, which transfers the loads to deep slurry trenched walls anchored in lime stone. The number and position of these bearing walls under each pier has been determined in relation to the magnitude of the transverse and longitudinal hori zontalloads transferred by the superstruc ture, particularly in the curved portion of the viaduct.
(a)
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FIGURE 10.14. \Iarne la Vallee and Torev Viaduct, l\pic~t1 deck sections. (a) .\larne la Vallee l;'estle and ['orey Viaduct cross section. (h) \!arne la Vallee Bridge over lhe .\£arne River.
2. Elevated viaduct: a. T Ofal length. 4482 ft (1367 m). b. The viaduct is divided into 11 sections separated by expansion joints. allowing compatibility of thermal stress between the continuous welded rails and the concrete superstructure. The typical section is 412 ft (126 m) long with four spans of 88, 118, 118. and 88 ft (27,36,36, and 27 m). e. The two south viaduct sections adjacent to the main river crossing carry the passen ger station and have _shorter spans 69 and 92 ft (21 and 28 m). d. Typical cross section is a single box carry ing the two tracks with two main vertical webs 35 in. (0.90 m) thick and two sharply inclined facia webs used essentially for ar chitectural purposes to reduce the appar ent structural depth of the box and focus the eye on the high parapet wall. e. Average length of precast segments 7.5 ft (2.:30 m).
The entire project was predicated on the use of precast segments with match casting and epoxy joints. A precasting yard on the south bank of the Marne, using four casting machines, produced the 690 segments with a maximum weight of 60 tons (55 mt) in eleven months. Segments were trans ported with a tire-mounted self-propelled carrier over the finished portion of the deck and placed in the structure with a launching gantry, Figure 10.15, in balanced cantilever. The gantry used on that project was that designed and built earlier for the B-3 Viaducts project. The gantry allowed all operations to be per formed from the top in complete independence from the ground and all its related constraints. Placing of all segments was performed in a period of nine months between March and December of 1976, including the three spans of the main bridge and the forty-four spans of the viaduct. The entire project was completed in 24 months (including preparation of the final design), for a total deck area of 190,000 ft 2 (l 7,600 m 2). Figure 10.16 shows
FIGURE 10.15. r-.larne la Vallee Bridge, precast seg ments placed with the launching gantry.
Segmental Railway Bridges
448
FIGURE 10.18. FIGURE 10.16.
:>Iarne la Vallee Bridge. crossing the \Iarne River and elevated passenger station.
Torey Viaduct, segment transporta tion frol11 l'Iarne la Vallee to Torc\,.
The total length of 1870 it (570 m) is divided into three separate sections: one fou r-span unit, on<:; nine-span unit, and one four-span unit.
FIGURE 10.17.
?-larne la Vallee Bridge, aerial view of the rin~r crossing. a passenger station. and the elevated viaduct.
Precast segments were placed in the structure with an overhead launching gantry of a type ,.;lightly different from the one used previously, although calling on the same sequence of mm'e ments. T\\'o parallel longitudinal trusses make the track for a transverse overhead portal crane carrying and placing the segments between the trusses. Figures 10.19 and 10.20 show the general view of the gantry a~d the detail of one segment placing. The overall view of the finished bridge appears in Figure 10.21.
the northern span of the river crossing and the ele vated passenger station. Figure 10.17 is an aerial view of the overall project. 1n view of the success of this first application of segmental construction in urban railway elevated structures, the Paris Mass-Transit Authority de cided to extend the same concept to construct an other large structure a few miles eastward: the Torcy Viaduct. Fortunately, the precasting yard for the first bridge was still available and all seg ments could be manufactured there and trucked to the second bridge site, Figure HU8. Dimensions of this new bridge are as follows: Cross section: exactly the same as for the Marne la Vallee elevated viaduct.
Distribution of spans: 17 spans with typical span
length of 115 ft (35 m).
FIGURE 10.19. Torey Viaduct, precast segment plac ing with launching gantry.
elichy Railway Bridge near Paris, France
FIGURE 10.20. Torcy Viaduct, detail of segment handling between twin trusses of launching gantry. ~~l"~"':'~~
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10.6
449
vated metro. It crosses the Seine River adjacent to a new highway bridge between the cities of Clichy and Asnieres, as shown in Figure 10.22. Layout and principal dimensions appear in Figures 10.23 and 10.24. The prestressed concrete segmental structure is 1350 ft (412 m) long with a 280 ft (85 m) main span over the river with a deck of variable depth. The river piers of the two railway and highway bridges match exactly to minimize water flow and barge traffic disturbance. A provision is made for a sec ond future highway bridge at the other side of the railway bridge, as seen clearly in Figure 10.25a. The rest;icted transverse clearances between the three structures and their corresponding traffic explains the special shape of the piers for the center railway bridge, which was carefully studied architecturally to enhance the appearance of the project. Foundations were very close to one an other but could be maintained structurally inde pendent to better control settlement and avoid vi bration interference between bridges and in the ground. To carry the two railway tracks, the deck has a typical cross section consisting of three precast webs connected by a bottom slab, which forms es sentially the compression Aange over the piers, and an intermediate slab, which receives the ballast, Figures 1O.25b and 10.26. The depression thus realized between the web top flange and the tracks has several advantages, including providing full safety against derailing on one track and reducing the noise level. Construction of the superstructure included match casting of all webs in a yard near the project site. The webs were placed in balanced cantilever with a light portal crane carried by the finished
Torcy Viaduct, view of the completed
Clichy Railway Bridge near Paris, France
At about the same time the two structures de scri~ed aboye were built, a large and innovative railway bridge was constructed in the northeastern suburb of Paris for another extension of the reno
FIGURE 10.22. Clichy Railway Bridge, VIew of the completed structure.
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portion of the deck, Figure 10.27. Maximum weight of precast webs was 19 tons (17 mt), whereas segments that included the full three-web box (or even a more conventional single box for the equivalent span length) would have weighed in excess of 66 tons (60 mt), After assembly of precast webs with longitudinal post-tensioning, the two
twin slab sections were poured in place between the webs in balanced cantilever on very simple travel ers, Web segments were 7.3 ft (2.22 m) long for the constant-depth part of the deck and 4.8 ft (l.48 m) for the variable-depth part. In fact, the slabs were cast in place between the three webs in two or three increments of that length respectively (a length of
Clichy Railway Bridge near Paris, France
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14-.6 or 4"+·1 m) to reduce the number of site oper ;)tions. A three-day cYcle of operations could be constantly maintained, including some overtime work for the larger segments near the river piers. Overall, construction in cantilever of the total superstructure took one year between September 197.7 and September 1978. A special design aspect, specific to railway bl'idges, was the transfer of horizontal loads (in
FIGURE 10.26. Clichv Railwav Bridge, pier seglllCIIt and ca ntilever con~rrllerion.
duced through braking or starting of the trains over the bridge), to the piers and foundations. A single fixed bearing was provided over pier P6, the foundation of which was designed to transfer to
Segmental Railway Bridges
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the need arise in the future. Two families of ten dons could be added:
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Above the lower slab in the two voids of the box section, anchors being provided in blisters already built in the structure. Atop the center precast web and on the outside face of the two facia webs, anchor blocks and de viation saddles being prestressed by high-strength bolts to the precast webs.
FIGURE 10.27.
Chehv Railw,1\ Bridge, placing pre
cast \\Ths for can1 ile\"t'r constnlClion.
the limestone stratum the total maximum hori zontal load of 660 tons (600 Int) applied to the bridge. There are three pot bearings between the deck and the pier shaft, each capable of safelv transferring half of the maximum horizontal load. Each bearing can thus be changed under traffic without I-educing the capacity of the structure. Special provisions were also included at the de sign stage, Figure 10.28, to allow additional pre stressing to be incorporated in the structure should
The large precast architectural panels on hoth sides of the deck could be temporarih' removed to allow this work of additional prestressing to be per formed. Cpon completion, all additional tendons would be full\' protected and concealed behind the panels. The new line has been open to traffic since May 1980, and the first months of operation confirm that the precautions taken to reduce noise and vi: bration disturbance through welded continuous rails and sound-barrier panels make such elevated structures an acceptable solution for mass-transit lilies in urbanized areas.
10.7 Olifant's River Bridge, South Africa
(b)
FIGURE 10.28. Clichy Railway Bridge. (a) View of adjacelll highway and railway hridges crossing the Seine River. (b) Provisions for future additional prestress.
This structure is part of a line carning iron ore on special heavy trains 7500 ft (2300 m) long made up of 200 cars with a lotal weight of 19,000 tons (17,000 mt) to connect the Sishen mines to the har bour of Saldanha 110 miles north of Capetown. Olifant's River Viaduct is today the world's longest incrementally launched prestressed concrete structure (refer to Chapter 7) with a total length of 3400 ft (l035 m) and 23 spans of 148 ft (45 m), Figure 10.29. Shown in cross section in Figure 10.29, the single box girder deck accommodates only one track on ballast. The equivalent uniform live load of the 33 ton (30 mt) axles is 7.1 kips/lineal ft (l0.5 mt/lm), which is increased by an impact factor of 1.29. The 23 spans are divided into two II-span sec tions, each anchored to the end abutment, and one single transition span at the center. This scheme allows all horizontal loads to be transferred to the abutments. The maximum horizontal reaction in cluding all thermal effects is in excess of 1200 tons (1100 mt). The piers, which vary between 80 ft (25 m) and 150 ft (55 m) in height, are extremely flexi ble and do not, therefore, have an important effect on the horizontal restraint of the structure, except during construction. The pier shafts have an 1
Incrementally Launched Railway Bridges
453
(b)
FIGURE 10.29. Olifallt's Rin'r Viaduct. (II) General view of the structure. (b) '[\Vic~\ll"ross section.
shaped cross section with longitudinally tapered faces. Neoprene bearings are used for the piers near the abutments and teAon sliding bearings in the center of the structure. The deck was entirelv constructed behind one abutment (see schematic view in Figure 7.29) and incrementally launched in one direction. Construc tion time for the superstructure was nine months, with a theoretical cycle of 10 working days for a . typical 148 ft (45111) span realized after 10 spans; it was further reduced to se\en days with two shifts toward the end of the project. The total weight of the superstructure of 14,500 tons (13,000 mt) called for two 200 ton jacks for the push-out oper ations in increments of 3.5 ft 0.00 m). A 60 ft (18 m) long launching nose was used in front of the first span to reduce the variation of bending stresses in the superstructure during the ·successive stages of construction, Figure 10.30. The bridge nearing completion is shown in Figure 10.31; it was opened to iron ore trains in 1976.
10.8 Incrementally Launched Railway Bridges for the High-Speed Line, Paris to Lyons, France To meet increased competition by domestic air lines, the French National Railways decided to
FIGURE 10.30. Olifant's River Viaduct, launching nose reaching bevond a high pier.
build some new very-high-speed train lines (safe maximum speed of 200 mph or 320 km/hr) and started the construction of the first such line be tween Paris and Lyons, which included an entirely new structure over a distance of 250 miles (400 km) with proper connections to the existing met ropolitan track and station system. The new project required 400 bridges including nine large viaducts. such as the structure shown in Figure 10.32. A very comprehensive optimization study followed, and a set of guidelines and struc tural standards were prepared for the French Na tional Railways by a team of engineers headed by one of the authors. Results of the preliminary in vestigations and of this optimization study can be summarized as follows: L Track alignment is chosen to keep the curva ture in plan more than 10,500 ft (3200 m) and preferably more than 13,000 ft (4000 m). The
454
Segmental Railway Bridges
4,
5,
6.
FIGURE 10.31. Olifallt's Ri\cr Viaduct. \'ie'\\" of the s\ nln llre lIe'a ri IIg com plet ion,
FIGURE 10.32. Railwa\ Viaducts for Paris-Lnms high-spcl'd lil1c, \'ie\\' of the \'iadun O\;er (he Saone Ri\'er.
corresponding cross fall between rails is 7 in. (180 111m), 2, All rails are to be continuously welded and placed on a ballast bed with a minimum thick ness or 14 in. (0,35 m). 3. Maximum rigidity of the structures is obtained by using a continuous box section with slen derness ratio of 1/14. The corresponding
maximum deflection under design load is therefore 1/2000 of the span, whereas conven tional specifications for normal-speed lines allow up to 1/800, Adopt as much as possible single box girder decks for the two parallel tracks with minimum web thickness of 14 in. (0,35 m) and a minimum top slab thickness of lOin, (0.25 m). The optimum span length is between 150 and 170 ft (45 to 50 111), which lea\es the construc tion method open to various solutions (can tilever, spar1-b\'-span or increlnental launch ing). The horizontal loads should be transferred to one abutment equipped with a special fixed bearing, allowing all piers to be relieved of am appreciable longitudinal bending. A tvpical H-section was adopted as the most appro priate except for certain specific locatioos where a box section might be required.
Because many of the \'iaducts were located in en virolll11elltalh sensitive areas, all overall architec IUral study was also conducted to establish a unitv or appearance for all hrid~es ill terms of t he shapes of deck and piers, parapet or guard rails, abut ments and approach fills, Of the nine viaducts, two were finally con structed with conventional methods and the re maining seven wert' incrementally launched, This method proved economical in view of the moder ate span lengths, the depth of the box section avail able, and especially because the superimposed dead and live loads were so much more important than for a highway bridge that the increased dead-load moments during construction were in proportion of much less significance. Table 10,1 gives the essential characteristics of the seven segmental viaducts, including principal quantities of materials for the superstructure. Ele \'ations or fi\'e hridges appear in Figure 10,33, As an example of the construction method, some details are given ror the bridge over the Saone River, where a launching nose 93 ft (28.50 m) long and weighing 71 tons (65 mt) was used in front or the first span to reduce the stress variations in the superstructure during launching, Figure 10.34. "fhe bridge superstructure was cast in successive increments in a fixed location behind the right bank abutment in the length of a half-span, Figure 10.35. A typical sequence of operations is shown schematically in Figure 10.36. Each superstructure section is in fact cast in two stages
~
(Jt (Jt
(Ill))"
41.0 (12.50) 40.0 (12.10)
429
(131) 279 (il5)
Long. grade: 0.2% Straight in plan
39.0 (11.90)
1260 (385)
-10.3 (12.30)
1112 (339) 39.0 (11.90)
41.0 (12.50)
662 (202)
1370 (419)
41.0 (12.50)
(ft)
Total Witllh
662 (202)
!:Iritlg.: Length
Long. grade: O.S5% Slraight in plan
Long. grade: 2.5% Straight in plan Long. grade: 3.5% Radius in plan: 10,61l0 ft (3250 Ill)
Long. gradt.:: 1.3% Radius in plan: 20,000 ft (6000 m) I.ong. grade: 0.95% Radius in pia,,: 26,000 ft (8000 m) Cin·ula. ptofile in elevation: R 130,000 h (40,000111)
Bridge I.ayolll
7.8 (2.37)
13.1 (4.(H»
(:UO)
10.8
10.8 (S.30)
11.5 (3.51)
10.8 (3.30)
10.8 (3.30)
(tl)
Heighl
19.0 (5.80)
190 (5.80)
IB.O (5.50)
18.0 (5.50)
IS.O (5.50)
111.0 (5.50)
IS.O (5.50)
(It)
Box Widlh
eft
12 (0.30)
24/35 (0.60/0.90)
10 (0.25)
(0.28)
II
12.5 (0.32)
24 (0.60)
12.5 (0.32)
12.5 (0.32)
II (0.275)
11 (0275)
Top (in.)
Pi.:,. (III)]
(0.20)
8
12/20 (0.30/0.50)
14 (0.35)
14 (0.35)
43/105
43 (1'1)
36 (II)
43/115 (l:W5)
(! :I/:I:!)
2.30 (0.70)
2.30 (1l.70)
84 (50)
84 (50)
84 (50)
190 (110)
250 (150)
250 (150)
210 (125)
84 (50) 2.46 (0.75) 46 (14)
12.5 (0.32)
240 (140)
78 (46) 661148 (20145)
10 (0.25)
2.52 «(l.77)
[Ib/yd' (kg/lll')]
Reinf. Steel
240 (140)
[Ib/yd' (kg/m")]
HT. S.ed
Quantities of neck
78 (46)
(m'/Ill")]
[fI'/ft'
:i.52 (0.77)
4611:i1
1ft
Heigh.
ConCi.
(HI:;7)
10 (0.25)
Bottom (in.)
Flange Thick
24 (0.60)
20 (0.50)
18/49 (0.45/1.25)
(0.45/1.25)
IHI4!J
(in.)
Web Thick.
Dimensions of Deck or in. (m)]
Characteristics of Segmental Viaducts on the Paris-Lyons High-Speed Line
uSlfunures are nUlnhet eLI with increasing nlunbers, fronl Paris to Lyons.
109-S~v 144-109 (33.4 - 8 @ 44 - 33.4) @ Roche 108 7 @ 149 - 108 (33.1 - 7 @ 45.5 - 33.1) CD Sei1lE River 114 - 201-114 (34.8 - 61.1 - 34.8) ® Center Canal (length) 85 105 85 (26 - 32 - 27)
@ Digoille
Saulieu 115-3«v 144-115 (35 - 3 @ 44 - 35) CID Sereill 115- 3 @ 144 - 115 (35 - 3 @ 44 - 35) (J) Same River 155 - 5 @ 164 - 137 (47.2 - 5 (iiJ 50 - 41.8)
CD
1ft
Bridge Location and Span Lengths
Table 10.1.
Year
1978
1980
1978
1978
1979
1979
1978
Cmn pk,,·!!
...
LYON
Viii/due sur la Seine.
ttl
II
Viadue du Serrein.
t\l
It
Via due de la Digoine.
Viadue de /a RO'ihe.
I
I
tlUl I
r=m=.
-~.~.. •-
=;;=a'""1I
ji
tuttli,
',."
~
'1.111
!:==1~~~?F~~~::::,E*' i "J ",' '" ,,',
JI'JOI
Viadue sur fa Sa6ne.
FIGURE 10.33. 456
Elevation of five segmental bridges for Paris-Lyon!> line.
Segmental Railway Bridges inJapan
457
(bottom slab during the first stage, webs and top slab during the second stage). The typical con struction cycle allowed casting a half-span every week-that is, constructing two spans per month. The launching operation proper called for a very efficient system, developed and perfected previously in Germany, including under each web of the box section: One vertical jack with sliding plate Two coupled horizontal jacks for actual launching, allowing movements in 3 ft increments FIGURE 10.34. Saone Ri\'er Bridge, launching nose approaching pier.
Typically, launching of an 80 ft section took three to three and a half hours, despite the large weight of the concrete superstructure, reaching 9000 tons (8000 mt) at the end of construction. Figure 10.37 shows a completed structure, and Figure 10.38 shows another aspect of the con struction of these seven viaducts.
10.9 Segmental Railway Bridges inJapan Many railroad bridges have been built in Japan using the segmental construction technique. The sketches shown in Figures 10.39 through 10.42 de pict the elevation and the cross section of the fol lowing cast-in-place segmental bridges: FIGURE 10.35. Saone River Bridge, aerial view with casting vanl in behind abutment in foreground,
TE~PCRARY
SLiOINI>
FOR
PADS
50 DOm
-
SUPPORT PUSHt£ (WITH JACK)
50.00
~-
4300
Kyobashigawa Bridge Natorigawa Bridge
-
APPROACH
SPt.N
,
PRECAST Yt.RO
23!10
....---~~.-~,.....
SITUATION DURING FABRICATION OF SEGMENT 7
-
2(\.50 1025 2070. 2500 -~
.......................25.00
--~.
SrTUATION AFTER PUSHING OF SEGMENT 7 GENERAL PRINCIPLE OF THE CONSTRUCTION METHOD BY PUSHING FIGURE 10.36. Saone River Bridge. typical construction stages of incre mental launching.
Segmental Railway Bridges
458
FIGURE 10.37. Saone River Bridge, view of the completed structure.
FIGURE 10.38. Digoine Bridge, incremental launch ing over high piers.
Kisogawa Bridge Ashidagawa Bridge Figure 10.43 shows the Kakogawa Bridge during construction. The superstructure is made of twin constant-depth box girders, one box girder carry ing one railway track. The total length of the bridge is 1640 ft (500 m), with typical span length of 180 ft (55 m). Each box is 13 ft (4 m) wide and 11.5 ft (.3.50 m) deep. The precast segments were handled by a launching gantry and assembled by longitudinal post-tensioning tendons. The erection used the balanced cantilever system. The most outstanding prestressed concrete rail way structure, however, is the Akayagawa arch
bridge shown in Figure 10.44. Total length is 980 ft (298 m) and the center arch span is 410ft (126 m). The 13 ft (4.00 m) deep box girder carrying two railway tracks is continued throughout be tween abutments and rests over the center gorge on a very flat arch rib through ten spandrel col umns. The respective proportions are such that the deck carries all bending moments and the arch rib carries the normal load induced by its curvature. The erection scheme was unique and called for cantilever construction starting from both sides. A very strong back stay made up of a prestressed concrete member with a prestress force of 5300 tons (4800 mt) was installed diagonally between the top of the main transition piers between the arch structure and the approaches on one hand, and the foundation of the adjacent piers in the approach structures on the other hand. While erection progressed, high-strength steel bars were placed diagonally between the vertical members, forming a temporary truss structure until the crown was reached from both ends. Con trol of tensioning of those steel bars was very criti cal and complicated. Finally, all steel bars and the two temporary back stays were removed after clo sure of the arch at midspan.
10.10 Special Design Aspects of Segmental Railway Bridges 10.10.1
M.AGNITUDE OF VERTICAL LOADS
Most bridges carry tracks laid on ballast with a minimum thickness of 10 to 14 in. (0.25 to 0.35 m).
Special Design Aspects of Segmental Railway Bridges
459 HAKATA
ELEVATION
CROSS SECTION
FIGURE 10.39.
Hvobashigawa Bridge, Japan.
Live loading used in design of railway bridges varies between countries-Cooper loading for Anglo-Saxon countries, new UIC loading for most European countries-and also according to the na ture of the structure: mass-transit lines are usually designed for much lighter loads than normal train lines. The heaviest loadings are for are freight trains. To exemplify the basic diff.erence between a highway and a railway bridge, Figure 10.45 com pares a typical 150 ft span and a 36 ft wide deck normally designed for three highway lanes of traffic or two railway tracks. The total superim posed dead and live load is 3.6 times greater for the railway bridge. hi addition, the weight of bal last (representing 40% of the total load) must be considered as a live load to cover the cases where the ballast is removed from the deck or has not yet been placed on a new bridge.
/0./0.2
HORIZONTAL FORCES
Railway bridges have to carry very important hori zontal forces, between five and ten times the hori zontal forces carried by a highway bridge of similar size. The standard current practice for long via ducts is to have a fixed bearing on one abutment if the bridge length is less than 1500 ft (450 m), and on both abutments and on intermediate special bents if it is greater. The order of magnitude of this horizontal force on the abutments carrying the fixed bearings is often 1000 tons for a two-track viaduct. The various forces involved are described below: Long-itudinal Forces
Braking and acceleration forces
Segmental Railway Bridges
460 TOKYO
r
r-----------51.95
52.00
~---t--
524.90 m
•
~
-1- H
!Jl:Ur '0
I
--
52.00 I 52.00 - 54.50 . 54.50 - 52.00 , 52.00 52.00 T"---r-O ·--~---T----·---I--------r..----..-'---....---
10,.
:~
--
0
MORIOKA
_ 5195
------~.
. '
[2
I
•
~#M~" 8·"~ Ff;1~ F9r ELEVATION
~---,;:-
- --
I]
-----1 -:
J L...2:=====i' .. - - .. i
I
-----j _-=-5::-9--t--t-....:2:::,:.2::..::5......,.1_-=-2.:.:.,75::...--li 2. £,5 6.00
I I
2.45
~~-_---~--~l~l.l~O~m~------~ CROSS SECTION FIGURE 10.40.
Natorigawa Bridge, Japan.
Forces due to box girder deformations: creep, shrinkage, and temperature variations Loads induced by the length variations of long welded rails under temperature variations Longitudinal component of wind forces Braking and acceleration forces are one seventh of the total weight of live loads, with a ceiling of 285 tons for braking and 53. tons for ac celeration (French regulations). Forces due to longitudinal deformations of the box girder vary because of creep, shrinkage, and temperature variations. The bearing displace ments induce horizontal loads by distortion or friction. Length variations of the long welded rails due to temperature variations create a horizontal force parallel to the rail. This force can be estimated at 50 tons per rail (length of rail more than 100 me ters). For a two-track bridge it is 2 x 2 x 50 = 200 tons.
Longitudinal component of wind forces are de scribed in the AASHTO specifications for bridges. Transverse Horizontal Forces Centrifugal horizontal force can be very important for high-speed trains. For the 200 mph train from Paris to Lyons this force is more than 400 tons for some viaducts 1200 ft (380 m) long with two tracks and radius of cur vature of 10,500 ft (3200 m), The lateral accelera tion is more than 20% of that of gravity. Transverse wind force is described in the AASHTO standards (50 Ib/ft2 ). 10.10.3
BEARINGS
In order to gain complete control of these very large horizontal forces, the bearings are specially designed to take care of the vertical loads and ro tation of the box girder and simultaneously to pro vide all possible horizontal restraints (fixed bear ing, bearing free lengthwise or crosswise, or both),
Special Design Aspects of Segmental Railway Bridges
461
----1
m
---
I HAGOn, -=>
ELEVATION
76
or-b5~~~:~
I-Iii
~1~IL
I
co
:1,
0
Ii ' 2.00
,I
1 '9 .u
'I'1
2 40 !.' 5:30 ,. 2.00 9.30m
I
I
CROSS SECTION FIGURE 10.11.
Kisogawa Bridge. Japan.
These bearings are specially manufactured for this type of structure. Figures 10.46 and 10.47. The sliding parts consist of a teflon-coated plate resting on a stainless steel plate, and the restraints are pro vided by steel keys.
ference of potential with the ground may be mea sured at regular intervals, and a permanent con nection with the ground may be decided on as a result. 10.10.5
10.10.4
DURABILITY OF THE STRUCTURE
STRAY CURREVTS
For structures carrying electrified railways there is some uncertainty about the long-term effect of stray currents generated near the power lines. In order to preclude electrolytic corrosion of rein forcing steel and prestressing steel, the following precautions are now taken in prestressed concrete structures: The deck is electrically isolated from the ground, piers, and abutments by e1astomeric plates. The reinforcing and prestressing steel svstems of the entire deck are interconnected by mild steel bars to equalize the electric potential. The dif
Because very difficult problems of train traffic would arise during repairs to these bridges, their durability needs special attention. The following provisions were established for the high-speed bridges between Paris and Lyons: Under the worst service loads the concrete must remain under a 140 psi minimum compression. For continuous bridges, the design shall be checked by weighing the dead-load vertical force on the bearings. The stressing force of the post-tensioning tendons shall be less than 80% of the ultimate strength of the tendons.
462
Segmental Railway Bridges
HAKAlA
----::..
ELEVATION
FIGURE 10.42.
CROSS SECTION Ashidagawa Bridge, Japan.
10.10.6
FIGURE 10.43. Kakogawa Railway Bridge, placing precast segments with launching gantry.
The ultimate strength of the structure should be capable of supporting the service loads increased by 30%, if 30% of the post-tensioning steel were missing. Provisions shall be made for installing additional tendons while the structure is under traffic. The additional post-tensioning force shall be 15% of the designed force minimum. It shall be possible to replace all the bearings.
CONCLL'SlON
This review of specific design problems of railway bridges should raise no doubts whatsoever about the advantages of prestressed concrete and seg mental construction in this field. Prestressed con crete is the safest material known today to resist indefinitely the large variations of loads such as those applied to a railway bridge. The problem of fatigue has been covered briefly in Chapter 4, and the results mentioned there apply particularly well to railway bridges. The main objective in the design and construction of prestressed concrete bridges should be to minimize and even eliminate concrete cracking, which is al ways a source of weakness in a structure subject to cyclic loading. . The use of the provisions laid down in Section 10.10.5 should result in practically crack-free structures with an expected life free of major maintenance.
(a)
Arch rib
(b)
FIGCRE 10.44. .\k;n;lg;ma I<.;lil\,·;I\ l)ridge. general dimciisiolls. \.lliOl1. (/1) rq)ical ClOSS sectioll .\-.\.
55 k 125t)
5A ,
III.'IIIIIIIIIII!IIIIIIU
j
55 k (25t) .
55 k (25!)
I
J
55 k (25t)
(II)
Fk
5A k/cF
j j
(8 t/ml)
1IIIIIIIIIIIIIlIIIIIIIIIIII
. 2.6'
I i80l
Railwav Bridge
Description Span length Deck width :\ umber of lanes or t LICb Superimposed dead load: Ballast Curb, pavement. etL Total S.L. Live loads: Equivalent uniforlll load
Impact bctor
Total L.L.
Total (S.L + L.t.)
150 ft (45 m)
150 ft (45 Ill) %ft(lllll) Three lanes
:.16 ft (11 Ill) Two tracks 6.:3 kips/h 0.& kips/ft
L5'kipslft
i.O kipslft
1.5 kips/ft
6.8 kips/It
2.4 kipslll
30%
2.8 kips/ft
8.8 kips/ft
4.3 kips!!t
15.8 kips/ft
FIGURE 10.45. Venical loading on railway bridges. (II) Typical U Ie track loading. COlllparison of superimposed dead and live loading on highway and r,lilw
(b)
463
Segmental Railwa)' Bridges
464
10.11
... ... :.".
.,"
' ,",
·t~....: ......
'" '-. , r ,... "
.
• I'.. • •
'"
.
. ..
) ~
,
.
.
.
FIGURE 10.46. pOl bearillg \\'ith unidircc· I jona! horizollla!lII01'cmclll.
Proposed Concepts for Future Segmental Railway Bridges
We should note that many types of structur:es de scribed for highway bridges are equally appropriate for railway bridges: the structures described in this chapter were essentially girder or arch bridges built in cantilever or incrementally launched. Today, many design projects are based on stayed bridges. As an example, Figure 10.48 shows a pro posed crossing of the Caroni Ri"er in Venzuela for hea"y iron ore freight trains.
I
!
I
I !
i
I I
,
131',/31"129'
,-=-+-'.
~-.
t
!3/tJ' 318'.
FIGURE 10.48. Pmpmt'd iron ore ]'ail"'
('J()s~jng
of Rio Camni iOl
11
Technology and Construction of Segmental Bridges 11.1 SCOPE AND INTRODUCTION 11.2 CONCRETE AND FORMWORK FOR SEGMENTAL CONSTRUCTION 11.2.1 Concrete Design and Properties 11.2.2 Concrete Heat Curing 11.2.3 Dimensional Tolerances 11.2.4 FOTmwork for Segmental Construction 11.3 POST-TENSIONING MATERIALS AND OPERATIONS 11.3.1 General 11.3.2 Ducts 11.3.3 Tendon Anchors 11.3.4 Tendon Layout 11.3.5 Friction Losses in Prestressing Tendons 11.3.6 Grouting 11.3.7 Unbonded Tendons 11.4 SEGMENT FABRICATION FOR CAST-IN-PLACE CANTILEVER COr-;STRUCTION 11.4.1 Conventional Travelers II.U Self-Supporting Mobile Fonnwork
11.4.3 Two-Stage Casting 11..1..1 Combination of Precast Webs with Cast-in-Place Flanges 11.4.5 Practical Problems in Cast-in-Place Construction Camber Control 11.5 CHARACTERISTICS OF PRECAST SEGMENTS AND !\fATCH-CAST EPOXY JOINTS
11.1
Scope and Introduction
Certain problems are common to all tvpes of seg mental construction-for example, the selection and control of materials. prestressing operations. and choice of bearings, joints, and wearing surface. Other prohlems are specific to a particular con struction method. The use of form travelers in cast-in-place cantilever construction and the cast ing ~U1d handling of segments in precast cantilever construction are two such examples. This chapter covers these various topics in the following order:
11.5.1 First-Generation Segments 11.5.2 Second-Generation Segments 11.5.3 Epoxy for Joints 11.6 MANUFACTURE OF PRECAST SEGMENTS 11.6.1 11.6.2 11.6.3 11.6.4 11.6.5
Introduction Long-Line Casting Short-Line Horizontal Casting Short-Line Vertical Casting Geometry and Survey Control Segment Precasting in a Casting Machine Segment Casting Parameters Survey Control During Precasting Operations Survey Control During Construction Conclusion 11.6.6 Precasting Yard and Factories 11.7 HANDUNG AND TEMPORARY ASSEMBLY OF PRE CAST SEGMENTS 11.8 PLACING PRECAST SEGMENTS 11.8.1 Independent Lifting Equipment 1 1.8.2 The Beam-and·Winch Method 11.8.3 Launching Girders Launching Girders Slightly Longer Than the Span Length Launching Girders Slightly Longer Than Twice the Typical Span REFERENCES
I. Problems common to all segmental bridges 2. Problems specific to cast-in-place cantilever construction 3. Problems specific to match-cast segmental bridges with particular emphasis on cantilever construction, which is the most widely used method. In designing segmental bridges, it is important to pay attention to certain details at the time of conception, in order to keep the project as simple as possible and thereby achieve economy and effi 465
466
Technology and Construction of Segmental Bridges
nellC), during construction. The following guide lines apply to both cast-in-place and precast con struction: 1. Keep the length of the segments equal, and keep the segments straight even for curved stnlCtures (chord elements). <) :\1aintain constant cross-section dimensions as much as possible. Variations of cross-section dimensions should be limited to change of depth of webs and thickness of bottom slab. ~~. Corners should be beyelcd to facilitate casting. 4. Segment proportions (shear keys, for example) should be such as to allow easy form stripping. 5. Ay(lid as much as possible surface discon tinuities on webs and flanges caused by anchor blocks. inserts, and so on. 6. Use a repetitive lavout for tendons and all chors. if possible. 7. Minimize the number of diaphragms amI stif fencl'S. H. Avoid dowels passing through fonnwork, if possihle. 11.2
Concrete and Formwork for Segmental Construction
11.2.1
COXCRETE DESIG.\' /i,VD PROPERTIES
Ullifonll qual it v of concrcte is essential for seg mental construction. Procedures for obtaining high-quality concrete are covered in PCl and ACI publications. 1.2 Both normal weight and light weight concrete can be made consistent and uni form by means of proper mix proportioning and prod uction con t ro1s. Ideal concrete will have a slump as low as prac ticable. notwithstanding the possible use of special placing equipment such as pumps, and a 28-day strength greater than the minimum specified by structural design. It is recommended that statistical methods be used to evaluate uniformity of con crete mixes. The methods and procedures used to obtain the concrete characteristics required by the design may vary somewhat, depending on whether the seg mCllIS are cast in the field or in a plant. The j'csults will be affected by curing temperature and type of curing. Liquid or steam curing or electric heat curing may be used. In tem perate climates and where cu ring is car ried out in an isothermal enclosure, only small ad
ditions of heat are required to maintain the curing temperature, full advantage being taken of the heat of h\'dration generated by the fresh concrete. In this case heat demand will be a function of the ambient temperature, more heat being required in winter and little or no additional heat during hot summer weather. 'Where segment production rate is not critical, it may be possible to do without accelerated curing and simplY use a normal curing period of a few dm's, during which the concrete is well protected against excessive temperature variations and a!J exposed surfaces are kept moist. A sufficient number of trial mixes must be made to assure uniformity of strengt h and modulus of elasticity at all important phases of construction. Careful selection of aggregates, cement, admix tures, and water will improve strength and mod ulus of elasticity and will also reduce shrinkage and creep. Soft aggregates anc! poor sands must he' avoided. Creep and shrinkage data for the con crete mixes should he determined bv tests. Corrosive admixtures such as calcium chloride should nevcr be used, since thc\' can have a det rimental effect on hanlelled cOllcrete and can cause corrosion of reinforcement and prestressing steel. \Vater-reducing admixtures aud also air entraining admixtures that improve cOllcrete re sistance to environnienlal effects, such as de-icing salts and freeze and thaw actions, are highlv desir ahle. Yen careful control at the batching stage is required, however, since the advantages of air entrained concrete callnot be relicd upon ullless the qualltitv of entrained air is within specified limits. The cement, fine aggregate, coarse aggregate, water, and admixture should be combined to pro duce a homogeneous concrete mixture of a quality that will conform to the minimum field-test and structural design requirements. Care is necessary in proportioning concrete mixes 10 insure that they meet specif1ed criteria. Reliable data on the poten tial of the mix in terms of strength gain, creep, and shrinkage performance should be developed to serve asth~ basis for improved design parameters. Proper vibration should be used to permit the use of low-slump concrete and to allow for the op timum consolidation of the concrete.
11.2.2
CONCRETE HEAT CURiNG
An early concrete strength usually is required to reduce the cycle of operations and to maintain the
Concrete and Formwork for Segmental Construction
efficiency of the special equipment used either in cast-in-place or in precast construction. Two methods may be used for this purpose, either sepa rately or together: (a) preheating the fresh con crete, before placing it in the forms or in the cast ing machines, (b) heat curing the concrete after consolidation in the forms. In the first case the concrete is preheated to about 85 to gO°F (30 to 35°C). This operation is achieved in several ways: 1. Steam heating the aggregates-a simple solu tion that presents the disadvantage of chang ing the aggregate water content 2. Heating the water-a solution that has limited efficiency, owing to the small proportion of water in comparison with the other compo nents (water at l40°F raises the concrete tem perature bv only 20°F). 3. Direct heating of the concrete mix bv injecting steam into the mixer itself-the best solution and the one lllost easily controlled. To a void heat loss, the [or!11S are generally in sulated and some source of radiant heat is installed inside the segment (radiators or infrared ele ments). In the second case, the concrete is heated in its mold inside a container in which low-pressure steam is circulated. I n this way it is relatively easy to obtain the strength required for prestressing oper ations [350n to 4000 psi (25 to 28 MPa)] after one or two days, even in winter. If however, tensioning operations are to be performed earlier, after 24 hours for example, modifications must be made to the concrete in the anchorage zone. Electrical resistances mav be embedded in the concrete. or precast end-blocks may be used. Pre cast end-blocks were used notably for the Issy les-~IoulineaLlx, Clichy, and Gennevilliers Bridges. For the Gennevilliers Bridge, despite the excep tional dimensions of the box girder deck, two segments were cast each week .through an early stressing of the prestress tendons. In the case of precast segments, the accelerated curing of the concrete must attain two apparently contradictor\' objectives:
1. 2. 3.
467
Conventional kilns. Direct heating of forms with electric resis tances. Direct heating of forms with low-pressure steam.
The use of a conventional kiln entails several precautions. First, a constant temperature must be maintained in the kiln. Second, the segment sec tions of varying thickness are all heated to the same temperature, which may produce unacceptable local thermal gradients and cracking if heat curing is excessive.' Finally, the heated segment may be subjected to a thermal shock when removed from the kiln, if the difference between the ambient temperature and the kiln temperature is greater than 60°F. However, kiln curing is a simple solu tion and is acceptable for long curing cycles-for example. of 10 to 14 hours. Form heating by means of electrical resistances is perfectly adapted to long curing cycles. This sys tem permits a wide range of adjustment per zone, varying the temperature between the thick and thin sections of the segment and thereby minimiz ing thermal gradients and eliminating the risk of permanent damage to the concrete at the begin ning of its solidifying phase. The heating of forms with low-pressure stearn is preferable for short curing cycles lasting less than five hours, as it permits the distribution of a large quantity of calories over a short period, causing a rise in the internal temperature of the concrete of the order of 20 to 30°F (10 to l5°C) per hour. This system, however, requires a complex regulator to ensure an equal temperature in all the form panel enclosures, at all times during the treatment, what ever their thermal inertia and the external influences to which they are subjected, Figure 11.1.
1. Accelerated curing to permit rapid stripping. 2. Final compressive strength as near as possible tQ thaL of the design concrete.
Several curing systems may be considered:
FIGURE 11.1. Viaducts).
Heat-curing control system (B-3 South
Technology and Construction of Segmental Bridges
468
The different systems (kiln, electrical resistances, and low-pressure steam) have all been applied suc cessfully to segmental bridges. The segments for the Choisy-Ie-Roi and Courbevoie bridges were kiln cured. Electric heating was adopted for the construction of the upstream and downstream bridges on the Paris Ring Road and the Blois Rridge. among others. Form heating using low pressure steam was used for the Pierre Benite Bridges. the Oleron Viaduct. and the B-3 South \'iad ucts. Whether forms are heated bv electricity or bv steam, it is relatively easy to produce a long curing ocle, and the desired final concrete strength is easih' ohtained. A short curing cycle, on the other hand, reguires a great deal of caution and meticu lous preliminary calculations. Particular attention must be given to:
I. Choosing a cement, the performance of which
is adapted to the accelerated curing of concrete (preferred is artificial Portland cement with: C"A ~ II (If and C: I S/C 2S ~ 3). 2. Consistently manufacturing concrete with a minimum water content and a maximum tem perature ol9S"F (35°C) at the time of pouring. 3. Using sufficiently rigid forms to resist the thermal expansion of the concrete in its plastic state while heating.
212
In order to avoid a drop in the long-term me chanical properties of the concrete. the tempera ture curve during the heat curing must necessarily include. see Figure 11.2: An initial curing period of two to three hours, during which the concrete is kept at the ambient temperature
An increase in temperature at a low rate of less than 36°F (200C) per hour
A period (depending upon the concrete strength be attained) during which the temperature is held constant and below 150°F (65°C)
to
A period during which the concrete is cooled at a rate similar to that used for the temperature in crease The loss of strength greater:
III
If the initial curing period is short
It' the temperature increase is rapid II the lIJaximum telllperature is high
As an example, the short-cycle treatment used lor the B-3 Viaduct segments was the following, see Figure 11.3: Initial period of H hour at 95°F (35°C) (mixing temperature)
PREHEATING ALTERNATIVE
95
65-1---
'-v--I~ '-----r----I\'---~.,------il INITIAL TEMPERATURE CONSTANT CURING INCREASE TEMPERATURE PERIOD
FIGURE 11,2.
the long term will be
COOLING
Heat-treatment cycle.
Concrete and Formwork for Segmental Construction 11.2.4
SHORT CYCLE
GO F
LONG CYCLE f'1---- r--_
11.0'
FIGURE 11.3.
Example of shl-H·t and long cycles.
Temperature increase of 27°F (l5°C) per hour for 2 hours A constant temperature of IS0°F (65°C) for H hours Figure 11.3 shows an example of long-cycle heat treatment, the Conflans Bridge, which had a total heat-treatment duration of 19 hours.
11.2.3
DI.HE.YSIOXAL TOLERAA'CES
Formwork that produces typical bridge box girder segments within the following tolerances is consid ered to be of good quality~·4: Width of web Depth of bottom slab Depth of top slab Overall depth of segment Overall width of segment Length of match-cast segment Diaphragm dimensions
FORMH'ORK FOR SEGMENTAL CONSTRUCTION
Formwork along with its supports and foundations must be designed to safely support all loads that might be applied without undesired deformations or settlements. Soil stabilization of the foundation may be required. Since economical production of cast-in-place or precast segments is based on repetitive use of the same forms as much as possible, the formwork must be sturdy and special attention must be given to construction details. Where form work is to be assembled by persons other than the manufacturer or his representatives, particular care must be taken with erection details and assembly instruc tions. All elements of the formwork must be easy to handle. 1.2 Formwork for structures of variable geometry will need to be relatively flexible in order to allow adaptation at the various joints. Both external and internal forms are usually retractable in order to leave a free working space for placing reinforcing steel and prestressing ducts. 3 Special consideration must be given to those parts of the forms that have variable dimensions. To facilitate alignment or adjustment, special equipment such as turnbuckles, prefitted wedges, screws, or hydraulic jacks should be provided. Tendon anchors and inserts must be designed in such a way that they remain rigidly in position during casting. Projecting anchorage blocks or other such irregularities should be detailed to permit easy form stripping. 3 If accelerated steam curing with temperatures of the order of 130°F (55°C) is to be used, then the deformations of the forms caused by heating and cooling must be considered in order to prevent cracking of the voung concrete. In general, internal vibration using needle vi brators should always be applied. External vibra tors, if used, must be attached at locations that will
::d in. +! in.
to 0 in. ±t in. ±~ of depth with t in. min. ±iooo of width with t in. min. Hl.
±~
469
in.
10 mm)
(+ 10 mm to 0 mm)
(±S mm)
(5 mm min.)
{5 mm min.} (±S mm) (± 10 mm)
470
Technology and Construction of Segmental Bridges
achieve maximum efficiency of consolidation and permit easy replacement in the case of a break down during casting operations. External vibration may lead to f~ltigue failure in welded joints, and regular inspection should be made to help prevent am sudden failure of this kind. 3 Paste leakage through formwork joints must be prevented by suitable design of joint seals. Nor mally this can be achieved by using a flexible seal ing material. This is particularly important at the joint face with the matching segment, where loss of cement paste can lead to poorlv formed joint sur faces and subsequent spalIing and loss of matching, requiring repair. Special attention must be given to the junction of tendon sheathing with the forms. 3 • 4 All form surfaces, especially welded joints in con tact with the concrete, must be perfectly smooth and free from reentrant areas, pitting, or other discontinuities, which could entrap small volumes of UlllCl'ete and lead to spalling during form strip ping. 3
11.3
Ducts must have sufficient grouting inlets, shut off valves, and drains to allow proper grouting and to avoid accumulation of water during storage. Vent pipes should not be spaced more tha'J1 ap proximately 400 ft (120 m) apart. 7 This spacing may have to be reduced, depending upon the ex pertise of the personnel performing the grouting. Particular attention must be paid to the quality of duct connections at the joints between segments. At the joints, accurate placing is mandatory. The method of duct connection depends on the type of joint 3: Telescopic sleeves pushed over projecting ducts -wide joints Screw-on type sleeves-wide joints Internal rubber or plastic sleeves-malch-cast joints Gaskets or other special seals-match-cast joints' No special provisions: clean ducts with a torpedo after jointing to remove penetrated epoxv if any-match-cast joints
Post-Tensioning Materials and Operations 11.3.1
CEA'ERAL
Techllical details relating to the different methods available are described in the various post tensioning manuals 5 •6 and in the specific docu ments issued by su ppliers. 113.2
DUCTS
Ducts are used to form the holes or enclose the space in which the prestressing tendons are lo cated. The ducts may be located inside or outside the concrete section. Although in some instances the tendons are placed in the ducts before concreting (cast-in-place and span-by-span construction), post-tensioning tendons will normally be threaded into the ducts after erection of the segments. The' duct cross section must, therefore, be adequate to allow proper threading; and in general it will be about t in. (5 mm) larger in any direction than for ducts in which the tendons are placed before concreting. The duct dimension must allow not only the in stallation of the tendons but also free passage of grout materials after stressing. The ratio or pro portion of cross-sectional area of the duct with re spect to the net area of prestressing steel should conform to appropriate specifications or codes. 4 A minimum value of 2 usually leads to satisfactory re sults.
Connection tightness is essential in order to pre vent penetration of joint material, water, or other liquids or solids into the ducts, which would intro duce a risk of blockage, and also to prevent leakage at the joint during tendon grouting operations. 3 ,
11 33
TENDOlv' ANCHORS
Tendon anchors usually consist of a bearing plate and an anchorage device either in combination or as separate units. Shape and dimensions of the an chors must conform with the applicable specifica tions, particularly insofar as bearing stresses are concerned. Choice of anchor positions in the segments should take into account the following considera tions;}: Tendon layout requirements and installation se quences. Stresses generated around the anchors. Ease of tendon threading and stressing. Ease of formwork preparation, stripping and con crete placing. Certain anchorage positions, such as the anchorage block on a thin slab shown in Figure 11.4, should be avoided. If this type of detail cannot be avoided, then particular care must be taken in design and construction of the zone concerned.;}
,,
=
Post-Tensioning Materials and Operations
FIGURE 11.4.
.-\nchoragc
block
position
to
be
avoided.
Bearing plates are usually emhedded in the seg ment at the time of casting. In certain cases they are installed against the hardened surface of the concrete with a dry mortar bed or a suitable cush ioning material such as asbestos cement or syn thetic resin. 11.3.4
TEVDON LAYOCT
This subject has been covered in Chapter 4 relating to design. The choice of tendon layout must be treated carefully, with special attention paid to the following factors: Construction sequence with respect to tendon placing. segment casting (or erection), and other construction imperat.ives Standardization and repetition of essential fea tures, especialh· duct and anchor positions at joints (in order to facilitate formwork design) Various loading conditions throughout the con struction period and in service When using large tendons. it is not advisable to couplers or crossed splices. for reasons of con gestion and formwork complication. Also, couplers and splices should not be located in areas where yielding mav occur under ultimate load condi tions. 3 I n order to limit friction losses, and to facilitate tendon threading. excessively curved tendons should be avoided if possible. u~e
Il.3.5
FRICTION LOSSES LV PRESTRESSI.VG
TE,VDOSS
Segmental construction usually calls for prestress ing tendons to be installed through a succession of short duct lengths coupled to one another at the joints between segments, these being at approxi mately 8 to 30 ft (2.5 to 10 m) intervals. The friction factors (for curvature and wobble) usually accepted for long tendons in cast-in-place structures may not be realistic for this type of con
471
struction under ordinary working conditions and supervision. The actual results obtained in a seg mental bridge built in Europe are given below by way of example for the benefit of future project designers. Cantilever tendons were placed along a straight profile in the roadway slab and anchored either on the segment face or in a block-out inside the box girder. Continuity tendons were either anchored in a block-out at the bottom slab level or draped upward in the webs and anchored in the same block-out of the cantilever tendons. All tendons were made up of twelve 0.6 in. diameter strands. Soluble oil for reducing friction in the ducts was not allowed by the consultant. The calculations were carried out using the following values for curvature and wobble friction coefficients: f.L
0.20,
K
= 0.007/ft
0.0021/m
The Young's modulus of the tendon samples tested in the factory or in the laboratory varied between 28,000 and 29,000 ksi, and the variation between various heats over the whole structure was very low. According to direct tests carried out on site, and a systematic analysis of all results of ten don elongations recorded during the stressing op eration, the actual Young's modulus of a (twelve 0.6 in. diameter strand) tendon at first tensioning varied between 25,000 and 26,000 ksi, which is only 90% of the value recorded during factory and laboratory tests. Figures 11.5 and 11.6 show values of the wobble friction coefficient K measured for all the tendons in the structure's 18 cantilevers. All the tendons are shown in Figure 11.5, while Figure 11.6 shows only those tendons in the spans without hinges. and separates the tendons anchored on the segment face from those anchored in block-outs (the ten dons had the same lavout except a rather severe curvature at the end). It is obvious that: 1. As construction proceeded and the quality of manufacture and supervision improved, the results got better. 2. At the beginning of the job, the effect of the curved ends of certain tendons was lost in the generally mediocre results. As these results got better (value of K equal to that used in calcula tion from cantilever lIon), this effect became preponderant, counteracting that of the im proved standard of work. 3. As the site staff became accustomed to the work and the effort and supervision dropped, the results became gradually worse (compare cantilevers 13 and 17, for example).
472
Technology and Construction of Segmental Bridges
3+--------------
2+-----------~-
+------~~----"~-"
;tV\
-+
5 6 7 8 9 10 11 12 13 1" 15 16 17 18 CANTILEVER 2 3 " FIGURE 11.5. Prcstressing in
3
+----<~------ -----,--,~~~
2
+-~.__~..,....-__\---_T_ENDONS
ANCHORED
nO
IN
BLOCK - OUTS
TENDONS ANCHORE_~. It..T __ THE SEGMENT FACE
2
3
S
7
9
11
13
1S
I
I
17
18
CANTILEVER
FIGURE 11.6. Prestressing in a cantilever bridge. Wobble friction coefficient for can tilever tendons in the 10 spans without hinges.
As an example, a straight tendon in the top slab fillet between slab and web was isolated. The wob ble friction coefficient depends on the care exer cised in fastening the duct to the reinforcing steel
cage as the concrete is poured (when the tendon is in the slab rather than in the fillet, the accidental deviations are much smaller). For the first seven cantilevers (see Figure 11.7) the wobble coefficient
Post- Tensioning Materials and Operations
II')
-
I
I
FL EXI f3LE.
0... )(
:::t:.
RIGID
T
DUCT
3
473
DUCT
I Z
W
c,:? lJ...
lJ...
w 2 0
()
z
Q I
~
a:: lJ... 1 W
...J
CO
OJ
~ 2
3
"
5
6
e
9
10
11
12
13
1~
15 16
17 1!
FIGURE 11.7. Prestressing in a cantilever bridge. Wobble friction coefficient for a 'itraight tendon locat.cd in the upper fillet.
reached up to six times the assumed value used in the calculations, and yet very careful construction will enable this assumed value to be reached or at least approached closely to obtain the desired pre stress with little room for uncertainty. Th~ presence of hinged segments not only com plicates the tendon profile and the construction phases, but introduces uncertainty about obtaining
the required prestress force. Owing to the techni cal restrictions imposed by the consultant, the tra ditional prestress layout employed in earlier bridges could not be used. Consequently, long ten dons stressed only at the opposite end had to be accepted. It was thought that a realistic value of the final force for each of the tendons (twelve 0.6 in. diameter strand) would be 350 kips (160 mt). It is
474
Technology and Construction of Segmental Bridges
fortunate that a direct check was made at the site, which revealed the actual initial load at transfer to be the following for the four tendons under con sideration: 130 kips (60 mt), 210 kips (96 mt), 130 kips (60 mt), and 200 kips (90 mt). The average initial prestress load per tendon was therefore 170 kips (i8 ml), and the probable final force would ha\'e been 150 kips (70 mt) as compared to the as sumed \'alue of 350 kips (160 mt). Fortunateh', the situation could be easily corrected and remedial measures put into effect as follows: 1. The reinforcing steel and local prestressing tendons allowed for a certain margin of safety. :2. 11 was possible to restress t\\'o of the four cables in the flrst cantilever and then to change the profile and method of placing segments in order to stress all the tendons at both ends for the rest of the cantilevers. 'rhe above results, quoted rigoroush· so as to il lustrate se\'eral important aspens of friction losses, must not lead the reader to suppose that the safety of the structure was at any time compromised. The force ill a tendon \'aries much more slowly than any changes in the friction coefficients for ordinary tendon profiles. For example, in a 270 it (80 m)
tendon stressed at both ends, if the friction coefficients are multiplied by 4, the minimum force in the tendon is reduced by only 16%. It is interesting to examine the results for the actual prestress obtained in cantilevers 2 and 3 (the ones having the worst results) shown in Figure 11.8 for each section, compared with the prestress used in the calculations. The lack of prestress, most marked at midspan, was compensated by addi tional tendons to bring the force back up to that required by the calculations in the first two spans. Afterward, the Ol;jginally calculated prestress was always sufficient. To summarize, the authors wish to underline the following points: I. Bench tests should be performed on site to determine a realistic value of the modulus of elasticity of the tendons to be used 1.0 compute the theoretical tendon elongations. 2. Realistic values of curvature and wobble fric tion coefficients should be used in the design and further controlled on site. Direct friction tests should be made together with a statistical analysis of the measured elongations for all tendons.
r----------.-.---- --------.----------------, SUPPORT
\cXXl
0950
0.900
0.650
3
FIGURE 11.8.
Prestressing in a cantilever bridge. Effecti\'e prestress in spans 2 and 3.
Segment Fabrication for Cast-in-Place Cantilever Construction
475
3. Provisions should be made at the design stage for additional prestress to compensate for any unexpected reduction in the design prestress force due to excessive friction. This may be done as follows: a. By adding additional ducts over and above the number required by design calcula tions; if this method is used, the unused ducts at the end of construction must be grouted to prevent water from seeping in side and subsequently freezing with disas trous effects on the structure. b. By using larger than required sizes for some of the ducts, so as to allow the use of larger-capacity tendons if required. c. By providing anchor blocks and possible deviation saddles so as to allow the instal lation of external tendons located inside the box girder but outside the concrete section.
used because it increases the moisture content of the air and reduces the natural corrosion protec tion. Another important and sometimes acute prob lem relates to potential grout leakage at segment joints, which can lead to the passing of grout from one duct to another. For this reason ducts must be well connected and sealed at joints. To check the grout tightness of the joints and to avoid blockages, it is advisable to flush the ducts with water under pressure before grouting. Any leakage points thus detected may then be sealed. If communication is discovered' between tendon ducts, the tendon groups affected should be grouted in one opera tion after threading and stressing of all the tendons involved. 3 If couplers are being used (notably for single-bar tendons), precautions must be taken to limit the risk of grout blockage at the coupling points. Couplers must be housed in special enlarged en closures with two essential features:!:
[f the correct approach is taken at the concep tion stage, perfect con trol of this aspect of prestress rnav be obtained and very satisfactory structures can be built that give maintenance-free long-term performance.
1. Clear cross-sectional area for the passage of grout equal to or greater than that for the rest of the tendon. 2. Independent grout inlets and vent pipes.
I
"
II.J.6
..
'
GROLTI:VC
As in conventional post-tensioned structures, seg mental construction requires the grouting of pre stressing tendons after tensioning to provide cor rosion protection and to develop bond between the tendon and the surrounding concrete. Current recommendations and provisions of good practice are therefore applicable to segmental bridges. However, several important points need to be ex amined. Grouting must not be carried out if the temper ature in the ducts is less than 35°F (2°C) or if the surrounding concrete temperature is less than 32°F (2"C). This requirement virtuallv precludes grouting operations during the winter months in the northern and middle western United States, unless very special winter precautions are used. It is preferable to postpone all grouting operations until the following spring, even though some ten dons may be left tensioned and ungrouted for a long period. Attention must then be given to cor rosion protection of the high-tensile steel bars or strands. Satisfactory protection is obtained by seal ing all tendon ducts at both ends after blowing out with cool compressed air. Hot air should not be
11.3.7
USBONDED TESDONS
Unbonded tendons may be used in segmental con struction provided that the performance require ments of the post-tensioning steel are also met by the tendon anchorage, notably with respect to fatigue characteristics. In unbonded post-ten sioning a corrosion protection system must be provided to guarantee at least the same degree of corrosion protection as for bonded tensioning. This may be achieved by enclosing the tendons in flexible ducts (such as polyethylene pipes) and by cement grouting after tensioning.
11.4
Segment Fabrication for Cast-in-Place Cantilever Construction
11.4.1
CONVENTIONAL TR::lVELERS
The conventional form traveler supports the weight of fresh concrete of the new segment by means of longitudinal beams extending out in can tilever from the last segment in order to support the forms and service walkways.
I :1
476
Technology and Construction of Segmental Bridges
Form Travelers with Top Main Beams (Figure 2.83) The longitudinal main beams or girders are usually located above the segment to be concreted, in line with the webs. The outside forms, the bot tom forms, the work floor, and the service walk ways are hung from the main beams with the help of cross beams. The inside forms are supported on a trolley, which travels inside the deck. The main beams are anchored to the previous segment. In order to maintain stabilitv during the pouring operation a counterweight is sometimes used to reduce the uplift forces applied to the con crete section. When the traveler is transported to its new position ready for the next segment, the counterweight keeps it in balance between two suc cessive anchoring positions. The main beams that suppon the load due to concrete, forms, walkways, and so on are often subject to large deflections, which can give rise to transverse cracking along the joints between segments. These cracks appear at the upper face of the bottom slab and at the con nection between web and top slab. This undesir able condition can be avoided by using a rigid structure; the weight of the traveler is increased together with the prestress required in the can tilevers. The form traveler used for the Oissel Bridge weighed 120 tons (110 mt) and may be considered as a heavy form traveler. . If the travelers are light, care must be taken to compensate deflections during concreting by ad justing jacks. This type of traveler weighs (exclud ing counterweight) a little less than half the maximum concrete segment weight. An example of a light form traveler is shown in Figure 11.9 for the Tourville Bridge. Each traveler weighs 33 tons (30 mt).
Form Travelers with Lateral Main Beams (Figure 11.10) Travelers with their main beams above the bridge deck present the disadvantage of hindering the construction operation concerning the upper part of the segment. For this reason ·certain form travelers have their main beams disposed laterally parallel to the outside webs, underneath the bridge deck. This solution leaves a clear working surface and allows easy access to all surfaces to be formed, reinforced, and concreted. In this way, the tech nology originally developed for precast segmental construction can be applied to cast-in-place can tilever methods, resulting in shorter construction cycles. The Moulin-Ies-Metz Bridge in eastern France, Figure 11.1 I, was constructed using this type of form traveler.
FIGURE 11.9. eler. 11.4.2
Tourville-la-Riviere Bridge form trav
SELF·SUPPORTING MOBILE FORAHV()RK
I n the case of traditional form travelers, the re sulting deflections seen during construction are almost entirely due to the main beams. The formwork as such IJ.sually acts only as a mold and does not support any part of the total load, even though it comprises very stiff walls. In several recent bridges the traveler concept has been modified so as to use the rigid form work as the weight-carrying member, thus producing a self-supporting rigid mold. Several advantages are gained with this concept: Surveying control and correction of bridge deck geometry are easily obtained. Cracking near the joints caused by the deflection of conventional travelers is completely eliminated. The work area is maintained completely free and allows prefabricated reinforcing steel cages to be used as in precast segmental construction. This type of mobile formwork was first used for constant-inertia bridge decks such as the Kennedy Bridge, Dijon, and the Canadians Interchange in Paris, Figure 11.12. During the concreting operations, the mobile formwork is prestressed to the existing deck. The exact positioning of the formwork is obtained by
Segment Fabrication for Cast-in-Place Cantilever Construction
477
, _ CONCRETI NG PHASE
Rear support
Horizontal
'\
Pre5tre!>sed suspension / rod!>
restress
Self su
form
2_ LAUNCHING PHASE LIpunq t' " I ey ..rOI
I
..
!
I
i
•
Vi I'\J
I
FIGL'RE 11.10.
FIGURE 11.11.
rypical form traveler with lateral main beams,
\Ioulins-les-\Ietz form traveler.
FIGURE 11.12. Canadians Viaduct (Paris), VIew of form traveler in operation.
means of adjusting pins located at the rear in res ervations provided in the previously poured seg ments. The formwork is transported to its new po sition, ready for the next segment, on an overhead trolley, which travels along short steel girders can tilevered out from the existing hardened concrete in line with the webs. A further refinement was to use pretensioned reinforcing to add to the stability of the traveler
while pouring the segment. Figure 11.13 shows the arrangement for the Canadians Viaduct in Paris, France. Monostrands located in the webs are provi sionally anchored to the front of the traveler and embedded in the webs of the concrete segments to be incorporated in the reinforcement of the per manent structure. The use of the self-supporting mobile formwork was later extended to variable-depth bridge decks
478
Technology and Construction of Segmental Bridges
Is
fA
/l.JpperB~ar.Fixa1ion
1
i
I
Pre$tres$ Tendons ( 12 xO 6")
!
SIng 1~2t~and~~ (4x06~)
I
~
l§
SECTION B.B
SECTION A.A
. Uppe r Fiulio ns
"
Single FIGURE 11.13.
/
~.!rands
Canadiam Viaduct
(Pari~).
as well as three-web cross sections, as in the Clichy, Orleans, and Gennevilliers Bridges. The structural members of the mobile formwork are therefore the side forms of the exterior face of the outside webs and the bottom forms of the underside of the bottom slab, both of which are stiffened transversely by front and rear frames braced together for additional rigidity, Figure 11.14. In this manner a rigid box is formed, which is prestressed to the existing deck. The change of section height is achieved by vertical displacement of the bottom forms, which are fastened to the front stiffening framework and bottom slab of the last segment. The stability of the self-supporting mobile forms I of the Gennevilliers Bridge was ensured by (Figure 11.15): l. Two steel pins fixed to the top of. the outside forms and matching imprints provided on the outside face of the previous segment, the con nection being assured by high-strength bars going through each web. 2. Two steel pins fixed to the upper surface of the bottom forms and matching the corresponding imprints provided in the last segment bottom slab, again held by prestress bars.
The self-weight of the mobile forms and the fresh concrete creates an overturning moment, which is
details of the self-supporting form Ira\'eler.
balanced by two forces F sustained by the previ ously described locating pins. Practically all the shear force is taken by the upper pins. Because of the large forces transmitted through the top pins to the concrete, precast concrete elements are used to avoid the transmission of high stresses to young concrete, Figure 11.i6. These forces are transmit ted by friction between pin and concrete, and this determines the necessary prestress force. 11.4.3
TWO-STAGE CASTING
The method of two-stage casting involves, first, the fabrication of the bottom slab and the webs to gether with a small part of the top slab in order to create a flange in which all or some of the can tilever tendons can be located. This operation, car ried out using a conventional form traveler, pro duces either a U-shaped or a W-shaped section, depending on the number of webs, Figure 11.17. After the cantilever tendons are stressed the form traveler is moved to the next position, the top is poured using a mobile formwork of relatively sim ple design. This second stage usually follows the first with a minimum interval of two or three seg ments, and concrete can be placed in a simple pour over the length of several segments. This method has the advantage of reducing the concrete volume to be supported by the form traveler, thus reducing the weight of the traveler.
Segment Fabrication for Cast-in-Place Cantilever Construction
479
SII/{ suppllrtin IIXtirior
Hobll,
truss
Bottom FIGURE 11.14. Self-supporting mobile forms for \;ll'iable-depth bridge decks. Concreting. (/I) ~IO\il1g forward.
In addition, the second stage is independent with respect to the first and so is no longer on the critical path of concreting operations. The bridge decks of the Saint Isidore and Mag nan Viaducts on the Nizza A-8 bypass were con structed using this method. All of the 130ft (40 m) spans of the Saint Isidore Viaduct were completed for stage one only, including closure to the pre ceding> span, before the second stage was com pleted, using mobile formwork which rolled along the bottom slab from one abutment to the other. As regards the Magnan Viaduct, the second stage followed the first with an interval or three seg
(a)
ments, because of the long spans in this structure. The same procedure was used for the Clichv,Join ville, and Woippy Bridges, Figure 11.18.
11.4.4 COAtBINATlON OF PRECAST WEBS WITH CAST-IN-PLACE FLANGES
The preceding methods allowed a considerable re duction in the construction cycle. Two pairs of segments could thus be completed every week, cor responding to an average rate of construction of 7 to 10 ft (2 to 3 m) per working day.
MOBILE
FIGURE 11.15.
FORM - STABILITY
Stabililv of the GellllC\illiers Bridge self-supporting lllobile forms.
PRECAST
JOIN T
Prestressing
FIGURE 11.16.
Precast gusset for GelllJ(.'\·ilJiers Bridge.
/
st
\ U' SECTION - 1
FIGURE 11.17. 480
STAGE
Two-stage construction of a two-web bridge deck.
bars
Segment Fabrication jor Cast-in-Place Cantilever Construction
_~a_'"':......... ~_--:::--~_ _ ~~_~~~ __ -~- _
-
--
-
-
481
~.-
~
FIGURE 11.18. \voippy Viaduct, France. Detail of the self supporting form traveler and two-stage casting.
The main obstacle preventing further reduction in the construction cycle and therefore a closer ap proach to the speed of precast segmental construc tion is the lack of strength of young concrete and the consequent interference with stressing opera tions. Apart from several other methods already discussed, the problem can be partially overcome bv using precast end blocks or precast webs or both. This was first tried for the construction of the Brotonne Viaduct approach spans. Figure 11.19. The webs, which were rather thin and heavily in clined, were precast in pairs and pretensioned. Figure 11.20. The deck was cantilevered out from the piers using 10 ft (3 m) long segments assembled in two phases. In the first phase. the precast webs weigh ing up to 18 tons (16 mt) were placed inside the ·form traveler, previously adjusted to the bridge profile including the desired camber. The webs were then prestressed to the preceding segment with provisional prestress bars, the joint being
FIGURE 11.19. rier.
Brotonne Bridge, mobile form car
match-cast or cast in place. The second phase con sisted of casting the rest of the segment inside the form traveler. which was now suspended from the newly stressed webs. This procedure, which requires partial prefabri cation of the segments using light casting equip ment, enables a considerable simplification of the form traveling equipment, the limitation of total weight to 39 tons (35 mt), and a reduction in the construction cycle such as to produce, even for a cable-stayed bridge, as many as four segments per week for each pair of form travelers.
COUPLER FOR \TENSION RODS 36 mm dia TENSION RODS
STEEL FORMS
7
DISTRI BUTION BEAM
\ ADJUSTABLE BRACKETS
BRACKETS
SOFFIT
BED FOR PRETENSION ED WEBS
FIGURE 11.20.
Brotonne Bridge, precasting of webs.
CASTING BED
482
Technolog), and Construction of Segmental Bridges
During construction of the Brotonne cable stayed bridge, the precast wehs were placed hy tower crane traveling parallel to the bridge deck above the river banks and by an overhead gantry crane above the Seine River. Another example of the use of precast webs is found in the Clichy Bridge carrying the met ropolitan line over the Seine in the northwest of Paris. The bridge deck with a 280 ft (85 m) maximum span consists of a three-web box girder without cantilever flanges and with the deck sup porting the live loads as low as possible in order to reduce the length of the access ramps to the struc ture. The 8 ft (2.5 m) long segments were also con SI ructed in two stages, Figure 11.21. The precast wehs, with epoxy match-cast joints, are placed with the aid of a mobile handling system rolling along the webs of the previously placed segments. They are then prestressed 10 the existing structure before the lOp and bottom slabs are poured in place on the length of two segments. 11.4.5 PRACTICAL PROBLEMS IN CAST-IN-PLACE CONSTRUCTlON CAMBER CONTROL
Before proceeding with the cantilever construction proper, a starting base must first be completed on the various piers. This first special segment, called a pier segment or a pier table, is generally con structed on a temporary platform anchored by
FIGURE 11.21. Precast web placing equipment for Clichy Bridge carrying the metropolitan line over the Seine River.
E ~EV!~TlON
SECTION
7·
~/
J;
1:
nOll \ \
FIGURE 11.22.
Con~truClioll
of the pier segment for
a cast-in-place camile\'cr deck.
prestressing the pier top, Figure 11.22. This spe cial segment may either be given the minimum length to insure adequate connection to the pier for the stability of the future cantilever or else be of such length as to allow both travelers to be installed simultaneously, Figure 11,23. Another important problem relates to the safety of the travelers during construction. Chapter 4 de scribed the difficulties of ensuring pier safety in the event a form traveler fell during transfer from one position to the next. The difficulties would even be greater in the event of an accident during the casting operation. Consequently, all precau tions must be taken both at the design stage and during construction to eliminate this potential hazard. The load-carrying members of the traveler must be carefully inspected and may even be load tested before use so as to practically eliminate the danger of structural failure. The most critical areas are in the safety of the suspension rods and the transfer of the traveler reactions to the concrete. Preferably all suspension rods and anchor bars should be doubled. Also, the prestressing tendons must have an adequate mar gin of safety. Use of a single strand or a single bar in each web of the box should be avoided. Rather a multistrand tendon with individual anchors for each strand or two prestress bars should be used. Worldwide use of cast-in-place cantilever con struction has established an extremely good safety record, much better than that for cast-in-place con struction on falsework. Accidents are very few and far between; however, designers and constructors must always be safety conscious.
Segment Fabrication for Cast-in-Place Cantilever Construction
483
stress forces impose upon the cantilever a new deflection curve. 3. Deflections of the various cantilever arms after construction and after removal of the travelers before continuity is achieved with the other parts of the deck. 4. Short- and long-term deflections of the con tinuous structure, including the effect of superimposed dead loads (curbs, railings, pavements, utilities, and so on) and live loads. 5. Short- and long-term pier shortenings and foundation settlements.
FIGURE 11.23_ Start of GlIltiIever construction from the pier segment. (a) Short pieI- segment succeSSIve installatioll of tr;l\-elers. [iJ} Long pier segment '-siIllultaneous installatiolJ of travelers.
The most critical practical problem of cast-in place construction is deflection control, partic ularly for long-span structures. There are five categories of deflections (or space geometrical movements of the structure) during construction and after completion: 1. Deflection of the travelers under the weight of
the concrete segment. This value is given by the manufacturer or may be computed and checked at the site during the first operations. 2. Deflection of the concrete cantilever arms ,during construction. For each casting of a pair of segments, the weight of the concrete seg ments and the corresponding cantilever pre
Using the data available on concrete properties and foundation conditions, the designer should compute the various deflections mentioned under items 3,4, and 5 above, assuming the bridge un loaded for foundation settlements and long-term concrete defltfctions and half the design live load for computation of the short-term concrete deflec tions. The sum of the various deflection values ob tained in the successive sections of the dcck allows the construction of a camber diagram, which should be added to the theoretical longitudinal profile of the bridge to determine for each can tilever arm an adequate casting cUrve. This casting curve is the goal toward which construction pro ceeds during cantilever casting. The essential difficulty is that no absolute coordinates are avail able in a system where everything changes at each construction stage (transfer of traveler, concrete casting, or cantilever prestressing). A very simple example may illustrate the solu tion of the problem of accommodating the deflec tions described under item 2 above. For simplicity. assume only a four-segment cantilever arm. for which a horizontal longitudinal profile is required, Figure 11.24. As outlined in Chapter 4 and summarized briefly above, the designer analyzes the various deflection curves for each construction step (casting segment and precasting). The typical results are shown in Figure 11.24. The cumulative deflection curve is immediately obtained together with the camber dia· gram, Figure 11.25. The use ofthe camber diagram for determining the adequate deflection at each con struction stage is simple; however, it is much less simple to use in a proper manner in the field, and experienced surveyors have often made mistakes. When properly used, the camber diagram allows the determination at each joint, of offset values such as YI-2, Y2-:l, and YH at each point, which will
484
Technology and Constructio:: of Segmental Bridges
I ELEVATION OF TYPICAL CANTILEVER
-- 3
NOTE
8
I)
CD
Denotes projection of deflection curve outboard in the following joints
Downward deflection is posItive
I CASTING AND PRESTRESSING SEGMENT
(0
~-~
FIGURE 11.24. struction sLage.
B
c0
Ed:V (-23)
1-11)
(-17)
1
5
(9)
(13)
5
10
20
130)
8
18
29
49
+9
+22
41
69
-5
CD 0 8 TOTAL DEFLECTION
I
I
VERTICAL DEFLECTIONS (in mm)
,
.
Partial deflections due to girder weighL and prestressing at each con
bring the traveler in the proper position to realize the desired final geometry. The sketch and table in Figure 11.26 show how to use the camber diagram properly. It is very important to realize that at no construction stage does the profile of the cantilever coincide with either the final deflection curve or the camber diagram. The natural tendency would be to build up the traveler to the required offset to make its nose fall
exactly on the camber diagram. The results of this improper procedure are shown in detail in Figure 11.27. The bridge is built with an undesired double curvature, particularly undesirable toward the end of the cantilever. When the mistake is discovered, it is usually too late to put into effect any remedial measures, because the final shape of a cantilever depends essentially upon the accuracy of the geometry near the piers, where the deck is sub
Characteristics of Precast Segments and Match-Cast Epoxy Joints
485
C;lmber curve
\
.
\
\
o
FIGURE 11.25. camber.
Cumulative deflection curve and choice of
jeeted to the highest moments and where its detleetions have the greatest effect at midspan.
11.5 Characteristics of Precast Segments and Match-Cast Epoxy Joints Developed originally to allow a rapid and safe as sembly of precast segments at the construction site, the technique of match casting was progressively refined as experience was gained. We shall de scribe the characteristics of segments in the early structures to further highlight the latest improve ments and variations of the original concept. 11.5.1
FIRST-GENER1.TION SEGMENTS
In those early structures the epoxy resin played several important roles: 1. During assembly before hardening: a. To lubricate the mating surfaces while final positioning took place.
b. To compensate for minor imperfections in the match-cast surfaces. 2. In the finished structure after hardening: a. To ensure the watertightness of the joints, especially in the top slab. b. To participate in the structural resistance by transmitting compression and shear forces. However, before hardening of the epoxy resin, the joints present no shear re sistance whatsoever, because the epoxy behaves like a perfect lubricant. It was therefore necessary to provide shear keys in each web in order to ensure the shear force transfer between segments. These keys, as well as those situated in the top slab, also allowed a very accurate assembly of one segment with respect to another. During assembly of the deck, some sort of tem porary fixation, either mechanical or by means of prestress bars, allowed the placing equipment (launching girder, crane, and so on) to be quickly
486
Technology and Construction of Segmental Bridges
/J
CD
i
i SEGMENT
cD i SEGMENT
CAMBER
L .
LOADS TOT~L
CAMBER
0 +~'
0 SEGM£NT
LO~D5
TOTAL
-13
CAMBER
0
0
LOADS
:,
10
TOTAL
8
I
0
I
I
-18
29
C
0
0
+B
+18
+ 29
0
0
a
- f
j
! .
FIGURE 11.26. Follow-up camber diagram.
j-
or
ullloadcd without wailing for the cantilever len· dons to be stressed. Figure 11.28 shows how a typical first-generation segment can be assembled to the existing structure using a temporary apparatus'located on the top and boltom slabs, which is used to create forces F I and F2 which ensure the equilibrium of the new segment at the joint. These two forces, combined with the weight W of the segment, give the resultant force R, which is inclined with respect to the joint. Because of the very small coefficient of friction of the epoxy, the shearing component of R produced by W can be balanced only by the vertical component of the reaction C, which exists normal to the bottom face of the web shear keys, Figure 11.28. The resultant R is composed, therefore, of the oblique reaction C supported by the shear keys and a horizontal reac tion N, which is responsible for securing the joint. The axial stress distribution at the joint cross section differs in this case from what would be ob
--i
+1.9
0
deflectiolls with proper' use of
tained by ordinary calculations. I t is obvious that N is smaller than F (the sum of forces F 1 and F 2)' Let Q' be the angle of the key support faces with respect to the horizontal; then F N == W tan Q', and for a typical case of tan Q' = 0.50, F N == W 12. Consider a segment weighing 50 tons (45 mt), temporarily assembled by a prestress force of 100 tons (90 mt) located in the top slab; the axial force reduction is 25 tons (23 mt)-that is, 25% of the total applied prestress force. If the rate of erection of the precast segments is sufficient to ensure the positioning of four seg ments before the resin in the first joint has set, then the reduction in the effective axial force in this joint will be 100 tons (90 mt), which more or less corresponds to one tendon of twelve! in. diameter strands. The same conclusion would be valid when the permanent prestressing was used to ensure the temporary stability of the cantilever. In conclusion, it is recommended that this re duction of the effective prestress force be taken
Characteristics of Precast Segments and Match-Cast Epoxy Joints
487
I!oIPROPI:R CAM9ER
SEGM£N'T
( -35)
--,--
CAMBER
(
LOAD~
-1~
TOTAL
o
CAM8ER
UJAOS
(]) ~
SEGMENT
CD SEGMENl
(0
23) +_.
10TAL
0
CAMSER --.----~
LOADS
5
TOTA ....
-8
CAM8ER
a
LOADS
6
rOTA i..
0
+
FIGURE 11.27. Follow-up of deflections with improper use of camber diagram.
. TEMPORARY
SEGMENT
ASSEMBLY
JOINT
EOUILIBRIU~
N
(v)
F2
(b)
(a)
FIGURE 11.28. Temporary assemblv. (a) Elevation of temporary assembly. (b) Joint equilibrium.
into· account while verifying the cantilever resis tance and stability. Failure to do so may result in temporary joint opening. which is undesirable al though not dangerous for stability.
It is also preferable to choose the intensity and the point of application of the forces F I and F 2 such as to allow the axial force N to be as close as possi ble to the section centroidal axis, thus ensuring a
Technology and ConstructiQll of Segmental Bridges
488
nearly uniform axial stress distribution over the total height and hence a resin film of constant thickness.
be satisfied, however, in order that the resin cure properk 1. Mixing the constituents
Permanent Assernbl,·; Structural Importance of Epoxy Resins As regards 'the final prestress tendo.n pro files, it was shown in Chapter 4 how the resIstance of the different cantilevers is ensured by a first group of tendons, known as cantilever tendons, which may be straight or curved in profile and an chored o~ the various segment faces. The stressing operations remain in the critical path of construc tion because a new pair of segments cannot be placed before the last pair has been stressed to the existing cantilever, Figure 11.29. The second grou p of tendons joins the different cantilevers together and makes the structure CO~1tinuOllS. Thev are anchored either in block-outs m the bottom slab or in the fillets at the junction be tween the top slab and the webs after upward de viation (0 (OP slab level. . . The service shear forces that act upon the Jomts \ar" according to the type and characteristics .of the structure. In variable-depth bridge decks WIth draped prestressing tendons the shear stress across the joints is usually low. In a long-span, constant depth bridge deck with straight tendons, howev.er, the shear stresses at the joints can exceed 600 pSI (4 MPa), as was the case in several structures men tioned in Chapter 4. A bad choice, or improper use, of the epoxy resin can be a critical factor con cerning the shear resistance of th~ joint:, and f.or this reason joints of this type reqUire strIct quality control. In general, the different t}:pes of epoxy resins available have final strengths substantially exceed ing that of concrete, so they do nOl c.o~stitute a weak point in themselves. Several condItIons must
III their correct· pro portions. 2. Eliminating any solvents that have a fatal effect on the properties of the resin. 3. Avoiding any flexible additives, such as thiokol, that greatly increase the deformabilitv of the epoxy. 4. Mixing and applying carefully.
With respect to the last point, the surfaces to be joined must be specially treated if the best results are to be obtained. Comparative tests have shown that sand blasting gives the most satisfactorv re sults, the surfaces being kept clean, dry, and free from grease d Ul'ing placillg. I n damp or raim weather alcohol is burnt on the joint surfaces t
FINAL SEGMENT ASSEMBLY J J.5.2
FIGURE 11.29.
Final segment assembly.
SECOXD-GEXERATIOX SEGMEXTS
Although the characteristics and performance of the first structures built with match-cast joints are not in doubt, it seems a good idea to investigate new types of joints allowing the transmission of shear forces without relying on the strength of epoxy reslIls. Second-generation segments do just this, being equipped with interlocking keys in the top and bottom slabs and in most of the height of the webs. This configuration of shear keys at regular inter vals, which improves the behavior of joints by re lieving the epoxy of its structural role, has the
Characteristics of Precast Segments and Match-Cast Epoxy Joints
advantages of simplicity and safety. This type of segment has been used with success in several bridges, notably the Alpine Motorways, the Saint Andre de Cubzac Bridge, and the Sallingsund Bridge, and more recently in several structures in the United States such as the Long Key and Seven Mile bridges in Florida.
with properties that depend upon the type of resin and hardener used. Three grades of epoxy resin are commonly used, depending upon the ambient temperature range under which the resin is to be applied: 40 to 60°F (5 to 15°C)
60 to 75°F (15 to 25°C) Ribs and Interior Anchorage Block, Anchorage blocks (blisters) or stiffening ribs are currently used inside the segments for the final longitudinal prestress anchors. The tendons, ensuring the sta bility and resistance of the cantilever and placed progressively as construction proceeds, can be an chored away from the joint faces, thereby render ing the stressing operations and the segment placing operations independent of one another. The ribs and anchorage blocks are generally used to house the temporary prestress that ensures the provisional stability of the cantilever, thus leaving the top slab completely free. Bolted Ribs Despite the tensile strength of the epoxy resin at a glued joint, no tensile resistance is usually considered, as 'preca~t segmental structures are nearly always totally prestressed and so no ten sile stresses can develop across the joint. However, we can further improve epoxied match-cast joints bv giving them a certain resistance to tension by using bolted ribs, which ensure the continuity of the longitudinal reinforcing steel, Figure 11.30. 11.5.]
EPOXY FOR JOINTS
The structural importance of the thill layer of .epoxy resin forming the joint between two adjacent precast segments was discussed in Section 11.5.1. We now take a closer look at the physical and me chanical properties of these resins and the various precautions to be taken to ensure satisfactory and consistent results.
Epoxy Types Epoxy resin glues are made up from two components: the epoxy resin and the hardener. Mixing these two components in the correct proportions gives a thermostable product
489
Fast-reacting epoxy Medium-fast-reacting epoxy Slow-reacting epoxy
1. COLO'T The resin and the hardener must be of clearly contrasting colors thus avoiding any con fusion. When properly mixed, the final product is to be a homogeneous gray color similar to that of concrete. 2. Shelf life of components Both components may be stored for up to one year, provided that the storage temperatur; is kept between 50 and 70°F (10 and 20°C). After three months' storage it is necessary to check that the epoxy resin shows no sign of becoming crystalline. If it does, then special treatment must be given to the resin, followed by tests, before use. 3. Pot Life of the :Hixed Glue The pot life of an epoxy resin is a measure of the time interval be tween the mixing of the components together and the moment when the glue becomes no longer workable. The workability of the glue is deter mined by its internal temperature, depending upon the grade of epoxy resin employed. For a 10 Ib (5 kg) mix used on site, mixed under isothermic conditions until an even color of mix is obtained, the following results are required: Workability Limit Temperature
Epoxy Grade
{oCe
5 to 15°C
c
(104°F)
e (104°F)
15 to 25°C
40
25 to clOoe
55 to 60°C (131 to HO°F)
The pot life must be approximately:
Ambient Temperature Epoxy Grade 5 to 15°C 15 to 25°C 25 to clODe
41°F
50°F
we)
( looq
40 min.
15 min.
59°F ( 15°C)
68°F (20 o q
20 min.
15 min. 25 min.
18 min.
490
. Technology and Constructiop oj Segmental Bridges
BOLTED RIB JO INTS
FIGURE 11.30.
On site, each 10 Ib (5 kg) mix of epoxy resin must be applied to the concrete surhlce within the pot life period as specified above.
f!l
the Applied Epoxy Glue The open time of the glue is defined as the period be tween its application to the concrete surface and the moment when it reaches its workability limit temperature. Because of the much greater heat dissipation from the thin layer [~ to ~ in. (l to 3 mm)] on the concrete surface, the applied glue takes much longer to reach the workability limit temperature than the mix in the pot. 4.
Opm Time
The open time must never be less than one hour, regardless of the grade used. One measur ing device used to determine open time is the Vicat's needle shown in Figure 11.31. A 1 mm layer of epoxy glue is spread onto a steel plate. and the stopwatch is started. The time lapsed before the needle will penetrate only 0.5 mm into the glue layer is defined as the open time. 5. Thixotropy This characteristic gives an in dication of the epoxy resin's ability to be applied to vertical surfaces with relative ease and yet with sub sequent running. Thixotropy may be. measured using Daniel's gauge, Figure 11.32. The gauge is placed on a level surface with the gutter section horizontal. The gutter is then filled with freshly mixed resin and hardener and abruptly turned to the upright position, as shown in the diagram. The flow time relationship is recorded. The test should be carried out at the maximum temperature for which the resin is specified. A resin that flows less than 30 mm in 10 minutes is suitable for applica tion to vertical concrete surfaces. Other testing methods are available such as the sag flow ap paratus according to ASTM D2730-68.
Bolted rib joints.
Other characteristics of the epoX\' glue that may be resred on sile are: The angle ol internalfric/ion: The ease with which the excess resin may be squeezed out of the joinl when subject 10 uniform pressure.
..!'Iungf!r
300gr weight
Nf!l!'dll!' lmmt
~~
FIGURE 11.31. Open-time testing-Vicat's needle.
Characteristics of Precast Segments and Match-Cast Epoxy Joints
491
4 X 4cm p
E
u
!£>
FIGURE 11.32. Thixotropv testing-Daniel's gauge. Shri rz}wgl':
\1 ust be praltiLall \' nil.
Wilta absorption mtl' and solubility in water:
Maximum permissible true water absorption 12%. Maximum permissible quantity of epoxy sol uble in water at 25°C (77°F)-4%.
FIGURE 11.33. Shear-resistance test. ceptable ultimate shear stress at the interface is 1400 psi (10 MPa).
2. Shear i'vl()duhL~ The instantaneous shear modulus (G i ) must be greater than 220,000 psi (1500 MPa) at:
\Iinimum required value accord ing to :\fostells (Dl;\J 53458) on week-old 10 x 15 x 120 1ll!11 test rods is 50°C (122°F).
25°C (77°F) for grade 15 to 25°C
,\1 ahlt niw[ /Jrojil'l't iI'S
40°C (104°F) for grade 25 to 40°C
Heat resistance:
I. Shm r rf,li,I/(J1/('1' The shear resista nce of the mixed epoxv glue is determined on rectangular concrete test specimens with the following dimen sions: 1.6 x 1.6 x 6.3 in. (4 x 4 x 16 cm) with a resin interface at 17° to the vertical, Figure 11.33. The concrete test pieces are made from a high quality concrete comparable to that used in precast segment manufaLture and are cured under water seven days from time of casting. After removal from the water the pieces are dab dried and the surfaces to be assembled are pre pared by shot blasting, wire b!'ushing, or other similar methods to remove laitance. The test pieces are then resubmerged in water for three hours, after which they are removed and dabbed dry with a clean cloth. The resin is then applied in a layer of jj\ in. (2 mIll) on one surface and the test beam clamped in an assembly that maintains a normal pressure on the interface of 21 psi (0.15 .:vIPa). The assembly is stored for seven days at a temperature repre'sentative of the desired working conditions, and then the test is carried out. The minimum ac-
15°C (59°F) for grade 5 to 15°C
The long-term shear modulus must be greater than 14,500 psi (1000 .:vIPa) after 28 days at the same temperatures as above. Solid cylindrical test pieces are used for measuring these values in con junction with the easily made test apparatus shown in Figure 11.34. - Certain epoxy resins show an excessive sensitiv ity to high temperatures that makes them unac ceptable in warm climates. Figure 11.35 shows comparative results of ten different resins tested for the Rio Niteroi Bridge. It is obvious that a produLt that becomes practically plastic with no shear modulus at 60°C is completely unacceptable. 3. Tensile Bending Strength A three-point bending test is carried out on a pair of glued con crete cubes with a compressive strength of 5700 psi (400 kg/cm 2 ), Figure 11.36. The faces to be glued are shot blasted, or bush hammered, so as to re move laitance. The cubes are then submerged in water for 72 hours. When taken out of the water the surfaces to be glued are dried simply by dab bing with a clean cloth. Immediately after the dab
Technology and Construction of Segmental Bridges
492
Dial
X....J vi~
X-X
Vie-w from one- side-
FIGURE 11.34. Shear-modulus test.
2500
2000
1500
1000
500
o
~---------L--------~--------~------~~----~--~t('C)
20
30
FIGURE 11.35.
40
50
60
70
\'al-iatioll of shear l1]odulus G wit h tcmpcrature.
drying the glue is applied in a layer of II,; in. (1.5 mm) to one of the prepared faces. The corre sponding face of the other cure is placed against the glue layer, and the two cubes are clamped to gether with a clamping force of 300 Ib (150 kg). The assembly is then wrapped in a damp cloth, which must be kept wet until the three-point bending test is carried out. 4. Compressive Strength The compressive strength is determined according to DIN I I 64 on 4 cm (H in.) cubes of cured epoxy glue. After 24 hours (from the time of preparing the samples) at the maximum temperatures for each grade the compressive strength must be not less than 12,000 psi (SO MPa). The loading rate is to be approxi mately 3600 psi (25 MPa) per minute. 5. Elastic modulus in compression The instan taneous modulus (E j ) is determined on cubes of pure epoxy after curing for seven days at the
maximum group temperature. These cubes are the same size as those used for the compressive· strength determinations. The modulus must not be less than 1,140,000 psi (7850 \IPa) Prartical u.\(' of E/JOx)' ill Malch·Cast joillfl III regard to the me of the resin, the two compo nents should be mixed carefully and quickly as near as possible to the surfaces to be coated. Under no circumstances should oil or grease be allowed to come into contact with surfaces that are to be glued. Most standard de molding agents are suita ble for use, but care should be taken to ensure that no oil-based de molders are used. Exposure to weather during the storage period is often sufficient to remove the demolding agent. For best results, surface laitance should be removed by shot blasting or bush hammering. This treatment is normally carried out in the storage yard. With the use of multiple keys, the structural role of the
Manufacture of Precast Segments Loa~ied
here
EPOXY JOINT
FIGURE 11.36.
Tensile bending-strength test.
epoxy is considerably reduced and a special prepa ration of the Sli rbce is' not a mandatory feature. lmmediatelv before the glue is applied, the sur faces are to be cleaned to remove traces of dirt, grease or oil. and dust. C nder normal climatic conditions it will not al ways be possible to avoid dampness on the surfaces to be glued. If the surf~lCes do show signs of mois tllre, the\' mllst be dab dried with a dean cloth. and no gluing mav proceed until all free water has been eliminated. The thickness of the glue laver should be about 1.~ in. (1.5 mill). A.s soon as possible after the resin has been applied, the surfaces must be brought to gether. Pressure must be applied before the open time of the epoxy resin expires. The pressure applied by either tern porarv or final prestress should !lot be less than 30 psi (0.2 "'IPa).
11.6
ing along the bed for the successive casting op erations. 2. Short-line casting (with either horizontal or vertical casting), where segments are man ufactured in a step-by-step procedure with the forms maintained at a stationary position. For match-cast joint structures, the accuracy of the segment geometrv is an absolute priority. Ade quate surveying methods and equipment must be used to ensure an accurate foilow-u p of the geometry and an independent verification of all measurements and adjustments. Immediately after the manu facture of a segment the as-cast geometry should be controlled and compared to the theoretical geometry to allow any necessary adjustment to be incorporated in sub sequent casting operations. This aspect of match casting is particularlv important for the short-line method and will be covered later in this chapter.
Manufacture of Precast Segments 11.6.2 11.6.1
1. Long-line casting, where all segments to make Lip either half or a full cantilever are manufac tured on a fixed bed with the form work mo\'
=
=
LONG-aVE C-ISTING
INTRODL'CTlON
The various methods used until now for precasting segments fall into two basic categories:
I
!
493
In this method all the segments are cast, in their correct relative position. on a casting bed that exactly reproduces the profile of the structure with allowance for camber. One or more formwork units travel along this line and are guided by a preadjusted soffit. With this method the joillt sur faces are invariablv cast in a vertical position.
·I.
,.
.'
l._:
Technology and Construction of Segmental Bridges
494
Figure 11.37 shows the casting sequence.:l The pier segment (3) is cast first. then the segments on either side of the pier segment (l) and (2). If a pair of forms is llsed, then the symmetrical segments on eacb side of the pier segment can be cast simul taueously, thus saving casting time. As segment casting progresses, the initial segments may be re moved for storage, leaving the center portion of tile casting bed free. If enough forms are available, tben the casting of a second pair of cantilevers may proceed even though the first pair is not com pleteh cast. Figure 11.38 shows the typical cross section of a long-line casting bed with the formwork in opera tion. The method was initially developed for constant-depth box girders (Choisv-le-Roi and C(lurbevoie Bridges). It was later extended to the case of variable-depth decks such as the Oleron Viaduct (the two sketches of Figures 11.37 and 11.38 refer to this structure) and also adopted in other coul1tries (Hartel Bridge in Holland). The importallt advantages of the long-line cast ing method are: It is e;lsy to set out and cOlllrolthe deck geometry.
'After form stripping, it is not necessary to im mediatel\' transfer the segments to the storage area in order to continue casting. The disadvantages are: Substantial space may be required. The minimum length is usually slightly more than half the length of the longest span of the structure, but it depends upon the geometry and the symmetry of the structure. The casting bed must be built on a firm foundation that will not settle or deflect under the weight of the segments. If the structure is curved, the long line must accommodate this curyature. All equipment necessary for casting, curing, and so on must be mobile. 11.6.3
SHORT-LISE HORIZO.\T·IL C"IST/.\'(;
The short -line casting method requires all seg ments to be cast in the same place, using stationan' forms, and against the previously cast segment in order to obtain a match-cast joint. After casting and initial curing, the previously cast segment is
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FIGURE 11.37.
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Segments completed.
Typical long-line precasting bed.
Mobile outside formwork
Telescopic inside form work
FIGURE 11.38. Tvpical cross section of long-line casting bed with form work.
Manufacture of Precast Segments
removed f()r storage and the freshly cast segment is moved into its place. The casting cycle is then re peated. This operation is illustrated in Figures 11.39 ami 11.40.~·4
TO STORAGE
BLANK END
,
t FIGURE 11.39.
l\pictl ,llOrt-lille precaslillg opcra
II Oil.
It is important that the reader fully comprehend the principle of the method insofar as building a deck of a given geometry is concerned. When a straight box is desired, Figure 11.41, the match marking mate segment (n - 1) is moved from the casting position to the match-cast position along a straight line, and this is usually verified by taking measurements on four elevation bolts (a) em bedded in the concrete roadway slab and two alignment stirrups (b) located along the box cen terline. A pure translation of each segmellt be tweell the cast and match-cast positions therefore results in t.he construction or a perfectly straight bridge (both in elevation and in plan view), within the accuracy of the measurements made at the casting site. To obtain a bridge with a vertical curve, the match-cast segment (1/ - 1) must first be translated from its original position and then give a small ro tation in the vertical plane (angle a shown in Fig ure 11.42). Usuallv the bulkhead is left in a fixed position, and all sef!;ments have ill devatjon the shape of a rectangular trapezoid with the tapered face along the match-catch sef!;llleni. It is thcl'efore onlv necessarv to
CONJUGATE UNIT
FIGCRE 11040.
495
Formwork used in casting scgmellls.
, ELEVATION
TRANSVERSE
SECTION
STRAIGHT BRIDGE
PLAN VIEW
FIGURE 11041.
Straight bridge.
[ J ELEVATION
TRANSVERSE SECTION
BRIDGE WITH
CURVE
VERTICAL
PLAN VIEW
FIGURE 11042.
496
Bridge with vertical curve.
497
Manufacture ofPrecast Segments
TRANSVERSE SECTION
ELEVATION
BRIDGE WITH HORIZONTAL CURVE
PLAN
VIEW
FIGURE 11.43.
Bridge with horizontal curve.
Change in the superelevation of the bridge may also be achieved with a short-line casting; however, the principle is a little more difficult to properly grasp. Figures 11.44 and 11.45. A constant trans verse fall of the bridge does not need to be re peated in the casting machine. Segments may be cast with soffit and roadway slab both horizontal and placed at their proper attitude in the bridge by offsetting the bearing elevation under the webs to obtain the desired cross fall. Only a variable superelevation must be accounted for in the cast ing operation, and this is the normal case in bridges with reverse curves and in transition areas between curves and straight alignments. In such a case match-cast segment (n - 1) needs to be ro tated by a small angle such as y around the bridge centerline. Because the bridge geometry is usually defined at roadway level and not at soffit level. the rotation given to the match-cast segment results in a slight horizontal displacement of the soffit in the casting machine, which must be accounted for. Also all surfaces of the box segment (top slab, soffit. and webs) are no longer true planes but are slightly warped. To allow the form work panels to adjust to this change of shape, it is absolutely man datory to eliminate all restraints such as closed tor sionally stiff members.
The basic advantages of the short-line casting method are therefore the relatively small space re quired and the fact that all equipment and form work remain at a stationary position. The mobility of equipment necessary for the long-line method is no longer needed. Also, horizontal and vertical curves as well as variable superelevation are obtained with short-line casting without the major change in soffit configuration that would be required in the long-line casting method. How ever, success will depend upon the accuracy of ad justment of the match-rast segments, and precise survey and control procedures must be initiated (Section 11.6.5). This last aspect represents the major potential disadvantage as a direct conse quence of the intrinsic potential of the method. 11.6.4
SHORT-LINE VERTICAL CASTING
Normally. for both the long- and short-line methods, the segments are cast in a horizontal po sition. A variation in the short-line method is that used for the Alpine Motorways near Lyons, France, where the segments were cast in a vertical position (cast on end) as shown in Figure 3.100. The procedure is as follows: after the first segment is cast, the forms are removed and moved upward
498
Technology and Constru:tion oj Segmental Bridges
TRANSVERSE
ELEVATION
SECTION
BRIDGE WITH VARIABLE
SUPER ELEVATION
PLAN VIEW
FIGURE 11.44.
Short-lille cast.illg-hridge with \';triable supcrelc\"atioll"
CONJUGATE UNIT
END BULKHEA:!
FIGVRE lI.45. su perele\'a tioll.
Short-line casting-isometric view of segment casting with \"ariable
so that each succeeding segment can be cast above the previous one. After a segment is cast and cured, the segment beneath it is transferred to storage and the one removed from the forms is moved down, 10 rest on the floor. The advantages
claimed for vertical match casting include easier placing and vibration of the concrete. However, special handling equipment and procedures are required to rolate the segment from the vertical to its final horizontal position.
Manufacture of Precast Segments 11.6.5
499
GEQ,lMnRi' AND SURVEY CONTROL
Segment Precasting in a Casting lHachine
The principles described in this section apply to short-line horizontal casting hut may be easily ex tended to vertical casting. The apparatus used to form the concrete segment is usually referred to as a casting machine and is made up essential! y of five components: 1. 'rhe bulkhead that forms the front section of the segment. 2. The match-cast segment, properly coated at the front end section with a suitable demolding agent and used to form the back end section of the newly cast segment. 3. The mold hottom (or soffit). 4. The side forms, properly hinged for stripping and firmlv sealed to the bul khead and the match-cast segment during casting. The inside forms, which pivot and retract for stripping. 5. The imide forms, which pi\ot and retract I'or stripping. The relationship between ail individual segment and the finished structure is established bv means of three different svstems of reference: 1. The final ,,),stnn of nferenre, which is the refer
ence for the finished geometry of the struc ture. I n this s\'stem each segment is described by its basic geometrY. 2. The auxiliary system of reference, which corre sponds to the precasting machine and is at tached thereto. 3. The elementary reference s)'.,tem, which is attached to each segment and would be the equivalent of intrinsic coordinates ill space geometry. The principle of the precasting method is as follows. During the casting of segment A (segment B being in the match-cast position) the elementary reference system of A is identical with the auxiliary reference system, that of the casting machine. To position B with respect to A becomes simply a matter of positioning B with respect to the pre casting machine. It is the task of the design office to provide the theoretical geometric information nec essary for positioning. The values are computed from the basic geometry with the addition of the relevant compensatory values for deflections. The definitions of these reference systems are pre sented below.
Joint A
FIGURE 11.46. Auxiliary I-eference system (casting IIlachine reference).
The auxiliary reference system refers to the casting machine and is defined in Figure 11.46. The plane of the bulkhead is perfectly venical. The upper edge of the bulkhead is a horizontal in this plane except when segments do not have pla nar top surfaces. The x, y and z axes refer to the casting-machine reference system, whereas XA, y,!, and Z,I refer to the elementary system of reference. The elementary system of reference is materialized on each segment in the following manner: I. The x" axis: This axis is represented by marks (such as saw cuts) made on two steel stirrups anchored in the top slab as near as possible to the joints. 2. The origin 0,,: The origin 0" is located at the point where the x" axis intersects the plane of the joint at the bulkhead. 3. The plane x"' o",y,,: This plane may be defined by three fixed leveling points, the position of each point with respect to the plane x, 0, y being arbitrary but invariable. For practical reasons, four leveling points are used and materialized by bolts anchored in the top surface of the segment above the webs and as close as possible to the joints.
Now that the elementary system of reference has been established (all measurements and readings being made while the segment is in the casting machine before the forms are removed), the seg ment can be positioned with respect to the aux iliary reference system, so that it can be placed in the correct countercasting position according to the calculations supplied by the design office.
500
Technology and Construction of Segmental Bridges
In order to correctly position the countercasting segment. information is needed about the final geometry of the structure. The overall geometrv of a bridge structure is lIormallv defined by thc geometry of the roadway. From this roadway geometry it is necessary to determine the geometry of the concrete structure itself. The longitudinal reference line to which all the necessary parameters are related is known as the /lox ,I.,rirdtr IiJl!' (BGL). This line may coincide with the top concrete surface of the box girder. but it IlJa\ also he a fictitious line of reference if the box girder top slah shape is not regular. The box girder line is ustlally described using two ClInes, Figure 11.47:
zontal plane and follow the curvilinear abscissas. The segment lengths chosen on this basis may be retained, but in calculating the real lengths of cast-in-place closure joints and t hree-dimel13iollal s curve must be used. Because of the way a casting machine works, the segment joint at the bulkhead end is ill\'ariably perpendicular to the axis of the segment. There fore, ill plan view, the segments are generally of trapezoidal shape. except for segments over the piers which are rectangular in order to provide a constant starting- point for each cantilever, Figllre 1 1.48.
Olle curve (fT) ill a horizolltal plane, which gives}'
All measurements on a segment are made when the segment is still in the casting machine. Readings mllst be taken when the (,OIIOTtc has hardened and hefore forlllwork st ripping, Figure 11.49. Horizontal alignment readings give t he dis tance of the segmellt axes as marked on the stir rups frolll the casting-machine reference line. Longitlldinal profile le\·e1 readings are given In the fOllr bolt elevations relative to the horilontal refer ellce plane. Readings Illllst be taken Oil the segment jllst cast and also on the match-cast segment. Correuiol1s are applied \0 allow for the geollletric defects in the preceding segl1lent, Figure 11.50, and are lIsed as "theoretical yalues for adjustment."
Olle curve (s) in a developed vertical plane giving z as a fUllction of (T for the same points mentioned abo\'e. Thisl curve is the real box girder line. BGL. To complete t he definition of the segment posi tion ill space-at each joint line and at support centers-we must define the transverse slope of the theoretical extrados line. It is important for both the bgl and the BGL to calculate the fT and .1 parameters, respectively, ill order to obtain an accurate determination of pro jected and real span lengths. The calculations and structural drawings refer to Ilominal segment lengths and span lengths. Usu ally these lengths refer to the projection on a hori-
Pil!'f
Surue'li Control During
Precastillt.;
Operatum)
The surveyor in charge of the operations mllst complete a data sheet for each segment containing essentially: 1. Theoretical basic data supplied In' tlte design office, allowing the preparation of the hori 100ltai alignment and the two parallel bolt lines.
2. Corrected values defined eit her graphically or
3
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Pjrt
by computer.
3. Survey control readings_
2
I
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lHorizontat proJPction o! box 9trdeor 'Iobgt lf
FIGURE 11.47.
SCfPlll'lI1 CaS/III/?: Parmlll'/cr.1
Box girder line cunes.
"Of'
4. Linear measurements on the segments. 5. Schematic representation of the segment to rapidly verify the relative positions of the seg ment axes. 6. A level check to pick up any gross error in level readings on the same segment
7. Comments on the casting operations.
1 I lHanufacture of Precast Segments
501
(St'gmt'nt axis
,r-Segment
over pier Pier
~
FIGURE 11.48.
'\
Box girder line "bg ," or c:r ( sigma) curve Short-line casling-position of sel-{Illent joillls in plan \'iew.
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I CASTING
MACUINE
, RUE. RENeE Ll NE
FIGCRE 11.49. me;lsurcnleIHs.
Ca,ling-machine
As an example, Figure I L5I shows the typical survey control made on the first four segments of a tvpical cantilever. Control of alignment and. levels rnav be followed graphicallv or numerically by computer, using the basic geometric data obtained in th~ casting machine and shown in Figure 11.52. In order to avoid any significant deviation from the theoretical geometry, it is necessary to provide
orientation
and
segmenl
for corrections when casting the next segment. Figure 11.53 shows how this would be done for the plan alignment. Similar corrections are made for the longitudinal profile on the two parallel bolt lines. It is essential not only to follow carefully the trajectory of the two bolt lines separately but also to check for each segment that the superelevation (given by the crosswise difference in level between
502
Technology and Construction of Segmental Bridges
w~'
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R!'FER!'IYC{ iJ¥E
FIGURE 11.50. Plan yjew of casting operation readings using sunf)' instrumems.
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FIGURE 11.51.
Casting operation-typical survey control.
the two boll lines) varies regularly according to the theoretical geometry. Failure to do so has resulted in important geometric imperfections on certain projects. Sun1ey Contml During Construction The nature of match-cast segmental construction is such that the structure is really "built" in the pre casting yard. Although corrections can be made in the field, such corrections are undesirable and al ways a source of additional expense and delays. Close control of precasting is far more efficient. It is nevertheless important to check the evolution of the structural geometry during segment placing: 1. To compare actual deflections with computed values,
2. To ensure that no major errors have escaped the control in the precast yard or factory. Such checks at the site should include: 1. 2. 3. 4.
Pier positions, height and in plan. Bearing positions, level and orientation. Pier segments, level and orientation. Cantilevers proper, every third segment, in cluding levels, superelevation, and orientation. 5. Overall geometry of the structure after con tinuity is achieved between the individual can tilevers. Conclusion The principles of geometry and survey control are more complicated to explain than to use, once the
Manufacture of Precast Segments
503
THEORfTICt1L1I)IIS Of 0
REIlL /lXIS
OF" 0
Se:GME.NT1
SeGMENTO
I
:nU:'ORE:TICAL LEVEL FOR 1
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5EGME:NT 0
FIGURE 11.52. Sliney control-horizontal alignment and longitudin;ll profile results. (1/)
Horiwnt;tl alignment. (b) Longitudin;t1 profile.
FIGURE 11.53, Typical alignment corrections during casting operations.
basic principles of a casting machine are thor oughly understood. The short-line method has great potential to construct segments for bridges, cycn . those with very complicated trajectories, rapidly and economically. Outstanding examples
are the Chillon and St. Cloud Viaducts in Europe and Linn Cove Viaduct in the United States. At Saint Cloud, 120- to 140-ton segments were cast on a one-day cycle, and the final geometry of the bridge was obtained with no on-site adjustment.
,['
ii
I I
Technology and Construction oj Segmental Bridges
504
Oil the other hand, a loose approach to, In the case of wide decks or long spans, where the segment length is reduced to reduce the unit g('ometry control at the casting yard mav lead to weight, the usual geometric proportions may vary serious difficulties at the pn~ject site. considerably; stich is t he case for two notable structures: 11.6.6
PRECASTlNG fA/W AND FACTORIES
The precasting operations are usualJv carried out in a vaHi or e\'en a facton if the size of the project allows the corresponding im'estmenl. All opera tions, such as: Preparation of the reinforcing steel cages and ducts for post-tensioning tendons l\lanufacture 01 concrete !\1anufacture
or segmellts including heat curillg
Storage of segments including finishing and qual i1\ control are performed in a repetitive fashion under facton conditions. :\s all example or typical precasting-yard lay outs, Figures 11.54 and 11.55 show \'iews of: The Saint Cloud Viaduct precasting :anl with short-Ii lie casting The Oleron Viaduct precasting yard with long-line casting The tvpical precasting c\'c1e (with either the long-line or t lIe short-line met hod) is of one seg ment per fOrIllwork per day with a one-day work shirt, COIHTele hardenillg laking place during the night (at least 14 hours between the completion of conuete plaeing ill the evening and the stripping of forms the Ilexl morning), Shorter construction cn:\cs may be obtained hy reducing the time of concrete hardelling, but quality mav decline if all the operatiollS are not kept under very strict COI1 t rol. Heat (urillg of the concrete 10 reduce the con struction cvcle and accelerate the rotation of the casting machines is perfectly acceptable. Its im proper use, however, may alter the. accuracy of joim !natching bet ween segments, as shown in Fig ure 11.56. This effect would be particularly significant ror wide but short segments. Typical segments usually have the following di mensIOns: Width Length Ralio width/length
30 to 40 ft (9 to 12 m) 10 to 12 ft (3 to 3.6 m)
3 to 3.5
St. Cloud St. Andre de Cubzac
width iO ft, length i It. ratio 10 width 58 ft, length 5.8 ft, ratio 10
For sllch segments, heat curing is more likely to create smail changes in the segment shape, which may build up progressi\ely and so alter the ef fectiveness of joint matching. This is due to the development 01 a temperature gradient in the match-cast segment, which is in contact on one side with the newly cast heated segment and on the other side with the lower uutside temperature, The problem may be completely eliminated by always heat curing both segmt'llts simultaneollsly so as to avoid any temperature gradient. Experi ence has proved the method totally eHicient. When the project lIl\'olving segment precasting is of sufficient magnitude or \\'here climatic comii tions al'e adverse, precasting ElClOries are a logical extrapolation from the short-line method per formed in an open precasting yard. Segment man ufacture takes place in a completely enclosed building with a better use of personnel and a more consistent quality of products. An interesting e~ample is afforded by the B-3 South Viaducts. requiring production or 2200 pre cast segments weighing between 2H and 5H tons (25 to 53 mt). The precasting site was installed close to the project and included four main areas: 1. An assembly workshop. where the reinforcing steel cages were prepared and the prestressing ducts positioned. The finished cages were handled by a 5 ton tower crane, 2. A concrete mixing plant. 3. A precasting factory where the segments were cast and cured. 4. A storage area where the finished segments were left to cure adequately. These segments were handled by a traveling portal crane. The precasting factory was equipped with four precasting machines, all of which were entirely protected from the outside environment. Two machines were reserved for the manufacture of 15 to 20 ft (4.5 to 6 m) segments and two for the 20 to
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FIGURE 11.54. Sl. C10tld Viaducl, precislillg rani IalOtll. (I) I ami trolle~·. (~) Access ramp. (3) Loadillg pOilll for segmellts. (-1) assembly wile. (5) Segmellt storage. (6) Tral'dillg crane track. (7) :\(old bottom. Presll'essillg Sled stor;lge, (9) rower (Jalle Irack. (10) Reiul()lu'1I1elll asselllbly. (II) COliC rete plallt. (1~) Precast ('1('IIll'llIS. (I:~) Prestress (elldon mallufaCiure. (H) Of'fices. (15) (;clleral ,ell ices. (Ifi) '1011 g:lIe pmilioll. (t7). hUlIll' clrri
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506
Technology and Construction of Segmental Bridges Staff quarters
:....- Duct storage area
FIGURE 11.55.
O]cron \'iaduCi. precasting
L
Office
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CONJUSt.TE
UNIT
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EFFECT OF IMPROPER CURING OF SEGMENTS IN SHORT LINE CASTING
FIGURE 11.56.
Effect of improper curing of segments in
31 ft. (6 to 9.5 m) segments, Figures 11.57 and 11.58. Each casting machine was made up of a mobile form, an end form or bulkhead, two hinged out side forms, and a telescopic inside form, Figure 11.59. Handling of concrete and reinforcing steel inside the factory was performed by two 10 ton travel cranes.
~hort-line
casting.
The production of the different segments volved the following operations: 1. 2. 3.
111
Assembly of the steel cages in a template. Steel-cage storage.
Final steel-cage preparation and duct installa
tion.
Handling and Temporary Assembly of Precast Segments
FIGURE 11.57.
B-3 South Viaducts, inside view of the precasting factory.
Casting machine
FIGURE 11.58.
507
Concrete Plant
Control System
B-:, Sou th Viaducls. pIa n \'iew of I he precasling
Inside formwork
facLOlV,
of the newly cast segment to the match-cast po sition by means of an independent motorized trolley.
11.7 Handling and Temporary Assembly of Precast Segments Bottom formwork
FIGURE 11.59. machine.
B-3 Somh Viaducts, detail of a casting
4. Positioning of steel cage inside the formwork. 5. Adjustment of casting machine, including alignment of match-cast segment and sealing of all form panels. 6. Concrete casting and finishing. 7. Steam curing. 8. Fonnwork stripping, followed by transfer of the match-cast segment to the storage yard and
In either long- or short-line casting, segments can not be handled before the concrete has reached a sufficient strength to prevent: Spalling of edges and keys Cracking of the parts of the segment subjected to appreciable bending stresses due to self-weight Inelastic deformations that would ultimately Im pair proper matching of the segments Critical sections in a typical single-cell box segment are, Figure 11.60:
Technology and Construction of Segmental Bridges
508
FIGURE 11.60.
Critical ~ecljollS ill a t\'jlical seg-mellt at time of IOrlmmrk ~Iri]l]lillg.
Section A where the side calltilevers are attached to the wehs Sectiolls Band C at midspan oflhc top and bottom slab Sectioll A is allllost alw
j;i
= 30()O to 4000
psi (21 to 28 MPa)
In the casting yard, segme!1\s are usually handled hv a portal crane traveliIlg on rails or on steeriIlg wheels for added mobility. A typical portal crane in the Olel'On Viaduct precasting yard is. shown in Figure I 1 .61. Proper handling of the segment requires proper pick-up poillts to keep the stresses in the section within the allowable limits. A typical example of halJ(llillg three different shapes of box girders is shown in Figure 11.62. For the conventional single box, inserts or through holes are provided near the web in the roadway slab, allowing lifting to be accomplished by a simple spreader beam.
FIGURE 11.61.
OlclOll \'iatiuct, portal cralle ill 1'1('
casting \·anL
For the twill-box, three-web section, a four-point pick-up is usually nccessarv to eliminate excessive transverse bending of the top and bottom slab. A triple spreader-beam arrangement allows the load transfer from the four pick-up points to the single lifting hook. For a triple-box, four-web section (such as used ill the Saint Cloud Bridge), temporary ties are pro vided in the outer cells to transfer the reaction of the outside webs 10 the center webs. A simple spreader beam is then sufficient to lift the segment. Segments must be stored in a manner designed to eliminate warping or secondary stresses. Con crete beams installed at ground level provide a good bearing for the segments, which must be supported under the web or very close thereto. If stacking is required to save storage space, precau tions must be taken to transfer weight from the
=
Placing Precast Segments
FIGURE 11.62. H;tlldlil1~ prct,l~l segments. Illellt. (i) Four-wcb ~l'gnlt'lll.
upper to tltc lov,.-er lavers of se~mellts without ex cessive bendin~ of th(' slab. _ 11.8
Placing Precast Segments
Transportation and placement of segments may be performed bv one of several methods. depending Oil t he site location and the ~eneral characteristics or the strllcture. These methods can be divided illto three main categories: 1. Transportation by bnd or water and place Illelll b~ an independent lifting apparatus. 2. Trall5porlation bv land or water and place ment with the help of a beam and winch carried by the bridge deck itself. 3. Transportation b~ \;tnd. water, or along t!le bridge deck alreadv constructed and place ment with the help of a launching girder.
There are methods that fall into none of these cat egories, such as the use of a cableway, but their use is limited. 11.8.1
IXDEPEXDEXT LIFTING EQCIPJIENT
This method, where feasible, is the simplest and least expensive. It W;IS llsed for the Choisy-le-Roi, Courbevoie. Juvisy, and Conflans bridges, where the navigable stretch of water lent itself to the use
(II)
509
T\\,()-\\Tb segmt'Tlt. (hl I"hrl't'-\\'ciJ s<'g
of a barge-mounted crane, ensuring tile colleUiol1 of segments from the precasting site and their po sitioning in the final structure. A terrestrial crane was employed for the Cardon, Bourg-Saint An
510
Technology and Construction of Segmental Bridges
positioning of the key segments at midspan, be cause the finished structure on either side of the key segment prevents the crane from maneuvering properly and hinders the positioning of the seg ment, which may be carried out only from the side of the structure. For the B-3 Motorway Bridges a special apparatus was designed to place those seg ments in the cantilever arm to be constructed in the direction of the completed structure, Figure 3.95. Two longitudinal girders are braced together and rested on the pier head of the cantilever to be con structed at the front, and on the existing structure at the rear. The apparatus consists of a mobile winch-trolley, ensuring the hoisting and position illg of the segments, and an advancing trolley situated at the rear and equipped with a translation lllotOr. The front and rear supports are conceived in such a manner as to transmit the vertical loads through the segment webs. The segments 011 the other side of the cantilever are easily placed by the mobile crane. This beam lIlay easily be used to ensure cantilever stability
The total construction time for such an overpass, including the piers, usually does not exceed two weeks, of which less than one week is spent .on the bridge supel'structure itself. This method has been used with great success for the Rhone-Alps motor way o\'erpasses, with spans varying between 60 ft (18 m) and 100 ft (30 m).
11.8.2
THE BEA,\1-AXD-Wll\'CH METHOD
The beam-and-winch method of placing precast segments was conceived for the construction of the Pierre-Benite Bridges over the Rhone River. This construction method requires a fairly simple ap paratus rolling along the already constructed part of the cantilever and ensuring the lifting, transla tion, and positioning of all the segmelits. The ap paratus is shown diagrammatically in Figure 11.63. I t consists of the lifting gear B carried by the trolley C rolling along the bridge deck on tracks D. The segment A is brought, by land or water, beneath the pier in question, where it is lifted by the equipment. It is then transported to two laun~hing beams E that cantilever out from the bridge deck, upon which it contillues to advance until reaching its final position, whereupon it is lifted to its final level next to the previous segment, Figure 11.64. This system can, of course, be simplified if the segment can be brpught by some independent means to a location vertically below its final posi tion in the structure. As originally conceived, this system was not completely independent; another construction procedure was required to erect the pier segment. The pier segment was cast in place in the Pierre Benite Bridges. It was precast and placed by a crane for the Ampel Bridge in Holland and by a floating barge crane for the Bayonne Bridge over the river Adour. This weakness was eliminated in the construction of the Saint-Andre-de-Cubzac Bridge. For this structure, the pier segments, which form the starting point for each cantilever, were placed by the same equipment that placed the typical span segments, Figure 3.72. The equipment was hung, with the help of cables, to an auxiliary mast fixed to a lateral pier face. The pier segment was brought in from the opposite side, lifted and placed by the mobile equipment's winches. In the same position the following segment was located and the auxiliary mast removed, Figure 3.73. At this point it was a simple matter to reposition the mobile lifting equipment in order to place the typi cal span segments, Figure 3.70.
Placing Precast Segments
511
PLACING SEGMENTS NEAR RIGHT BANK
LIFTING APPARATUS
I
rANTILEVER BEAM LIFTING APPARATUS TRANSFER
TROLLEY
TRANSFER TROLL Y SERVICE WALKWAY
PIER
BLOCK
SEGMENT BEING PLACED
FIGURE 11.63.
cn
Paris Downstream Bridge, placing apparatLls.
~------:--::-".
~'~:r'\'~)
evolved and how the original concept has been modified.
,
•
Launching Girders Slightly Longer Than the Span Length
FIGURE 11.64. ing a segment.
11.8.3
Paris DO\\nstream Bridge, position
LAU.vCHI,VG GIRDERS
This last method, by far the most elegant, uses a launching girder above the bridge deck to bring the segments to their position in the structure. Employed for the first time during construction of the Oleron Viaduct in France, this method has now been successfully used for many different bridges throughout the world. We shall now look at the most important structures constructed by this method to see how the launching girder has
We first consider the construction method of the OIeron Viaduct Bridge superstructure, Figure 3.32. The segments were brought along the top slab until they reached the launching girder, then lifted by the latter, transported to their final posi tion, lowered so as to come into contact with the previous segment erected, and prestressed to the cantilever. The launching girder itself, slightly longer than the span length, was made up of a steel trellis beam with an entirely welded rectangular section weighing 124 tons (l13 mt) and measuring 312 ft (95 m). The maximum span length of the bridge was 260ft (79 m). [he launching-girder system consists of two fixed supports, called tunnel legs, allowing the segments to pass between them, one at the rear of the girder and the other at the center. At the front end is a mobile prop enabling the girder to find support on the next pier. The bottom chords of the girder are used for the rolling track that supports the segment trolley, which can move the segment horizontally and vertically and rotate it a quar
512
Technology and
COllstruct~on
Placing center segment
- - 1 1 8 ' --~-.-~ 141'~...............
- - - 259'-~·--·--
~- ---~-~-
Moving gantry to next pier
I~~~ f.,
I
i
I
II,I
i ~---141'
i
I Placing segments '" daub:" cantilever
FIGURE 11.65.
Olewll
"l)('r;ttioll.,. tAl Rear
Viaduct,
bunciIing-girder
~UppOrl.
(H) cellter support. (e) IClIlfJOlan from prop, (D) prop SlIp]>OI·t. (E) pier seg
IllCIlt,
(I-')
tellljloran'
SlippOIi.
ttT-turn. Three phases
Plw.W' J: Placing tlie l)il'1' ,\egllll'lIt The launching girder rests on three supports-the rear SUppOI't, the center support near the end of the newly constructed cantilever, and the front prop, which is attached to the front of the next pier with the help of a temporary prop support.
of Segmental Bridges
A wpport adjustment was carried out with the help of hydraulic jacks when the girder was resting on the rear and central supports and the te,mpo rary front prop, before installing the pier segment. The purpose of this adjustment was to obtain the optimal distribution of the launching girder self weight alllong the three supports. While the frollt prop is being installed, the central support rests on the end of the pre\'ious cantilever in the same po sition in which the rear support will be during the erection of the t\'I?ical segments. In this phase tbe launching girder rests on two supports and is therefore staticall\' determinate: nothing call be done (() change the rear-support reaction. While the pier segment is being placed, howe\'er, the girder is resting on three supports and is staticallv indeterminate. It is therefore necessary to ensure that the reaction at the central support is less than or equal to that which will he produced 1)\ the rear support during the next construction stage. in cluding the weight of the trollcy alld the tractor placed ill the near \·ieinit\'. Se\'eral other strllctllres have been built with launching girders of the same generation (I, the one used for the Oleron Viaduc\. The Chillol1 Viaduct, Figures :i.43, 1 1.66, and 11.6i, along the bank of Lake Leman used a 400 ft (122 Ill) launching girder weighing 253 tons (230 mt). The maximulll span length was 341 it (104 111). The launching p;irder, of constallt rectangular sec tion, was of the suspe.nsion type, being suspended at the one-quarter points bY'cahle sta\'s anchored at the central mast, which extended above the level of the launching girder. The supports were h\ draulicallv a(Uustable, allowing the girder to cope with different angles of superclevation, Figure
Phase 2: [Hoving the launching girrll'T furward The girder rolls along on the rear support and the segment trolley, which is rigidly attached to a metal framework known as the temporary translation support, which is fixed to the pier segment. The rear and central supports are equipped with bogies and roll along a track fixed to the bridge deck while the girder is being moved forward. Phase 3: Placing typical segments The launching girder rests on two supports, the central support anchored to the pier segment and the rear support tied with prestressing bars to the end of the previously constructed cantilever.
FIGURE 11.66.
operatioll.
ChillOll Viaduct. laullching-girder in
Placing Precast Segments
513
zndSt,uge PI;;.clil-3 p'¢r Sti:'3I"'t",~,at5
4th '5t.;;q~ Glr~<:i !dUC'Nlr'g
ur1""I.,"' ' FIGL'RE 11.67.
(:hill,,11 \'iadllCl. blltlchillh-ginkr
llH)\,('llIl'llls.
11.68. The laullching- girder included three means of adjustlllent:
,!;\,
/
I
I
/
/
'
I
Ai/illstllll'lIt DI:
Lateral movement of the trollev in order 10 place eccentric scg-mctlls "'lriiustltll'llt D2: Lateral translation of the celltral support ill order to cope with horizontal curvature of the structure "1 diu.,tml'lIt D 3: Vcnical ,l(ljustlllem of bog-ies to take up the slIperelevatioll and so keep the central support vertical.
\ \
1\ /
\
\ \
Horizontal chassis
FIGURE 11.68. ,ldjllstllll'llt s.
Chilloll
\'iadllcl.
lalillchillg-ginier
III order to follow the horizontal curves the launching ginler rotated about the rear support while llIo\'ing- sidew;:vs across the central support, Fig-ure 11.69. The mobile temporary front prop was conceived in the same way as the other sup ports so as to allow the passage of the first segments to either side of the pier segment. The Blois Bridge on the Loire River in France had a 367 ft (112 Ill) long launching girder weigh ing 135 tons (123 mt). Figure I L70. The maximum span length was 300 ft (91 m). The launching girder. of constant triangular section. could be dismantled and transported by road. All of the girder components were assembled wilh high-strength bolts. ensuring the transmission of
514
Technology and Construction of Segmental Bridges CONSTRucnON
CONSTR.UCTION
OF
Of"
HQIl!I'ZONTIl.L..
~OR'Z:ONTAL
FIGURE 11.69. struction.
eURvl:.
CURve
( STAGE 1. )
(STAGE 2 )
Chillon Viaduct, cun-ed span con
ELEVATION
FIGURE 11.70.
I}~~I
Blois Bridge, launching girder.
SECTION A
forces by friction between adjoining plates, Figure 11.71. The use of a very light structural steel framework carried with it the risk of large deflec tions. These were reduced and controlled by two sets of cable stavs, passive and prestressed, which came successively into play during maneuvering of a segment (upper passive stays) and during the launching-girder advancement (lower prestressed stays). This launching girder was later used for the erection of two other structures: the Aramon Bridge on the Rhone River, Figure 11.72, and the 2950 ft (900 m) long Seudre Viaduct. The Saint Cloud Bridge on the Sei~e, Figure 3.78, is a recent example of the use of a large launching girder. The girder could place segments weighing up to 143 tons (130 mt) in spans of up to 335 ft (102 m) with a minimal radius of curvature in plan of 1080 ft (330 m), Figure 3.79. The weight of the launching girder was 260 tons (235 mt) and its total length was equal to 400 ft (122 m). The adjustments adopted were similar to those used for the Oleron, Blois, and Chillon bridges. The launching girder, which used upper passive stays and lower prestressed stays, was constructed
FIGURE 11.71. sClllhh delail.
Blois Bridge. launching-girder as
FIGURE 11.72. River.
Aramon
Bridge over the Rhone
with a constant triangular section made up of indi vidual elements assembled by prestressing. This launching girder is notable, apart from its assembly by prestress, for its ability to follow extremely tight curves. The movements used for the Chillon Via
Placing Precast Segments
duct were, of course, lIsed for this purpose. How ever, in the Saint Cloud Bridge it was necessary also for the launching girder to take up several in termediate positions during the erection of a given cantilever so as to bring each segment to its final position in the structure. The total lateral transla tion reached 19.7 ft (6 Ill) at its maximum. Con struction speed of the bridge deck was 130 ft (40 m) per week, including all launching-girder ma neuvers. Two other structures erected with the help of the Saint Cloud launching girder were the Angers Bridge and the Sallingsund Viaduct. The launching girder used for the Alpine \lotorw;JV network was conceived for spans and segment weights of more modest dimensions; it is typical of lightweight universal equipment that can be easily dismantled for reuse in another structure, Figure 11.73. This girder allowed the h,mdling of segments weighing lip to 55 toIlS (50 !lit) over spans lip to 20() ft (00 m). Reflecting on the launching girders mentioned above, we note that their evolution centers on two major characteristics: the structural conception or the girder and the assembly method (collnection types, number of elem~nts, and so on). Launching girders tend lIlore and more to be of the lightweight tvpe, relving on exterior forces to cope wit h diflerenl loadings. rhese exterior forces arc provided by the exterr1
FIGURE 11.73.
.-\[pine
:-"[OlOn\
launching- girder.
515
tions that can be interchanged and assembled on site. In this way the girder length can be varied ac cording to the span length and the weight of the segments. Connectjons are made with tensioned bolts, Figure 11.74, which reduce considerably the number required and consequelltly the time needed to assemble or dismantle the structure. These connections have recentlv replaced those made with high-strength bolts and fish plates, nota ble on such structures as the Deventer Bridge and the B-3 Viaducts. Means of erection adjustments also have im proved, tending to reduce the forces applied to the deck itself by ensuring thal the girder supports are located over the piers or at Icast in t he very near vicinity. This natural evolution leads liS toward a new type of launching girder, one whose total length is slightly greater than twice the typical span length, allowing the simultaneous placing of the typical segmellls of cantilever N and the picr segment of cantilever N + I. LIIUIIChilig Girr/('n Sligh/tv Lllllg!'r Thall Twice lhl'
'(VjJical Spa n The tirst launching girders of this type were used 011 the following bridges: Rio ;\;iteroi ill Brazil; De venter ill Holland, Figu re 3.50; and B-3 South Viaducts in the eastern subudlS of Paris. Figure 3.93. The Rio \literoi Bridge (Section 3.8), linking the city of Rio de Janeiro with \literoi, consists 01 10 miles (16 km) of bridge deck constructed by four identicallaul1ching girders, Figures 3.55 and 3.51>. Each 545 ft (160 111) long girder could be com pletel\' dismantled. The const;Jllt lI·ianglllar sec-
FIGURE 11.74.
Prestressed conneClions.
"I"
Technology and Construction of Segmental Bridges
516
tion, weighing 440 tons (400 mt), could cope with spans of up to 260 ft (80111). The conncctions were identical in principle to those used for the Blois girder. Each installation was equipped wit h three supports of nontullnel type, olle fixed and the other two retractable. The erection sequence was as follows, Figure 1.51 : Phose 1: Se{;IIII'IIII)/aciug The girder rests on three supports, each one O\'er a pier. Two segmellts are erected sillluitaneously, one on either side of the douhle cantilever under COllst ructioll. Thc pier segment of the nex t GlII tilenT is also placed with the launching girder in t his position.
It'
Phose 2: ,\J01'ill{; Ihe /mJl/cilin{; {;irrirr/imL'flrd The girdcr rolls on two telllporan' translation sup ports, olle placed ahove t he pier of the finished c
Owing to the Jengt h of t he bridge and t he pres ence of a large stretch of water beneath the struc ture, the segments were brought to the launching girder Oil bargcs. The ca nt ilc\'cr stahilit y (.)1' the bridge was assu red \)\ the launching girder itself, and ties and props were positioned as construction proceeded. The launching girder used for the Devenler Bridge in Holland, Figures 3.49 and 3.50, were also capable of being entireh dismantled alld of triangular seclion. Its total length was 512 ft (156 111) for a weight 19H tOilS (IHO 1111). The maximulll span length was 243 ft (74 111), Assembly of the launching-girder elements was COllsllllllllated by prestress hars norlllal 10 the joints. It was supported by the fixed supports, of which the rear and the ccntl'al allowed the passage of a segmcllt, and two sets of cable st;.IYS: celltral sla\'s alld launching st
or
'TYPICIl.L CR055_.:5ECTIQN
t L{t.ng tl'"OUflJ
(
J
l.Ifttng tmlk,!l
[
Cent.rat $uppor-t,
CanlA
FIGURE 11.75,
~I
u
B-:1 Smull Viaduct Iaullching girder. gcneral layout.
517
Refere1lces
that IS, between four and SIX segments per day. The average construction speed, including launching-girder maneuvers, was therefore 200 ft (60 Ill) per week. The B-3 launching girder was recently reused for the ,'.Iame-Ia-Vallee Viaduct, which carries high-speed suburban rail for the Paris transport authorit\', References
FIGURE 11.76.
B-:) South \·iadllCl. segment t rallS
I. Anon., ,\1111/1/(/1 jill' Quality CUll/ml/o,- PIIIII/.1 111111 Pro Iiflcliol/ Q/Premsi Pre,'Iressed COlladl' Pmliutls, .\I::\L Itti.70, Prestressed Concrete Institute, Chicago, 1970.
port (I'actor.
which varied between 100 and 164 ft (30 and 50 m). Figure 11,75. The ginler support reactions were thus applied in the region of the piers, and the cantilever stabilitv was ensllred bv the launch ing girder itself. This stabilizing device can be seen to the left of the central support in Figure 1L75. The segments were supplied 1)\ a special eight wheeled tractor Illoving along the top slab. Figure 11.76. :\ special de\'ice llsed to unload and store the seglllents hrought ·bv the tractor freed the lat ter and remo\ed the suppl\' ()f segments from the erection critical path. The c\cle of segment place ment and girder ;td\'ancelllent is represellted in Figure :3.9~~. The next pier segmellt was placed during the sallle phase as the tvpical segments. About two spalls were cOllStl'llcted each week-
Anoll.,.{CI Jtw/l/aloj COl/tTell' i'raf'Iif'!', Part 1, Allleri can Concrete Institute, Detroit, 197~I, :{, "Proposed Recolllmendatiolls for Se~lllelltal COll structioll ill Prestressed Concrete," Fl P COllllllis' sioll-I'refabricuioll. 3d Orall, Scptclllher I(li7. 'l
4. "Recolllillenc!ed Practice for Se~lllelltal Const rlletioll ill Prestressed Concrete," Report bv COJlllllinee 011 Se~Jllelltal COllstl'llLtioll. jOIlrt/([1 oj 1/[1' Prnlrt'lS/,d Co/Ur!'ie 1lI"Iilllil'. Vol. :!O, ::\o.:!. ,\/arch-.\pril 197'i. .'). Anoll .. PCI PO.l/-TfIlsifJllillg ,\1([1/11([1. Prestressed crete Institute. Chicag-o. 1972.
fi.
:\!lOIl .•
COI1
PTI PosI.Tensioning .\lfll/wd. Post-Tensioning Phoenix. Arizolla. 1970.
r Ilslit ute. 7. T.
J
Ikzouska, Field III'I}('!'/ioll of Grollieli Po,II T!'IIt/olls. Post-Tensioning- Illstitute. Phoenix. :hizOIl;l, \fa rch 1977,
T!'IIsiouillg
'r' I
12
Economics and Contractual A·spects 0,[ SegJnental Construction
12.1 BIDDING PROCEDURES
iI "
12.1.1 Single Design 12.1.2 Design and Build 12.1.3 Value Engineering 12.1.4 Alternate Designs 12.1.5 Summary Remarks on Bidding Procedures ]2.2 EXAMPLES OF SOME INTERESTING BIDDINGS AND COSTS 12.2.1 Pine Valley Creek Bridge, California 12.2.2 Vail Pass Bridges, Colorado 12.2.3 Long Key Bridge, Florida 12.2.4 Seven Mile Bridge, Florida
12.1
Bidding Procedures
A bridge design ~hould 011 principle be economical awl as a practicalll1atter must fall within budgetary rest nctiolls of a particular project. The economic "moment of truth" for a given bridge design occurs when hids are recei\'ed and evaluated, III a hasicallv stable economy where material and lahor costs are predictable within relativelv small fluctuations, the selection of structure t\'pe and materials is reiali\'Cly straightforward. This situa tion prevails when the time required fe)r the design is relativelv. short and thus is not affected by eco Ilomic cycles, or, if the design time is relatively long, the economic cycles are mild. In an inflation an ecollomy there is no economic stability, and de signers are hard put to make rational choices, as they have no control over economic parameters that can influence their design decisions. In short, the problem is whether economic assumptions made during the course of design are valid at the time of bidding. ,
518
12.2.5 12.2.6 12.2.7 12.2.8 12.2.9 12.2.10
Zilwaukee Bridge, Michigan aine Avenue Bridge, Indiana Napa River Bridge, California Red River Bridge, Arkansas North Main Street Viaduct, Ohio Summary of California's Experience
12.3 INCREASE IN EFFICIENCY IN CONCRETE BRIDGES 12.3.1 12.3.2
Redesign of Caracas Viaducts, Venezuela Comparison between Tancarville and Brotonne Bridges, France
REFERE.">lCES
Orn'ioLlsh, the design and the bidding (tender ing) of a project are closeh related. Contractual bidding procedure!> \'ar~' from countn 10 countrv, and current economic pressures are leading to changes in these procedures. The various bidding methods used in \'arious countries can be broadlv categorized (with sOl11e possible variations) as fol lows: (I) single design. (2) design and build, (3) \alue engineering. and (4) alternate designs. 12. Ll
S/.\'GLE DES/G.\'
Heretofore, single design was the major method used in :\orth America and Great Britain. In this method, in general, design drawings prepared for bid are very detailed, to the extent that even the length and other dimensions of every reinforcing bar may be given. The bidding period is followed by a tight construction schedule. The contractor bids and executes the project in strict accordance with the bidding documents, No variation from the documents is allowed unless an error in design is
Bidding Procedures
discovered, or a specific detail proves impractical to consummate, or geological perturbations are dis covered that differ from what was assumed in de sign and delineated in the contract documents. These changes are authorized by a change order, and if there is an increase in cost the contractor is paid an "extra." This system worked well for many years when the economy was fairly stable and predictable and when economic changes were gradual over an ex tended period. Its disadvantage is its lack of flexi bility to accommodate a n inflationary economy, sudden price changes in materials, a rapidly ad vancing technology, and the current emergence of specialty contractors with unique equipment or skills, proprietary designs, and patented construc tion methods. Its biggest advantages are ease in administering the contract and absolute control over the final design. 12.1.2
DESIG,V A,VD BUILD
In some European countries. by contrast, bid documents are prepa.red with the intention that the contractor will prepare' and submit his own detailed design for the project. Thus, bid plans will be more general and, for a bridge, may show only span lengths, profile, and typical sections. The cnntractor may then refine the original design or submit an alternate design of his own choice, the responsibilitv for producing the final design and details being his rather than the engineer's. This procedure allows the contractor to use any special equipment or technique he may have at his dis posal. For example, a cast-in-place concrete box may be substituted for a steel superstructure where the contractor has special know-how in concrete construction, or the change may be less drastic and involve onlv a reduction in the number of webs in a box girder. Verification of the adequacy of the contractor's final design is generally carried out by a "proof en gineer" who is retained by the owner or is on the owner's engineering staff. In 'order to minimize disagreements between the contractor and the proof engineer, European codes have been made very specific. As a result, European contractors usually maintain large in-house engineering staffs, although they may also use outside consultants. The outcome apparently is a savings in construc tion cost, achieved by the investment of more de sign' time and effort than in the single-design method.
519
The advantage of the design-and-build method is that in an atmosphere of engineering competi tion, innovative designs and construction practices advance very rapidly. The state of the art of de signing and constructing bridges advances in re sponse to the need for greater productivity. The disadvantage is the lack of control over the selec tion of the type of structu re and its design. There is some concern, too, that quality of construction may suffer as a consequence of overemphasis on pro ductivity and initial cost. However, the contractor is usually required to produce a bond and guaran tee his work over some period of time, and anv de fects that surface during this period have to be re paired at his expense. Whether such a system could be adopted in the United States is debatable. 12.1.3
VALUE ENGI,VEERING
Value engineering is defined by the Society of American Value Engineering as "the systematic application of recognized techniques which iden tify the function of a product or service, establish a value for that function, and provide the necessary function reliability at the lowest overall cost. In all instances the required function should be achieved at the lowest possible life-cycle cost consistent with requirements for performance, maintainability, safety, and esthetics."l In 1962 the concept of value engineering be came mandatory in all U.S. Department of Defense armed services procurement regulations (ASPR). Before this time value engineering had been applied to materials, equipment, and systems. The advent of ASPR provisions introduced value en gineering concepts to two of the largest construc tion agencies in the United States-the U.S. Anny Corps of Engineers and the U.S. ~avy Bureau of Yards and Docks. Soon thereafter the U.S. Bureau of Reclamation and the General Services Adminis tration (GSA) adopted and inserted value en gineering clauses in their construction contracts, and the U.S. Department of Transportation estab lished a value engineering incentive clause to be used by its agencies. Several value engineering clauses (or incentive clauses) are in use today by many agencies. In gen eral, they all have the following features l :
,f
1. A paragraph that defines the requirements of
a proposal: (a) it must require a change to the contract and (b) it must reduce the cost of the contract without impairing essential functions.
I
I
520
Economics and Contractual Aspects of Segmental Construction
.~ hdocllIIlenlalion'1 paragraph that ilelnizes the information the contractor should furnish with each proposal. It should be comprehen sive enough to ensure quick and accurate evaluations, detailed enough to reflect the contractor's confidence in its practicabilitv, and refined to the point where implementation will not cause undue delay in construction opera tions. Careful de\'e\opment of this paragraph and meticulous adherence to its requirements will preclurle scatter-shot proposals bv the contractor and burdensome review bv the agencv. :\. :\ paragraph on "submission." This paragraph details the procedure for submiual. 4. A paragraph on "acceptallce," which outlines the right of the agency to accept or reject all proposals, the notification a contraClor may expect to receive, and appropriate reference to proprietary rights of accepted proposals.
2.
paragraph on "sharing," which cOlltaills the forl1lula ror determining the contract price a!ijustlllent if the propo.sal is accepted alld sets forth the percentage of sayings a contractor lIlay expect to receive.
!), :\
As generally practiced by highway agencies III the United States, a value engineering proposal lIlllst indicate a "substantial" cost savings. This is to pn>clude minor changes such that the cost of pro cessing offsets the savings to be gained. SOll1e other reasons for which a value engineerillg proposal llla\' be dellied are as follows: Technical 11OlIcOllIpliance. Delay ill construction such that the cost saYlllgs would be subst alllialiv nullified. Proposed change would require resubmission of tlIe pn~jeCl for any number of \'arious permits, slIch as environmental impact statement, wetlands permit, and navigation requirements. Resubmis sion would in all probability delay construction anrl II ulli fy any cost savings. Savings resulting from a value engineering pro posal are generally shared equally by the agency and the contractor, after an allowance for the con tractor's development cost, the agency's cost in processing the proposal, or both. As practiced in the United States, all cOntractors must bid on the design contained in the bid documents, and only the low bidder on the base bid is allowed to submit
a \'alue engineering proposal. This is, of course, value engineering's biggest disadvantage. Ally !lumber of contractors rnav have more cost effective proposals that they' are not allow'ed to submit because they were not low bidder on the base bid, Its advantage is that to some degree it aI lo\\'s contractor inno\,
ALTER.\'ATF /)ES/(;\'S
Alternate designs, as it is developing ill the United States, basically is an attempt to produce a hybrid sYstem cOllsisting of the besl elements of the single-design and the design-and-build methods. It attempts to accomplish the following: Retain for the authorizing agency cOlltrol over the "t\Ve selection" of the structure and it~ design Provide increased competition bet ween lIIaterials (structural steel versus concrete or prestressillg 5t ralld verSll s hal'S) or const ruet ion proced 1I res (cast-in-place VerSlIS precast segmental or halallced cantilever versus increlllelltal launchillg-, and so OIl )
Pn)"i de COlI t raet or fkxi bi Ii t y (const ruct ion proce dures, methods, and/or expertise) This met hod has de\'eloped, wit h encouragement from the Federal H)gh way Ad millist ration, as an
Balw..'>!' offluc/ualillg I'col/ollli( (of/diIIOIlS, II Isfdl Ihlll mulliplp rr/Jl'litizll' SflaW, IOllg .1/11/11\ or ml1jor hndg!'s, or where Ihere is 1111 ('xlnuled /)aiod of design from (011 (1'/lllOn of IiiI' /lmjerl 10 (J ),I'I('(J,\CfOT hids, Ihere CI1II he I/O (LISUrIJllC(, /lri«(' slabilily /1)1' (l parlilll/aJ' malnial or (ollslruc/ioll mel/wr/olof-',," Wilh allerllal!' des ig 11.1, no Il/al/a how lite ('COllOm), rhallges, lfIore del'lgns 111'1' m'oi/ aille at IiiI' lime of fn'r/ding thai are tike/,,' 10 lie SlIill'd 10 Ihe ml
or
/)revailing ('col/Olnir (ollditiolls.
General recommendations regarding alternate designs from the same document2 are as follows: 1. To receive the most economical construction
between basic structural materials, consistent with geographic, environmental, ecological or other site restrictions, there should be maximum opportunity for competition he tween structural steel and concrete.
Bidding Procedures
2. \Vithin environmental, aesthetic, site, and other constraints. the plans and bid docu ments should show or otherwise indicate what alternative types of structures will be allowed or considered. The contractor should be al lowed the option to bid any designated alter native design that is consistent with the con tractor's expertise, available equipment, and so on. 3. Bid documents and the contract plans should clearly indicate the design criteria and what type of alternative designs andlor con tractor options will be acceptable. Determination of practical and economical alternatives and/or contractor options should be developed in the preliminarv design. 4. Bid documents should be considered as "open" documents in regard to construction method, erection systems, and prestressing systems. 5. Consistent design criteria should be used for alternatives; for example, if load factor de sign is llsed, it shollid be used for all alterna tives. 6. Span lengths should be identifled on the contract plans. However, other than where pier locations are constrained by physical and geological conditions at the site, consideration should be given to allowing a tolerance in pier location lo avoid placing a particular alterna ti\'e at an economic disadvantage. For exam ple, in a typical three-span structure, the side span should be approximately HO percent of the center span for structural steel, 70 per (ellt for conventioll;;! cast-in-place concrete 011 falsework, and 65 to 70 percent in seg lllellt~ll balanced cantilever cOllstruction. 7. 'To avoid an economic disadvantage lO a par ticular Sli perstructure alternative. alternative substructure designs mav be required. Limi tations Oil the substructure, such as allowable axial load and moment, should be clem'lv identified on the contract plans. ' 8. Where specific design requirements are not covered by the ;\merican Association of State Highwav and Transportation Officials (AASHTO) Bridge Specifications, the con tractor should be allowed to use other recog nized codes and standards where applicable. However, the alternative design should document where these provisions are to be 'used, why the AASHTO requirements do not
521
apply, and which articles of the substituted code or standard are to be used. Such provi sions should be subject to approval by the en gineer and appropriate agencies. 9. Prebid conferences are to be encouraged as a means of communication between the en gineer, high way agencies, and contractors. 10. In order to allow a contractor adequate time to investigate the various alternatives and prepare plans, it is recommended that the advertising time be commensurate with the size and complexity of the project with a minim.um of 60 days. 11. In order to allow adequate review and checking of the low bidder's proposal, award of contract should be extended commensu rate with the size of project. Specific recom mendatiom/ regarding prestressed concrete alternates are as follows: 1. To increase the competition in post-tensioned
concrete construction, it is recommended that plans and other bid documents allow cOllven tional cast-in-place Oil falsework, precast pre stressed span units, and segmental construc tiOll or combinations thereof. 2. Segmental construction should· allow the fol lowing at the contractor's option: a. Precast or cast-in-place segmental COll struction. b. An\' of the post-tensioning ,>vstems-that is, strand, WIre, or bars or combinations thereof. c. :\nv of the following construction methods: balanced cantilever, span-bv span, progressive placing, incremental launching, or combinations thereof. d. Exterior dimensiolls 0(' the cross section should be fixed, At the cOlltractor's option, the thickness of wehs and Hanges 111;1\' be \'aried to accommodate proposed con struction and erection methods a nel post-tensioning systems, provicl ing that any changes in the dead weight, shear, and so on are accommodated in the design. 3. The contract plans should indicate the maximum and minimun final prestressing force (Pf ) and moment (Pf X e) required, after all losses, for the final condition of the structure -that is, dead, live, impact, and all superim posed loads. Any increase in prestressing force
522
Economics and Contractual Aspects of Segmental Construction
requirements as a result of the method of con struction, election, or type of tendon system should be evaluated at the shop drawing stage. 4. Changes in eccentricity of prestress should be accompanied with appropriate changes in pre stress force to produce the same minimum compressive stress due to prestress. 5. The minimum prestress force should be such that under any loading condition, both during and after construction, stresses will be within allowable limits. Consideration should be given to secondary moments due to prestress, redis tributed moments due to creep, and stresses resulting from thermal gradient (between the top and bottom of the girder and between the inside and outside of webs). G. Contractor revisions to contract plans, with supporting calculations, should be submitted to the ellgineer for apprO\·al.
12.1.5
SU,HMARY REMARKS ON BID])].\'(; P1WCEDURES
All or the bidding procedures described above have one thing in common: they all attempt to produce the lowest initial cost by competition in construction and/or design. All of the last three approaches (design-and-build, value engineering, and alternate designs) require decisions based on comparisons or basic structural materials, structure types, construction methods, and so on. This im plies that the basic premise in the selection process is equivalency-comparable service, performance, and life-cycle cost of the facility. Life-cycle costs refer not only to initial cost, but also to maintenance and any rehabilitation costs during the life of the structure. True cost of the project must be considered. What may be initially least expensive may in the long run, when future costs are accounted for, be actually most expensive. Some newer structure types and designs are at the fringe of the state of the art and have only been used in the United States within the last decade or less. Thus, an adequate background of experience is unavailable to evaluate life-cycle costs. The esti mation of life-cycle costs may be difficult in many cases, such as for new and progressive bridge de signs. Functionally, alternative structures are de signed to the same criteria. Only years of opera tjonal experience can provide the data base for reasonably estimating life-cycle costs and thereby true equivalency in design insofar as cost is in
volved. However, the problem of adequacy of data does not diminish the importance of the question and the need to attempt to answer it. Allother anti-inflationary measure lIsed in l't:cent years is that of stage construction. This concept may take one of two forms .. Major structures, be cause of their size, lend themselves to stage construction-that is, separate substructure and superstructure contracts. Usually several years will elapse between bidding and awarding of the sub structure contract and the superstructure contract. The economic superstructure span range for dif ferent alternative types and materials is a variable. In this form of stage construction the substructure is let first; thus the spans for the superstructure de sign become fixed. This mayor may not impose an economic disadvantage to specific superstructure alternates. The substructure must be designed for the largest self-weight superstructure alternati\·e, which mayor may not be the successful super structure alternative. It appears that this form of stage construClion maybe to some extent self canceling or counterproductive to cost savings. \Vith a total alternative design package, the sub structure (foundation, piers, span arrangement) can also have alternatives commensurate with the superstructure alternatives. The other form of stage construction concerns a large project. containing many bridges, that is sub divided for bidding purposes into a number of smaller prqjects. Its f>rimaq,' purpose is to encour age small contractors by pn)\iding pn~jects of manageable size, thus increasing competition. However, certain construction techniques, by vir t ue of the investment in sophisticated casting or erection equipment, require a certain volume of work to amortize the equipment and be competi tive. Depending upon the size of the subdivided contract, this form of stage construction in some instances may also become counterproductive. The value engineering concept can be divided into two major areas of application: during design and during construction. Value engineering pro cedures in the design stage may result in very specific recommendations based on a certain set of assumptions at a particular point in time for the design. If conditions change during the interval between the design decision and the actual con struction, which can be several years, conditions on which the assumptions were based may have changed. Such changes could make the original value engineering decision incorrect. The alterna tive design concept, on the other hand, does not make all such specific design decisions at an early
Examples of Some Interesting Biddings and Costs
stage but retains some options in order to allow a later response to changed conditions. Therefore, there is an apparent incompatibility between the application of value engineering principles in the design stage and the concept of alternative designs for bidding purposes. However, the concept of value engineering is a powerful tool and can be made compatible with the concept of alternative designs if its principles are used to determine whether a given project should require alternative designs and, if so, what structure types should be considered as equivalent alternates.
12.2
12.2.1
Examples of Some Interesting Biddings and Costs
PISE VALLEY CREEl\. BRIDGE, CAUFORSIA
The Pine Valley Creek Bridge (Section 2.7) was the first segmental bridge in the United States to in corporate the concept of value engineering (cost reduction incentive proposal) in the bidding docu mellts. The origi nal design assu med cast-in place balanced cantilever construction with the prestressing force (P f ) ;ind nHllllent (Pf X e) based on strand capabilities. Project plans developed by CALTRA:--JS re quired construction of the cantilever~d sections at piers 3 and 4 before those at piers 2 and 5 (refer to Figure 2.40). Because of rigid specification re quirements for the protection of the valley slopes, TABLE 12.1.
the contractor was faced with a difficult and costly erection procedure. At least one cable way span ning the entire valley would have been required to transport men and material to appropriate loca tions during the construction procedure. Complete site installations on both sides of the valley would have been required, which were accessible only with a great deal of difficulty. The superstructure design alternative submitted under this proposal employed the Dywidag system, which included the following: (1) use of the threaded-bar system especially suited to segmental construction, (2) increased prestress-force eccen tricities, since most longitudinal prestressing bars could be placed and anchored in the slab, (3) diagonal prestressing in the webs to cater to the shear stresses, and (4) a modification in construc tion sequence so as to work from piers 5, 4, 3, anci 2, Figure 2.44. Changes proposed under the value engineering clause are summarizied in Table 12.1. Total sav ings as a consequence amounted to $382,000.:1 12.2.2
Structural svstem
Concrete stresses: Construction Tension Concrete shear
VAIL PASS BRIDGES, COLORADO
The Vail Pass structures are part of Interstate 1-70 near Vail, Colorado, in an environmentally sensi tive area. Environmental considerations played a dominant role in the selection of the bridge types and the design thereof. Another factor considered was the relatively short construction season at the high elevations of the sites.
L
Pine Valley Creek Bridge, Value Engineering Proposal
Original Construction sequence
523
CRIP
Long cantilevers before shorr to minimize creep ..ls Cantilever for D.L., continuous for L.L. + added D.L. :\0 Redistribution
Reverse to facilitate constr. from abutment
0.-1f;.
3vr:.
o "63" .\CI, mild steel
Slab designs
.\.\SHTO loads, method and distribution reinf.
Hinge
Two diaphragms
Savings estimated
$ 88,0()()
Conti n uous for all loads Full redistribution
0.55/;.
Pri nci pal stresses diagonal prestress A.\SHTO loads with "Hornberg" graphs, no distri bution rei nf. No diaphragms
$228.000 22,000 22,000
22,000 $382,000
r
~
Economics and Contractual Aspects of Segmental Construction
524
Of the 21 bridge structu res in this project, 17 were designed and bid on the basis of alternative designs. One alternative design considered trapezoidal steel hox girders composite with a con crete roadway flange. The other alternative design was for precast concrete segmental box girder de sign, with the Federal Highwa\ Administration re quiring that the contractor be given the option of cast-in-place segmental construction. At two locations, the site constraints were such that thev were bid without alternatives as steel box girders. Two other locations required 80 ft (24 m) long simple-span underpass structures to provide lor wildlife migration. These structures were built of cast-in-place concrete box ~irder construction. The remaining 17 structures were completelv de signed and detailed for the two alternatives, one in structural steel and the other in precast concrete segmental (with a coni ractor option of providing a cast-in-place segmental design). Spans varied in nUIIIber from t\\"o 10 five and ill length frolll 30 to :260 ft (9 to 79 111). Table 12.2 tabulates the five contracts that in volved the 17 hridges hid 011 the basis of alternative designs and lists them in the order in \\'hich the} were hid. 4 Approximately a year elapsed between the lettillg of the first and last COlllracts. Although considerable differences in bid prices are shown in individual projects, for the lotal pn~ject there is less than $80,000 difference oul of an approximate total cost $17 million, or less than 0.5% dif
or
TABLE 12.2.
ference in bid prices for the alternatives. Precast segmental was the low bid on project I and cast in-place segmental was the low bid on project 4. Based upon length (width was constant), the seg mental concept was successful in approximately 60o/c of the total project. The consultants, I nternational Engineering CompanY, Inc., estimated that the additional cost 10 produce alternative designs \vas about 2.So/c of construction cost. It is difficult to estimate what savings were achieved by bidding alternative de signs rather than· a single design; however, overall sa\'jngs of 7 to 10% of Ihe construction costs ale not unreasonable. 4 12.2.3
LOXG;..,:n BRlJ)(;E. FlDUlJ)A
The Long Kev Bridge in the Florida ~eys was hid lit ilizi ng t he concept 01' alternate designs. Fou r complete sets of contract plans were prepared for the alternative construction schemes indicated in Table 12.3. Plans for the AASHTO precast, pre tensioned I girders were prepared by the Florida Department of Transportation. Plans for the three basic precast segmental schemes were prepared by the state's consultant, Figg and \luller Engineers, Inc. III the prciiminan design stage three methods or segmental COllst ructioll were considered lor this pn~ject: balanced cantile\er, span-by-span, and pl'Ogressi\e plat-ing. The progressi\e placing
Results of Alternative Bids, Vail Pass Bridges
TOlal Proj.
Hridge
:":0.
:":0.
4
5 Totals
F-II-AX F-I I·:HV F·II-A\, F-II-.\C F-12·AK F-12-A\1 F-12-:\:": F-12-AO F-12-AI' F-II-AP F-II-AO F-II-A:\' F-II-A:>'1 F-II-AL F-II·AK F-12-AT F·12-AS
:..: o. Spa I1S
4 5 4 4 3 2 3 ~-I
:-i 3 2 4 4 4 3 4 4
Length (It )
Length (it )
Low
Steel
Hid
Cost IF!". Steel
Low Connete Bid
Cost/Ft 2 ,
COllcrele
7'27
880 6YO 668 220 240 350 368 600
2965
S5,992.155
$48.12
1778
$3,777,549
$50.59
$4.111,170
$55.05
$994.347
$44.50
$1,053,364
$47.14
2448
$4,257,771
$41.41
$4,108,057
$39.96
1452 9175
$2,29S,409 $17,320,231
$37.69 $44.95
$2,598,938 $17 ,39S,84 7
$42.62 $45.15
$44.39
310
222 740 744 514 450 726 726
Examples of Some Interesting Biddings and Costs TABLE 12.3.
525
Long Key Bridge, Alternatives Substructure
Su pers t rucw re
Precast Piles
Drilled Shalts
A
B
C
D F H
Precast I!;irders, .\,\SHTO Segllle n tal: Span bv span, V piers Span by span, vertical piers Cantilever, \'ertical piers First option. slab reinforcing
E G RIC epoxy coated Pretensioning Cast.-in-place conventional Precast (never integral)
Second option, barrier curbs
method was discarded because it was felt to be (at the lime) too new for acceptance in L' .S. practice. It was later introduced on the Linn Cove Bridge in :--Jorth Carolina. The basic difference in the two span-by-span alternatives for the Long Key Bridge is in the pier configuration: V piers or vertical piers, Aside from the const ructioll alternatives and pier t.-pes, the contractor was offered the option Oil all segmemal alternatives of transversely rein forcing the top flange' either~ with epoxy-coated conventional reinforcing steel or by transversely pretensioning with ~ ill. (1~.7 mm) diameter strand. Further, he had the option on all segmental alternatives of either precasting or casting in place the traffic barriers. The contractor also had the option of casting the segments rightside lip or upside down. Casting the segments upside down was intended to facilitate transversely pretensiol1ing the top Bange. How ever, since no waterproof membrane or wearing surface was specified, the top flange surface of the deck was required to have a grooved or tined sur face for sUd resistance. If the segment v.rere cast upside down, then, the form would be required to produce the desired texture. Specifications were left open such that strand or bar prestressing ten dons could be bid. All conventional steel rell1 forcement was required to be epoxy coated in all alternatives. The eight basic alternatives for this project pro duced bids from eight contractors, as indicated in Table 12.4. :--Jote that there were six bids for the span-by-span method, one for the balanced can tilever method, and one for the precast preten sioned AASHTO I girders. The low bid in precast segmental was $2.6 mil lion less than the AASHTO I-girder bid. Low bid was for the span-by-span alternative with precast V
TABLE 12.4. Bid Rank
Long Key Bridge, Bid Tabulation
A!ternati\'e Chosen
Relative Bid
D F F F B F F H
1.0000 1.0225 1.0539 I .0911:) 1. I 7:11 1.1HH 1.2557 1.306:)
2 :)
-t :i ()
7 H
piers and drilled shaft foundations. The contractor elected to precast the segments near the project site and cast the segments rightside up, using trans verse prestressing in the top flange. He slip formed the cast-in-place barriers after segment erection. Further, he elected to move the scaffold ing trusswork from span to span by using a barge-mounted crane as opposed to having the falsework trusses mOllnted on barges. Table 12.5 presents a cost analvsis of the low bid as compared with the AASHTO pretensionecl 1 girder alternative." TABLE 12.5. Long Key Bridge. Cost Analysis of the Low Bid and the AASHTO I-Girder Bid Sp
Precast AASHTO I Girder
TOl,d cost"
$26.63/h~
Su perstructure cost Substrnctllre cost Segments erected Total bid Total area
:$2 I. 43 1ft2
$30.95Iftl :$23.59/ft2
:$ 5.20/ft2 $19.16Ift 2 515.307,375.91 468,30 I ft2
$17.956,538.75 470,277 ft Z
"The mobilization bid items were proportioned to the structural items in all cases. The Florida Department of Transportation estimate was $14,550,000.
Economics and Contractual Aspects of Segmental Construction
526
TABLE 12.6.
Seven Mire Bridge, Alternatives Substruct ure
SuperstrucLUre
Precast Piles
Drilled SlJafts
A
B
C E
D F
Precast AASHTO I-girders Segmental: Span-by-span, vertical piers Cantilever, vertical piers First option, slab reinforcing
RIC epoxy coated Pretensioning Cast-in-place conventional Precast (n~ver integral) Cast-in-place conventional Precast
Second option, barrier curbs Third option, box piers
12.2.4
SEVEN MILE BRim;};, FLORIDA
Seven Mile Bridge in the Florida Keys had the same basic alternatives as Long Key Bridge, except that the span-by-span with V piers was eliminated and the contractor had the further option for the vertical piers of casting in place conventionally or precasting, Table 12,6. Six bids were received, with all bidders se lecting alternative D, Table 12.7. Low bid was $44,986,942.31. There were no bids for the AASHTO I-girders. The low bidder optioned to reinforce the top slab with conventional reinforce ment, epoxy coated; to cast the barrier curb in place; and to precast segmental box piers. The low bid included $5,128,600 for waterline, roadway approaches, and navigational requirements. Anal ysis of the bid items revealed a superstructure cost of $23.22/ft2 and a substructure cost of $5.68/ft2 , resulting in a $28.90/ft 2 total cost. The Florida Department of Transportation estimate was $52 million ($7 million higher than the low bid).
12.2.5
ZILH'AUKEE BRIDGE, ,\1/CHIG,4N
This structure was designed with ailernatives of steel plate girders and precast segmental concrete box girder. Bids were first taken in November ] 978, Table 12.8. The engineer's estimate for the concrete alternative was $60,609,614.30 and for the steel alternative $71,3] 6,854.90. On the basis that the low bid of $80,999,445.50 was 33% higher than the estimate, the bids were rejected. The design underwent revision, and the bid documents allowed tbe contractor to make design and prestressing system changes under a "cost re duction incentive," and an escalation clause was introduced. The pr~ject was rebid in August] 979 (nine months later), Table 12.9. The engineer's es ti mate was $71,645,661.50 for the concrete alter native and $71,965,516.70 for the steel alternative. The low bid of $76,787,252.65 was 7% over the estimate-5% below the previous low bid. By re bidding the pi oject (after nine months of inflation) a savings of $4.2 million was achieved.
TABLE 12.8. TABLE 12.7. Bid Rank
2 3 4 5 6
Seven Mile Bridge, Bid Tabulation Alternative Chosen
Relative Bid
D D D D D
1.0000 1.0214 1.0768 L1404 1.2297 1,2556
D
Bid Rank I
2 3 4 5 6
Zilwaukee Bridge, Ranking of
First Bids
Relative Bid
Alternative
1.0000 1.0115 1.0562 1.0816 1.1 071 1.1375
Concrete Concrete Steel Concrete Steel Steel
527
Examples of Some Interesting Biddings and Costs TABLE 12.9. Bid Rank
Zilwaukee Bridge, Ranking of Second Bids Relative Bid
Alternative
I.(JOOO 1.0798 1.0829 1.1231 1.1501
Concrete Concrete Concrete Sleel Steel
2 3 4 :)
12.2.6
CUSi:' .4VEXUE BRIDGE, ISDIANA
The Cline Avenue bid documents were very liberal towarcl redesign, with the bidder only having to in form the state of the intention to redesign at bid opening. As designed, the plans and specifications provided the option of a steel plate girder or pre cast segmental box girder structure. The structure was redesigned as cast-in-place on falsework, pre stressed concrete box girder, except for the main channel spans which are cast-in-place segmental. rhe steel option was a composite load factor de sign. The low concrete bid was for $53,545,770.55 with the engineer's estimate being $53,560,259.78. Relative bids are listed in Table 12.10. 12.2.7
SA.P..!. RIVER BRIDGE, CAUFOR.Vl.4
The Napa River Bridge (Section 2~ 11) is another example of the lise of alternative designs. For this prc~ject. because the lower structure height made falsework feasible, bid documents were prepared for three alternati\'e schemes: !\. Conventional
continuous cast-in-place box
Alternative C used a transverse prestressed deck in order to reduce the number of girders. Strong competition was expected from the steel industry, as this site is readily accessible by water from the yards of two major fabricators. However, the low bidder, G. F. Atkinson Company, selected alterna tive C and cast the bridge generally in half-span segments on falsework to the ground as a series of balanced T's. About 60 ft (18 m) of the 250 ft (76 m) span over the navigation channel was con structed in three segments on falsework suspended from the cantilevered boxes on each side." There were six other bidders, of which only one bid the steel alternative and none bid alternative A. Relative bids are listed in Table 12.11. The first six bids were for alternative C, and the last and highest was for alternative B. 12.2.8
RED RIVER BRlDGE, A.RI\.ANSAS
This is a seven-span structure with five imerior spans of 210ft (64 m), end spans of 135 It (41 m), and a roadway width of 32 ft (9.75 m). Estimated cost was $3.3 million. Eight bids were received, six in structural steel and Iwo for concrete segmental. Bids ranged from $3.22 to $4.89 million. The con crete segmental was completelv open as to the method of construction (both concrete bids were based on the incremental launching method). Rel ative bids are listed in Table 12.12. TABLE 12.11.
Napa River Bridge, Ranking of Bids Relative Bid
Bid Rank
girder bridge B: Trapezoidal continuous structural steel box girder bridge C: Cantilever prestressed segmental concrete bridge with either precast or cast-in-place segments, and erection either bv the balanced cantilever method or on falsework Because of poor fOll ndation material and a readily available aggregate su pply, all alternatives used lightweight concrete in their superstructures. TABLE 12.10. Bid Rank
2 3
~
Cline Avenue Bridge, Ranking of Bids
1.0000 1.00~H
2 3 4
I. I ~ !i'l I. I H:I 7
:)
1.~7h5
6 7
1.-{:lll5 1.5:!IO
TABLE 12.12. Bid Rank
Relative Bid
Alternative
2 3 4
1.0000 1.0252 1.0596
Concrete Steel Steel
6 7 8
5
Red River Bridge. Ranking of Bids
Relative Bid LOOOO 1.1437 1.2685 1.2800 1.3099 1.3229 1.4267 1.5175
Alternative
Steel Steel Steel Steel Concrete Concrete Steel Steel
Economics and Contractual Aspects of Segmental Construction
528
Structural steel prices \'aried from a low of $O.65/Ib to a high of $O.9:1/Ib \\'ith an a\'erage of $0.78/lh. Structural steel prices in Arkansas for this t \'pe of const ruction had pre\'iOllsly been i 11 the range of $0.80 to $O.85I1b. The low bid price of $O.6S/lb represents a reduction of approximateh 19 to 2:17£-. All steel prices were for domestic steeL Note that the bid prices included the demolition of the existing bridge. If this item were deleted, the bidding would be rearranged as illciicated in Table 12.1 :1. The IUIllp-sum price for the concrete super structure was, for the low cOllcrete bicider, $~H.3i/ hZ. which cOlllpares fan)rabl\' with the Keys bridges ill Florida. However. this price was 110t cOl1lpetitive. Cndoubtedl\, there are numerous reasolls why. One m;1\' he that there was no pre castillg plant within sufficient distance of the site, and thus the (ost of shipping the seglllellts ma\' ha\'e beell prohihitive. The project was not large ClloUgiJ to attract contractors with the expertise to set up a precaslillg operation at the site. The two cOllcrete seglllelllal hids recei\'ed were based 011 ill crclllcl1tallaunching, and evideIIlI\' the proiect was Ilot large ellough to a
.VOFOII .HAI:\, STRFl':T
~submilled, three optional concrete redesi~ns were
bid. As designed, the plans and specifications pro vided the option of a steel plate girder or precast segmental box girder structure. Rici documents were quite liberal for redesign but requireci quite a hit of cietail with the hid docillnents. The winning bid was steel girders, as desiglleci, priced at about $R7!fi2 without one abutment, which was to be con structeci under another contract. The steel girders were a noncomposite, working-stress design. The approximatelv 15 mil lion pounds of A5RH structural steel was bid at SO. 7 5!1b. It shoulci be noted that aciditional sa d ngs in steel could have been accolllplished ,,·ith a com posite design. Tahle 12.14 is a reiatiH' summarv of the eight bids. Note that the low concrete hid was ollh· 3.7(lc abo\'e the low bid, which indicates the co'mpetiti\,e ness. 12.2.10
SC.\1.HAR}' OF C.,/UFO!?X!A·5., 1-:XPfJUF,XCE
California\ experience with a cost reduction in cewive proposal (CRIP) (\';!luc el1~illeerilJg) and alternative designs for projects in\'olving segmen tal construction is sUll1marized in Table 12.15. 6
,'",mucr, ON f() 12.3
The low hid 011 this project was $25,715,733.00, as compared with the ellgineer's estimate of $2~,2()O,OOO. Probahly a llIajor reason why the 1m\' hid was 127r under t he en gi neer's estimate was the cOlllpetition offered In the two plan alternative de signs ill concrete and structural steel, resulting in a minimulll savings of at least $3,500,000. The com petitive situation was further enhanced by allowing bidders to propose additional optional designs. Alt hough no additional steel optional ciesigns were
Increase in Efficiency in Concrete Bridges
As stated ill previous charitCl's, prestressed con crete segmental bridges ha\c extended the prac tical and competitive economic span range of concrete bridges. An interesting comparati\'e exercise is to look back at bridges built in the past anc! evaluate them in the light of presenl ciaI' de\'elopments.
TABLE 12.14. TABLE 12.13. Bid Rank"
4 :! H :~
:'> 6
7
Red River Bridge, RerankingofBids Relative Bid 1.0000 1.1147
1.l6:!O 1.2841
1.3379 1.3919 1.40:'>4 1.:'>276
Alternative Steel
Steel
Steel
Steel
Steel
Concrete
Concrete
Steel
"Ranking corresponds with lhal presented in Table 12.12.
Bid Rallk
2 3 4
Relative Bid 1.0000 1.0370
:>
1,()40 I 1.0579 1.0884
6
1.1128
7 8
1.1508 1.4099
North Main Street Viaduct, Ranking of Bids Alternative Sleel alternative as per plan Redesign concrete alternative Steel alternative as per plan Concrete alternative as per plan Steel alternative as per plan Steel alternative as per plan Redesign concrete alternative Redesign concrete alternative
TABLE 12.15.
Length!:'I!ax. Spall (ft)
Date
Bid
Summary of California's Segmental Prestressed Bridge Experience
Bridge
Design AlterllatiH:' Provided
Cost-Hndge Work Olll)"
Remarks
------~--------------------~.
21i2
Pine \. alley Creek
I iOO/-I:JO
S H.2 \\
= S69/1t2
A.
Camilel'er prestressed concrete scgrnenlal nox girder with
either: I, Prestressed rock anchor I()()tings" 2. :'v!ined rock shaft
CR I P hy contractor re I'ised superstnldllre de sign and cOllstruct;oll Se quence. Savings to slale, Sl9I,OOO,
foundatioll
'1172
SI27 1111 (ind, S]2,0 :'II prol'. lor future widelling)
Stanislaus River at ~e\\' '(clones
A.
Cantilever prestressed t:oncrelC segrnenlal
B.
box girder Sth'Clllral steel box g-inlcr(J Both with either: I, Prestressed rock
Seven contractors bid steel and t\\'o hid concrele \.1>'..1 separated lo\\' sleel and low concrete.
anchor footiugs
:).:"i:\
h'l Riln BL ;llld Overhead
1:IK71:\ 10
S;i.O :'1
= S:I'i lit"
,.\,
2, :'v(illed shaft f'H1mlatiolls
hox girdep; I Ie 71
:\"I'a RiltT :\;'1"1
.li
.\.
COil vel1l iOllal si x -celi cast-ill-place pre stressed box girder
I'.,
Struclli ral steel bo:., girder Cantilever prestressed
C.
CRll' lllodilied design to single-cell hoxl's. 'ttx. f:d"'I\'ork height 92 i't ::. Salings to statc', S I l2,M2 L Sj" 01 ,el'('!] h"lders chos(' C. Fal.s<,work heights lar ied Irom ti! 10 1:12 IL se;~me11lal
COJJcrete se)..{lllL'lltal
\117;-)
Colorado River
;1[
7.1 \1
S:I lilt'
.\.
Y1I1ll;1
two-cd I box ginkr" Segmental pre 'it
rc'O,'icd concrete
sin:-\Ie cell h"" wilh criteria pro"ided to COllven to cantilever
12:7(;
S2.1; \1
Cu"dalupe
S2Kilt'
A.
COlll'emi()llal sel'Cll
I'.,
cell prest ressed con tTCle hox II .\ four-cell pre
Riler at S;lll JOS('
stressed box dcsig-tH2d I'DI' segmclItal Cllll
<:alltilel'er cOllslructioll
('oll,icie!'ed I,,' lOllt rannr bUI Hot lIs('d
bccau,,<,
cot)
tfado!' 0\\ lled ade'lU
or
\(axilllllm lalsework height ,HJ l't ()\ er a ,,'aSOl! alII, dry ril'er. COlltr;Wl()r lnexpl:'rlt'tlccd iIi '\('f{Illt"ll Lal ('()t1strllctioll,
SIl"llClion
3,76
S;m .Jo;''luiu
'HO Id(j()
STU \1
,\.
Pn:strl'ssed Cllnerele with three main ,'pallS designed t(lI' call tilel'er seg'lllemal COll struction and 20 300 I't ~,pproach spallS de signed ['or segmelllal construction with provisions to modify
B.
Structll ral steel welded plate girders (unpainted A-588) wi th 29 200 It ap proach spans" Same as :\ with 200 ft approach spans
River ;u ,\llti oell
.-\I1I;\'e bidders ,ito,,' 'IVl'l. L()wer-thalhllltilil"lte,1 (rorl'i~J)1 .,tel'l prices pre I';liled.
to cantilel'cr
C,
529
530
Economics and Contractual A.fpects of Segmental Construction
TABLE 12.15. Date Bid
Bridge
II7K
San Francisco Bay al Dumbarton (ap proach spans)
Length/Max. Span (n)
Cmt-BJ-idge Wmk Only
46501150
$24.3 M = $59/ft2
(Cimillillni)
Design Allel'nalin~s Pnwided A. B.
C. "Select('d by
123.1
Im\
Precast delw girders" Twin single-cell pre stressed box gJrders designed for seg mental constructJon with criteria for rede sign for canlileH'ring or launching Structural steel hox girder
R('mark~
I\luch bidder interest in all choices during prebid stage. Final results: ,e\en chose A. one chose C. Some uncertainties about nileria provided in B.
1)I(lder.
/a,f)J,.'iIGS OF C·IR.4CAS VIADUCTS, l'ESEZl.TLA
Tlte Caracas Viaducts in Venezuela (Chapter 8) were completed in )952, approximately thirt~ rears ago. If these viaducts were built today, the chosen strtlclure would probably be very differ ent from that chosen at the time after exhaustive feasibility studies. III 1973 these structllres were ree\'alua;ed ill terms of the more conventional halanced cantilever method of girder construc tion. Figures it~~O and 8.31 compare the actual project COllst rutted in 1952 with possible alter native designs in 1973 and 1975. The three-arch rib and eight-beam superstructure would be re pl;tced by a variable-depth twin box section (cantilever construction using precast segments) Sllppol'\C'd 011 slip-formed piers. Today, with the same span arrangement consid ered in '1973, possible alternatives might be a single two-cell box similar to that used in the Kipapa Stream Bridge, or a ribbed single-cell box as in the V(~jle I-Jord Bridge, Figures 4.24 and 4.22, respec tively. This approach would require only single shaft piers.
Tancan'ille Bridge designed in ) 956 incorporating a 2000 it (6 10m) span steel suspension bridge Brotonne Bridge designed in 1973 incorporating a 1050 ft (320 Ill) span concrete stayed "bridge These two structures are oilly 20 miles (32 km) apart and are located in very similar surroundings topographically and geotechnicalh (see Figures 12.1 and 12.2). On the left bank, a flat expanse of meadows and fields requires a long approach viaduct to reach the desired altitude of the main crossing above the navigation channel, while a deep formation of soft soil overlying the load-bearing strata requires deep pile foundations. On the right bank, the limestone cliff extends close w the river bank and calls for only a short transition bet\.\'een the main river span and the approach highway. The comparison pre sented here pertains only to the left-bank approach viaduct of each structure, although interesting comments could be made also on the relative char acteristics of their other parts. The Tancarville approach viaduct has eight 164 ft (50 m) spans, having five 140 ton (127 mt), 10 ft
123.2 CO.HPARISO!\' BETH'EEI\' TA,VC4RVILLE AND IWOTOY\'F, BRIDGES, FRANCE
Progress is made slowly through accumulated ex perience, and it is worthwhile to look back pe riodicallv and try to measure such progress. With this in rr;ind, and as a conclusion to this chapter, a comparison is offered between two similar con crete 5t ructures separated in time by seventeen vears. , As mentioned in Section 9.8, the Seine River between the maritime inland harbor of Rouen and the English Channel is now crossed twice by two outstanding structures:
FIGURE 12.1. Tancarville Bridge, aerial \'iew the south\\'est showing left bank approach viaduct.
531
Increase in Efficiency in Concrete Bridges
FIGURE 12.2.
Bmlollne
Ihidt-;c. aerial vicw from the southwest sh(m ing left bank ap
proach viadlH \. deep precast ginlers in each span, Figures I :l.:> and I :lA. Piers are fOllfHthl on precast con crete piles and were cast ill place with a box section. When the design was prepared. it represented the most advanced technolog\' ill terms of lise of matc rials. rhe elastic stabilit v of these very long, slender precast ginlers was even the occasion of interesting illllO\'at ive st tidies. COllst ruct iOll methods were also far from conventional. .\11 gi rders were prefabricated in a vanl located at the original ground level. ~I()\illg and lifting op eratiotls for one girder (see Figure 12.5) included: (3 m)
Placing hrirdt;'r 011 dollies, lIlo\'ing in two perpell dicular directiolls to bring it at the foot of the sup porti ng piers
FIGURE 12.3.
Hoisting girder along the piers with special steel rigs, Figure 12.6 Placing girder on top of the pier with the rotating arm of the special rig, Figure 12.7 Transverse displacement of girder tion
to
its final posi
Suspension of the girder at both ends was achieved by the means of special cantilevers to provide the highest safety against lateral buckling during lift ing operations of such slender girders, Figure 12.8. The project was carried out smoothly and com pleted successfully a long time ahead of the other contracts for the entire crossing. Fifteen years later. the same problem of safelv and economically building an aesthetically pleasing
Tancaryille Bridge, elevation of approach spans.
532
Economics and Contractual Aspects of Segmental Construction 43'-10" 40'-10"
4'-0"
i· '.
l..k;W
-.. 9)'
.... 1
~i
4'-0"
'I'," .....
.,
-.,
7'-5"
..
.1,
i
.
.~
'-1
r
I
I
I
P .
,
..
It ~
V'L.-": ~'\
~y
11'-4'
11'-4"
4'-0"
,.
~ ~
:
4'-0"
::-:-::-::
W~,
L:.o:l~
P
11'-4'
.1
I .1
11'-4'
FIGURE 12.4. Tancan'ille Bridge, typical cross section of approach spans.
FIGURE 12.5. Tancarville Bridge, lifting one precast girder for the approach spans.
TABLE 12.16.
approach viaduct for the Brotonne crossing was solved with very different methods, both of design and construction. The light single box section se lected for the stayed structure was also used for the approach spans. Precast piles were replaced in the foundations by cast-in-place slurry load-bearing walls. Box piers were slip-formed instead of incre mentally cast in successive lifts. The superstructure was cast in place in balanced cantilever with travel ers, Figure 12.9. Today precast segments would probably be preferred, although the characteristics of the deck would remain substantially unchanged. A comparison between quantities of materials per square foot of deck appears in Table 12.16. The savings in concrete volume of Brotonne over
Cost Comparison Between Tancarville and Brotonne Approach Viaducts Tancarville, 1956 (Adjusted 1973)
1. Quantities (per ft2) (super- and substructure) Concrete (yd 3 ) Reinforcing steel (Ib) Prestressing steel (I b) 2. Labor (hr/ft 2) 3. Cost ($/ft2 ) Labor Materials Equipment, plant, and job overhead Su bcontracts Design, overhead and fee
4. Tolal
0.14
Brotonne, 1973
6.4 4.1
0.11 14 3.1 1.6
14.20 6.90 15.70 3.70 12.90
5.60 6.30 5.00 4.20 4.20
11
$53.40
--
$25.30
Increase in Efficiency in Concrete Bridges
533
0' P'ltt~ jTop ----- ..._ _
~.~~v
~
~ -r
LOW1!:R
~L.OCl<$
;---~-
,
I
~-
bi .'1
"I
I
--t
FIGURE 12.6. spans.
fancarville Bridge. equipment for lifting precast girders in approach
Tancarville is justified only by the fact that minimum weight was vital for the concrete stayed bridge and was maintained in the approach spans. Weight of prestressing steel is approximately half because the deck is continuous at Brotonne and the box section is more efficient than the I-girder sec tion. More important, however, is the comparison of costs and the components thereof, Table 12.16 and Figure 12.10. One is struck by the total labor re quirements for both sub- and superstructure: Tancarville Brotonne
~---.----.------.----~.----.
PLACinG GIRDE.R on PIER
FIGURE 12.7.
Placing precast girder over pier cap.
4.1 hr/ft 2 1.6 hr/ft 2
In the 15 years that elapsed between the two proj ects, the combination of design improvements and more efficient construction methods allowed the labor to be divided by 2.5. A similar trend has been observed in other fields. For example, a complete survey of all hydroelectric
534
Economics and Contractual Aspects of Segmental Construction 60 $53.40 50
CAMTIL.f:VER
12,90
.t:: 40
3.70
II Q; C.
30
15.70
.E
..,
$25.30
~
u I
\r+-:::~
20
4.20 4.20
6.90
5.00 10
6.30
14.20
5.60
0
I,.A"~t::I"'L. 5ADQ..L.~~.-t'+....~...
Tancarville
Brotonne
(readjusted 19731
(1973)
FIGURE 12.10. Cost comparison bet \\'een rancanille and Brolonn<:' approach yiaduCls. (:'» Desigh o\crhead and fee. (4) subcontracts. C1) equipmcnt. plallt. and site O\'crhead. (;!) materials. (I) labor. DOLLI~&
Df!:TAIL Of" GIRDER SUSPEHS10H
FIGURE 12.8.
Lifting de\'ice at precast girde,- ends. 0::
<1
LLl
>
50 o:x;
( ,
, ~.-'*
,
-i(: l, '. -: I
"~",'
YEAR
FIGURE 12.9. Brotonne Bridge. cantilever construc tion of superstructure of approach spans.
FIGURE 12.11. Increase of productiyil\ on power projects in France,
projects carried out by French Electricity between 1950 and 1970 showed that the annual value of in vestment for each worker was multiplied by 2 without allowance for inflation and by 3 including inflation, Figure 12.11. Cost wise the true gain would be somewhat less significant, because labor
rates have constantly increased faster than material rates. The comparison between other items of the cost breakdown of Tancarville and Brotonne is equally instructive. Material costs are almost equal, in cluding the value of subcontracts (pile foundations
References
and roadway work in both projects). The essential differences are seen in the two following areas: Equipment, plant, and job overheads: reduced from $15.70 at Tancarville to $5 at Brotonne. This difference is due essentially to increased efficiency in management but also to a climate of fierce com petition. Design, overheads and fees: reduced from $12.90 for Tancarville to $4.20 for Brotonne. The same two reasons explain this drastic reduction, which also reflects the change in the overall operation of large construction companies during the last twenty years from family-owned or controlled craftsmen such as building contractors to modern management industrial companies. When Eugene Freyssinet designed his Plougastel Bridge masterpiece (see Chapter 8), he was per sonally involved in the project for more than three years and probably involved in little else. One generation later, an experienced engineer would have to control or at least participate in many dif ferent projects during the same period. In summary, the c6mpari~~on of costs between Tancarville and Brotonne approach viaducts with prices of both projects reduced to 1973 levels is: Tancarville Brotonne
$53.-tO!rt 2 $2S.30/fr 2
Both projects were bid completely on a design and-build basis and awarded to the lowest bidder. The above costs are a true picture of the technol
535
ogy and of the level of prices for the two respective periods. To estimate both projects at the level of today's prices (1980) it would be necessary to multiply the labor rates by 2.3 and the materials and equipment rates by 1.7.
References 1. "Guidelines for Value Engineering (VE)," prepared by Task Force 19, Subcommittee on New Highway Materials, AASHTO-AGC-ARTBA Joint Coopera tive Committee.
2. "Alternate Bridge Designs," FHWA Technical Advi sorv T5140.12, December 4, 1979, Federal Highway Administration, Washington, D.C. 3. Richard A. Dokken, "CALTRANS Experience in Segmental Bridge Design," Bridge Noies, Division of Structures, Department of Transportation, State of California, Vol. XVII, No.1, :Yfarch 1975. 4. A. B. Milhollin, and C. L. Benson, "Structure Design and Construction on the Vail Pass Pnuect," Trans portation Research Record 717, Transportation Re search Board, :-Iational Academy of Sciences, Washington, D.C., 1979. 5. James M. Barker, "North American State of the Art Current Practices," Prestressed Concrete Segmental Bridges, Structural Engineering Series No.6, Fed eral High\\"ay Administration, Washington, D.C., August 1979. 6. Donald W. Alden, "California's Experience with Cost Saving Contracting Techniques," Prestressed Concrete Segmental Bridges, Structural Engineering Series No. 6, Federal Highway Administration, Washington, D.C., August 1979.
13
Future Trends and Developments
13.1 INTRODUCfION 13.2 MATERIALS 13.2.1 Prestressing Tendons 13.2.2 High Strength Concrete 13.2.3 Fiber Reinforced Concrete 13.2.4 Polvrner Concrete 13.2.5 Co~posite Concrete Materials 13.2.6 Material Limitations 13.3 SEGMENTAL APPUCATION TO BRIDGE DECKS 13.4 SEGMENTAL BRIDGE PIERS AND SUBSTRUCTURES
13.1
1ntroduction
As observed in previous chapters, prestressed con crete segmental bridges have extended the practi cal and competitive economic span range of con crete bridges. The Bendorf Bridge in Germany (Section 2.2) constructed in 1964 with a navigation span of 682 ft (208 m) was a monumental achieve ment. Because of economic differences bf'tween Europe and the Cnited States (primarily the ratio of labor cost to material cost) it was not until the early 19705 with the JFK Memorial Causeway (Section 3.10) with a span of 200 ft (61 m) and shortly therafter the Pine Valley Creek Bridge (Section 2.7) with a span of 450 ft (137 m) that segmental construction was introduced in the Lnited States. Today these spans are somewhat commonplace when one considers the Three Sis ters Bridge (Section 1.10). the Koror-Babelth uap Bridge (Section 2.12), and the Houston Ship Channel Bridge (Section 2.14), with spans of750 ft (229 m), 790 ft (241 m), and 750 ft (229 m), re spectively. When combined with the cable-stay concept, spans increase to 981 ft (299 m) for the Pasco-Kennewick Bridge. 1050 ft (320 m) for the Brotonne Bridge. and 1300 ft (396 m) for the Dame Point and Ruck-A-Chucky Bridges.
536
13.5 APPUCATION TO EXISTING OR NEW BRIDGE TYPES 13.5.1 Overpass Structures 13.5.2 Arches, Trusses, Rigid Frames 13.5.3 Wichert Truss 13.5.4 Stress Ribbon Bridges 13.5.5 Space Frame Bridges 13.6 SL'MMARY REFERENCES
In earlier years these spans for concrete bridges would have been considered incomprehensible and certainly not economical. The fact that they have become achievable. -only within the last decade. stands as a testimonial to 'rapid technological ad vances and to the courage and vision of those engi neers who participated in this development. In the United States as of November 1980, 19 segmental bridges had been completed and there were 16 under construction. 22 in design, and 29 under slUdy-a total of 86 bridges. We may con clude that segmental prestressed concrete con struction is a viable concept for highway bridges and that there are no known major problems to inhibit its use. \Vhat, then, is the potential for seg mental bridge construction in the 1980s? This chapter will look at this potential in terms of new or improved materials, potential application in bridge decks, piers, and substructure, and application to existing or new bridge superstructure types.
13.2
Materials
During the nineteenth century timber, stone, and masonry were the common materials for bridge construction. Then iron, steel, concrete, and rein
Materials
forced concrele emerged successively as favorite materials. culminating in the twentieth century with prestressed concrete. The present materials used in bridge construction have some or all of the following disadvantages: weight. cost. or inherent weaknesses in one form or another. In the recent past. development of improved bridge systems has evolved primarily by more exact methods of cal culation made feasible by the electronic computer or by innovative bridge systems such as the cable stayed and segmental types of bridges. Intensive development of the materials themselves has barely begun. 13.2.1
PRESTRESSI,Vc TE.VDO.VS
Until recently. corrosion of prestressing tendons has caused few problems and little concern. How ever, with the advent of segmental construction and transverse prestressing on the top flange, an increasing concern has been expressed about the potential deterioration of the tendons resulting from their closeness to the deck surface and expo sure to the action of de-icing chemicals. Current methods of alleviating this concern are the use of polyethylene ducts or the pOssibility of epoxy coat ing the duct, epoxy coating post-tensioning bar tendons, alld possibly epoxy coating the prestress ing strand. A research effort is required to deter mine the production feasibility and cost; the effect, if any, that nonmetallic coatings might have on the bond of strand to concrete; and the compatibility of strains between the coating and the tendon. An other potential method uses individual unbonded strands with successive coatings of teflon, a corro sion inhibitor, and polypropylene, Figure 13.1. An old idea that may need to be resurrected is that of using glass fibers for prestressing. This material was being investigated in the I950s, I but for either technical or economic reasons it never reached fruition. There were problems of chemical reaction of the glass fibers with the cement; how-
"'7'
537
ever, Owens-Corning Fiberglass Corp. has de veloped a coating for glass fibers for fiber reinforced concrete. Perhaps this coating could be used for a glass fiber prestressing strand. An ulti mate strength of 400 ksi (2758 MPa) and a low modulus of elasticity ranging from 6000 to 10,000 psi (41 to 69 MPa) might be expected. The high strength and low modulus would indicate a low percentage of prestress losses-a decided advan tage. The high strength would produce, for a given required prestress force, fewer or smaller tendons. th us reducing congestion. Smaller tendon sizes would reduce web thickness, thus reducing dead weight an'd prestress force requirements, and so on. Obviously. suirable end anchorages would have to be developed. 13.2.2
HIGH-STRENGTH CONCRETE
Early prestressed concrete designs were based on 3000 psi (20.7 MPa) strength concrete. As knowl edge of concrete properties and quality control in creased, it became more feasible to use a 6000 psi (41.4 ~[Pa) strength concrete for man y prestressed concrete structures. In the Pacific Northwest an 8000 psi (55.2 ~IPa) strength is readily and routinely available. Use of such concrete has per mitted the design of longer-span, lighter-weight concrete structures. Within the past few years it has been found that strengths of 10,000 psi (68.9 MPa) and higher can be obtained where special attention is given to (I) selecting the constituent materials, (2) propor tioning the concrete mix, and (3) handling, plac ing, and curing the concrete. It has recently been demonstrated that the appli cation of ultrahigh-strength concrete is not on Iv practical but also economically feasible. High strength concrete, 9000 to 11,000 psi (62 to 75.8 MPa), has been used in the columns of five high rise buildings in Chicago. The concrete was pro duced in a local ready-mix plant and trucked to the
Bonded low friction
7 Wire prestressing Slra
'T'''oo)
Polyproplylene covering
FIGURE 13.1. Corrosion-resistant strand tendon.
538
Future Trends
project site. An economic study for a short tied column indicated that the cost per foot varied with the concrete strength and steel percentage as fol lows: $15.50 for 9000 psi (62 MPa) concrete and 1% steel compared to $39 for 4000 psi (27.6 MPa) concrete and 8% steel. Over the past five to ten years considerable re search has been conducted on high-strength con crete, dealing primarily with selecting materials,
developing concrete mix design criteria, and de termining basic physical properties of the con cretes. Very little, if anything, has been done regarding the implementation of high-strength concretes, especially in bridge structures. In an interim report,2 "Applications of High Strength Concrete for Highway Bridges," pre pared by Concrete Technology Corporation for the Federal Highway Administration, a segmental bridge segment at a pier was redesigned with high-strength concrete. The purpose was to de termine to what extent the thickness of the lower flange could be reduced, and in turn what effect this reduction would have on the overall moments. For purposes of this study, the Shubenacadie Bridge in Nova Scotia (Section 2.15.4) was selected as a design example. Overall dimensions of the bridge are shown in Figure 13.2. It has a 700 ft
{r A
r
..l
an~
Developments
(213.4 m) main span and 372 (l13.4 m) side spans. The bridge was constructed with a 5000 psi (34.5 MPa) concrete strength and used It in. (32 mm) diameter Dywidag bars for post-tensioning." For the analysis, the top flange was assumed to be uni form and I Ii in. (292 mm) thick. The bottom flange was assumed to taper uniformly from its thickest point at the su pport piers to 6 in. (152 mm) at midspan. The centroid of the prestressing force r4a.' assumed to be located 5/ in. (146 mm) below the top of the section-that is, centered in the top flange. AASHTO Bs 20-44 was used for loading, as in the actual bridge. Prestress force was provided by It in. (32 mm) diameter Dywidag bars with a minimum yield stress of 150 ksi (1034 ,MPa). These bars were as sumed to provide 104 kips (0.46 MN) of final pre stress force each. This assumes a jacking force of 70% of the minimum yield strength and 20 ksi (137.9 'MPa) losses. Maximum allowable compres sive stress in the concrete was assumed to be O.4f~, and an allowable tensile stress was assumed to be zero. Significant benefits were found in the use of high-strength concrete to reduce the thickness of the lower flange. As shown in Figure 13.3, the total flexural prestress demand is reduced by approxi
ELEVATION
=t= 35'.
35'· 6"
I
L..
6~
ll'lillhv
I I'· 2"
1'.2"
I
I I
20'·0"
.., ~
SECTION B-B
M
I I
,
•
1/ 20'.0"
.1 ~ ,
I 6"
SECTION A-A
FIGURE 13.2. Shubenacadie Bridge.
B
Materials
539
36,000
B
35,000 -0
.9: "" ':":
"'
o
...J
34,000
.2
~
'" .t
33,000 2'-6"
Deflection
1'-6"
32.000
FIGURE 13.4.
31,000 5
6
8
9
10
Concrete strength SKI
FIGURE 13.3. Variation of prestress force with con crete strength-Shubenacadie Bridge.
mately 10% as a result of the red uced dead load, The optimum lower flange thickness is about 1 ft 8 in. (508 mm), obtained at 8 ksi (55 MPa) concrete strength, 13.2.3
FlBER-RFLVFORCED CONCRETE
A relatively new material that has not yet seen much application in structures is fiber-reinforced concrete. Fibers have been used to reinforce brittle materials since ancient times; straws were used to reinforce sun-baked bricks, horsehair was used to reinforce plaster, and more recently various fiber:> have been used to reinforce Portland cement. 3 A state-of-the-art report 1 prepared by ACI Commit tee 544 defined fiber-reinforced concrete as "con crete made of hydraulic cements containing fine or fine and coarse aggregates and discontinuous dis crete fibers."
Schematic load-deAection diagram.
Several types of fibers along with several of their properties are listed in Table 13.1.3,1 As can be seen, fibers have been produced from steel, plastic, glass, and natural materials in various shapes and sizes. Two stages of behavior in the load-deformation curve have been generally observed when fiber reinforced concrete specimens are loaded in flexure. The load-deformation curve may be con sidered as approximately linear up to point A in Figure 13.4. Beyond this point the curve is significantly nonlinear, reaching a maximum at point B, The load or stress corresponding to point A has been called first-crack strength, elastic limit, or proportional limit, while the stress corresponding to point B has been termed the ultimate strength. Two theories have been suggested for predicting the first-crack strength of fiber-reinforced con crete: the spacing concept and the composite-materials concept. The spacing concept attempts to explain or determine the first-crack strength by a crack-arrest mechanism derived from the field of fracture mechanics. The basic mechanism that controls the
TABLE 13.1. Typical Properties of Fibers Young's Modulus ( 103 ksi)
Cltimate Elongation
Type of Fiber
Tensile Strength (ksi)
Acrylic Asbestos Cotton Glass Nylon (high tenacitv) Polyester (high tenacity) Polyethylene Ra yon (high tenacity) Rock wool (Scandinavian) Steel
30-60 80-140 60-100 150-550 110-120 105-125 100 60-90 70-110 40-600
0,3 12-20 0.7 10 0.6 1.2 0.02-0.06 1.0 10-17 29
25-45 0.6 3-10 1.5-3.5 16-20 II 13 10 10-25 0.6 0.5-35
Specific Gravity l.l 3.2 1.5 2.5 1.1
1.4 0,95 1.5 2.7 7.8
540
Future Trends
an~
Developments
WITHOUT FIBERS
•WITH FlBERS
Section A-A FIGURE 13.5.
Schematic
or arrest mechanism.
first-crack strength depends primarily on the spacing of the fibers." The crack-arrest mechanism for fiber-reinforced concrete, as presented by Romualdi and Batson,6 can best be described with the aid of Figure 13.5, which represents a mass of concrete in tension. The reinforcement consists of a rectangular array of rods at a spacing 'A and located parallel to the direction of tension stress. At some interior loca tion an internal flaw exists in the form of a flat disk-shaped crack. The basic rationale is illustrated by section A-A, which is a side view of an internal crack between two fibers. I n the presence of a gross stress the ex tensional strains in the vicinity of the crack tip, by virtue of the stress concentration, are larger than the average strains. These strains, however, are re sisted by the stiffer fiber, and there is created a set of bond forces (assuming that the bond between the mortar and the steel is intact) that act to reduce the magnitude of stresses at the crack tip. Under proper conditions of fiber spacing and diameter, an internal flaw could be prevented from prop agating tojoin up with other flaws into microcracks which then join with other microcracks to form macrocracks. The basic philosophy is that if the internal flaws can be locally restrained or retarded from extending into adjacent material, thereby re straining crack propagation, the tensile-strength characteristic of the concrete is improved. The crack-arrest mechanism in bending may be idealized as indicated in Figure 13.6. When a criti cal strain is reached, the beam cracks; unlike the nonreinforced beam, however, the cracks do not propagate through the beam but are arrested by the fibers that span the cracks.
FIGURE 13.6. bending.
Idealized crack-arrest mechanism
III
The composite-materials concept hypothesizes that the properties of fiber-reinforced concrete, in· eluding the first-crack strength, can be. predicted from the individual properties of matrix and fibers. It assumes that fiber-reinforced concrete can be analyzed as conventional reinforced con crete, the main difference being that the rein forcement is shorter, thinner, and randomly dis tributed. Table 13.2 summarizes the improvement of the properties of a steel-fiber-reinforced concrete as compared to plain concrete. 3 13.2.4
POLYMER CONCRETE
Concrete produced with Portland cement and air entraining agents can contain approximately 13% voids, which are interconnected and distributed throughout the mass. When this concrete is heated to drive out the chemically unbonded moisture and TABLE 13.2.
Concrete Reinforced with U.S.S.
Fibercon Steel Fiber
Properties Compression Flexural modulus of rupture Tensile strength I mpact strength Crack and spall resistance Fatigue strength to 2 million cycles Abrasion Shear and torsional strength Corrosion resistance Freeze-thaw Conductivity (thermal and electrical)
Approx. I mprovement over Plain Concrete
10-30% 70-300% 50-300% 150-1000% 70-300% 100% 30% 50-300% Good as or better Good as or better Conducts both
Materials
541
TABLE 13.3. Summary of Properties of Concrete-Polymer Material
Property Compressive strength (psi) Tensile strength (psi) Modulus of elasticity (psi) Modulus of rupture (psi) Flexural modulus of elasticity (psi) Coefficient of expamion (in.!in. OF) Thermal conductivity at 73°F (23°C) (BTu/ft-hr-OF) Water permeability (ft/yr) Water absorption (%) Freeze-thaw durability: Number of cycles Percent weight loss Hardness-impact ("L" hammer) Corrosion by 15% HCI (84-dav exposure), % weight loss Corrosion by sulphates (300-day exposure), % expansion Corrosion by distilled wa~er
then impregnated with a chemical monomer, such as methyl methacrylate CM~lA), and irradiated with gamma rays, some startling changes in its properties are produced, Table 13.3. 7 Tensile and compressive strength are almost quadrupled. Modulus of elasticity is increased by a factor of 1.8 and modulus of rupture by more than 3.5. A com pressive stress-strain curve for this material shows complete linearity up to more than 75% of failure load, Figure 13.7. 7 Thus far, research with this material has aimed toward its application in bridge decks. Problems in polymerizing large units such as bridge segments have yet to be solved. Practical resolution of these problems could offer a tremendous advantage for concrete structures.
Concrete Control Specimen (Type II Cement)
Concrete with up to 6.7 Weight % Loading of Polymeth yl Methacrylate, Co-60 Gamma Radiation Polymerized
5,267 416 3.5 x 10 6 739 4.3 x H)6 4.02 X 10- 6 1.332
20,255 1,627 6.3 x 10 6 2,637 6.2 x 106 5.36 X 10-6 1.306
6.2
X
o
10-4
5.3
0.29
590 26.5 32.0 10.4
2,420 0.5 55.3 3.6
o
0.144 Severe attack
No attack
18
16
Impregnated CP concrete 5.4 wt %MMA
14
12 E = 5.5
;;;
X
106
Cl.
o 10 0 0 ~
~
8
Unimpregnated CP concrete
Ul 6
4
13.2.5 COAIPOSITE CONCRETE MATERIALS
2
Assuming that the materials previously discussed can be developed to a point of practical usage, what improvement in properties might be expected if these materials were combined? Sukiewicz and Vir 0la8 have presented flexural-load-versus-deflection data for concrete and composite materials, Table
0
1000
2000
3000
4000
Compressive strain (m,croinchesiinch)
FIGURE 13.7. Compressive stress-strain .curve for MMA-impregnated concrete.
542
Future Trends and Developments TABLE 13.4.
Relative Load Versus Relative Deflection
Approx. Relative Max. Load Plain concrete Steel-fiber reinforced Polymer impregnated Pohmer impregnated and steel-fiber reinforced
Approx. Relative Midspan Deflection at Max. Load
5 18
20 100
5 20 13 105
13.4. It is obvious that a vast improvement in be havior and toughness can be expected. 13.2.6
MATERIAL LIMITATIONS
With improved material properties, not only would structures become lighter but also the depth of superstructure and thickness of individual ele ments would be reduced. There are some practical limitations, however, as to how much the thickness of a web, for example, may be reduced. The prac tical limitations of placing the concrete in the forms and of congestion of supplemental reinforcement and prestressing tendons must still be considered. To some extent this could be alleviated by the use of external tendons, as implemented in the Long Key Bridge in Florida, Figure 6.53. This also has the advantage of reducing the complexity of fabri cation for precast segments. Perhaps a more important limitation in using materials with improved properties is that at some point in the design, stress no longer becomes the controlling criterion. Deformations, both global and local, may govern. Because of the reduced section required from a strength point of view, there may be more concern not only with flexibility of the structure in a global sense but also with the possibility of web buckling and limberness of the deck slab.
13.3
Segmental Application to Bridge Decks
-prestressing has been used to a greater extent in the construction of segmental bridges-to provide greater load capacity and load distribution for large overhanging flanges and between adjacent single-cell box girders. Although a few bridge designs have included transverse prestressing, much greater use could be made of it for more economical bridge structures. For replacement of the decks on existing bridges, precast prestressed concrete segmental construc tion offers great advantages, only some of which can be associated with identifiable costs. As with the segmental box girder, a full-depth segmental panel bridge deck may be precast in short segment lengths longitudinally and may be full deck width or partial deck width, Figure 13.8, depending on the width of deck required for a particular application. Also, in addition to the transverse prestressing, segmental bridge decks may be conceived as having expoxied transverse joints and longitudinal prestressing. A transversely prestressed segmental fuil-depth panel bridge deck, Figure 13.9, has been proposed by T. Y. Lin International as an alternative design for SR 182, Columbia River Replacement Bridge, in the state of Washington. This proposal has the following features: 1. Pru:ast full-depth panels of lightweight con crete to reduce dead load. 2. Transverse prestressing to achieve large can tilever overhangs and ·thus economies in the superstructure. 3. Attachment of the panels to the superstructure with shear studs in block-outs of the panel to achieve composite action with the superstruc ture.
I\
\_---1 t
J
f
)J
1\
\ ...... ,..T a
[
1\
To date, there has been very little use of precast ing, prestressing, and segmental construction for bridge decks. Transverse prestressing has been used in the top flange of large, Gist-in-place on falsework, concrete box girders. Lately, transverse
]
I I I I FIGURE 13.8.
Deck configurations.
a
4
Segmental Bridge Piers and Substructures 62'· O' 18',6"
18' 6'"
] ~!
~
::
543
made to act compositely by means of shear-transfer devices placed at regular intervals through block outs cast into the deck. To date, the incremental launching method has been implemented for the construction of ten bridge decks in Switzerland. IO • 11
~
~
---~
13.4
Segmental Bridge Piers and Substructures
FIGURE 13.9. SR-182 Columbia River Bridge.
--t. Longitudinal prestressing of the deck to maintain a compression across the transverse joints. Another segmental method of constructing a bridge deck is a transfer of technologv from the incremental launching of segmental box-girder bridges. H• w. 11 This methodology, as applied to bridge decks, has been pioneered in Switzerland alld consists of the following operations: 1. The casting of a convenient segment lengt h of
bridge deck behind an abutment, Figure I:LIO, or at midlength,of the bridge, Figure 13.11, whichever is more convenient. Segmet.t length is normallv 65 to 80 ft (20 to 25 m). 2. The jacking forward of the segment, Figure L}.12, onto the flanges of the steel super structure, Figure 13.13, thus freeing the cast ing bed. :~. Preparing the casting bed for concreting the next segment. --t. Repeating the c'ide until completion of the bridge cleek. The finished deck, therefore, consists of seg ments that have been incrementall\' cast and lon gitudinallv launched. As in conventional structures the deck is attached to the SlI perstructure and
Piers do not have to be massive solid cross sections; a tubular cross section may be more effective and more economical. In the U nitecl States it is gener ally felt to be more economical to cast a solid pier. However, for tall piers the economics of solid-pier casting should be evaluated against the cost of the additional dead load the pier is supporting and transferring to the foundations. It may be desira ble to precast the pier as tubular segments that are prestressed vertically to each other as well as the foundation. In the Vail Pass Bridge structures the piers were constructed of diamond-shaped segments, stacked vertically and post-tensioned to the foundations, Figure 13.14. Footings were cast in place with ducts to allow the placing of prestressing tendons. Other examples of segmental application to piers and substructure, previously discussed, are: I. Linn Cove Viaduct, Section 6.3.2, Figure 6.1 i 2. 1-205 Columbia River Bridge, Section 5.4.3, Figures 5.25 ami 5.26 3. Sallingsund Bridge, Section 5.4.2, Figures 5.20 and 5.21 The Long Key Bridge, Section 6.5.1, used precast V piers; and the Seven Mile Bridge, Section 6.5.2, used precast segments stacked vertically. It is to be hoped that these concepts will be refined and utilized for future structures where applicable. l,ng1h 01 d,ck (cas"ni bed) - . - - - - .
~I
FIGURE 13.10. IncrclIlcntallaullching. behind abutmcllt. frolll refercnce 10 (courtesv of AlIlericlll Societv of Civil Engineers).
544
____ r-
Future Trends and Developments -.
Bracket
Jack
Unillenglh 01 deck t casl!ng be
'T/7TT7777TTTTT77T/7T/7T/7T/7T'/
FIGURE 13.11. Incremental launching, midlength of bridge. from reference 10 (courtesy of American Society of Ci\'il Engineers).
Prestressing tendons
Precast segments
FIGURE 13.12. deck slab,
Incremental launching, jacking of
FIGURE 13.14.
FIGURE 13.13. slll)crstructure.
13.5
Incremental
launching.
deck
on
Application to Existing or New Bridge Types
With the exception of the Pasco-Kennewick and Dame Point cable-stayed bridges, the implementa tion of the concept of segmentally constructed bridges in the United States has been limited to the girder type of bridge. I n other parts of the world,
Vail Pass Bridges, segmental pier.
the segmental concept has been applied not only to the cable-stayed bridge, but also to rigid frames, arches, trusses, and to a limited extent to overpass structures. Segmental construction is versatile and should not be stereotyped to girder bridges only; it can be applied to other types of bridge construc tion. 13.5.1
OVERPASS STRUCTURES
The main application of prestressed concrete seg mental bridge construction has been to the long or intermediate span range and to viaducts. However,
Application to Existing or New Bridge Types
this method of construction has been applied to highway overpass structures, proving its versatility. Examples of overpass structures previously pre sented are: 1. Rhone-Alps Motorway, Section 3.15 2. Motorway Overpasses in the Middle East, Sec tion 8.6.4 The Federal Highway Administration (FHWA) in cooperation with the American Association of Highway and Transportation Officials (AASHTO) is embarking on a study of the feasibility of standard sections for segmental box girder bridges. If feasible, standardization of sections, especially for overpass bridges, could provide ad ditional economy for bridge construction. An important and costly problem in building overpass structures over heavily traveled highways and freeways is that of traffic control during con struction. An idea that might minimize this prob lem can be borrowed from the construction pro cedure for the Vienna Motorway cable-stayed segmental bridge. Be.cause construction was not allowed to interfere with navigation on the canal, the structure was built in two 364 ft (Ill m) halves on each bank and parallel to the canal. Upon com pletion, the two girder halves were swung into final position, Figure 9.66, and a cast-in-place closure joint was made. In other words, each half is con structed as a one-time swing span. This concept was considered for a long skewed overpass in Il linois, but the contractor elected a more conven tional procedure. 13.5.2
ARCHES, TRUSSES, RIGID FRAMES
The adaptation of segmental concepts to arches, trusses, and rigid frames has yet to be im plemented on the North American Continent. As indicated in Chapter 8, there are ample examples to indicate that segmental technology can be used for these types of structures. As previously noted and adequately illustrated, segmental construction should not be stereotyped to girder bridges only. 13.5.3
WICHERT TRUSS
The resurrection of the Wichert truss principle,12 Figure 13.15, might yield economies in segmental cantilever construction. This type was developed for· structural steel trusses and has the curious property of providing a fixing moment while re maining statically determinate. The fixing moment is provided as a function of the geometry of the
<>
545
_ __
FIGURE 13.15.
Wichert truss principle.
quadrilateral support, any desired degree of fixing moment being obtained by arranging the geometry of that quadrilateral, with the structure remaining determinate. Consequently there is no danger of complications from settlement of supports or parasitic moments caused by prestressing. The Wichert truss principle has, among others, the following advantages: 1. 2. 3. 4.
Economy of girder material Economy of foundations Elimination of intermediate hinges Stresses unaffected by temperature difference between chords or flanges
The Smithy Wood Footbridge, Figure 13.16, in the United Kingdom is one of three footbridges constructed in about 1970 over the M-l Motorway using the principle of the Wichert Truss. 13.5.4
STRESS RIBBON BRIDGES
Another new type of bridge, introduced relatively recently, is the Spannbandbrucke or stress ribbon bridge. 13 • 14 Its origin is obscure and can be traced back to early societies. Basically the early versions consisted of wood planking supported directly on main catenary cables. It is still used in certain parts of the world, Figure 13.17. The first modern attempt at the implementation of this concept was in 1958, when Ulrich Finster walder unsuccessfully entered the concept in the Bosporus Bridge competition, Figure 13.18, and again in 1961 for the Zoo Bridge at Cologne. The first successful construction of a stress ribbon structure was in 1963 and 1964 in Switzerland for a conveyor-belt bridge at the Holderbank-Wi/deck Cement Works, with a span of 710 ft (216.4 m). The Freiburg, Germany, footbridge, Figure 13.19, constructed in 1969 and 1970 has an overall length of 448 ft (136.5 m) with a center span of 130 ft (39.5 m). Notice that the tops of the piers, in effect, form a large-radius saddle for the catenary cables. The deck has a width of 14.4 ft (4.40 m) and a thickness of 10 in. (0.25 m). In 1971 the Rhone Genf-Lignon stress ribbon bridge, Figure 13.20,
546
Future Trends
FIGURE 13.16.
FIGURE 13.17. Oriellt.
Early stress ribbon bridge
In
am!. Developments
Smithy Wood Foothridge.
the
FIGURE 13.19.
Freiburg Stress Ribbon Footbridge.
FIGURE 13.18. Stress ribbon concept for the Bosporus Bridge.
was constructed with a single span of 446 ft (136 m) and a width of 10.2 ft (3.10 m). This type of structure has used prefabricated transverse and longitudinal prestressed precast segments supported on the main catenary cables. Wind-tunnel tests have indicated that a stress rib-
bon bridge is safe against torsional oscillation.1 5 It can have a relatively flat sag, such that the grade at the abutments and piers can be kept at approxi mately 4%. Its largest disadvantage is the large abutments required to sustain the large tensile force in the main cables.
547
Application to Existing or New Bridge Types
1
____:"".,,_-l
~
.. FIGURE 13.20. Bridge. 13.5.5
--=-~-.
Rhol1e Cl'Ilf-Ligl1o!l S!lTS~ Ribboll
FIGURE 13.21. Elc\ati()lls of Bubiv;tll Bridge Pro posal prepared bv Bouvgues. I';lris. SPACI:' FR.,HIE BRJf)GF,S
In 1980, one of the authors served in an advisorv capacity to the Kuwait \Iillil\try of Public Works to eraluate responses to a re(luest for proposals for the Bubiyan Bridge Project. :\11 interesting pro posal was subll1itted by Bouvgues, a Frencb firm. This proposal consisted of a three-dimensional trLlSS or space frame concept, Figures 13.21 through 13.2;). • The concept of prestressed concrete trusses is not a new one. Concrete trusses have been used in building construction and in bridges (Chapter 8) in rarious projects throughout the world. For exalll ple:
1. The \Iangfall Bridge in :\ustria (Section 8.7.2) is a three-span, cast-in-place, prestressed con crete structure. It ma~· be described simply as a box girder consisting of solid top and bottom !lange;; connected by two vertical webs. which are trusses. 2. The Rip Bridge in .\ustralia (Section 8.7.;», just north of Sydney, is a three-span cantilever arch-truss structure. The upper chord (road way slab), diagonal and vertical truss members, and lower chord are composed of precast ele ments, which are made integral by cast-in place concrete and post-tensioning. 3. At least th ree prestressed concrete cantilever arch-truss bridges have been constructed in Yugoslavia, induding the Kirk Bridge (Section 8.5.4), which presently holds the record for the longest concrete arch in the world, a 1280 ft (390 m) span. 4. 'Other prestressed concrete truss bridges ha\·e been constructed in France, the C 'is.R., and Japan.
..
-'
.
-
F IGURE 13.22. IS()IlH.~lric of Bubi\;tn Bridgl' Proposal prepared bv BOll\gues. Paris.
FIGURE 13.23. COllstruction-slage model of Bubi\;tn B ridge Proposal.
548
Future Trends and-Developments
All the structures mentioned above have one thing in common: the prestressed concrete trusses are all oriented in a vertical plane. The concept is the same as in conventional truss bridges con structed of structural steel members. The three-dimensional truss concept presented for the Bubiyan Bridge is essentially a multitri angular-cell concrete box girder wherein the lon gitudinal solid webs are replaced by an open lattice system of trusses. Because the lattice truss webs are oriented in an inclined plane, as opposed to a ver tical plane, adjacent trusses have common node points (intersection of diagonal and vertical truss members with the flanges). This spatial geometry then forms in the transverse direction another system of trusses. Thus. the flanges are connected by a system of inclined orthogonal trusses (a system of mutually perpendicular trusses). Figure 13.24. Because the trusses are inclined to each other, with the diagonal and vertical members intersecting at common node points, they form a space frame composed of interconnecting pyramids. Thus, the structural behavior of the bridge with regard to distribution of load resembles that of a two-way slab in building construction. This structural concept is new in regard to its application to a bridge structure. However, the concept of a space frame truss has been previously applied to roof structures for large column-free sport facilities, auditoriums, civic centers, and the like. These space structures have been constructed primarily of metallic (steel or aluminum) tubular sections. There is no reason to believe that with the current state of the art in prestressed concrete, segmental construction and existing concrete truss construction, a prestressed concrete space frame
FIGURE 13.24.
Model of typical segment with top flange removed (note external post-tensioning tendons), Bubiyan Bridge Proposal.
concept cannot be consummated-in particular for a bridge structure. The advantage of this concept is that as a result of the "openness" of the trellis framework of trusses the dead or self-weight of the superstruc ture is much less than that of conventional pre stressed concrete construction. This comparative reduction in weight of the superstructure reduces the dead load to be transmitted to the substructure and thus reduces the mass of the substructure, with resulting eCQnomies. Further, there is an advantage in the manner the load is distributed throughout the structure. That is to say, there are many load paths. I n the unforeseen event of a member failure, the load would redistribute by seeking an alternative load path. Therefore, there is a greater degree of redundancy, which means that there is greater safety from a collapse failure. Or, in other words, by virtue of the spatial geometry there is an inherent reserve capacity. I n all other respects the fabrication and erection of the superstructure is consistent with state-of the-art conventional prestressed, precast segmen tal construction, including the external prestress ing. Although the concept of a space frame struc ture is new to bridge construction, its newness is only in assembling existing concepts into a single concept.
13.6
Summary
The last decade has seen considerable changes in bridge design and construction, many of which have been evolving since the 1950s. As we move into the 1980s, we must remain aware of change. Research already underway on inproved materials may have dramatic impact in the indusry. Applica tions of new systems to existing bridge types are being attempted along with new and improved types of bridge structures. Many of the improved materials and new concepts will reach practical ap plication; others will be abandoned for technical or economic reasons. Unforeseen improvements in materials and new types of bridge structures are certain to evolve in the next decade, which prom ises to be one of excitement and challenge. As engineers whose basic responsibility is the betterment of mankind, we must be constantly open to new concepts and ideas that will technically and economically improve the structures we at tempt to build. However, at the same time we must anticipate a new generation of problems that changes in methodology are certain to bring. Of
References
prime importance, we must not fall into a trap of oversophistication in design at the expense of simplicity and thus economy in construction. As we strive for longer spans and improved means of constructing bridges, it would be well to remember the words of F. Stussi, an eminent Swiss engIneer: The problem of Long Spans has always fascinated the specialist as well as the layman. The realization of a bridge with a length of span hitherto unattained not only requires great technical knowledge and capability, but also intuition and creative courage; it signifies a victory over the forces of nature and progress in the battle against human insufficiency.
This philosophy applies not only to the achieve ment of longer spans, but also to the changing technology of the future.
References 1. LA. Rubinskv and A. Rubinsky. "A Preliminary In vestigation of the Use of Fiberglass for Prestressed Concrete," Magazine IJf Concrete Research, September 1954. 2. James E. Carpenter, "Applications of High Strength Concrete for Highwav Bridges," Interim Report. July 1979, Concrete Technology Corporation, Contract ~o. DOT-FH-1l-9510 (unpublished re port). 3. w. Podolny, Jr., "Properties of Fiber-Reinforced Concrete." HIghway Focus, Vol. 4. :\io. 5. October 1972, Federal Highway Administration. Washing ton, D.C. 4. "St<1te-of-the-A.rt Report on Fiber Reinforced Con crete," Reported by ACI Committee 544.J()umal of the American Concrete Institute, November 1973.
549
5. J. P. Romualdi and G. B. Batson, "Mechanics of Crack Arrest in Concrete," Proceedings of the lISCE. Vol. 89, No. EM 3, June 1963. 6. J. P. Romualdi and G. B. Batson, "Behavior of Rein forced Concrete Beams with Closely Spaced Rein forcement," Joumal of the American Concrete Institutf', Vol. 60, Title No. 60-40, June 1963. 7. "Polymer Concrete," FIP Notes, 38 January/ February 1972, Federation Internationale de la Pre conlrainte. 8. Jan Sulkiewicz and Juhani Virola, "Future Aspects of Bridge Construction," Intl'Tnational CIVil En gineering ,Honthly, Vol. lIi. ~o. 2, 1974 Uerusalem). 9. G. H. Beguin, "Vergundbriicken-Ausfiihrung-s problerne beim Fahrbahn planen-Schietlevcr fahren, Der Stahlb(mm, Heft 12, Dezember 1975. 10. G. H. Beguin, "Composite Bridge Decking by Stage-Deck Jacking:' Journal of the Structural Divi sion, ASCE, Vol. 104, No. ST I.Januarv 1971'1. II. Rene Ryser. Discussion of "CompOSilf' Bridge Decking by Stage-Deck Jacking," Jllun/al of thl' Structural Division, .-ISCE. Vol. 104, :\0. ST 10. October 1978. 12. D. B. Steinman, The Wichert Truls, Van :-.lost rand Reinhold, :\ew York, 1932. 13. Rene Walther, "Stressed Ribbon Bridges," Interlw tional Civil Enbrineering Monthlv. Vol. 11, No. I, 197111972 Uerusalem). 14. Heinz :\ehse, "Spannbandbriicken," in Festschnji Ulrich FInster-walder 50 Jahre/iir D';wiriag, D:vckerholf & Widmann. A.C., Munich, 1973.
15. Ulrich Finsterwalder, "Free-Cantilever Construction of Prestressed Concrete Bridges and :'vIushroolll Shaped Bridges," First I ntematwl1ll/ S,wnposillm, Con rrele Bridge Design, American Concrete Institute Publication SP-23, Detroit, 1969.
Index ofBridges
Abeou Aqueduct (France), 345 Akayagawa Uapan), 379, 458, 463
Algiers (Algeria), 393
Alpine Motorway (France), 83, 129-134, 135, 139, 390,489,
510,515,545
A-I Motorway Overpass (France), 352
Ampel (Holland), 510
Anet (France), 360
Angers (France), 122,515
Aramon (Fmnce), 98,100,514
Ardrossan Overpass (Canada), 8, 11
Arnhem (Holland), 57-59
Arrabida (Portugal), 375
Ashidagawa Uapan), 458, 462
Balduinstein, see Lahn River
Barranqui1!a (Colombia), 401-404
Barwon River (Australia)' 401,402
Basra (Iraq), 346
Bayonne (Fmnce), 510
Bear River (Canada), 83, 84,108-112
Bendorf (Germany), 19, 35-37,164,167,283-284,296,536
Benton City (Washington, U.S.A_), 401, 402
Bezons (France), 31-33
Black Gore Creek, see Vail Pass
Blois (France), 98,100,233,245,468,513,514
Boivre Viaduct (France), 350
Bonhomme (France), 15, 387-392
Bonpas (France), 509
Borriglione Viaduct (France), 344
Bosporus (Turkey), 545, 546
Bouguen (France), 34, 38-40
Bourg-Saint Andeol (France), 509
Briesle Maas (Netherlands), 385-388
Brotonne (France),17, 29, 30,198,199,233,234,236,374,
401,405,419-427,481,482,530-535,536
Bubiyan, Kuwait, 547-548
B-3 Viaduct (France), 14, 18,124,128,139,145,162,165,
46~ 507,510,515,516,517
Calix (France), 139, 140
Canadians Interchange (France), 476-478
Canal du Centre (Belgium), 401, 402
Capt. Cook (Australia), 20, 136-139
Caracas Viaducts (Venezuela), 363-372,375,530
Carpineto Viaduct (Italy), 401, 402, 404
Center Canal (France), 455
Cergy-Pontoise (France), 444, 445
Chaco/Corrientes (Argentina), 401-404, 408-410,432
Cha~pigny (France), 173,343
Changis (France), 360
Chillon Viaduct (Switzerland), 18, 99-103, 162, 167,226,254,
256,503,512-514
ChoisY-1e-Roi (France), 12,13,17,20,83-88,139,155,165,169,
226,253,254,255,361,362,468,494,509
Clichy (France), 233, 234,449·452,478,479,482
Cline Avenue (Indiana, U.S.A.), 527
Colorado River at Yuma (California, U,S.A.), 529
Columbia River at Astoria (Oregon, U.S.A.), 238
Columbia River, 1-205 (Oregon, U.S.A.), 142·144, 158, 161, 162,
169,238,241,543
Columbia River, SR 182 (Washington, U.S.A.), 542, 543
Conflans (France), 95, 96, 469, 509
Corde (France), 228
Courbevoie (France), 20,88,89, 165,226,254,468,494,509
Crie! Viaduct (France), 333, 335,344
Dame Point (Florida, U.S.A.), 40 I, 402,405,433-436, 536, 544
Danube Canal (Austria), 401, 402, 427-431, 545
Danube River at Worth (Germany), 26, 345, 346
Dauphin Island (Alabama, U.S.A.), 256, 257, 258
Denny Creek (Washington, U.S.A.), 22,34,304-311 Deventer (Holland), 20, 105, 106, 162,515,516
Digoine (France), 455, 456, 458
Dijon (France), 476
Dnieper River (U.S.S.R.), 401, 402
Drummondville (Canada), 8, 9
Dumbarton (San Francisco, Calif., U.S.A.), 530
Dusseldorf-Flehe (Germany), 21, 23, 303-307
Eastern Scheidt (Holland), 134-136, 139
East Huntington (West Virginia, U.S.A.), 401,402
Elztalbrucke, (Germany), 296-300
Eel River (California, U.S.A.), 529
Esbly Bridge (France), 5, 360
Eschachtal (Germany), 73, 80
Felsenau (Switzerland), 168
F-9 Freeway (Australia), 145
Firth of Forth (U.K.), 3
Flying Lever Bridge, 3
Fontenoy (France), 25
Foyle River (N. Ireland), 401,402
Freiburg (Germany), 545, 546
Gardon (France), 509
Gennevilliers (France), 52-55,164,478,480
Givors (France), 151,152,163
Gladesville (Australia), 371-374, 375
Grand'Mere (Canada), 55-58
551
552
Index of B1;.idges
Great Belt (Denmark). 14.401-405,430-433 Gronachta1 (Germany), 345
Guadalupe River at San Jose (California, U_S_A.), 529
Guadiana Viaduct (Portugal), 300-301
Hartel (Holland), 103-105,494,509
Hen'al (Brazil), 31
Hobbema (Canada), 8, 10
Hokawazu (Japan), 378
Holderbank-Wildeck (Switzerland), 545
Houston Ship Channel (Texas, U.S.A.), 28, 68-71, 161, 169,
212-222,232,238-239,241,536
Hyobashigawa (Japan), 457, 459
Incienso (Guatemala), 71, 74, 75
Ingolstadt (Germany), 345
Inn (Germany), 345
Interstate 1-266, Potomac River Crossing, see Three Sisters Bridge
Iquacu (Brazil), 375
Islington Avenue Ext. (Canada), 84
J FK Memorial Causeway (Texas, U.S.A.), 27, 83, 84, 109, 112 114,536
Joinville (France), 164,479
Juvisy (France), 95,96,233,254,509
Kakogawa (Japan). 441,462
Kennedy (France), 476
Kentucky River (Kentucky, U.S.A.), 84,142,143
Kettiger Hang (Germany), 293-294
Kimonkro (Ivory Coast), 344
Kipapa Stream (Hawaii, U.S.A.), 72, 76, 169,530
Kirk (Yugoslavia), 15, 16,374,375,379,382-384,547
Kishwaukee (Illinois, U.S.A.), 84, 141,142, 143, 169
Kisogawa (Japan), 458, 461
Koblenz (Germany), 162, 167
Kochertal (Germany), 45-46, 47, 48,168
Koches Valley (Germany), 345
Koror Babelthuap (Pacific Trust Territory), 13, 30, 61-63, 81,
536
Krahnenberg (Germany), 293-295,296
Krummbachbrilcke (Switzerland), 379
Kwang Fu (Taiwan), 401,402
Lacroix Faigarde (France), 34,40-41
Lahn River (Germany), 11, 33
Lake Maracaibo (Venezuela), 400-403,405-408,432
La VouIte (France), 34, 441, 442
Lievre River (Canada), 83, 84
Linn Cove Viaduct (N. Carolina, U.S.A.), 23, 35, 8f, 178-181,
228,233,282,290-293,308,503,525,543
Loisach (Germany), 301-303
Long Key (Florida, U.S.A_), 18, 22, 23, 84, 159, 169, 308-313,
489,524-525, 526, 542, 543
Luc Viaduct (France), 333-335, 344
Luzancy (France), 11, 13, 82, 357, 359, 360
Madison County (Tennessee, U.S.A.), 5
Magliana (Italy), 401-404
Magnan Viaduct (France), 72, 77,256,257,479
Mainbrilcke (Germany), 401, 402, 405, 410-412
Mangfall (Austria), 395, 396, 547
Marne la Vallee Viaduct (France), 441, 444-448, 517
Marne River Bridges (France), 5, 357, 361, 362, 363
Marolles (France), 344
Medway (U.K.), 71
Miller Creek, see Vail Pass Mirabeau (France), 21, 509
Morand (France), 442-444
Morlaix (France), 163
Moulin a Poudre (France), 163
Moulin-Ies-Metz (France), 476, 477
Mount Street (Australia), 401, 402
M-25 Overpass (U.K.), 401, 402
Mtihibachtalbrticke (Germany), 338-339
Muscatuck (Indiana, U.S.~.), 84
Napa River (Napa, California, U_S.A.), 59-61, 81, 527,
529
Napa River (Vallejo, California, U.S.A_), 10
Natorigawa (Japan), 457, 460
Neckarburg (Germany), 370, 376-380
Neckarrews (Germany), 33
New Melones (California, U_S.A.), see Stanislaus River
New Orleans, Greater (Louisiana, C.S.A.), 3
Niesenbachbrucke (Austria), 378, 380-382
North Main Street Viaduct (Ohio, C.S.A_), 528
Nuel Viaduct (France), 344
Oissel (France), 163, 476
Ol~ron Viaduct (France), 2,18,20,22,96-99,108,157,158,
165,175,177,241,243·245,249,468,494,504,506,508,
511,512,514
Olifant's River (South Africa), 26, 331-333, 343,441,452-454
Oli Viaduct (France), 333-335, 344
Oosterschelde (Holland), see Eastern ScheIdt
Orleans (France), 478
Ottmarsheim (France), 145, 165
Overstreet (Florida, U.S.A.), i45, 146
Ounasioki (Finland), 281, 284-285 .
Pag (Yugoslavia), 375, 378
Paillon (France), 344
Paris Belt, Downstream, (France), 91-94, 155,233,234,263-266,
468,509,511
Paris Belt, Upstream, (France), 94, 95, 245-248, 468,509,511
Paris-Lyon high-speed railway line (France), 453-457
Parrots Ferry (California, U.S.A.), 72, 77
Pasco-Kennewick (Washington, U.S.A.), 17,84,401,402,405,
418-419,536,544
Penn DOT Test Track (Pennsylvania, U.S.A.), 84
Pfaffendorf (Germany), 393
Pierre Benite (France), 21, 89-91, 92,468,510
Pine Valley, California (U.S.A.), 27,29,34,35,46-52,81,161,
169,523,529,536
Pleichach Viaduct (Germany), 295-296
Plougastel (France), 15,31,355,358,359,375,535
Polcevera Viaduct (Italy), 401-403
Pontchartrain (Louisiana, U.S.A.), 6, 7
Pretoria (South Africa), 401, 402
Puente del Azufre (Spain), 71,73
Puteaux (France), 73, 78, 151
Pyle (France), 229
Quebec (Canada), 3
QuerJin Guen (Germany), 345
Index of Bridges Ravensbosch Valley (Holland), 329-331
Reallon (France), 151,153
Red River (Arkansas, U.S.A.), 527, 528
Rhone Genf-Lignon (Switzerland)' 545, 547
Richmond-San Rafael (California, U.S.A.), 238
Rio Caroni (Venezuela), 24, 321-327,345
Rio Caroni railway (Venezuela), 464
Rio Esla (Spain), 375
Rio Niteroi (Brazil), 20, 22, 106-108, 139, 169, 176, 178, 190,
200,201,515,516
Rio Tocantis (Brazil), 71, 72
Rip Bridge (Australia), 14, 395-397, 547
Roche (France), 455, 456
Rombas Viaduct (France), 282, 288-290, 317
Ruck-A-Chucky (California, U.S.A.), 401, 402, 436-439, 536
Saint Adele (Canada), 37-39
Saint Andre de Cubzac (France), 101, 113-116,122, 162,165,
489,504,510
Saint Clair Viaduct (France), 375
Saint Cloud (France), 14, 18, 29, 30, 114, 117-122, 139, 150,
160, 16~ 165, 205, 20~ 234, 503~05,50~ 514, 515
Saint Isidore (France), 479
Saint Jean (France), 41-44,163.235,265-269
Saint ~1ichel (France), 384-385
Sallingsund (Denmark), 101, 122-125, 158,167,236-238,240,
489,515,543
Sando, (Sweden), 375
San Joaquin River at Antiocj1 (California, U.S.A.), 529
San Mateo-Hayward (California, U.S.A.), 238
Saone River (France), 454-458
Sathorn (Thailand), 348
Saulieu (France), 455
Shubenacadie (Canada), 71, 74, 81, 538, 539
Schwarzwasserbnicke (Switzerland), 379
Sebastian Inlet (Florida, U.S.A.), 10, 12
Seine River (France), 455, 456
Serein (France), 455, 456
Setubal (Argentina), 72, 75, 76
Seudre Viaduct (France), 98, 101. 165
Seven Mile (Florida, U.S.A.), 22, 28, 159, 169,312-314,489,
526,543
Sheldon (:'-iew York, U.S.A.), 11
Shepherds House (U.K.), 339-343
Shogun's Bridge Oapan), 2
Sibenik (Yugoslavia), 375, 378
553
Siegtal (Germany), 19,43·45
Smithy Wood Footbridge (U.K.), 545, 546
Stanislaus River (California, U.S.A.), 529
Sugar Creek (Indiana, U.S.A.), 84
Tancarville (France), 419, 530-535
Tarento (Italy), 168
Tauemautobahn (Austria), 141, 142
Tempul Aqueduct (Spain), 400·402, 405
Tet Viaduct (France), 344
Three Sisters Bridge (District of Columbia, U.S.A.), 27,34,
536
Tiel (Netherlands), 401, 402, 412-418
Tonneins (France), 355
Torcy Viaduct (France), 447-449
Tours (France)', 509
Tourville (France), 476
Trent Viaduct (U.K.), 140, 141
Tricastin (France), 73, 79,80,151,153
Trilbardou (France), 360
Turkey Run State Park (Indiana, U.S.A.), 84
Ussy, France, 360
Vail Pass (Colorado, U.S.A.). 84,140,141,228,285-288.523,
524,543.544
Val Ristd (Italy), 25, 327-330
Van Staden (South Africa), 375, 378
Var Viaduct (France), 345
Vejle Fjord (Denmark), 63-67, 162, 167,530
Veurdre (France), 354, 355
Villeneove (France), 355, 356
Viosne (France), 164
Waal River (Holland), see Tiel
Wabash River (Indiana, U.S.A.), 26, 34, 84, 324, 335-338
Wadi Kuf (Libya), 401·403,407,408,432
Walnut Lane (Pennsylvania, U.S.A.), 5, 6
Wandipore Bridge (Bhutan), 2
Weirton-Steubenville (West Virginia, U.S.A.), 401, 402
Woippy (France), 479, 481
Worms (Germany), II, 13
Zilwaukee (~lichigan, U.S.A.), 84, 144, 145, 158, 162, 169,526,
527
Zoo (Germany), 545
Index of Personal Names
Abrahams, M.j., 30,147,224
. Alden, Donald W., 535
Ballinger, C. A., 30,147,224
Barker,james M., 535
Batson, G. B., 540, 549
Baumgart, E., 31
Baur, Willi, 24, 30, 323, 352
Beloff, G., 20, 138, 139
Bender, Brice, 104, 105, 330,331
Benson, C. L., 535
Bequin, G. H., 549
Best, K. H., 353
Bezouska, T.j., 517
Bezzone, A. P., 81
Bockel, Manfred, 296, 298, 302
Bouchet, Andre, 147
Breen,john E., 109, 112, 113, 147 Brown, R. C.,jr., 147
Brunel,339
Bryant, Walter, 419
Burns, N. H., 147
Hadley, Homer M., 401, 439
Hale, Phil, 61
Heinen, Richard, 81, 411, 412
Henneberger, Wayne, 109
Hoyer, E., 4
jackson, P. H., 4
Kashima, S., 147
Kingston, R. H., 353
~
Caquot, Albert, 31
Carpenter, james E., 549
Chang, F. K., 439
Cooper, R. L., 147
Dill, R. E., 4
Dehring, C. E. W., 4
Dokken, Richard A., 81,535
Downing, Dale F., 81
Eiffel, Gustave, 41, 43
Esquillan, M., 34, 375
Lacey, G. C., 147
Lenglet, C., 440
Leonhardt, Fritz, 24, 25, 26,30, 149,224,323,325,345,405,
420,439
Lin, T. Y., 30, 436, 440
Lindberg, H. A., 67
Lu, H. K., 440
MacIntosh, D. W., 81
Maddison, M., 353
Mangnel, G., 4
Mathivat,j., 147, 260, 280
Milhollin, A. B., 535
Moch, Elizabeth B., 30
Morandi, Riccardo, 400,401,403,404,407,430,432,
439
Muller, jean, 12,30,147,224,399
Navier, Claude Louis Marie, 83
Nehse, Heinz, 549
Podolny, W.,jr., 30, 147,224,320,439,549
Pope, Thomas, 3
Feige, A., 439
Finsterwalder, Ulrich, 11, 23, 30, 33, 36, 81, 320, 401, 402,
404,410,432,545,549
Fleming, j. F., 439 .
Freyssinet, E., 4,5,11,31,210,226,354,355,363,375,392,
394,398,399,535
Redfield, C. :1.1., 440
Resal, 196
Romualdi, j. P., 540, 549
Rothman, H. B., 439
Rubinsky. A., 549
Rubinsky, 1. A., 549
Ryser, Rene, 549
Gallaway, T. M., 147
Garrido, L. A., 403
Gerwick, Ben C.• 147, 238, 280
Graham, II.j., 440
Grant, Arvid, 325, 326, 353,418,419,420, 439,
440 Gray, Normer, M., 401, 439
Scalzi, j. B., 30,439
Schambeck, H., 320, 439
Schell, Herb, 310
Shama, Robert, 399
Steiner, C. R., 4
Steinman, D. B., 549
S t iissi, F., 549
555
556 Sulkiewicz, Jan, 541, 549 Tang, Man·Chung, 30, 62,81,288,319
Thul, H., 81, 319, 320,439
Torroja, E., 400, 401, 405, 439
Troitsky, M. S., 439
Tyrrell, H. G., 30
Vatshell, J. L., 308·311
Virola, J uhani, 541, 549
Index of PersC?nai Names Walther, Rene, 549
Whatley, M. J., 353
Whitman, R. A., 81
Wittfoht, Hans, 43,
282,319
Yang, Y. C., 440
Zellner, Willhelm, 3i7, 3~0, 439
Zublin, 377,380,399
Index of Firms and Organizations
American Association of State Highway and Transportation
Officials (AASHTO), formerly American Association of State
Highway Officials (AASHO), 5, 6, 8, 30, 55,148,149,190,
193,199,230,243,363,460,521,524,525,526,535,538,
545
American Concrete Institute (ACI), 30, 36, 81, 97, 98,147,193,
199,280,295,319,324,325,326,353,404,439,466,517,
539, 549
American Consulting Engineers, Inc., 335
American Institute of Steel Construction (AISC), 439
American Railway Engineers Association (AREA), 148, 190
American Road and Transportation Builders Association
(ARTBA),535
American Society of Civil Engineers (ASCE), 30, 81, 352, 364,
365,367,399,409,410,439,440,543,544,549
Arvid Grant and Associates, Inc., 419
Associated General ContraCtors of ~merica (AGC), 535
Associazione Italiana Cemento Armato E Precompresso (AICAP),
353
Associazione Italiana Economica Del Cemento (AITEC), 353
Florida Department of Transportation, 524, 525, 526
French National Railways, 453
Freyssinet International, 11,439,440 General Services Administration (GSA), 519
G. F. Atkinson Company, 527
Heavy Construction News, 81
Hensel Phelps Construction Company, 304
Howard Needles Tammen & Bergendoff, 433, 434, 435, 440
Indiana State Highway Commission, 335
Institution of Civil Engineers, 340, 341, 342, 353, 439
International Association for Bridge and Structural Engineering
(IABSE), 149,224,319,439
International Engineering Company, Inc., 524
International Road Federation, 30, 147, 224
Julius Berger·Bauboag Aktiengesellschaft, 403, 405·408 Kuwait Ministry of Public Works, 547
Beton·und·Stahlbetonbau, 35, 36, 81, 284, 320
Bouygues, 547
British Rail, 340
Bullen and Partners, 340
BVN/STS, 104, 105,330,331 California Department of Transportation (CALTRANS), 10, 27,
47,59,61,81,523,535
California Division of Highways, see California Department of
Transportation
Concrete S!:!ciety (London), The, 341, 342, 343, 353
Concrete Technology Corporation, 538, 549
Der Bauingenieur, 297, 298, 299, 320
DRC Consultants, Inc., 62, 288
Du Pont de Nemours, 249
Dyckerhoff & Widmann, 13, 19,30,33,35,62,63,76,81,284,
285,296,301,303,307,320,404,412,432,549
Engineering News·Record, 37, 38, 39,81,353,399,439,440
Entreprises Campenon Bernard, 12,122,419 Federal Highway Administration (FHWA), 30, 147,224, 310,
419,439,440,520,535,538,545,549'
Federation Internationale de la Precontrainte (FIP), 224, 517,
549
Federation Internationale de la Precontrainte, Co mite Europeen
du Beton (FIP-CEB), 190, 193
Figg'and Muller Engineers, Inc., 313, 524
Leonhardt and Andra, 24, 323, 419
L'Industria Italiana del Cemento, 403, 404
~1ain
Roads Department, Australia, 20,138,139,147,399 Museum of Modern Art, New York, 30
Owens·Corning Fiberglass Corp., 537
Polensky·und·Zollner, 43
Portland Cement Association (peA), 5, 8, 9, 10, II, 12, 37, 49,
50, 5~ 74,81, 135, 13~ 147,309,320,353
Post·Tensioning Institute (PTI), 81, 320, 353, 517
Prescon Corporation, 419
Prestressed Concrete Institute (PCI), 5, 6, 8·12, 30, 81,110·112,
147,224,320,466,517
Ralph Rodgers Construction Co., 335
Roads and Transportation Association of Canada, 81
Siemens·Bauunion, 296
Society of American Value Engineering, 519
Structural Engineers Association 0 f California, 190
Texas Highway, 27, 109
Transportation Research Board, National Academy of Sciences,
30,319,439,535
Travaux, 147,280
T. Y. Lin International, 436, 542
557
558
Index ofFirms and. Organizations
U.S. Army Corps of Engineers, 519 U.S. Bureau of Reclamation, 519 U.S. Coast Guard, 61 U.S. Department of Defense, 519 U.S. Department of Transportation, 519 U.S. Navy Bureau of Yards and Docks, 519 United States Steel Corporation, 540 University of Texas at Austin, Center for Highway Research, 109,147
VSL Corporation, 308, 335 Washington Department of Transportation, 307-311 Wayss & Fretag, 296 Weddle Bros. Construction Co., Inc., 335 White, Young and Partners, 401-404, 430 Zement and Beton, 283, 294, 295, 319
Index of Subjects
AASIITO-PCI I-girders, 5, 6, 8
Abutments, 8, 9, 24, 56, 132, 150,205,207,232-235,271-276,
333,336,363
Aesthetics, 232-234,354, 424
Alignment, 25
Alternate designs, 29, 59, 60, 63,114,285,371,520-522
Arches, 12, 15, 16, 31, 47, 354-382
frames, 12
Assembly truss, see Truss, falsework
Balanced cantilever, see Cantilever construction
Ballast, 62
Bars:
Dywicag, 36, 52, 284,330,377,380,382,404,408,411,
412,432,433,538
high-strength, 34
Macalloy, 340, 341, 342
Beam and winch, 20, 91, 114-116, I !8, 140, 510
Bearings, 25, 29, 40, 41, 43, 83,125,132,138,203·205,460,
461
elastomeric, 68, 83, 96,151,158,241·253,418,426
lateral guide, 325, 338, 341
sliding, 326, 333, 414
temporary, 325, 338, 341
Bidding procedures, 518-523
alternate designs, 520·522
design and build, 519
single design, 518, 519
value engineering, 519, 520
Box girder, 10, 12, 14,15,21,35,37,41,43,47,48,49,58,
59,68,83,88,89,103,107,109,117,138,159,160,203,
322
cast·in-place on falsework, 28, 29, 103
efficiency, 159, 160
torsional moments, 169, 170,205
transverse load distribution, 164, 169, 170,202
transverse moments in deck slab, 170
variable depth, 37, 52,203,205
Box sections, see Box girder: Cross section
Braking force, 331
Cable-stay, 12, 14, 16, 28, 400-440
adVantages, 401-403
structural style and arrangement, 403-405
temporary system, 333, 349, 350
Camber, 40, 63, 71, 97, 205-210, 482-485
Cantilever construction, 2-4, 11, 12, 17, 18, 23, 29, 31-146,
149
cast-in·place, 17,18,29,31-80
cast-in-place operation sequence (cycle), 18, 19,38,43,
63
precast, 17, 1.8, 20, 29,34,82-147
Casting yard and factories, 20, 103, 135, 138, 504-507
Climbing forms, 45, 49
Competitive bidding, see Alternate designs
Concrete:
composite, 541
creep, 40, 6~ 71, 8~ 83, 151, 155-158,206,231,363,365
curing, 114, 126,466-469, 506
design and properties, 466
fiber-reinforced, 539, 540
high-strength, 537-539
lightweight, 58, 60, 72, 145
polymer, 540,541
shrinkage, 17,62, 71,82,83, 365
shrinkage damage, 324
Construction:
critical-path, 82
joints, 21
push-out, see Incremental launching
segmental, see Segmental construction
sequence, see Erection sequence
speed, 18
Continuity, 34, 49, 85, 87, 158, 206
Continuous superstructures, 155·158
Contractual aspects, 518-535
Contraf1exure, 9,21,97,113,124,150,205
Cranes:
barge (noating), 20, 2:':, 86, 87, 91,109,112,138,139,237,
238,239,311,312
crawler, 20, 509
noating, see Barge
portal, 20, 103, 105, 509
swivel,23
truck, 20, 128
Creep, see Concrete
Cross section, 162-169, 202, 203, 217-219
DeBections, 17,40,157,158,159,205-210,483
Demolition, 352
Depth-to-span ratio, 35,43,52,69,89, 149,322,402,405
Design of segmental bridges, 148-223
Deviation blocks, 310
Diaphragms, 41, 53, 54, 57, 62, 67, 85, 90, 112, 124, 203, 204,
205,207,332
Differential settlements, 276-280
Dimensional control, see Geometry control
Double-T, 21, 322, 333
559
560
Index of.Subjects
Earthquake, 49, 59, 71, 363, 390,418
Ecology, 28, 47, 304
Economics, 518·535 Environment, 18, 23, 27, 28, 29, 48, 99, 122, 304
Epoxy, 488·493 joints, 17, 83, 87, 96,103,112,124,127,150,199-202,414
Erection sequence, 66,105,127,132,133,136,341,367,397, 410,417 Expansion joint, 12, 29,41,57,68,83,97,99,107,113,125, 155, 15~205, 208,303,331,345,414,418 Expansion of long bridges, 158-159
External post-tensioning, 23
Falsework bents, 25
Fatigue, 210-212, 441
Finger joints, 138
Form traveler, 1, 17-21,23,36,38,40,43,50,54,58,62-64, 70,206,302,303,475-478 Free cantilever, see Cantilever construction Friction, 321, 323, 330, 351
Foundations, 225-280
I ,!
Geometry control, 321, 322,495-497,499-504
,I
Hinges, 21, 34, 35, 49, 50, 62,124,126, 150,205,208,363
Frcyssinet concrete, 357, 365
mid-span, 151, 155-159,354
I
I
I-girder, 8·10, 28,29,525,526 Ice breaker, 124,238,239 Incremental launching, 12,18,24-27,34,84,321·353 alignment requirements, 343
balanced casting, 322, 323
casting area, 349
construction principle, 343-346
continuous casting, 322
demolition by, 352
design, 343-352
launching methods, 349
piers and foundations, 350-352
span arrangement, 343-346
superstructure type, shape and dimensions, 343-345
Investment, 18, 29
Jacking, lift-and-push, 323
Jacks, Freyssinet flat, 360, 365, 374
Joints, see Construction; Expansion joint; Finger joints; Hinges; segments Keys, 11,112,124,136,199-202,409 Launching gantries, 20,22,64,67,96,98,103,105,106,109, 117,120-122,124,126-128,134,135,141,145,511 517
Launching girder, see Launching gantries Launching nose, 25,46,322,325,331-333,338,341,346-350, 380
Launching sequence, see Erection sequence Live load requirements, 149
Long-bed, see Long-line method Longitudinal bending, 212, 213
Longitudinal closure strip, 112
Long-line method, 85, 97,103,142,143,493-494
Match-cast, II, 17, 43, 82, 83, 85, 96, 97, 117, 124, 130, 199 202,409,418
Match-cast joint, 199-202
Material quantities, 219-220, 223
Mayreder system, 377
Median frame, 9, 11
Model, 109, 112, 200, 201
Mushroom girder, 21, 296, 298
Natural frequency, 418
Negative moment tendons, see Cantilever construction; Prestress
ing tendons
Neoprene bearings:
double-row, 230, 241·253
influence of thickness and arrangement, 251-253
properties, 245-248
sec also Bearings, elastomeric
Piers, 39-41, 49, 63, 68, 89, 91,99,100,113,225-280,301,304,
308,321,424
aesthetics, 232-234
caps, 49
deformation, 230, 231, 248-250, 257-261
double elastomeric bearing, 241-253
elastic stability with flexible legs, 261·263
flexibility, 83, 158, 229,230,331
foundation, 49, 68, 234-241
for incremental launching, 350-352
loads, 230·232
moment-resistant, 228, 230, 234-241
precast, 23, 228
properties with double-row neoprene bearings, 250, 251
properties with flexible legs, 257-261
segmental, 543, 544
stability during construction, 263-271
temporary, see Temporary bents .
temporary bracing, 105, 270, 271
temporary stays, 271
twin flexible legs, 228, 230, 253·263
Polyethylene pipe, 310
Positive-moment tendons, see Continuity; Prestressing tendons
Precast outrigger struts, 45, 73
Precast piles, 135
Prestressed concrete:
evolution, 4, 5
evolution of bridges, 5-8
precast girders, 8-10
Prestressing:
continuity, 178,179,182
future provisions, 212
longitudinal, 69,107,109,125,213
temporary, 83,103,132-134,334,348,414
three-dimensional, 36, 63, 69, 117
transverse, 17,49,60,61,69,94
vertical, 17, 41, 69, 70, 125
Prestressing tendons:
anchors, 470, 471
cantilever, 87,109,114,173
continuity, 87, 109, 114, 149, 173
corrosion protection, 537
ducts, 470
friction losses, 471-475
glass fiber, 537
Index of Subjects grouting, 475
layout, 173,174, 183,184,313,471
straight, 175,176,177, 348
unbonded, 475
Prestress losses, 61, 190, 206
Principal stresses, 197, 198, 201, 216
Problem areas, 220-222
Progressive placement, 12, 18, 22-25,35,37,84, 281-293
design aspects, 314-319
Push-out construction, see Incremental launching
Pylons, 16, 17,408,410,411,415,418,424,426,428
Railway, 26, 441-464
design aspects, 458-464
horizontal force, 459,460
loading, 441, 458, 459, 463
Redistribution of moments and stresses through concrete creep, 183-189,213-215
Reinforcement, compression, 36
Relaxation, 155,231
Resal effect, 196, 263
Rigid frames, 12, 14, 15, 382-392
Segmental bridge decks, 542, 543
Segmental construction, 10-12, 17, 29, 30, 485-489
Segments:
cast-in-place, 17, 18
dimensional tolerances. 469
fabrication, 82. 83, 85
formwork, 469, 470
handling, 507-509
precast, 17, 18, 22, 23
size, 18,83
weight, 18, 83
Shear, 193-199,202,203,215-217 Short-line method, 90, 91,109,124,126,130,494 498
Shrinkage, see Concrete
Slip-form, 43, 49, 99, 243, 298, 321,424
561
Space frame bridges, 547, 548
Span arrangement, 149-151
Span-by-span construction, 12, 17, 18,20-22,34,84, 282, 283,
293-314
Span-to-depth ratio, see Depth-to-span ratio
Splice, 9-11
Standardized cross section, 130
Stationary forms, 24
Stray currents, 461
Stress ribbon bridges, 545, 546
Superelevation, 29,103, 125,302
Superstructure:
cross section, see Cross section
shape in elevation, 160, 161
Swing span, 428
T-beams, 21, 301
Teflon,49,83,132,323,326,338,414,418,430
Temperature, 285, 302, 332, 365
Temperature gradient, 170-173, 199
Temporary bents, 323, 333, 336, 338, 341, 345, 396
Thermal movement, 62, 83, 231, 345, 390
Torsional moments in box girder, see Box girder
Transverse load distribution, see Box girder
Transverse moments in deck slab, see Box girder
Transverse ribs, 67, 114
Traveler, see Form traveler
Truss, 12, 14,47,392-399
auxiliary, 31,43,45,50,52,125,128
falsework, 22
Two-stage casting, 478,479
Ultimate bending capacity, 190-193
Uplift, 151,204,205
Value engineering, 143,519-520 Wichert truss, 545
Width-to-depth ratio, 149