A STUDY OF
VARIOUS VARIOUS METHODS M ETHODS ADOPTED BY
WORLD RAILWAYS TO
CONTINUE LWR OVER BRIDGES
By
K R Chaudhary Chaudhary
SrDEN/S/WCRly/KOTA
A N Sinha
DyCE/C/WR/ADI
COURSE NO. 623 Sr PROFESSIONAL COURSE (P WAY)
1
INDEX
Sr No.
DESCRIPTION DESCRIPT ION
PAGE No.
1.0
Acknowledgement
3
2.0
Introduction
4
3.0
Historical Background
4
4.0
Technical Requirement
5
5.0
Track Bridge Interaction
7
6.0
World Railways Present Scenario
13
7.0
Conclusion
36
8.0
References References
38
9.0
Annexure I
39
2
INDEX
Sr No.
DESCRIPTION DESCRIPT ION
PAGE No.
1.0
Acknowledgement
3
2.0
Introduction
4
3.0
Historical Background
4
4.0
Technical Requirement
5
5.0
Track Bridge Interaction
7
6.0
World Railways Present Scenario
13
7.0
Conclusion
36
8.0
References References
38
9.0
Annexure I
39
2
ACKNOWLEDGEMENT The project preparation is an important part of Sr Professional Course. This course is mainly to update and refresh r efresh the knowledge of the advancements in track technology world over. It is highly relevant rele vant that the project is also related with advance subject. We W e are highly grateful to Shri Shiv Kumar, Director, IRICEN and Shri R K Verma, SP/T and Course Director for selecting the useful and relevant topics for the project. We also acknowledge gratefully the direction, guidance and support extended by Shri R K Yada Yadav, v, PT/2 PT/2 during the project p roject preparation. We also acknowledge the valuable and timely ti mely support given by the Library staff and Computer Cell staff of IRICEN.
K R Chaudhary SrDEN/KOTA
A K Sinha
DyCE/ADI
3
1.0 INTRODUCTION
The issue of permitting LWR on bridges has assumed lot of im i mportance of late due to a number of bridges with ballasted decks having PSC sleepers sleepers having h aving been constructed. It is desirable d esirable to continue LWR on these bridges bridges to avoid problems problems on maintenance of fish plated joints on PRC sleepers and consequent bad running etc. and to fulfil the long cherished cherished dream of jointless track. Even on girder bridges, it is considered considered desirable d esirable to continue LWR to elim eli minate the chances ch ances of any mischief or sabotage, sabota ge, which can take place with disastrous consequences, by intentional removal of single rails on bridges. brid ges. It shall be easily realised that all railway lines are dotted with major bridges bridges with/without ballasted ballasted girders girders at close intervals and full advantages of LWR cannot be availed in case continuity continuit y is broken on this account. In view of the above, it is pertinent to study various provisions and methods adopted world over including Indian Railways to continue LWR over various types of long lon g bridges bridges i.e.ballasted deck as well as ballastless deck bridges. An attempt has been made in this report to study the various practices as ava a vailable ilable in various literatures. literatures. 2.0 HISTORICAL HISTORICAL BACKGROUND B ACKGROUND
Welding of rails was started as early as in 1905 but comm co mmercial ercial welding on considerable scale became comm co mmon on only after a fter 1932. During the thirties, the weights and lengths of standard rail sections varied from 22kg/m to 65kg/m 65k g/m and lengths from from 5.5 m to 27 m respectively. respectively. The length len gth of welded rail panels varied from 18 m to 380 m. In In India in thirties, the GIP GIP and BN railways railways started conducting trials on welded rail joint. From 1947 to 1966, large nu mber of 5 rail panels and 10 rail panels were put into track. track. At the same sa me time in USA about 57,000 track kilometres have already been been converted into CWR.
4
Railway Board has taken a policy decision in 1967 making LWR as the standard track structure on trunk routes and main lines as a part of modernisation plan of IR. But as per the first LWR manual i.e. Manual of instructions on LWR (provisional) oct’70 in para 5.6.2 , in regard to girder bridges, with unballasted decks, accordingly stipulates that LWR shall not be continued over girder bridges of single spans exceeding 13 m or multiple spans of overall length exceeding 18m . On girder bridges ,where LWR is laid , the fastenings shall rail free fastenings so that the rail and the girders expand and contract independently. Nothing much has changed from that ti me and as per latest LWR manual provisions the maximum overall length for 60 kg track in zone IV is a bare 11m with rail free fastenings and 23 m with partly box anchored sleepers on girders. At the corresponding period i.e. in year 1968 –1969 the bridges as long as 800m were provided with LWR without an expansion joint on German Railways. The LWR on girder bridges was studied in detail in connection with NEW TOKAIDO LINE in JAPAN in sixties. Axial forces in the LWR on a bridge and its displacement were examined quantitatively , resistance of rail to creep was adjusted and the arrangement of bridge supports was changed . As a result, JNR succeeded in using LWR on bridges continuously .In the American rail roads despite difficulties involved , many railways installed welded rails on bridges in sixties and seventies . Also in Europe, most of the lon g bridges were provided with ballasted decks and LWR was used extensively on girder bridges.
3.0 TECHNICAL REQUIREMENTS
The LWR causes additional thermal forces in the track due to thermal stresses developed due to restraining the free expansion/contraction of 5
rails. When such type of track is laid on the bridges two types of situation arises i) Bridges with ballasted decks without bearing: LWR can be continued over bridges without bearing like slabs, box culverts and arches where there is no relative movement between bridge and LWR track. ii)
Bridges with/without ballasted deck with bearing: When the bridge structure and the track exhibit movement relative to each other, then there is interaction effects which have to be taken into consideration. Further the interaction effect can be tackled in two different ways namely, a) The rails and bridges can be made independent of each other by providing rail free fastenings etc so that the movement of rail and bridge deck are independent and they will not exert force on each other. b) The rails and bridges are not made independent and both will exert inter alia force on each other and the forces such generated are calculated and assessed and taken care of in assessing the strength of existing bridges or in the case of new bridges the same are taken into account at design stage itself. Determination of interaction effects quantitatively is quite complex. No reliable method was available for this purpose till UIC recommendations for 6
calculations of these interaction effects were issued. To analyse and assess these interaction forces the ERR I specialists Committee D 213 has conducted detailed studies and the results of the same have been published in the form of a report named UIC774-3R. of the year 2001. 4.0 TRACK BRIDGE INTERACTION (UIC 774 –3R)
Interaction between track and bridge, i.e. the consequence of the behaviour of one on the other, occurs because they are interlinked, regardless of whether the track is directly fastened or has a ballast bed. The interaction takes the form of the forces in the rails and in the deck and its bearings , as well as displacements of the various elements of the bridge and track. If the interaction is within the control, then the bridge will continue to fulfil its functions i.e. supporting the track without the track being subject to anomalies. There are two types of anomaly: rail fractures or disruption of the link between track and bridge such that track stability is no longer guaranteed. Therefore interaction must be taken into account as a serviceability limit state as regards the bridge as well as being an ultimate limit state as regards the rail. The acceptable limit state for the track depend on its design and state of maintenance. The permissible values used in UIC report are the values that are most widely permitted for standard track components in a good state of maintenance. If a railway for its own reasons operates outside the scope o f application, that railway will still be able to use the calculation methods by replacing criteria given in UIC report with new criteria based on its own experience and observations. 7
Similarly, the track strength taken into account and the te mperature increase envisaged were drawn from the knowledge of the various railways. It is perfectly possible to use this method but with different values, if the need arises. It should also be noted that the displacements or rotations to be checked only concern what has to be checked to guarantee that the behaviour of the bridge cannot damage the track and alter its behaviour. There are other checks to be made as regards displacements and rotation of the structure , these bein g concerned with problems of comfort , dynamic behaviour or strength.
4.1 EFFECT OF THE PRESENCE OF BRIDGE IN THE TRACK Introducing a bridge under a LWR means, effectively, that the LWR track is resting on a surface subject to deformation and movements, hence causing displacements of the track. Given that both track and bridge are able to move, any force or displacements that acts on one of them will induce forces in the other. Interaction therefore takes place between the track and the bridge as follows: i) Forces applied to a LWR track induce additional forces into the track and/or into the bearings supporting the deck and movements of the track and of the deck. ii) Any movement of the deck induces a movement of the track and an additional force in the track and, indirectly, in the bridge bearings.
8
4.1 PARAMETERS AFFECTING THE PHENOMENON A distinction can be made between bridge parameters and track parameters. 4.1.1BRIDGE PARAMETERS a) Expansion length b) Span length c) Support stiffness d) Bending stiffness of the deck e) Height of the deck 4.1.2 TRACK PARAMETERS
a) Track resistance b) Cross sectional area of the rail 4.2 ACTIONS TO BE TAKEN INTO ACCOUNT
The cases that could lead to interaction effects are those that cause relative displacements between the track and deck. The cases concerned are as follows: i)
The thermal expansion of the deck only, in the case of LWR or the thermal expansion of the deck and the rail, wherever a rail expansion device is present.
ii)
Horizontal braking and acceleration forces
iii)
Rotation of the deck on its supports as a result of the deck bending under vertical traffic loads
iv)
Deformation of the concrete structure due to creep and shrinkage 9
v)
Longitudinal displacements of the supports under the influence of the thermal gradient
vi)
Deformation of the structure due to the vertical temperature gradients
In most of the cases, the first three effects are of major importance for the bridge design. 4.3 PERMISSIBLE ADDITIONAL STRESSES IN CWR ON THE BRIDGE
Theoretical stability calculations, on UIC60 CWR, 90 UTS, minimum curve radius 1500 m, laid on ballasted track with concrete sleepers and consolidated >300 mm deep ballast, well consolidated ballast, give a total possible value for the increase of rail stresses due to the track/bridge interaction are; i)
The maximum permissible additional compressive rail stress is 72 N/mm2
ii)
The maximum permissible additional tensile rail stress is 92 N/mm2.
4.4 ABSOLUTE AND RELATIVE DISPLACEMENT
Limits have to be placed on the displacement of the deck and track in order to prevent excessive deconsolidation of the ballast . The displacement limits also play a role in li miting indirectly the additional longitudinal stress in the rails. These limits are as follows:
10
i)
The maximum permissible displacement between rail and deck or embankment under braking and/or acceleration forces is 4 mm.
ii)
In the case of CWR on ballasted track with expansion devices, the maximum permissible absolute horizontal displacement of the deck under the same loads is 30 mm.
4.5 END ROTATION OF THE DECK
The end rotation of a bridge deck due to traffic loads is an important factor for determining satisfactory track/bridge interaction behaviour . In order to determine an appropriate limit to the end rotation of a bridge deck it is necessary to consider also other criteria such as dynamic effects (ballast maintenance) and passenger comfort. Under vertical loads, the displacements of the upper edge of the deck end must be limited in order to maintain ballast stability. Obviously, the effects of this displacement must be added to temperature variation and of braking/acceleration. i)
In the case of CWR on ballasted deck, the permissible displacement between the top of the deck end and the embankment or between the tops of two consecutive deck ends due to vertical bending is 8 mm.
ii)
The maximum vertical displacement of the upper surface of the end of a
11
deck relative to the adjacent construction has to be li mited. 4.6 SUPPORT REACTION
The interaction results in horizontal support reactions at the fixed elastic supports , and these must be taken into account along with conventional support reactions when calculating the structure and supports. 4.7 RAIL EXPANSION DEVICES
It is preferable to avoid expansion devices in the track, but one should always be inserted at the free end of the deck if the total additional rail stress or the displacements exceed the permissible values. Using the possibility of locating the fixed support at the middle of the deck , it is possible to increase the length of a single deck carrying CWR. Generally speaking , this will lead to the following conclusion: The maximum expansion length of a single deck carrying CWR without expansion device will be: i)
60 m for steel structures carrying ballasted track
ii)
120 m for steel structures deck with fixed bearing in the middle
iii)
90 m for structures in concrete or steel with concrete slab carrying ballasted deck track
iv)
180 m for structures in concrete with fixed bearing in the middle
In the case of unballasted deck ,a specific evaluation should be done. Even when the calculated stresses and displacements do not exceed the permissible values , it may be necessary to fit an 12
expansion device in the track. This is the case when the daily variation of the deck exceeds the permissible values taking into account the track maintenance conditions . The calculations are made using a precise track arrangement ( CWR ,expansion devices , joints ). When for any reason e.g. maintenance works consisting of severing CWR this track arrangement is modified , the service conditions on the bridge should be reviewed . The bearings could also be modified. A new analysis of the interaction effects should be made , when the function8ing of the bearings and/or of the supports is changed. 4.8 CALCULATIONS USING UIC REPORT
For dimensioning the structure from the point of view of track/bridge interaction, three different steps of calculation can be used: i)
Predimensioning method
ii)
Point 2 i.e. calculation without interaction and point 3 i.e. calculations with interactions
iii)
Calculations with computer program
5.0 WORLD RAILWAYS - PRESENT SCENARIO Presently various practices are being followed to continue LWR/CWR over ballasted as well as unballasted girder bridges world over. The new bridges are being designed taking into account the LWR forces with/without expansion devices and various types of fastening systems viz. Zero Longitudinal Restraint 13
(ZLR) elastic fasteners and low toe load elastic fasteners. Also innovative type of expansion devices to cater for large expansion/contraction is being tried. The simulated studies based on computer modelling are adopted to assess the realistic LWR forces as well as displacements due to track/bridge interaction. The some of them are being discussed b elow: 5.1INDIAN RAILWAYS
On Indian Railways Manual of Instructions on Long Welded Rails, 1996, govern the laying and maintenance of LWR/CWR. The various provisions regarding LWR on ballasted/unballasted girder bridges are mainly based on the concept of rail free fastenings and the maximum gap at fracture as 50 mm. However, for ballasted deck bridges no design of rail free fastening is available on IR. The details of provision in this regard are placed at annex I .The latest developments are as under: i) An extra ordinary meeting of TSC was convened at Pune in Oct’02to deliberate upon various issues connected with the subject. Following proposals were considered by the TSC: a) Fixing permissible span of bridge for provision of LWR pier to pier. b) Fixing permissible span in case of single span girder bridge with provision of SEJs on both the approaches. c) Use of existing provisions of 190 mm gap SEJs. d) Introduction of zero longitudinal resistance fastenings.
14
e) Procurement of software programme for analysis of forces interacting between bridge and rail. f) Experimental/field trials to understand the thermal interaction between bridge and track in case of LWR with elastic fastenings. g) Study of the provisions on foreign railways. During deliberations B&S Directorate of RDSO brought out following important points. a) Provision of LWRs pier to pier with SEJ on each pier results in discontinuity preventing dispersion of longitudinal force to approaches. This results in transfer of additional forces to substructure. This substructure and bearings in existing bridges will need to be checked for the additional longitudinal forces. b) Minimum 30 m approach length is needed for dispersion of longitudinal forces while the LWR manual provides for SEJ at 10 m distance from abutment. At the end of deliberations committee made following recommendations: 15
a) No change in existing provisions of LWR on existing bridges. b) All new bridges built or rehabilitated, whether ballasted or unballasted, should incorporate forces due to LWR. The design may be done using full toe load/partial toe load of ERC clips. Bridge rules should be accordingly revised. c) Field trials are to be taken up to study behaviour on LWR on ballasted deck bridges. d) RDSO should carry out checks in respect of dispersion of longitudinal forces to the approaches in bridges with pier to pier LWRs. RDSO should also obtain performance of pier to pier LWRs, wherever provided on Indian Railways. e) RDSO should develop drawings for provision of SEJ on FRP sleepers. f) Committee recommended following permissible length of single span for bridges with LWRs with provisions of 190 mm
16
gap SEJ at a distance of 30 m away from the abutments: Temp Zone
Length of span
I
146 m
II
110 m
III
87 m
IV
75 m
Committee recommended development of drawing for following new designs of SEJs: a) One/two gap SEJ using crane rails b) Fixed switch type SEJ similar to the design used by DMRC c) New design of SEJ already under trial Based on these, RDSO has developed a new design of SEJ using crain rail having web thickness of 44 mm avoiding any bend in stock & tongue rails. This will result in reducing fractures of stock rails. This design has not been provided with any bolt and therefore, maintenance of this SEJ will be much easier in field.
17
RDSO has also developed a new design of SEJ with 190 mm gap for UIC 60 kg rails with which continuation of LWRs on longer bridges would be possible. To facilitate continuation of LWR o ver bridges, the design of special PRC sleepers required for 300 mm gap SEJ has been developed. For continuation of LWR through bridges with channel sleepers, creep anchors are used on 04 sleepers as per LWR manual. There was a need to develop more effective creep anchors, as the present design of V type creep anchors was not very effective on channel sleepers. Keeping this in view, two new designs of creep anchors to drg no. EDO/T-2228 to 2231 & EDO/T-2232 to 2235 has been developed and issued to Railways for use with channel sleepers on trial basis. MRTS, Chennai approached RDSO for clearance of laying of LWR for a length of 7.6 km on elevated structure. LWR on such a long elevated track is being provided for the first time on Indian Railways. The proposal was scrutinised and the calculations of additional rail stresses induced due to interaction forces were checked. The proposal has been cleared on trial basis by RDSO and consequently Railway Board communicated their approval. This a long jump in the direction of provision of LWRs on long bridges in a bi g way.
5.2 SOUTH KOREAN RAILWAYS DangSan bridge of Seoul subway no 2 was rebuilt for safety reasons from Dec’ 1996 to Dec ‘ 1999. To have maintenance free system on the bridge, Cologne Engg alternative base plate and C WR with ZLR (Zero Longitudinal Restraint) were provided for 125m south approach section and 120 m long north approach section. This was adopted on Korean Railways for the first time.
18
5.3 GERMAN RAILWAYS (DB)
A unique system has been adopted on German Railways to avoid interaction between unballasted steel girder deck and track. In this design a solid steel bar with a side groove is welded on top of the stringers. On this rest special bearing plates, which have a jaw, which slide in the groove. Sleepers rest on these bearing plates, the connection being secured by bolts/sleeper screws. This arrangement permits relative movement between sleeper and girder instead of conventional rail free fastening concept of relative movement between rail and sleeper. In this design it is usual to provide a SEJ after 400 m
19
even though a length of 800m on a bridge was provided without an expansion joint with this system. The main advantages claimed are: i)
Track structure on top is unaffected and need for special fastening is obviated.
ii)
The arrangement is much stronger than rail free type against vertical buckling.
iii)
The arrangement maintains very good alignment.
iv)
No maintenance of anchor bolts/ special fastening is involved.
v)
There is no problem of sleeper seat corrosion.
The main problem with this design is that resistance to creep being very small; wider gap at rail fracture is to be exp ected. The Germans carry out USFD at increased frequency at such locations and their observation is that gap formed is not dangerous.
5.4BRIDGE ON HIGH SPEED LINE BRUSSELS-LILLE (JUNCTION FOR PARIS-LONDON)
The bridge is 438 m long consisting of 7 spans. The main span, which crosses the river Scheldt, is 120 m long. The bridge carries two parallel-ballasted tracks with UIC 60 rails laid on concrete sleepers.
20
The computer modelling with full CWR track was done using the computer program PROLIS20 developed by Delft University of Technology, Netherlands. The complete track and bridge configuration was modelled in a discrete system consisting of 263 nodes and 416 elements assuming construction symmetry over both the tracks and interaction forces and displacements were studied. It was concluded by the studies that the application of expansion devices in high speed tracks on existing bridges, as a means to prevent excessive longitudinal displacements and forces, is not attractive due to comfort, safety and maintenance aspects. An alternative and very effective solution is possibly the use of zero longitudinal restraint (ZLR) fastenings over some lengths of the track. The calculations, carried out in this respect, show a considerable reduction of track displacements, track forces and the relati ve sleeper/ballast displacements. This reduction depends upon the length over which these fastenings are installed. The use of ZLR fastenings, though not widely accepted yet and the construction perhaps requiring some further development, should be given more attention considering the favourable theoretical results achieved. Based on this conclusion the CWR
21
was designed on the bridge with partly ZLR fastenings and without expansion joints, which even resulted in saving in investment costs and fulfils the technical requirements. 5.5DIRECT FIXATION TRACK ON THE MISSION VALLEY WEST LRT EXTENSION
The Mission Valley West light rail extension in San Diego, California opened for service in November 1997.The Metropolitan Transit Development Board contracted with Boyle Engineering Corporation in 1992 to design the 6.1 mile extension and its three elevated and four at grade stations. CWR forces are generated as thermal expansion and contraction of the rails occur. Usually, bridges are free to expand and contract at the abutments and hinges, but attaching the rails directly to the bridge deck would prohibit normal movement. For this reason Boyle employed a design that allows the rails to move longitudinally or breathe near the hinges and abutments without forcing the bridge to move with it. However, some control of the rail is required to limit the size of the gap in the event of a rail fracture. The resulting design uses two types of direct fixation fastener plates (DFF’s) i.e. i)
One that allows longitudinal movement of the rail, Zero Longitudinal Restraint (ZLR) fasteners, and
ii) Another that restraints it, Standard Restraint (SR) Fasteners. The primary difference between the two is that the ZLR direct fixation fasteners use a special Pandrol Clip and a ste el toe 22
plate that prevents the clip from contacting the base of the rail. A small gap between the clip and toe pl ate combination and the rail leaves enough room for longitudinal movement but still confines the rail within the rail seat. The resulting desi gn allows the bridges to expand and contract as designed while limiting the effects of CWR forces on the structure. 5.7
5.6THE PANDROL RAIL FREE OR ZERO LONGITUDINAL RESTRAINT (ZLR) SYSTEM
The PANDROL Corporation has developed a fastening system based on rail free concept. It maintains the rail to correct track gauge, provides the desired restraint against rail roll, yet permits the rail to move longitudinally through the assembly. With the help of these fasteners long welded rails can be installed o ver and beyond
23
bridges without any additional requirement to compensate for the differential thermal expansion. The first rail free installation was made on the Ben Franklin Bridge, which spans the Delaware River in Philadelphia, USA. The rail free feature was obtained by incorporating pressed mild steel cover plates over the shoulder housing and firmly held in place by a special pandrol clip which is inserted into the base plate in the traditional manner. With the cover plate locked over the shoulder housing, the rail free action is obtained by designing into the assembly a nominal 4mm clearance between the underside of the cover plate and the rail foot. The pandrol Rail Free or Zero Longitudinal Restraint System provides necessary interface between the differing thermal movements of rail and its supporting structure. The Rail Free installations have been used in Jordan, Hong Kong, Australia, Canada, Liberia, Norway, Sweden and South Africa.
24
5.7DESIGN OF CWR ON A SUSPENSION BRIDGE (PORTUGAL)
A CWR track was designed for a 2.3 k m long suspension bridge over the river Tagus in Lisbon, Portugal. It is one of the longest bridge of world with CWR track. It also consists one of world ‘ largest rail expansion joint with a capacity of 1500 mm movement combined with the ability to disperse the angular rotation caused by the stiffening truss. The 2.3 km long continuous stiffening truss deflects 5.3 m (17 feet) at the centre of the bridge. The CWR is designed for such a flexible support and for the resulting change in grades. In addition, the CWR also has to negotiate, at the bridge ends, significant angular bend caused by the behaviour of the truss under railway loading. The track structure was kept independent of the longitudinal forces in the stringers but had sufficient fixity to maintain the vertical and transverse constraints of the track against buckling. The expansion assembly consists of moving telescopic girders mounted on vertical rollers and restrained by horizontal rollers between the stationary girders. Longitudinally split rails are mounted on these girders .The construction work was started in 1992 and completed in 1999 with a maximum permissible speed of 60 kmph. The choice of various components such as rails, guard/check rails, low toe load fasteners, slide plates, expansion assembly etc are described in brief below: 5.7.1 The original suspension bridge was constructed in 1966. The main span is 1012.88 m, the side spans are 483.42 m and the three backstay spans are approximately 100 m each. One of the 25
unique features of this bridge is its 2300 m (7472 ft) long truss continuing over the suspended main, side and ba ckstay spans. This was purposely done to prevent large break in grade under train loading. The bridge was built to carry four lanes of highway traffic at the upper deck level with design provisions for a second phase construction to allow future railroad track installation at the bottom chord level. In 1992, it was de cided to add two railroad tracks at the lower level and to widen the upper deck to accommodate six highway lanes with minimum interruption to the existing traffic.
26
5.7.2 SELECTION OF THE TRACK
The main considerations of track on a suspension bridge of this type are as follows: i)
Aerodynamically acceptable behaviour
ii)
Low dead load
iii)
Independence from stresses in truss
27
iv)
Lower noise and maintenance levels
v)
Safety during derailment conditions
vi)
Capacity to accommodate a large expansion joint at ends
After examining several alternatives such as steel ties, direct fixation etc CWR with elastic fasteners on wooden sleepers at 60 cm spacing was considered as the best suited for this type of bridge. The track was designed to UIC standards. The open deck was used in the section model for the wind tunnel testing and proved acceptable. 5.7.3 TRACK LAYOUT ON THE BRIDGE
The track layout on the bridge is divided into different zones on the 2300 m length of the bridge as follows: i)
standard zone
ii)
anchor zone
iii)
end zone
iv)
expansion zone
v)
creep free zone
The standard zone is also a rail slip zone, approximately 2150 m long and consists of CWR. The track in this zone can flex to follow the different deflected shapes of the suspended truss with maximum deflection at center is 5.3 m . The continuous rail can slip in its chairs longitudinally within the li mits of the zone without picking up the axial forces of the stringer that supports it. At either end of the bridge the CWR is terminated over a short length wherein the rail is anchored to the stringer through an 28
anchor joint. The anchor joint is a specially designed insulated connection where in the rail is rigidly connected in the longitudinal direction but the rail is allowed the usual resilient support. This connection will provide the uniformity of the track modulus and prevent uneven wear of the rail. End Zone – This is a short stretch of track between anchor
joint and start of expansion joint complex. Bonded rails at on e end and insulated rail joint at the other end is provided for bypassing the track circuit over the expansion joint. Expansion Zone – The expansion zone accommodates the
expansion complex. The expansion zone is kept free of CWR forces. Bonded rail joints are provided at each end for easy replacement of the expansion joint. Creep Free Zone – In order to protect the expansion zone and
to arrest any possible longitudinal movement, the creep free zone is provided with extensive creep anchors and an anchor joint at the approaches. A detailed track chart was prepared for every panel of the bridge specifying the grade, elevation, rails, check rails, joints, ties, fittings etc.
29
Tension Clip Mark 3 – The design and selection of the tension
clip is a salient characteristic of this track. The rail needs to adjust to the deflection of the long stiffening truss as the truss deforms under live load. The rail does that by slipping longitudinally. Therefore, a new clip was developed, by modifying the standard SKL-12 clip, as manufactured by Vossloh of Germany. The modified clip induced a low toe load of 300 kg instead of the standard toe load of 1300 kg. The modified clip has the added advantage of a partial rail free type
30
fastener, which allows the rail to slide longitudinally on its chair. As a result, the running rail stresses remain independent of the rail stringer stresses. Further, to facilitate sliding, a 3 mm stainless steel plate is provided underneath the rail.
5.7.4 EXPANSION ASSEMBLY COMPLEX. The suspension bridge truss is comparatively a flexible structure. The railway loading consisting of h eavy concentrated loads, when moving on this flexible bridge causes loc al and global deformation of the truss. The railway track experiences steep grades and changes of grades at the center and specifically at the ends of truss. This has a significant effect at the end producing an angular bend in the rail. The thermal expansion of the trusses is significant at the ends. In addition, the truss ends also move in and out due to deflection of the truss under the live load depending upon the location of the load. The maximum calculated movement at the ends for th e design was 1500 mm. If the running rail is rigidly fixed to the end stringer and the transition girder will result in a kink in the rail and high bending and fatigue stresses. Therefore, the rail is mounted on resilient chairs capable of allowing the rail base to
31
rise and fall to adjust for the imposed curvature. Handling of the constant cyclical longitudinal movements and the angular bends in the running rail is a complex problem with respect to a railway track, which was resolved by designing a unique expansion assembly complex. The expansion assembly used on this bridge is one of the largest and most complex expansion assemblies in the world. The expansion system is a combination of appurtenances located at either end of the bridge. The assembly was specially designed to address the existing conditions such as restricted space, high expansion range and construction of the unit under traffic conditions on an existing bridge and after a detailed research and studies of various existing systems the split rail type of expansion joint was developed. The other designs like switch expansion joint, moving sleeper type etc were not adopted due to large space requirements at the end of the bridge and more maintenance requirements due to large number of moving parts. Considering the limited space available at the end of the bridge, the telescopic girder type expansion joint was selected as the most suitable. This expansion joint is unique in those two functions, such as, longitudinal movement and dispersion of angular bend, have been accommodated in a limited space of 8.5 m. It is the most compact, yet one of the largest expansion joints in the world. The expansion assembly complex consists of the following important components i) Transition girder and telescopic girders ii)
Split rails for rail expansion
iii)
Check rail and its expansion arrangements
iv)
Angular bend dispersion components 32
v)
Telescopic girder mountings
In this arrangement to cover the expansion gap of 1500 mm at the ends and to flex for the angular bend, a short 6.0 m transition girder was designed. This also acts as the inner moving telescopic girders for expansion. The moving telescopic girder is inserted between the two stationary telescopic girders and held laterally and rigidly by two horizontal rollers with a preload force of 100 t in order to maintain clearance of 6 mm between stationary and moving girders. These girders are designed very stiff, structurally, to limit deflection to not more than 1 mm.
33
On these girders L shaped split rails having top profile of UIC 60 railhead have been used. These split rails are made of high manganese steel, forged and surface hardened in fine laminated perlite structure to a level of 1150 N/mm2 for a depth of 25 mm for wear resistance. In order to control and guide the wheel to roll at the gauge face, a U69 type high performance rolled steel check rail is placed at 45 mm clearance. The check rail is kept
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continuous over the expansion gap. It is extended continuously from the truss over the telescopic girder and expansion joint up to the approaches to provide lateral restraint to the wheel flange. The check rails have been provided with an expansion arrangement on the approaches. In order to uniformly distribute the angular bend of maximum .06 rad and permit rail to assume a curvature the rail is fixed on special type of chairs. A dispersion length of 2052 mm was considered sufficient on the transition girder and similarly on end stringer. The horizontal rollers are mounted on the stationary girders. The vertical steel rollers on the bronze bearings are mounted at the bottom of the telescopic girder at the far end. The steel assemblies in which the rollers are housed are designed with close tolerance to resist lateral forces and uplift forces caused by the passage of wheel loads. These rollers are critical in maintaining gauge and close clearances in the split rail. The double track with CWR and expansion joint unit has been successfully installed and after completion of required testing, the bridge has been officially opened in July 1999.
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6.0 CONCLUSION The world over efforts are being made to increase the l ength of the LWR/CWR track over ballasted/unballasted deck bridges to reap the overall benefits of LWR track in the form of improved safety, riding comfort, reduced maintenance and anti sabotage properties. But at the same time the issue of track/bridge interaction, being of complex nature, has to be studied in more detail. The UIC 774-3R report is a long step in this direction. Efforts are also on to develop various fastening systems in the form of zero longitudinal restraint (ZLR), direct fixing fasteners (DFF) and low toe load longitudinal restraints. Similarly to obtain joint less track in real sense even the CWRs are being designed without expansion joints in the near vicinity of the bridges. On Indian Railways, RDSO has been directed by the extra ordinary TSC meeting in 2002 to evolve methodology and technical know-how to have longer lengths of bridges under 36
LWR on existing bridges and to design all new bridges with LWR track taking into account the effect of track/bridge interaction at design stage itself.
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7.0 REFERENCES i) Long welded rails, 2005 (IRICEN publication) ii) UIC Code 774-3R Oct 2001 iii) Report on training in Germany part II by S M Vaish iv) Long welded rails on girder bridges by L S Mittal v) Long welded rails on bridges by Vinod Kumar vi) LWR on bridges by H K Jaggi (Article in IPWE journal) vii) Improved knowledge of CWR track by Coenraad Esveld viii) CWR for Seoul subway no. 2 Dangsan Bridge by ZLR by Lee Duck Young, Kong Sun Yong, Kwon Soon Sub, Kim Eun ix)
Direct Fixation Track on the Mission Valley West LRT extension by Dane Schiling, P. E. Associate Engineer, Boyle Engineering Corporation
x)
Design of High Speed Track on Long Bridges by Prof .Dr.Ir. C. Esveld , Professor of Railway Engineering TU Delft University, Netherlands
xi)
Annual report of RDSO Track Directorate for 2003- 2004
xii)
Design of Continuous Welded Rail on Suspension Bridge A Technical Paper for AREMA by Ranganatha r. Rao and Sudhir Sanghvi- Parsons Transportation Group
xiii) Pandrol Rail Free or Zero Longitudinal Restraint System by Pandrol.com xiv)
Manual of Instructions on Long Welded Rails, 1996
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Annexure-1 RELATED PROVISIONS OF THE LWR MANUAL FOR LAYING LWR ON BRIDGES.
4.5.5 Location of SEJ: The exact location of SEJ shall be fixed taking into account the Location of various obligatory points such as level crossings, girder bridges, points and crossings, gradients, curves and insulated joints. SEJ with straight tongue and stock shall not be located on curves sharper than 0.5 degree (3500 m radius) as far as possible. SEJ shall not be located on transition of curves.
4.5.6 Bridges with ballasted deck (without bearing): LWR/CWR can be continued over bridges without bearings like slabs, box culverts and arches.
4.5.7 Bridges with/without ballasted deck i) LWR/CWR shall not be continued over bridges with overall length as specified in para 4.5.7.1 for BG and not more than 20 metre for MG. ii) Bridges on which LWR/CWR is not permitted/provided shall be isolated by a minimum length of 36 metre well anchored track on either sides.
4.5.7.1 i) Bridges provided with rail-free fastenings (single span not exceeding 30.5 metre and having sliding bearings on both ends) Overall length of the bridge should not exceed the maximum as provided in Table-1 with following stipulations: a) Rail-free fastenings shall be provided throughout the length of the bridge between abutments.
b) The approach track upto 50 m on both sides shall be well
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anchored by providing any one of the following: i) ST sleepers with elastic fastening. ii) PRC sleepers with elastic rail clips with fair ‘T’ or similar type creep anchors. c) The ballast section of approach track upto 50 metres shall be heaped upto the foot of the rail on the shoulders and kept in well compacted and consolidated condition during the months of extreme summer and winter.
4.5.7.1 ii) Bridges provided with rail-free fastenings and partly box-anchored (with single span not exceeding 30.5 metre and having sliding bearings at both ends) Overall length of the bridge should not exceed the maximum as provided in Table-1 with following stipulations: a) On each span, 4 central sleepers shall be box-anchored with fair ‘V’ or similar type creep anchors and the remaining sleepers shall be provided with rail-free fastenings. b) The bridge timbers laid on girders shall not be provided with through notch but shall be notched to accommodate individual rivet heads. c) The track structure in the approaches shall be laid and maintained to the standards as stated in item 4.5.7.1 (i) (b) and (c) above. d) The girders shall be centralized with reference to the location strips on the bearing, before laying LWR/CWR. e) The sliding bearings shall be inspected during the months of March and October each year and cleared of all foreign materials. Lubrication of the bearings shall be done once in two years.
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4.5.7.1 iii) Welded rails may be provided from pier to pier with rail-free fastenings and with SEJ on each pier. The rail shall be box anchored on four sleepers at the fixed end of the girder if the girder is supported on rollers on one side and rockers on other side. In case of girder supported on sliding bearings on both sides, the central portion of the welded rails over each span shall be box-anchored on four sleepers. See Fig.4.5.7.1 (iii).
4.5.7.1 iv) LWR/CWR may also be continued over a bridge with the provision of SEJ at the far end approach of the bridge using rail free fastenings over the girder bridge (Fig. 4.5.7.1 (iv)). The length
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of the bridge in this case, however, will be restricted by the capacity
of the SEJ to absorb expansion, contraction and creep, if any, of the rails. The length of the bridges with th e above arrangement that can be permitted in various rail temperature zones for LWR/CWR with SEJs having maximum movement of 120 mm and 190 mm are as follows: -
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