CI/SfB 372 (21)
Sep t ember 1986
BRICK CLADDING TO STEEL FRAMED BUILDINGS
COMMENTARY
PUBLISHED BYTHE BRICK DEVELOPMENTASSOCIATIONAND BRITISHSTEELCORPORATION
F
BRICKCLADDING
TO
SEPTEMBER 1986
STEEL FRAMED BUILDINGS
Keens House, Andover forTSSTrust Company
PUBLISHED JOINTLY BY THE BRICK DEVELOPMENT ASSOCIATION AND BRITISH STEEL CORPORATION.
Ac knowledgements A number of Engineers and Architects have contributed to the development of this technical manual and by commenting on the final draft. There are too many to acknowledge individually but their assistance is acknowledged and appreciated. This manual was prepared under the direction of a Joint BOAIBSC Steering Committee consisting of the following :P. R. LUMBARD, CEng ., MISt ruc t E. - BOA.
J. MORTON, BSc ., PhD., CEng ., MICE., MlnstM. - BOA. B. W. J . BOYS, CEng ., FISt ructE. - BSC. J. ROBINSON, BSC., CEng., MIM., Mlnst M. - BSC . How to use the Manual 1. 2. 3. 4. 5. 6.
Read the text . Study the key location diagrams (Figs. 7.0.1 , 7.0.2., 7.0.3.). Study appropriate details. Modify if required. Refer to text if required. Refer to references if required.
Text and d rawings prepared by:·
-
R. E. BRADSHAW, MSc ., CEng., MICE., FIStruct E., MConsE. G. BUCKTON, CEng., FIStruct E., MWeid l., MConsE. S. W. SOUTHWICK, BTech., CEng., MISt ructE. BRADSHAW BUCKTON & TONGE
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CONTENTS Page 2
List 01 Tables List 01 Figures
3
1.0
Introduction
5
2.0
Bulidablll ty 2.1 General 2.2 Brickwork 2.3 Steelwork 2.4 Buildability - An Example Resistance to Rain Penetration 3.1 Brickwork 3.2 Assessing the Exposure 3.3 Design Details, Specification and Workmanship Durability 4.1 Brickwork 4.2 Cavity Wall Ties and Frame Ties 4.3 Structural Steel Frame 4.4 Bimetallic Corrosion Accommodation 01 Movement 5.1 General 5.2 Thermal Movement 5.3 Moisture Movement 5.4 Restrained and Unrestrained Movements 5.5 Assessment of Movement in Masonry 5.6 Preferred Locations of Movement Joints 5.7 Sealing Movement Joints 5.8 External Masonry Walls and Steel Framed Buildings Stability ............ 6.t General 6.2 Horizontal and Vertical Lateral Support Conditions 6.3 Cavity Wall Ties 6.4 Frame Ties 6.5 Methods of Fixing Wall Panel Restraint Ties to Steel Frames. 6.6 Masonry Panels Containing Openings
7
3.0
4.0
5.0
6.0
13
t7
29
43
Beddington House, Wallington for Haslemere Estates pic
LIST OFTABLES
I All Tables can be found within each relevant section and denoted asfollows:T2 .1 denotes Section 2, Table 1 Olympic House , Woking for Norwich Union Assurance pic
T2 .1 Clay brick tolerances in mm (based on BS:3921 Table 3limits of size) T2 .2 Calcium Silicate (sandnirne , f1intllime) BrickTolerances in mm (based on BS :187Table 1) T3 .1 Classi fication of exposure to local wind-driven rain (BS:5628: Part 3: Table 10) T3 .2 Mortar mixes (BS :5628 : Part 3 :Table 15) T4.1 Durability of masonry in finished construction (BS:5628: Part 3 : Table 13) T4.2 Anchorages , dowe ls and fixings (BS:5628: Part 3 : Table 1) T4.3 Protection of metal components (other than wall ties) built into masonry (BS :5628 : Part3:Table 14) T4 .4 Risk of additionai corrosion from bimetallic contact T5 .1 Properties needed to assess changes of size and shape of materials T5 .2 Examples of service temperature ranges of materials (UK only) T5.3 Recommended compression movement joint widths T5.4 Basic properties of suitable joint sealants T5.5 Theoretical deflections for steel frame members supporting and/or restraini ng an external masonry cavity wall T6 .1 Characteristic strengths of wall ties used as panel supports (BS :5628 : Part 1:Table 8) T6.2 Selection olties (BS :5628 : Part 3 :Table 9(b)) T6.3 Spacing olties (BS :5628: Part 1:Table 6) T6.4 Suitability of alternative fixings for wall panel restraint ties to steel frame.
2
LI ST OF FIGURES
I All figures can be found at the end ot each relevant section and denoted asfollows:F2.1 denotes Sect ion 2 Figure 1. F2.1 Accommodation of tolerance on brick sizes in short runs of brickwork F2 .2 Horizontal expansion joi nt for multi-storey buildings outl ining the fixi"li! of continuous support ang le to steel noo r beam in order to provide tolerances for vert ical and horizontal variations. F2.3 Horizontal expansion joint for mull i-stor ey build ings outl ining the fixinll of cont inuous support ang le to composite floor slab in order to provide tolerances for vert ical and horizontal variations . F3.1 The durability and resistance to rain penetration of different mortar joint profiles . F4.1 Masonry condition or situation affecting the spec ification of the bricks and mortar. F4.2 Designs for minimising bimetallic corrosion. F5.1 Typical expansion and contraction joint. F5.2 Preferred locations of movement joints. F5.3 Preferred location of movement joi nts at column positions . F5.4 Preferred locations of movement joints at cornercolumns . F5.5 Typical deflections and sway of single storey portal frame building. F5.6 Schematic illustration of differential movement between external wall and structure. F5.7 Comparison between external cavity walls in mult i-sto rey buildings :(a) supported off steel frame (b) independent of steellrame F6.1 Details provid ing simple and fixed vertical lateral support. F6.2 Details provid ing simple and fixed horizontal lateral support. F6.3 Typical examples of frame ties. F6.4a Frame tie details to accommodate vertical and/o r horizontal
movement.
-
F6.4b Frame tie details to accommodate vertical and/or horizontal
movement. F6.5 Mernative non-standard frame tie des igns for increased flexibility. F6.6 Typical spacings of double triangl e and vertical twist cavity wall ties and panel restra int ties in single storey and med iumlh igh rise buildings. F6.7 Methods of fixing fram e ties to the main structur e.
Hills Road , Cambridge for Caltrust Developments Ltd and Standard Life Assurance pic
3
30 Garrard Street , Reading for Bov is Property Division
4
SECTION 1
I
INTRODUCTION "Tt;e aim of this publication is to provide guidanceto
-
architects, engineers and technicians with illustrations of modern practice combining steel frames and brickwork cladding in non-domestic buildings to achieve stability, durability, buildability and long-term serviceability. The use of brickwork with a steel frame is not new it was the most commonly used cladding for framed bUildings during the 1920's and 1930's. Many of these buildings continue to give good service and will do so into the 21 st century. However, the way in which we use these two materials today has changed. For example, all structural materials are now designed to higherstresses than wasthe case 50 yearsago,withthe aim of reducing the amount of structural material within buildings. Most modern structures are thus significantly more slender and lighterthan their predecessors, and deflections and sways need to be considered more fully. When combined with an increasing requirement for longer spans, flexibilityof use and the abilityto accommodate a rangeof services, itwillbe appreciated that moderndesign is more complex. The publication includes a range of acceptable details in common use. No detail is universal, however, and slight modification by the designer may be required to suit a particular application. The annotation is intended to assist in highlighting the key factors involved. The text has been kept to a minimum. For an understanding of the background and principles involved, reference must be made to the various publications referred to in the text. This brochure is not intended to be definitive or exhaustive and the individual designerwill need to use his ownjudgementas to whichdetailsand which modifications are necessaryfor a particular project. There are clearly many special applications and situations which are beyond the scope of a publication of this type.
5
William Booth H for Salvation Ar::'~se, Hull
6
, SECTION2!
BUILOABILITV 2.1
GENERAL Tolerances inconstruction andmovement in all types of cladding and supporting structures need to be considered in combination. Both can affect fixings, bearings and joints and so influence watertightness and safety. For example, if joints are small as a
result ofinaccuracies andmovements large in relation to joint width, sealants may becom e over-strained, leading to rain penetration. Further movement after the joint has closed ca n damage fixings and dislodge cladd ing. Principal factors determ ining the effects of movements and inaccuracies are:i) Maximum size of external wall panels between horizontal and vertical movement joints, and expected change in size due to moisture content and temperature changes. ii) Expected changes to supporting structures due to moveme ntlthermal effects together with deflection and creep . iii) Relative direction of movements l.e, whether the two elements of a member move in the same or oppos ite direction. iv) Size and accuracy of components manufacturedoff site, suchas windows, required to fit into pre-forme d openi ngs.
Tab le 2.1
Dimensional inaccu racie s can only be accommodated at the joints and it is necessary to assess whether the proposed jointing method can adeq uately cope with such variations together with any subsequent movem ent. Guidance on the assessment of dimens ional accuracy and the select ion of appropriate jointing methods are given in the follOWing codes of practice:BS:5606 "Accuracy in BUilding" (Ref. 1). BS:6093 "Design of Joints and Joi nting in Building Construction". (Ref. 2).
2.2
BRIC KWORK When design ing in brickwork it is desirable to work in multiple s of half brick lengths (112.5mm co-ordinatinq size) to avoid cutting and unsightly jointing . BOA Design Note 3 "Brickwork Dimensions Tables" (Ref. 3) provides useful tab les. Clay and Calcium Silicate bricks are normally produced within the limits of size stated in BS:3921:1965 (Ref . 4) and BS :167: 1976 (Ref. 27). These are summarised in Table 2.1 for clay bricks and Table 2.2 for calcium silicate bricks .
Lim its of s ize of cla y bricks (based on BS 392 1 table 3 ) Work size
215 (lenl1th) 102'5 (Width) 65 (height )
Permitted limits of size
- - -- - - -- Minimum --Maximum for 24 bricks
for 24 bricks
5235 2505 1605
5065 2415 1515
Tab le 2.2 Calciu m s ilicate (sandlllme, flint/li me) bric k tole rances In m m (based on BS 167 ' 1978 Table 1)
-
Work size Max. limit of manufacturing size Min. limit of manufacturing size
Length 215
Wid th 102.5
Hei ght
217
105
65 67
212
101
63
Note: Special shaped bricks to BS 4729 : 1971 usually require longer delivery periods and are not manufactured to any stated tolerance. Always consult the manufacturer when incorporating architectural featuresrequiring bricksto a specifictolerance.
r - - - - - -- - -----,
Kings Meadow, Reading for Speyhawk Land Estates
7
The variation in brick sizes can normally be taken Into account by the.bricklayer adjusting the width of the mortar JOInts but special care may need to be taken with short lengths of brickwork. Bricks may need to be specially selected either on site or by arrangement with the manufacturer to obtain a satisfactory result. Examples of this include piers formed between adJacentope",~sor a single soldier course of bricks on end . FIg 2.1 shows some of the considerations necessary. Specific regurrements for accuracy 01 size need to be wntten Into the specification .
2.3 STEELWORK Hot-rolled sect ions such as universal beams, universal columns, joists and channels etc are produced to the requirements of BS4 : Part 1; 1980 (Ref. 25). A section is desiqnated by the serial (nominal) size in millirnetras and the mass per unit length in kilograms per metre. The designer should be aware of the following points which may affect critical areas of detaillng:a) The actual dimensions of universal beam and universal column sections of the same serial size but of different masses vary. For example, the 254 x 254 serial size UC has five different masses ranging from 73 - 167 kg/m . The actual overan dimensions (in mm) vary from 254 x 254 to 289 .1 x 264.5. A list of common section sizes available today can be found in BS4 : Part 1: 1980 (Ref. 25). b) The British Standard prov ides guidel ines on dimensional rolling tolerances within which all hot-rolled sections are
2.4 BUILDABILITY - AN EXAMPLE A difflCUtIdetail encountered with masonry cladding to mutli-storey framed structures is the horizontal support - and the associated expansion joint. The detail must accommodate variations both vertically and honzontally In the position of the continuous steel supporting angle. Figs . 2.2 and 2.3 Illustrate two possible solutions. The designer WIllhave to assess and specify with care the dImensIonal tolerances to which the contractor must work. CIRIA Technical Note 113"A sugl;lested Des iqn Procedure for Accuracy in BUIlding" (Ref. 5) suggests the followinll procedures:i) Choose details which aVOId conflict between very accurate components and relatively inaccu rate surrounding construction. ii) Choose details which facilitate the adjustment of continuous elements e.g. continuous steel angles supporting the external leaf of brickwork. iii) Generally, avoid specifying 'speci al' or 'high' degrees of accuracy, i.e. assume normal labour, normal construction methods, normal conditions. Special accuracy costs more ; it may not be justifiable. iv) Carry out check calculations so that effect of conflict between components and joints
is minimised. v) Assess and quantify any differential movement that may occur after construction and select the most appropriate type and size of joint. vi) Communicate all requirements clearly to the contractor.
manufactured. These tolerances cover depth and width of section, squareness of flanges and straightness. For example, for serial sizes up to and including 305mm the tolerance on section depth is 3 .2mm and on flange width +6.4mm or -4.8mm. c) Information on fabrication and erection tolerances can be found in BS. 5950 : Part 2: 1985 (Ref. 24) . Specific areas requiring attention include posrtion in plan of a column , verticality of a column, position in plan of beams connected to a column and the level of the steelwork at any sto rey.
B
Figure 2.1 ACCOMMODATION OFTOLERANCE ON BRICK SIZES IN SHORT RUNS OF BRICKWORK 102·5 215 1J.10
102·5
10-.11
_ 215--'._215 ....
J[
10
II
J[
][
)[
II
I
440
I
(a) Theoretical pier si2e - joint width and aJignmeent. 101
212
101
43 4
(b) UndelSized bricl
--
218
440
(d) 0ve1Sized bricl
(e) Piersi2e adjusted to maintain standa1rJ joint 104
104
218
104
446
(e) Pier size adjusted to maintain standardjoint
9
Figure 2.2 HORIZONTAL JOINT FOR MULTI·STOREY BUILDINGS. Detai l outlin ing fixing of continuous support angle to steel floor support beam in order to provide tolerances for vertical and horizontal variations. Construction seq ue nce 1. Build brickwork up to underside of angle . Carefully check brickwork/steel frame relationship as work proceeds. Any deviations preferably to be corrected by adjusting the brickwork. 2. Lay compressible joint filler on top of brickwork. 3. Lower angle onto JOint filler and bolt back to steel edge beam . Steel shims. full depth of angle, may be required to accommodate adjustments to lateral setting out of angle . Angle to be fixed by steelwork contractor. 4. Complete on site painting :Stainless steel angle - erther zinc chromate or bituminous paint along top edge and at each boll
position. Gaivan ised mild steel angle - bituminous paint asabove. Note! Underside of angle to be coated with bituminous paint prior to erections. Refer to SSC publication "Steelwork in cavity walls· (Ref. 15).
IMkal toIetanee provided by sJoned hole inangle.
t() f»npressible jointniter lor enIatged delJ3ils 01 movement joint see Jig. 7.2.8.
High strengt1I friction grip bolts rrwst be ust!d to boltangle to rilanneJ through sJoned holes. Skilled labour requil8d toensure that rontact surfaces are clean, load indicatols are correctly 5ned am that bolts are tightened to the speciliet:f lDIQue.
"kJrsionaJ restJaint beam can
also be utilised as a su{JlJOl1 lortheromposif1J IIoor construcIion.
10
Figure 2.3 HORIZONTAL JOINT FOR MU LTI-STOREY BUILDINGS. Detailoutlining fixing of continuous stainless steel support angle to composrteIIoor slab in O
~ slots
01 angle.
in senalEdlJat allow adjustment
Shims 5tted be_ slab andsenalEdlJat. lull
j
dep/Jl. allow toIeIance for imperfections in aJfICIfite
sulface.
Contmuous channel cast into
lloor slab allows adjustment 01 angle horizontJI/y.
-
CCmpressibie jointmler. For enlarged details 01 movement joint see fig. 7.2.8. Stainless steelsenalEdlJat welded tobad< 01 angle, Rxing detail courtesy 01
Ie to slab
::J:, I.imited.
11
SECTION
31
RESISTANCE TO RAI N PENETRATION 3.1 BRICKWORK The Building Research Establi shment warns that rain penetration is one of the mo st commo n buildi ng defects . It is, the refore, esse ntia l to cons ider how facing brickwork can resist rain pene tration to the interior of a bUilding by systematically assessing the degree of exposure, devising and specifying appropriate details and materials and ensuring skilled supervisio n and so und work manship , payi ng due regard to local experience.
3.2 ASSESSING THE EXPOSURE It has long been recogn ised that the quantity of rain falli ng on a vertical surface de pends on both the mtensity of rainfall and the
wind speed. Recent computer analysis of meteorological data has led to improved methods of assessing the degre e of expos ure so that designs can be based on the 'worst expected ' conditions in a spell of bad weather. A classification of exposure to local wind-driven rain, measured as a "local spell index " is given in Table 3.1. Six expo sure categories rang ing from Very Severe to Very She ltered are given in place of the three catego ries in CP121 : Part 1: 1973 (Ref. 8). The "loca l spell index" sho uld be calculated accordi ng to the method described in DD93 (Ref. 7) whic h assesses the quantity of wind driven rain per spell at a poi nt on a vertical face of a wall in Um2 . The calculations take into account the geographic location , the 'roughness' of the terra in, topographical features and the heigh t of the wall.
Table 3.1 Classification of exposure to local w ind-driven ra in (BS:5628: Part 3 : Table 10)
--
1
2
3
Exposure category
Local spe ll index calculated as described in DD 93 U m 2 per spell
Expo sure category in CP 121 : Part 1: 1973 (see note )
Very Severe
98 and over
Severe
68 to 123
Moderate/Severe
46 to 85
Sheltered/Moderate
29 to 58
Sheltered
19 to 37
Very Shelter ed
24 0r less
Severe Moderate She ltered
NOTE. CP 121: Part 1: 1973 defined three expos ure categories, namely Severe, Moderate and Sheltered, correspo nding to values of Lacy's Annua l Mean Driving Rain Index > 7m 2/s, 3m 2/s to 7m 2/s and < 3m 2/s respec tively (see BRE Report 'Driving Rain Index' 1976") . Development s since the publ ication of that code, such as the introductio n of insulation into cavity walls and the advent of improved meteorolog ical data, have made it necessary to increase the number of expos ure categories. "Available from the Build ing Research Station, Garston , Watford, Herts WD2 7JR .
13
RESISTANCE TO RAIN PENETRATION
3.3 DESIGN DETAILS . SPECIFICATION AND WORKMANSHIP The amount of water penetrating an o uter leaf of facing brickwork will depend on the amount of rain measured as described above and on the resistance of the wall to that w ind driven rain. Th is resistance . in turn . depends on a nu m ber of other factors which are listed in cI21.3.1 of B8 :5628: Part 3 and is subsequently referred to in more delail. These fact ors include: a. Types of Mortar Cement: lime : sand mortars are co nsidered to g ive more intimate contact and hence better adhesion between mortar and bricks and consequent resistance to rai n penetration than cement: sand mortars w ith plasticisers or those made with masonry cement (Table 3 .2). Mortar additives. such as styrene butadiene, can improve the brick/mortar bond when used in strict accordance with the ma nufactu rers' recommendations.
b . Joint Finish and Profile The tooling of joi nts to prod uce st ruck and weathe red or bucket-ha nd le prof iles improves the ir rain resistance while recessed joints reduce that resistance (Fig . 3.1). c. Filling of Joints All morta r joi nts mu st be filled and go od contact achieved betw een bricks and mortar to minimise the tra nsfe r of surface rainwater to the inne r leaf. "Tipping and tailing" of the vertical arrises with mortar leaves unfilled perpendicular joints - a path for rain penetration. The Code no tes that such poor workmanship is particularly cri tical where low absorption bricks are used. resulting in a rapid shedding of wa ter from the glass-like surface. However, it also clai ms that the type of brick is not a factor affect ing rain pe ne trat ion throu gh walls prope rly built wi th good wo rkmanship .
Table 3 2
-
Mortar mixes (B8:5628:Part 3 :Table 15 )
......
........ I...,.."""
Slrenglh (see note 1)
-
1........... . ~loty 10 accommodate movements due to lemperalure and rT'lOlslure
."" """""'.... .... "'""""
DncOQtl 01 c:hangtI ... ptOpertJeS ,1$ ShOwn by lhe anows
j
lype 01 mortar (see nole 2 ) Cement1lme:sand (see note 3j
CemenI:sand with
sand (see nol e 3)
plasbClZet (see noce3 )
ProporllQnS by volume
Proponl()(lSby IIOIume
1:1,;:4104"..,
1:2·..;103.,..,
1:1 :5 106 1:2 :8109 1:3 :101012
1 4105 1:5''';10 6 ,...., 1:6'.-'1 107
1 :3 104 1:510 6 1:7t08 1:8
PToportI(ll"lS by YOIume (seenote4) (oj (iI) (III) (iv)
M
AIr-entJa.ned rTll_es (see note 5)
Masonry cemenI:
1 :010 '10:3
IncrNN'lg resistance 10 frOstattack during oonstrucbon 10' .... 0 .... ' • • In adhesaon and ~ re&lStance 10 rawl penetralJOn
•
NOTE 1. Where mortar of a glWln COl'TIPl'8SSIve strength is requwed by the desfgner. the tests klIowIng the ,eex:w'~ndabOnsOl apptN'ldI .. Ad as 5628 . Part 1: 1978
ml..
proportions should be delttmW'led from
NOTE 2 . The llfteter1C types 01 mortar thaI c:ompnee ~ one deslgnallOr'l are apptOlltmalely 8QUlYalent In curnpresswe strength and ec no! generaly dllTer greatly Wllhelf other propet1JeS , Some generaillfterences between types of mortar are IndICated by the arrow s alltle bOnOm of Itle l aDle, buI these d,lTerences can be reduced (see 23 .2.1). NOTE 3 , Ttle range 01 sand contents is 10 allOw lor the ertects 01the dllTerences m grading upon the properties ollhe mortar. In general. the lower proportlOl"l 01 sand app lies 10 grade G 01as 1200 wh ilst the highe r proportlOf1 applies 10 grade S 01 as 1200 NO TE 4 , The proportIOnS aril based on dry hydraled lome. The proportlOl"l of lome by volume may be tncreased by up 10 50' (VN) Ofdet 10 obta." wcnat*ty
II'l
NOTE 5, AI the discretIOn at the des9'*. air entr8ll"lll"lQadmlJdurM may be adOed 10 hmesand rrues'to IIT'Ipl'OYe Ihetr eaIfy eost re5IStance . (Ready mI ..ed llme:1and mI.. 1ISmay cont8ln sud1 admul1ures )
14
RESISTANCE TO RAIN PENETRATION
d . Achieving Good Adhe sion Rapid abs orption of mo isture from the mort ar immediately after laying is a major ca use of poer adhesion. Highly absorb ent brick s should have their initial suct ion rate redu ced by "docking" , or wetting , not saturating , and in warm drying conditions newly built brickwork should be prot ected from rapid drying. Furth er advice is given in both the Design and Workmanship Sections of BS :5628: Part 3 (Ref. 6). e. Unfilled Ca vities Where a clear air space, whether with or without insulation, is provided to prevent the passage of wat er from the outer to th e inner leaf, the cavity width work size should be specified as a min imum of 50mm. Where there is a higher risk of rain penetration considerat ion should be give n to the use of
wider cavities. The use of part ial cavity insulation with insu lation board s fixed to the inner leaf should be subject to restrictions of height, exposure and construct ion, if the remaining air space is less than 50mm as described in the relevant Agrement Cert ificates. However, users are strongly urged to maintain a minimum cavity of 50mm as recommended in BRE Digests 236 and zrt (Ref. 10 & 11 ). I. Filled Cav itie s The Code recogn ises that filling the cavity
with thermal insulation mayincrease the fisk of rain penetration through the wall and notes that walls in wh ich the cavity is filled with Type A insulants (e.g. mineral fibre or polystyrene beads) should not be used in exposure conditions worse than those recommended for the equivalent unfilled cavity wall. When Type B insulants (e.g . urea form aldehyde foam and granular plastic fill )
are used. various additional restrictions
-
should apply, as noted in the relevant Agrement Certificate s. g. DPC 's and Cavity Trays The forego ing (a-f) describe means of minimising the amount of water passing
through the outer leaf and being transferred across the cavity. It is essential to recognise that lesser or greater amounts of rain water will inevitably pen etrate the outer leaf either as damp or free-running water during spells
of severe driving rain. Thi s water must be prevented from reach ing the interior and other vulnerable places by a properly designed and built system of dampproof courses, trays and drain holes . The more common materials used fordampproof courses are specified in the following British Standards:BS . 3921 : 1985 "Spec ification for Clay Bricks." BS . 6398: 1983 "Specification for Bitumen Damp-Proof Courses for Masonry." Table 12: BS. 5628 : Part 3 prov ides information on the performance of individual materials currently used for damp-proof courses. All damp-proof courses should extend through the full thickness of the wall or leaf, and preferably project beyond the external face , to prevent the penetration of water. All damp-proof courses should be bedded both sides with mortar to ensure a suitable bond . Particular attention should be paid to junctions, steps , angles and stop ends. Three dimensional drawings will greatly facilitate the visualisation and fabrication, whether on or off site , and BS : 5628 : Part 3 (Ref. 6) should be consulted for critical locations such as parapets, copings, cills, lintels and floor to wall junctions. Drain holes or weep holes are usually formed as open perpend jo ints at not greater than 1 metre intervals in the course of units immediately above the cavity bay, with not less than two weep holes over each open ing . Prop rietary filters are ava ilable for use in weep holes designed to minimise staining on the face of the brick and , in areas of
severe exposure. prevent rainwater from entering the cav ity.
15
Figure 3.1 THE DURABILITY AND RESISTANCE TO RAIN PENETRATION OF DIFFERENT MORTAR JOINT PROFILES.
8uckt handle
(/t.e}f!d)
St1lJCk or weathered
Rush
Jointing
Pointing
16
SECTION 4
DURABILITY 4.1 BRICKWOR K Saturation is the foremost factor adversely affecting brickwork durability. If freezelthaw cycl ing OCcurs when brickwo rk is saturated it will be liable to frost failure unless appropriate bricks and mortar are specified. If brickwo rk of normal quality fired clay bricks rema ins continually saturated over a very long period the mortar may suffer from sulphation although the risk can be minim ised by using mortar which is rich iri cement or contains sulphate-resisting cement. Such conditions are fortunately rare, for example where water is constantly in contac t with and movi ng through brickwork such as in earth -retain ing walls Without a damp-proof membrane. Brickwork should preferab ly be detai led so that the risk of saturation or near saturation is minimised by ensuring that water is thrown clear
of the wa lls by copings , sills and roofs wit h adequate overhangs and drips . Some arch itect ural features suc h as flush capp ings and sills can result in the brickwork being exposed and saturated locally and for these it is esse ntial to select durab le bricks and mortar. Inadeq uate or non-existent over hangs at eaves and verges and large areas of glazing or cladding can also cause saturation of the brickwork below. . Figure 4.1 highlights vulnerable areas and Table 4 .1 recommends suitable bricks and morta rs for various locations and deg rees of expos ure, base d upon the information give n in BS 562 8: Part 3, Table 13 (Ref. 6) . Further information on brickwork durability can be obtained by referring to BS 3921 : 1985 (Ref. 4), BS 5628: Part 3 (Ref . 6) and BOA Design Note 7 (Ref. 12).
Table 4.1 Durability of masonry in finished construction (8S5628: Part 3 : Table 13, To be read in conjunction with Fig. 4.1) (.4.) Wo r'Kbe low or near ellernal grotlnd level Masonry co ndition Of sIt uation A1 Low risk 01
saluration
Qualit y 0 1 m..onry unite and appro pri ate mort ar d• • lgn atlona ISH febl. 3.2)
Flred-clay un its
c.lclu m silica te uni te
Concrete brIc lta
Concrete bloc::lta
FL. FN. ML. Of MN in (i), (iii Of (iii)
Classes 310 7 in (iii) or (ivl
;a 15 Nlm m' m(lli)
la) of block density .. 1500 kgIm); or
with or without Iree zlng
(see remar1ts )
(b) made with dense aggregate complyi ng with
as882 or as 1047; or
Ie) having a compressive streng th .. 7 NImm ' ; or
(d) most types 01 autodaved aeraled block (see remarksi n (iii»)
--
A2 High risk 01 sal uratiort WIthout freeZIng
Fl, FN, ML. or MN in (i) or (ii) (see rem arll.sj
Classes 3 to 7 in (ii) or (iii)
.. 15 Nlm m 1 in (ii j or (iii)
As lor A 1 in (iil or (iiil
A3 High risk of salu ralion WIth freezing
Flor FN in (i) or (ii)
Cl asses 3 to 7 in (ii)
.. 2O Nlmm1 In (ii) or (iii)
As lorA1 in(ii)
Rem ar ks Some types 01aUloclaved aer ated conc rete block may no t be suitable . The ma nufactu rer should be consu lted . II sulphate ground cond itiOns eest. the recommendatlOOs in 22 .4 shou ld be fOllOwed. Where designatiOn (iv) mortar is used it ISessenn er to ensu re that an masonry units. mort ar and masonry under constructJon are protected tully lrom satu ratiOn and Ireezing (see clause 30 and clause 35 ).
The mason ry most vuln er able inA2 and A3 is loca ted between 1SOmm above. and 1SOmm be low, li nist'led ground 1ev91. lnthis area ma son ry will beco me wet and m ay rem ain wet lor long period s of time , part icularly in winter.Wh ere FN or MN fired-cl ay unit s are used in A2 or AJ , sulphate-resisting ce me nt sho uld be used (see 22.4 j .
17
(8) D.p.CII
Quality 01 ma.cmry unit' and appropri.te momr deslgn.tlon, " .lIOnry condition Of . ltuatlon
81 In buildtnOS
FIrN-clay units
Cllelum $Ilb t. unit .
0 o"","""""
NoC_
course ' .s deecribed in
Cone"', bricka
NoC_
BS 3921. In (i)
B2 In.uem.t WClfIls
~
NoC_
NoC_
NoC_
""""'2 ..
-~ B5 3921, 1"1 (i)
........ Muorwy d_p.cs can,..... riSing damp bul wiI not resist walei' ~nng downwards. "sutphal. ground c:ondrbons exiSt.1t'le lollowecI. D.p.cs oIlited-day urwtsare unllkety to be ~ lor walts of other masonary unItS , as dJflerenbal
w,,,,
f8COi' datiOnSin 22.4 should be mDY8m8nl: may occur (see 20.1I.
(C) U~ .rtetnal w,lI, (ott ..., tMn chimney., CIIppngS. ~ng• • p.rtlpe!:., , III.) Matonry condttlon Of
.ltuation F1Nd-c:ley un its
e,
.........
low .......
C2 HIgh risk of saturation
R. FN, ML. or MN in (i), (iii
r.) OI'
FL. or FN ... (i) Ot
(il (see remar1U )
calcium I llat, unit.
Qaues 2 1Q7
Concret. br1Cka
'" (.) or (iv)
>7 1"1 (iii)"'"""'
ClUMs2 10 7
.. 15N1mm ' in (ii)
Concret. bkK:1q
My 1'1 (Iii) or (...., (see remarks)
'CIM remaRs l
in(_)
Nty 1"1(iii)
Rem . rktI Walls should be ptOl ect ed by roof ovemang and ot her proJeCting te,lures to mini mIZe the fis k 01salurallOO. HoweYtlf, weathenng details may no! protect walla in conditiOns of very &ever. drivlng ra,n (see 21.3 ). Certa,n archl lectural leatures . e .g. bnckworll belo\N la rge glazed areas with ftus h sills. increase the fiSk of stUuratlOn (see 22 .5).
WhcWe deSig na tIOn (IV)mortar is used illS essential to ensurelt\lt all masonry UFllts, mortar and masonry under cons trucbon are protected tully lrom salurallOn and Iree zW'lg (see etauses 30 and 35 ). Where FN hred-day url1ts are used In deSlOl'\8tlOn (ii) mortar lor C2 . sulptlale·reSlSting cement should be used (see 22.4 ).
18
(D) RendeM ...Ierna! walla (othW thain chimney•• CtIpping.. coPing.. parapM" tills) Quality of m. .onry unItS and approprtIita mortIir
~Mtkln•
....onry condlUo" eM'altuliUon Fired-<:Iay unl1a
Clildum allleata
Concrwolabrick.
Conc:nrta blo<:u
.. 7 NImm '
Any In (Ill ) or (iv ) (see remarils)
unh. Rendered ._ternal
FN or MN tn (i)
walls (other than chimneys , capping s. par ape ts. sills)
or (iI) tsee remarll.s) {)f FL
or ML in (i).
Classes 2 to 7 (ill) or (IV) (see remark s)
In
In (IIi)
(ii) or (iii)
AttfTWrka
Rendered walls are usually surtable tor most ~ rill" conck1O'lS (see 21.3). Where FN Of MN flrecl-da'l LIl1Its are used , sutphe l&reSl:St'"9cement shol.Hd be used in the mortar and," the base coat at the render (see 22.4 ' Where desogoabOn (iv) mortar is used il lSessential to ensure that . . masonry unrts, mortar and ma sonry under constructJon are ptO(eclecI fuIy tram saturBI"," and free lll"l9 tsee clauses 30 and 35 1.
IE) l"terMl walla and Innef ...vu of c.lvlty walla
Quality 01 masonry unlt a and appropriate mortar d. .lgn_tlona Masonry condition or situati on
Internal walls
"""..,..-
of cavity walls
Concrete brick.
Concrete b loc ks
Classes2to7
.. 7 NJmm I
'" (iii) Of (IV) (see remar1l.s)
"' (IV) (see remar1l.s)
My In (iii' or (iv ) (see rema rllsl
Areck:a.y unlta
CIIk:lum alllCllta un lt a
Flo FN, ML, MN. Otor ON... (i). (ii) , (. ) or (IV) (see rematil.s l
.......... Where deslgnabon (iv) mortar is used illS essenballo ensure thai aI masorvy unrts. mortar and ma sonry under construe:tJOrtare protected fully tmm saluratlOn and free lll"lQ (see eiauses 30 and 35 ).
19
IF) Unrendered
~,.pet. (o ltter
t IMn ClIp p ings a nd coping. )
Qualify of masonry units arwt appropriate mortar d •• lgnatlon. M. .onry condition
or.ltuatlon
Flred-clay un it.
C11lclum . meate
Concrete brick.
Concrete bkM:k a
.. 20 Nlmm i in (iii)
(8 ) ct bloc k de nSIty
un it. Ft Low ri sk 01 saturatlon.
FL, FN, ML, or MN in (i) . (ii) or (iii)
Classes 310 7 in (iii)
e.g. low parape ts
.. 1500 kglm3 ; or (b) made With dense
onsomesingle-
aggregate complying with BS 882 or BS 1047 ; or
storey buildings
Ie) ha VIng a compreSSive $Irenglh .. 7 Nlmm2; or (d) mos t type s of autoclaved aerated block (see remarks )
in (iii)
F2 High risk 01 sahJration.
FL, or FN in (i) or (ii) (see remar1t.s)
ciesees3 to 7 in (iii)
.. 2ONlmm' in (iii)
As for Fl in (ii)
e .g. where. capping only is
...,..,..""
the masonry
R.......
Most parapets sr. likely to be severe ly ell:posed irrespective 01the clima tic expos ure of the build ing as 8 whole . Copi ngs and d.p.cs should be ptOVidedwheteveJ possible. Some types of autoclaved aerated co ncre te block may not be suitable . The manufacturer should be cons ulted .
Where FN fired-day urwtsare used in F2, sulphat.resisl ing cement should be used (see 22.4 ).
IG) Randered P8rapels (ot her thlln capplngs snd co pings) QuaUty of ma sonry un it s and app ro p riat e mortar des ignations Masonry condItion 01' situ ation
Rendered parapets (other than capptngs and copingsl
Flred -elay un its
Calciu m ,lIIcate units
Concrete bricks
Concrete block,
FN or MN in (i) or fii} (see remar1(sl 01 FL or ML in (i), (iiI or (iii)
Classes 3 10 7 ll"I(iii)
... 7 N/mm 2 in (iii)
Any in jiii )
R~arka
Sing le-leal walls shou ld be rendered only on one lace . All parapet s should be provid ed with a coping, Where FN or MN hred -clay uMS are used . sulphate-resistIng cement ShOuld be used '" the mortar and In !he base coat of the render (see 22.4 ).
20
(H) Chimneys
"'.-
O\gllty of ",..on ry u ntt. and approprillta rnona, r dHlgNtionS
"'MHtry condit ion Antd -e~y
unh.
H I Unrenderedwith lOw risk of saturation
FL, FN, ML 01 MN in (i). (ii) ot (iii)
H2 Unrendered with high risk of saturaoon
FL or FN in Ii) at (ill
CIIlcwm allk:ate un it.
eoncma brick.
Conc:fWCa bkJc:q
Classe s 3 107
~ 10Nlmm' In (IIi)
Any tfl (Iii)
In (iii)
Classe s 3 to 7 in (iii)
.. 15 Nlmm 1
(a) of bloc k density
"" (iii )
.. 1500 kglm3; Of (b) made with dense aggrega te compIylng with 8 5 882 04' as 1047; or
t\avniI a COf1'lPl'eSSIVe strength .. 7 NImrn' ; or
(e)
(d) most types of au lodave
In
H3 RendeI'ed
FL Of ML In tn. Iii)
Classes 3 107
.. 7 NJmm'
or (iii) Of FN or MN
in (iii)
1"(111)
AnVll'lliii}
in (I) or (ii)
.......... etnrn"ey $taell.s are notmally the most e..posed masorwy on any building Due to the possb~ty of sulphat e attadl, trom flue gases the use of sulphat&-resisllng cement in the mortar and in any render is strongly f6COiih l16i lded (see 22.4). Brickwor\( and tile cappmgs cannot be reIte
Some rypes of au1Cld8Yed aerated concr8le block may not be $UIIable tor use II"l H2. The manufacturer shoUld be consulted
(I) CIIPJNng a, coping. and ama
OuIillty of m..on ry unn, and appropriate mortar dMlgnatlona
"uonry condit ion or ahu81 10n
Flntd..c lay unit.
calcium sili cate
Concrete brlcka
Cone,.t. block.
~ 30 NJmml in (iii
(al 01block densrty ~ 1500 kglrn J; or
un".
Clppngs. coplf'IgS and siMs
FL or FN In (i)
Dasses .1O 7 in (iii
(bl rMde WIth dense
--
~ te~WIth
as 882 or as 1Q.47; or
(el haYing a compressive strength ~ 7 NImm' ; or (dl most aUlodaYed &efated btocks (see remarilJ ) In (iii
Aem.rk. Some autoclaved aerated concrete blocks may be unsuitable lor use in (i). The manulaClurer ShOuld be con sulted . Whet e cappings or copings are used
O.p.a
torcappmgs . ~ and
torchimney tem-llnals, the use 01SUlphate-r8SlSIIflQ cement is strongly ieoommended (see 22.4).
Sills 5houId be bedDed in the same monar as the masonry lM'\l1S
21
-
(J) Freestanding bOundliry end
..
....onry conditIOn
J l With copII'IQ
lie'""" .alls (o t_
F lrwd-day " nit•
CIIk:ium ai lka1 . un its
FN OI' MN In Ii)
Classes 3 107 "'(Ilil
or {ii>Of Fl or Ml '" til. 1_' or (!til J2 W lthcappM'lQ
thM1 CIIpptng. and copings)
Quality of rnuonry untt. and 8ppr0pri8te ~r dH'grwtlons
FL 01' FN In IIIor
Classes 3 to 7
(ii) (see re marks)
In (ill)
Concrete bric:u
ConcNte blocks
.. 15Ntmm 2 (NI)
Any 10 (nl)
;ar 20 Ntmm ' '" l lil)
(a) of block denSIty
In
.. 1500 kglm J ; Of (b) made with dense
aggregatecomplying with
as882 Of as 1()47 ; or
Ie) haVing ' comptes5IVe strengl h ill 7 Nlmm '
(see remar1<.sl . 0.-
ld) most types of autodaYed aerated tlIC:ioCiI (see ~s) ll"I (II) Remllrk s Masonry In free -standing wa IlS 1$ a.k ely 10 be IfMtrety ex posed, lITespectrve Ofcltma bc condtbons Suc h wans should be pt Ol8C1ed by a eopong wherever pO$sobIe and d p CSshould be provt()ed undef the copngs and at the base cure ....,aMtsee clause 21)
Where FN or M N 'Ired.-clay uMs are used lor Jl In conditIOnS of sever e dr lVll"lgrain (see clause 21). the use 01su!phale·reSlSIItlQ cemenl ls slro:ngly recommended teee 22.4 ' Wh ere des'9na11On (iii ) mor tar 's used for J2 , the use 01$ulph ate- reSlslIl'lg cemenl ,s strong ly
recowe eeeeo (see 22.4 )
Some typeS of autodawd iMfated concrete bloc k may also be unSUItable The manufactu rer should be consulted
-
(I<) brt~nlng .all. (other than capping. and coP'ngs ,
..
Ma.-yconditloft
"
W ith waterproofed reta,l'llng lace
Ou-lity of masonry unlb and approprial. rnofW deaigNlltons FlreO-cwy untt.
c.ldum silicat. units
Concret. bricks
Concret. blocks
Fl. FN . Ml or UN .n Ii) or 1111
Classes 3 to 7 .n (Ill or (_,
iJc 15Nlmm2 ,n l ,til
l a ) at block denSrty
"'" """""
;;It 1500~ J;or
(b) made w,1ttdense aggregate complying wIth a s eee or as 1047; or Ie) hawlg a com pressive strength ill 7 Nlmm 2; or Id) mosl typeS of aulodaYed aerafed block tsee remarlts) '" (II)
.......-
K2 With ClOP'l"O or
_but...,
FlorFN Il"lh)
ClassM410 7 Il"l (ii)
~ 30 "'"'""
Il"lIi) or (II)
As lor I( 1 but Il"lIi) or (il) (see remarks)
on retMWlg face
..Because of pOSSIble contammatlOO from the ground and saturatl(l(l by ground waters. Il"ladcllll(l(110 sutlteCtlOl"1lO severe ChmatlCexposure, masonry Il"lretanng wallS ISPlrtlCU larty prone 10frost and sulphate anack. Careful choice of matenals In relabon 10 the me lhods tor exdu$'Ol'l of waler '6COi,wnended in clause 21 is essential It is Slrongly recommended Ihal SUCh wall s be bac kl,lled wllh Ire edral ning m ater ial . The prOVis iOnof an ellectrvecop,ng wIth a d.p .c. (see d ause 21) and wa terproofing of lhe rela inlng face of the wall (see 22 .1.3 ) is deSlrabie . Where FN or UN flred-clay uMS are used. the use of SU!phate--resi$tlng cement may be necessary (SH 22.4 ).
Some types of autodawed Hfated concrete block are noc surtaIM lor l48 10K 1. The manufaewrer ShOuld be consuned
MosI conc:rele blocks are noI SUItable lor use., K2 . The manufacturer ShOuld be consulted
22
4.2
CAVITY WALL TIES & FRAME TIES
Cav ity wall lies shou ld comply with BS 1243 "MetalTI es for Cav ity Wall Construction"latest amendment Apr il 1981 (Ref. 13). The mos t freq uently specified ties are either of low carbon stee l protected with a zinc coating to BS 729 of min imum weight of coa ting 940g/m' , (Ref. 14) or austenitic sta inless steel. Frame ties are not covered by a British Standard and the de signer should take particu lar care when specifying galvanized frame ties to fix external brickwork to a structural frame. BS 5628: Part 3 (Ref. 6) req uires a high degree of corrosion resistance for ties embedded in the outer skin . The required degree of protection is provided either by a galvaniZed zinc coating of 940 glm' to BS 729 (Ref. 14), which must be obta ined by the use of
fully killed high silicon steel , or alternatively by the use of stainless steel ties . Virtually all frame ties available as standard have a maximum zinc coating of 460glm' wh ich according to BS 5628: Part :3 (Ref. 6) is not suff icient when embedded in the outer leaf of a masonry wall. In this situation it would seem safer to specify a sta inless steel frame tie. Generally all frame ties , fixings etc. embedded in masonry should be protected against corrosion as outlined in Tables 4.2 & 4.3. All bolts, nuts , shot fired nails etc. should be given a degree of protection compatible with the components with which they are to be used, e.g. consideration should be given to the possibility of electrolytic action between dissimilar metals. i.e. bimetallic co rrosion .
Table 4.2 Anchorages , dowels and Ilxlngs (BS 5628: Part 3 : Table 1) Category
Baa. ma la ria l
Form
Gra de and ata ndarel to be co m plied
with A
Hot..
5 ree,
galvaniZed low eertco
B5 298 9 , Zl or Z2. coaling type G 600. Minimum m ass of coa llf1g 600 gtm' including both SIdes
Protec tive m•••UI" . to be carr'-c:l oul after labrlc all on AUe xternal cu t edges to be protected USIng. one-pac k che mical- reSiSlant palm complying with HF1A 10 HF2F In part" of
table "'H of a s 5493: 19n and modlfted to give adequate adhesion to the ril ing
s teel
852989. Zl orZ2 . coaling type G 275 . Mtntmum mass of coallr'lg 275 gtm ' 1I"lCIudll"IQ bOth $Odes
-,
Coabng to be applied . "er labncabOn 10 !he ell1emaJ aurtaces and c:onSIstlng of (al blt utTW'lOUt sotubon complying WIth typeS 1 or 2 of 85 ~ 16 and of nwwnum
thICkness 25 I' m;
'"
(bl a ~ ~sta"' pa.nt
complying WIth HF IA IO H F2 F In part . 01 table . H of S493 . 19n anet moddl«t 10 gMt adequale adhe$IOtllO
as
lhebng
-=--.
Where lhe ZInC is removed on Inlemal surfaces dunng labncabon. elil by weidlng. furthet' prolecbOn IhOuld be appltecIlo these areas
B
Low cartlon 51ee1
Sinp
85 ' ....9 _P8f1 ' : 1983 (med'la1"llCa1 requH'emem5 In lat)le 11 only )
_.....
Post-galvaNZng complying WIth as 729 Y II'Ilr'r'IUm mass of coabng 460 gtm ' inCfudang
85"360 grade ..3A
23
Table 4.2 continued Ca i eg Ofy
8 • • e me le rt al
Form
Grade and standard to be compiled wit h
Protectlye mea.ures to be . n., fabrication
C
Low carbon steer
StriP
a s 1449 Part 1: 1983 (mec hanical reqUIrements in table 11 on ly)
Post-galvanizlng complying wi th as 729 Minim um mass of coalIng 940 gl m l incl ud ing bo th sides
D
Coppe<
e.rr~
out
a s 4360 gra de 43A
85601 7
as 2810
Copper alloy s
1980 . 9raoes Iisled
in table s 8 and 12
Matenal other than phosphor bron ze to be formed erther : (a) by bendIng at du ll red heat and allowing 10 cool in sll il er:
a s 2873 : 1969. grades listed in tables 4 and 6
'"
BS 2874 : 1968 . grades hsled In table s 6 . 8 and 9 f1Jecept CA 106
fbI by cold form ing and svbsequenlly stress ,ellef annealing at 25O"C10 3OO"C lor 30 min 10 1 h.
Enectiveness ct siress rell9YlO9 01colcI formed components to be tes ted by the supplier USIng the mercurousnrtrate test described in Clause 11 01 as 2874: 1969 Au stenitiC stainless stee l, minimum 1818 com pos ition and excluding Iree mac hirnng
sceeeceucoe
Stnp
BS 1449 : Par'l 2
." r,be
a s 6323: Par1 8
Wire
a s 1554 as 3111 ; Par12
88 970: Pert t
Rod
Table 4.3 Protection of Metal Components (other than wall ties) buill Into masonry (655628 : Part 3: Table 14) l'ype of component
snuallon
Catevory g l~ In Table 4.2 (M.l eri al & Reeommended Prot ect iv e ..... . u re.).
Anchorages , bondlng nee. s1tp brick lies and conilnUOUS support angle s
. 11
C", D
o
Dowels and restraint straps
Internal walls
A, a , C, D
A,a, C.D
JcMst hangers
In con tact With or embedded ,n Inner leal
A, a , C. D
A,B, C,D
In conl act With or embeoded ,n outer leal or $Ing le leal walls
Cor D
D
. 11
As spec ified in as 59n : Part 2 lo r the appropriate type 01 hnlel te. Insta lled With or WIthout
Nol normally appliCable. If used, spec ial ceecec nco e may be necessary
Three
ReinlOtCement for non -structural use
.torey. or Ie..
More th.n th ree . torey.
e.c.e. CavIty Irays
. 11
As ececnee ,n lor I,nl els ins tall ed WithOut
AS Spec ,lred In as 59n : Part 2 for nnters ,nstalled wrthoul
e.p.c
e.c.c.
as 59n : Part 2
24
4.3
STRUCTURAL STEELFRAME The Br itish Stee l Corporation has recen try
published a new advisory document (Ref. 15) dealing with the corrosion protection of steelwork encased or clad with masonry cavity walling. Briefly the document recommends that wherever poss ib le a 4Qmm minimum air gap should be maintained between the steel frame and the external brickwork. Under these circ umstances the protection required for stee l
frames in cavity walls is minimal and usually only involves simple coaling systems. An obvious exception 10 this is the use of a con tinuous angle 10 support the external
brickwork at horizontal movementsjoints in
-
mult i-storey bu ildi ngs . In such instances the corrosion protection 01 the angles should comply with Tables 1 & 14, as 5628 : Part 3 (Ref, 6). It is also recommended that wherever possible care sho uld be exerc ised to avoid ties directly between the external brickwork and the stee l frame , the ma in reason be ing to prevent any water wh ich penetrates the exte rnal facing br ickwork from comi ng into contact w ith the stee l frame via mortar droppings on t he ties bridging the cav ity or badly installed, downward slop ing frame ties. Assuming co ld bridges are avo ided, surface condensation is usually not a problem during per iods of occupation in new constructions having insulation meeting current u-vatces prov ided they are adequately heated and vent ilated. To ach ieve current If-valu es almost always req uires multi-layer construct ion , with one layer be ing a specific insulating material. As the vast majority of building ma ter ials and lnsulants are vapour permeable, interstitial condensation - with in the structuremay occur, If this is considered likely it is desirable to venti late cavities/velds or provide additional protection to structural steelwork with in the cav ity. Further information to enable an ass essment of the condensation risk to be
made can be obtained fro m the following Brit ish Standards:as 5250: 197 5 - "C ode of Basic Data for the Design of Buildings : The Control of Condensation in Dwellings." BS 6229: 1982 - "Cod e of Practice for Flat Roofs with Continuously Supported Covennq " as 5628: Part 1 "Structural Use of Unreinforced Masonry " (Ref. 6) pe rmits loads to be transmitted from a masonry panel to its supports by frame ties attached to the inner leaf provided that there is adequate connection between the inner and out er leaves, particularly at the edg es of the panel. How ev er, it is recognised tha t in some instances frame ties directly linking external brickwork and steelwork may be unavoidable . In such a sit uation, the designer must assess all aspects of durability, lateral stability, specification and quality control of workmanship on site , Further inform ation can be obtained from the BSC document "Steelwork in Cavity Walls" (Ref. 15) including guidance on al ternative paint protection systems for various locations of exposure.
4.4
BIM ETALLIC CORR OS ION
When two different metals are in electrica l contact and are also bridged by water containing an electrolyte, current flo ws between the anodic or base r metal and the cathodic or nobler metal. As a result , the nobler metal tends to be protected, but the baser metal may suffer from co rrosion. Bimetallic corrosion requires:(i) An electrolyte bridging the tw o metals. (ii) Electrica l connection betw een the m eters . usually involving direct physical contact. (iii) A suff icient diff erence in potential between the two me tals to provide a significant galvanic current.
25
Table 4.4 gives a quick. broad qualitative indication of the likely corrosion behaviour of bimetallic coup les in natural aqueous environments. The further apart the meters are in the ga lvanic series . the greater me risk . In atmospheric conditions. the severity of bimetallic corrosion is influenced by the length of time that the contact remain s wet. Hence cavities should be ventilated whenever possible. particu larly around steel col umns and perimeter floor beams .
The degree of bimetallic co rrosion is also affected by the relative volumes of the anod ic and cathod ic metals , For example. mild st eer tens in a stainless steel brick support angle will be at much greater risk than a mild steel ang le which is in contact with stainless steel bolts. Wh ilst the composition and COnductivity of the environment affects the severity 01 corrosion. in practice it is not uncommon for dissimilar metals to be in contact under conditions of occasional condensation or dampness without adverse effect.
Table 4.4 Bimet allic Co rro s ion Magnesium & alloys Zinc & alloys Alum inium & alloys Cadmium
Tendency to inhibit COI"I'O$iOIl of structural sleel
Struct ural steers Cast Irons Stainless Steels Lead Brasses
Tendency to acce lerat e corrosi on of structural steel
Co pper Bronz es Inform ation on ts-rretauc COlTOSiOn in atmosph enc conditions is sparse. By and large materials higher in the table wincorrode in preference (and thu s tend to protect ) materi als lower in the table. The relative surf ace area of the fWO meta lS in contaeI wi. have an effect . For example if equ al area s of stainless and milct steel are in contact the conosiOnrate of the mild sl eel winbe m eased . How ever the conosion rate winnot be so high if the area of stainle ss is much less than the area 01mild st eel.
In atmospheric conditions. the more important design considerations would be to minimise the accumu lation of ra inwater and condensation at the joi nts between dissimilar meta ls. te. maintain good cavity dra inage and ventilation. Methods of preventing or m inimising bimeta llic corro sion are based upon : (i) Insulating the dissimilar metals from each other. or (ii) Preventing the formation of a continuous bridge of electrol yte solution betwee n the two metals. i.e. exclude water from the joint. Insulation can be achieved using bushes and washers made out of non-conductive material. e.g. neoprene, pofvtet raf1uoroetheylene (P.T.F. E.), or nylon.
-
Imperv ious gaskets out ot similar materials may also be considered for larger contact areas , for example, stainless steel angles in contact with mild steel bea ms. Excluding water from the joint can be achieved by applying a continuous film of pa int to the assembled taint. This cou ld be further improved by incorporating an effective coating applied to the conta ct surfaces . Fig. 4.2 indicates som e artemenve method s for minimising bimetallic cor rosion. However the designer must assess each individual building and assoc iated environment on its own merit. For further informat ion refer to PO 6484 : 1979 "Commentary on Corrosion at Bimetall ic Contact s and its Alleviation" (Ref. 16) or consult the Nationa l Physics l aboratory.
-
Figure 4.1 MASONRY CONDmON OR SITUATION AFFECTING THE SPECIFICATION OF THE BRICKS AND MORTAR. (Read in conjunction with Table 4.1 )
C2
Cl
I
I
Cl
2
1IIl/dJ stJjning of brickwork
C2 L
Reintorred brick retaining
L
ci >
C2
L
Kl
2
C2
BrickDPC
A3.... A2
A2
A2
Detailsprovide some protection
waIl
Details do not provide
protection
27
Figure 4.2 DESIGNS FOR MINIMISING BIMETALLIC CORROSION
Continuous paint film compatible with overall ronnsion prorection scheme
tor main frame.
Suitable paints bituminous or
zinc rflmrnate (Ref. 15). (a) Continuous Paint film
I--------: ~~-:;;",..e:.----
Mild steel member
Stainless steel nut &1Jo/I
Neoprene. P.lF.E. ornylon washer
(b) IflSlJlated Joint
Not suitable when using HSFG bolts inskJtted holes.
28
SECTIONS
I
ACCOMMODATION OF MOVEMENT 5.1
GENERAL
5.2 THERMAL MOVEMENT
Few part s of any build ing are immune from small dimensional changes. These may be caused by one or more of the following factors:a. Change in temperature. b. Change in moisture content i.e. wetting and/or absorption. c. Chemical action (refer to BOA design note 7 'Brickwork Durability'). (Aef. 12). d. Deflection of the supporting structure under vertical and /or horizontal loads. e. Differential foundation settlement between the more heavily loaded pad base supporting the steel frame and the lightly loaded foundations supporting the external masonry cladding. It is essential to recognise where inherent discontinuities are likely to occur and to determine their effects so that adequate provision can be made for them in design. This is particularly important when assessing the laterai stability of external masonry panels since the disposition of both vertical and /or horizontal movement joints will affect the assumed edge cond itions along the edge of the panel.
The unrestrained thermal movement of a wall can be estimated from A = L cc t where: A, is the amount of movement 0:: , is the coefficient of linear thermal expansion of brickworkf'C L, is the length of wall considered t, is the change in mean wall temperature. Typical values of the coefficient of linear thermal movement for various masonry units can be found in Table 5.1. However, it is advisable to obtain the actual values for the particular materials being used . Examples of the service temperature range of materials can be found in Table 5.2. Vertical thermal movements within a wall are generally reversible. Horizontal thermal expansion, however, is unlikely to be fUlly' reversible. Often the partial restraint available, part icularly near the base of a wall , prevents the masonry from completely returning to its original length. Any contraction which is restrained may generate tensile stresses greater than the tensile resistance of the wall and so result in cracking. Design for thermal movement should therefore recognise the effect of restraints.
Table 5.1 Properties needed to assess changes of size and shape of materials. (BRE Digest 228) Note: Unless more specif ic data are available, design should be based on the higher value where a range is shown. (1) Mal erial
(2 )
(3)
CoeffiCient of
ReverSible moisture movement
linear thermal
movement
(5) Modulesol elasliCityE
(+ l expanSiOfl (- ) shrinkage %
k.Nlm rrr
0.02 -0.04 0.03 - 0.06
0,02- 0,06 (- )
10 -25
0.02-0.03 0.Q1- 0.05 0 ,02
0.05 - 0,09 - ) 0.01- 0.04( -) 0.O2 - 0,10 (+ }
t
t
expansIOn x
PtJroClI.10 8
-
Br lckwor1l.. blockwor1l .nd tUlng Concrete bnckwork and blockwork : Dense aggregate Lightwe~ ht a~regate (auloclaved) Aerated aul ae aved)
Calcium sacate bnckwork Cla y or sha le bnck work or blockwor1l. Clay lili ng
6- 12 8 - 12 8 8 - 14 5 -8 4- 6
Ple in cerbon Sleel
12
Auelenilic sl elnl... sl . .1
18
(4) Irreversible moi sture
%
-
0,02 -0.06
-
1-)
4 - 16
3-8 14- 18 4 - 28
t 205 200
t No data available
29
Table 5.2 Examples 01service temperature ranges 01materials (valid lor UK only) (BRE Digest 228) Min
Max
'C
'C
Range 'C
External
Cladding, walling, roofing Heavyweight Lightcolour - 20 Dar1
50
70
65
85
60
85 105
80 40
115 65
45 60
80
90
65
50 65
75
30 35
20 40
90
I
5.3 MOISTURE MOVEMENT a. Clay bricks expand and contract with changes in moisture content. The typical
range of unrestrained movement is negligib le, generally less than 0.02%. There is also an irreversible long term expan sion which occurs as a result of the absorption of moisture from the atmosphere. The rate of this long term expansion decreases with time. It is at its l/reatest as the clay bricks are cooled in the kiln. Atter leaving the kiln a minimum curing period of 14 days should elapse before the bricks can be used in construction. The amount of expansion depends on the type of clay and the degree of firing .
b. Calcium silicate bricks and concrete blockwork tend to dry out and shrink atter manufacture. If wetted the units will expand again but only part of the initial drying shrinkage is reversible . It is for this reason that good specification will insist that the units be protected on site and must never be allowed to become saturated, Table 5.1 contains typical percentage figures for both reversible and irreversible unrestra ined moisture movements of typical masonry materials. Any estimate of the moisture movement within a wall should be modified to take into account the effect of wall restraint discussed above . Because of the small shrinkage associated with calcium silicate bricks and concrete blockwork, movement joint centres are usually closer together than for clay masonry.
30
5.4 THE EFFECTS OF RESTRAINT
Small changes in length can result in either actual movement or, if the wall is restra ined from expanding, in the generation of compressive stresses. Such stresses can be high and it is normal design procedure to accommodate movement rather than to attempt to resist it.
In practice. some movement and some restraint will result. Thus small compressive or tensile stress may develop. The risk of cracking , normally associated with shrinking materials, is increased where there are stress concentrations, for example , at the corners of openings or at changes in height, thickness
or direction. To assess the likely movement. it is impcrtant to try to assess the degree of restraint.
5.5 ASSESSMENT OF MOVEMENT IN MASONRY a. BS.5628: Part 3 : 1985 suggests the following simple rule of thumb for clay brickwork. •... In !;leneral, unrestrained or lightly restrained plain masonry walls. e.g. parapets and non- loaded spandrels built off membrane type dpc's will expand 1mm/m during the life of the building due to thermal and mo isture movement chanqes ..." It is recommended thalthe desiqner consults the manufacturer for further information on the movement characteristics of any particular clay brick . Expansion of normal storey height walls is \lenerally less than 1mm/m sinceexpansion reduces with increasing restraint. However, the spacing between movement joints should never
exceed 15m in order to avoid cracking due to thermal contraction. Vertical movement of walls is of the same order as horizontal movement. The thickness of movement joints is governed by the spacinq between joints. the allowable compressibility of fillers and the performance of the sealant. BS.5628: Part 3 : 1985 (Ref . 6) recommends that the width of the joint in millimetres should be about 30% more than the predicted movement. At 1 mm/m this is 30% more than the distance between the joints expressed in metres. Table 5.3 gives recommended widths of expansion joints for various joint spacings for normal storey height walls. b. Calcium silicate masonry should be designed as a series of panels with the ratio of length to height not greater than 3 :t Generally, 10mm wide vertical joints to accommodate horizontal movement should be provided at intervals between 7.5m and 9m. c. In calcium silicate brickwork and concrete blockwork external walls containing openinqs, the movement joints may need to be provided at more frequent intervals or the masonry above and below the opening reinforced to restrain the movement. The reinforcement should be of sufficient length to distribute the stress to a position where the vertical cross-sectional area is able to accommodate it. Typical expansion and contraction joints are shown in Fig. s.t , Further information contained in the BOA Design Guide. 'Oesigning for Brickwork Movement" (Ref 28) .
-31
Table 5.3 Recommended w idths 01 movement Joi nts lor storey he ight panels. Joint spacIng 1m)
Recommended joint widths
Upco7
10 - 12mm
7-11
15nvn
11-15
15-2Omm
No'"
1. Maximum joint spadng specified in csause 20.3.2.2 ot par13 as 5628 : 1985 . 2. A Shear joint should be a minimum 01 l Omm wide . the width of the sealant being equal to Of greater lhan its dept h.
5.6
PRE FERRED LOCATIONS OF MOVEMENT JOINTS
The location of movement joints requires careful consideration to make sure that , in addi tion to accommodating the movements, the stability of the wall is not Impaired. Certain building featu res should also be considered when determining joint positions in masonry, for example:a. Intersecting walls , piers , floors etc. b. Short returns, less than 1 metre in length. c. External and/or internal corners. d. Window and door openings . e. Changes in he ight or th ickness of the wall. f. Chases in the wall . g . Movement joints in the bu ilding . No single recommendation regard ing the size , pos itioni ng and spacing of movement joints can be applicable to all structures. Each building design should be assessed on its own merit; Figs. 5.2, 5.3 and 5.4 show some examples.
5.7
WEATHERPROO FING MOVEMENT JOINTS
a. Amount of movem ent likely to occ ur at the joint. b. Type of substrate to wh ich the sealant is applied, and to which bonding is intended l.e, clay or ca lcium silicate bricks. c. Accessibility for application/maintenance. d. Economic considerations, inc luding both initial cost and costs in use , i.e. maintenance over 60 years period. The sealant should be applied against a firm backing so that it is forced aga inst the sides of the joint under pressure to ensure good adhesion. The joint filler material must not react with the sealant and must be highly compressible . Flex ible cellular polyethylene and cell ular pol yurethane are the most satisfactory materials for joi nt fillers. Fibre boa rd, cork and similar materials should not be used in ex pa nsion joints in cl ay brickwork. Further information on the sel ection and use of seala nts is given in 85.6213: 1982 "Selection of Constructiona l Sealant s" (Ref. 17). Table 5.4 lists the basic pro perties of suitabl e se alants for use in masonry movement join ts .
In external walls all movement joints shou ld be sealed or protected to prevent water penetration. The followin\l factors must be considered before selectIng a sealant for a particular application:-
32
Table 5.4 Basic properties of suitable sealants. Joi nt geometry widthldeplh
Sealant
Chemical type
Character
Gun applied 1 part chemically cu"",,
Potysulphide Polyurethane SiliCOne
Elasto-p1astic Elastic Ela stiC
ure
Movement accommodation
8ltpectancy
2 :1 to 1:1
10 - 20%
2 :1
Upto20yrs. Upto20yrs. Upto 20 yrs.
2 :1 101;1
Upto 20 yrs.
25"
50%
50
2 :1
UplO20 yrs .
25"
50%
25
2:1
20% 50%
(low modul us)
Gun applied 2 part chemically curing
PoIysulphide
Elasto-plaSlic
Polyurethane
Ela stiC
Max . joint width (mm )
ratio
But1join ts
Shear joints
20- 40%
,"""
20 20 25
Notes 1. Ela sto-plastic materiels have pred om inant ly elas tic properties but ex hibit some plastic propert ies wh en stressed for other than short per iods . 2. Elastic (elasto meric) m ate rials return rapidly to their approximate initia l d im ension and sh ape aft er substantia l deformation by a weak stre ss and release 0 stre ss. 3 . Under lavoura ble co nditio ns, the expected service lil e qu oted may be exceed ed . Co nsult the appropriate sealant manufac turer for such information. ReIer to as 6213 : 1982 Selection 01Const ructio nal Seala nts l or furt her deta ils .
5.8
EXTERNAL MASONRY WALLS AND STEEL FRAMED BUILDINGS
--
Extern al mas onry wall panel s in steel frame buildings should be des igned to prevent cracking resulting from stresses generat ed by differential movem ent between the panel and the frame. In the structural design of the building the designer must consider all forces wh ich may act upon the stru cture, i.e. dead. imposed and wind load s. and asse ss the likely theoretical deflections of those structura l elements required to provide lateral restraint to the external wall panel s. Such elements include main fram e columns, intermediate col umns, eaves beams, mid-height horizontal restrain t rails, floor beams etc. a. Single Sto rey Stee l Frames Single storey buildings. particularly port al frame s, have two particula r deflection modes wh ich influence the design detail of external masonry cladding panels. These are:(i) deflection or sway at eaves. particularly that due to latera wind loads, see Fig. 5.5. (ii) differential movement at eaves in the end bays between the braced gable frame and adja cent portal fram e, see Fig. 5.5.
Horizontal eaves defle ctions tend to be acco mmodated by the steel fram e and wall panel moving together. In such cases the wall must be free to rotate about its base . usually at the dpc level. As a result full fixity should not be assumed along the base of the wall when assessing the latera l stability of the panel. As a general rule perm itted theo retical eaves dell ection s approa ching 11300 of the height of the stanch ion should not impair the stability or the rain resistance of a cavity wall . The differential defle ction between a braced gable frame and the adjacent portal frame measured from corner to corn er should be restricted to U660, where L is the length of the diagonal. These deflection limits are shown diagrammatically on Fig. 5.5. For som e buildings a horizontal movement or sway at the top of the wall in excess of these limits may be accep tabl e although information on this topic is sparse . Th e roof sheeting will provide some stiffen ing by diaphragm action and in many cases will reduce the 'ca lculated' eaves deflection by transferring lateral load to the gab le frames.
33
The amount of any reduct ion will depend upon several factors, including the type of sheet ing or cladding , the fixings and the plan shape and size of the building . Standard profiled metal shee ting incorporating either sell-drillinglself·tapping screws, bolts or cartridge fired pins to connect both the individual sheets to the supporting roof structure and the seams between adjacent sheets is generally considered the most suitable form of roof construction for providing diaphragm actio n. However, not all forms of profiled metal sheeting are suitable, part icularty those with a standard seam profile which are normally clipped to the supporting structure . Asbestos cement sheets incorpo rating hook bon fasteners will provide some add ~ional stiffness . However, ~ is not recomme nded that the designer shou ld rely on this form of construction when considering critical deflections of the structural frame e.g. side sway single storey portal columns. For particularly tall portal frame buildings, i.e. height to eaves in the order of 7·8m, an alternative approach would be to consider the steel frame and the external wall as separate elements. Stab ility of the wall could be maintained by adopting a post tensioned brick diaphragm form of construction designed as a freestandi ng wall resisting lateral wind pressures. It is then poss ible to design a lighter structural steel frame (taking into account the reduct ion on wind loads) and utilise earty construction of the roof cladding leading to potential cost benefits and reduced contract periods. Freestanding post-tensioned brick diaphragm walls can also be utilised to minimise the possibility that a fire will spread from one build ing to anoth er under 'boundary wall' conditions. Furthe r explanation of the term 'boundary wall' can be obta ined from Building RegUlations. b, Multi-Storey Steel Frames In addition to the need to provide vertical joints to accommodate horizontal movement in masonry its useto clad multistorey framed bu ildings causes a number of other factors to influence the des ign and detailing. Account must be taken of (i) vertical differential thermal and moisture movements between the walls and frame , see Fig. 5.6.
(ii) vertical differential thermal and
moisture movements where walls are constructed of diss imilar materials i.e. clay bricks and concrete blocks. (iii) long term shrinkage and creep of struct ural columns. This last point relates more to concrete than to steel wh ich is more dimensionally stable. The most satisfactory method of accommodating these potential movements is to construct the external masonry walls comp letely independent of the steel frame . The walls carry their own dead weight to the foundation , the steel frame provid ing the walls w~h lateral suppport only.The walls are fixed back to the steel frame using flexible ties/anchors wh ich take tension and compression, but no shear, perm~ng differential longitudinal and vertical movements between the frame and the wall . Differential vertical movement must be accommodated at all junctions between the external cavity wall and the following internal elements:i) Non-load bearing internal partitions. ii) Floors at skirting board level. iii) Equipment/services . A schematic diagram for such a structural system is shown in Rg. 5.7. The problem of vertica l differential thermal and moisture movements would still be relevant if a wall were to be constructed with a clay brick oute r skin and a concrete block inner skin . This differential movement could be further reduced if a wall construction comprised two clay brick skins with compatible movement characteristics. Where other des ign or space restra ints necessitate that the inner skin has to be supported off the main structural framework, then horizontal movement joints will have to be incorporated to accommodate the vertical differential thermal and moisture movements (See Fig. 5.7). Because of the effect of different ial movement loosening wa ll ties , BS.5628: Part 1: (Ref. 6) recommends that the outer leaf shou ld be supported at intervals of not more than every third storey or 9m ,
1
whichever is less. However, forbuildings not exceed ing four storeys or 12m in height, whichever is less , the outer leaf may be uninterrupted for its full height. Alternative details for forming horizontal movement joi nts can be found in Section 7.
34
Th e eff ec ts 01 rotation 01 edge beams t hro ug h torsion and the deflection 01 cantilevers and edge beams under load must be considered in detail where these elements are attached to the brickwork claddi ng . With regard to deflections in the steel frame. 65.5950 : Part 1: 1985 (Ref. 23) calls for:a. A limit of 5panl360 (on imposed load) for beams carrying a brittle finish. This amount of deflect ion may not be suitable for beam s supporting a wall, espec ially on long spans where a more stringent limit might be necessa ry and where the wall weight is applied eccentrically to the beam , such as at horizontal movement joints.
b. A limit of Heightl300 per storey for columns in a building of more than one storey. This should be viable as a basis for the evaluation of allowab le sway in buildings up to about 6 storeys. If brickwo rk cladd ing is used for higher buildings this figure might need mod ification. For example in the U.S.A. a sway limrtation of Heightl600 is common for higher rise buildings. i.e. 2O-storeys or over. Table 5.5 lists some suggestions for limiting the deflection of various steel frame members eithe r supporting or restraining a maso nry wall .
Table 5.5 Theoretical deflections lor steellrame members supporting and/or restraining an external masonry cavity wall. Theoreticaldeflections Building
Single storey
..ult....tore y
Structural member
load supported
Eaves beam
Wind only
Eaves beam
Wind + 8WTrainwater gutter
Main colu mns (sway) '
Rool,deadand wind
Gable post
Wind only
Intermed ia te posl
Wind only
Horizontal restraint rail
Wind only
Main columns IswaylJ
Wind only
Intermediate post
Wind only
Horizon lal restra int
Wind only
Perimeterfloorbeam
Floor (dead + super)
Perimeterftoofbeam
FW (de ad + SUI*) + SWTimerleaf
Support angleat horizontal
8WT extemal brickwork (2 storey max .)
expansIOn
JoInt
~Ie + perimeter beam at horizontal expansion joinl
Jrdead +
Floor
+S
super) + SWTinnefleaf ex1efnall:Jrickworl(on angle
Vertical
-
...... -
-
Horizontal
.....
......
.....
..... ..... ..... .....
---
...... (lull load)
......
-
~ 10 Ylooo'
-
'noo (super)
Notes
1. L. is the horizontal or vertical span of the beam or post. h. is the height of the cotumn.
--
2. Referto figure 5.5. Maximum tneoretical dIfferential deflection between the braced gable frame and the first Ieng1l1 ot diagonal portal frame limited to
660 . 3. The theoretical deflections quo ted are per storey height. However, the permissibe cumul ative deflection at the top of a muhi·storey building will probably further limit the deflection of the columns. 4. The vertical deflectoo quoted is based upon the span . L, between bolt or fixing centres. In addition the maximum length of the outstanding 16t irrespective of whether the angle is mild steel or stainless steel . Maximum vertical deflection outstand ing leg in the order of 1mm. Suitable stai nless steel grades would be 304 or 316 (suggested perm iss ible bend ing stress 80% that of mild steel) . 5. The deflection must be quantified and related to the expansion joint thickn ess. This should be a minimum of 2Omm. As an alte rnative pistol bricks could be incorporated to minimise the visual appea rance of the expansk>n joint.
35
Figure 5.1 TYPICAL EXPANSION AND CONTRACTION MOVEMENT JOIN TS.
CD
'"
Outside
1. Sealant to external face of joint. 2. Brick wall external leaf. 3. Cellular preformed compre ssible sheet. 4. Joints in internal walls are at greater centres @) than in external walls.
,;
Cavity
Plan of expansi on Joint In clay brick external wall.
®QJZ;
Plan of contraction Joints In blockwork Internal walls.
1. Blocks are laid to give a continuou s vertical joint which is filled with mortar as wo rk proceeds .The mortar is then raked out on both r?\ / sides of the joint to a depth of 20mm and the ~ gap filled with a sealing compound . 2. Fair/aced concrete blockwork . 3 }->.,..-,.L--"" 3. Portland cement: Lime: Sand, 1:1:6 mortar. -'''''-_ _ --'_ ' -_ _ -"''''_ Inside
1. Concrete Block. 2. Building paper or sheet D.PC . 3. Plaster finish to inside face stopped either side of joint.
1. Joint pointed with a weak mortar instead of being filled with a seal ing compound. Portland cement: Lime : Sand, 1:1:9 mortar pointing . 2. Fair/aced concrete blockwo rk. 3. Portland cement: Lime : Sand, 1:1:6 mortar.
/LIZ
Outside
Plan of mov ement joint In calcium silicate brick external wall.
f1'I \.:.J
7
~
1. Sealant to external face of joint. 2. Calcium silicate/concrete brick. 3. Cellular preformed highly compres sible sheet.@)
/
I
Cavity
36
Figure 5.2 RECOMMENDED LOCATIONS OF MOVEMENT JOINTS.
Expansion jointin steel frames should be considelfJd torbuildings over 70m long.
Movement joint in brick cladding, frame and strucllJre atl coincide.
-
Gmnge of height - elevation.
z Change of wall thickness - plan.
,
/
,(
%'
Behind latye dJase- plan.
37
F1gul1l 5.3 TYPICAL LOCAnON OF MOVEMENT JOINTS AT COLUMN POSmONS. Note:Ties to the steel frame requi red to maintain lateral stabili ty of wall panels.
CJ (a)
(b)
EJ
(c)
EJ
Z,.t. IV+ /
(d)
EJ
7 ;4 II""' , 7..---_ /-,
(e)
/
(I)
EJ 71 -'--
1- 7--;7"-/
= ~ /~>t CJ
CJ
(g)
(h)
Key: _ - Direction of movement. EJ - Expansion joi nt clay brickwork. CJ - Contraction joint concrete blockwork. SJ - Shear joint to accommodate expansion or contraction.
38
Figure 5.4 TYPICAL LOCATIONS OF MOVEMENT JOINTS AT CORNER COLUMNS. Note:Ties to the steel frame required to maintain lateral stability of wall panels . SJ
]JJ~
~['Rf < ,< f~j CJ/SJ
(a)
(b)
.(
IfffiXX:Y;
r: ~
, (d)
(c)
(e)
.,
/'
,
--
CJ
;
"
.
••
'
f'
•
(f)
(g)
(h)
Key:
..-
- Direction ofmovement.
EJ
- Expansion joint clay brickwork.
CJ SJ
- Contraction joint concrete blockwork. - Shear joint to accommodate expansion or cont raction .
39
Agure 5.5 TYPICAL DEFLECTlON AND SWAY OF SINGLE STOREY PORTAL FRAME BUILDING.
~ limit 10 eaves
'1m e.g. 20mm tI
ronnm.
" -,
""
''- ,- 0
. >
'\ t ®
A
@)
Dellection orsway ateaves due 10 lateral wind loads.
DittetelJlia1 movement at eaves in endbay bel'MJen braced gable frame and adjacent portal frame. 1lestJict movement 10 length
660 Panel A - provide movement joint at 1st portal column Additional joint at gable column if preferred. Panel B - provide further movement joints at either every column or alternate columns. Panel rocks on d.p.c., thus simple support at base .
Load Case 1- Dead & Wind Loading.
~ ./»-
~
~
~-
"- ,
Suggested limit10 eaves del1eclion smaller of'1m e.g. 20mm in
ronnm.
-,
" -,
-,
-c -, "-
"I
<,
Load Case 11- Dead & Superimposed Loading.
40
Figure 5.6 SCHEMATIC ILLUSTRATION OFTHE DIFFERENTIAL MOVEMENT BETWEEN EXTERNAL WALL AND STRUCTURE.
Masonry cavity wall.
SlnJctIJre.
;If' . Differential
/7JOIfJII)OOt exaggemted (not 10 scale).
_ _ _--,1-_ 1
Difference incnJases wit1I increasing height
--e.g. 7 ~ approx. 25mm rnaxJfTlUm.
~ "
Although shown as ftapplies in /he
veroeaJ plane. relative dilleiential /7JOIfJII)OOt 0CClJ1S equally on plan. III
41
Figure 5.7 COMPARISON BETW EEN EXT ERNAL CAVITY WALLS IN MULTI-STOREY BUILDINGS. Cavily wall lies omitted for clarily. Vertical movemenl joints to accommodate horizontal movements also to be provided. External masonry wall Indepe ndent of ateel frame.
Internal skin and external above 9m height supported off ma in atructurallramework.
/lcrommodate ~ mowment
atwaJllrooI junction.
- . - - -....... <;;;;;;; ==
,,
"iii ~ c:
.,2! ".c: '" '0 .Q '" "in ~
t ~
8. ~
se "c:0
.g
.,c:
s;;;
"~
C>
c:
.~
:g
c :; '"
. .,8
.11 to
0.
c s:
~ ~ 0. >.; 'iii
cavity wall fiJred back to SllUcllJIaJfnune using llexible liesIanchors at ead1 storoy height
e- 8~ ., ...., .,'" '0
I~I .'
~
~
.'" >
WARNING :Where partitions or services are supported off the floor and abut the outer wall provi sion must be made for diffe renlial movement.
C> ~
c
32 ~ 0
.'-
':;
--
·i
.
8
.,.,c: ~
.0
C>
e
"0
c:
CD e ~c .S;
'"
!
"iii ~
~ 1lCic z
E ., Q
,.,,-
'" .,=
c: E ...
C > .. ou; ~ E,s; ~
-.' ~
~
Ground level. ,
d.p.c.
42
SECTION
61
STABI LITY 6.1 GENERAL The major structural requirement of nonloading masonry wa lls is to resist lateral wind loads. Alternative approaches for assessing the lateral stab ility of external wall panels are we ll documented. The most common approach for cavity walls to BS 5628: Part 1 (Ref. 6) is listed below:(i) Assess the wind loads to CP3 : Ch .V: Part 2 (Ref. 18) paying part icular attention to the panels situated at the corners of bu'.'dings which will be subjected to loca l suctions of higher magnitude. (ii) Establish vert ical and horizontal lateral support conditions at panel edges. taking into account positicns of movement jcin ts, openinQs . and check panel limiting dimensions. (iii) Determine section properties and flexural strengths for each leaf and calculate the orthoqonal ratios. p.. and design moments
of resistance. (iv) Determine bending moment coefficients. "'. based upon the panel edge r,:straints M. and p.. and calculate the deSign moments for each leaf . (v) Compare the total moment of resistance against the appl ied design moment. If the former is exceeded then re-assess the panel desi~n:. .. a) increasinq the edge restraint conditions. b) reducing the panel span by the use of intermediate vertical posts or honzontal rails, c) increase the thickness of inner leaf . d) increase the flexural strength of one or both leaves. For the purposes of this publication it is intended to concentrate on the following aspeets:(i) Horizontal and vertical lateral support
6.2
HORIZONTAL ANO VERTICAL LATERAL SUPPORT CONDITIONS
A simple support may be assumed where a panel is adequately tied to the supporting structure with metal wall or frame ties. The connection should be capable of res isting the tens'.'e or compressive load generated by the revers ible wind load . A simple support is also generally assumed at all dpc positions unable to transmit tens'.'e stresses. Continu~ may be assumed where a masonry panel is continuous past a column or beam and IS tied to it, Only one leaf is required to be continuous past a support, provided that the cav ity wall has ties in accordance w~h Clause 29.1 of BS 5628: Part I , between discontinuous leaf and the supporting structure. Where the leaves are of different thicknesses the thicker leaf is to be continuous. Figs. 6.1 & 6.2 show some typica l exam ples of sim ple and continuous support conditions.
6.3 CAVITY WALL TIES The BRE publication "Performance Specifications for Wall Ties' (Ref . 26) lists the main structural requirements of wall ties :(i) Ab'.'ity to transmit tension and compression forces without excessive deformation. (ii) Ab'.'ity to allow vertical differential movement. (iii) Ability to allow horizontal differential
movement. (iv) Ability to maintain functions (i). (ii) & (iii) during a fire.
conditions.
-
(ii) Performance of cav ity wall ties . (iii) Effects of size and locat ion of glazed open ings with in a panel.
43
The characteristic strengths quoted in BS 562 8: Part 1 (Ref. 6) for wall ties complying with BS 1243 (Ref. 13) and spacing and factors affecting selection of ties are summarised in Table 6.1, 6.2 and 6.3. The values quoted for shear are only valid for situations in which the tie is used as a shear connector and do not apply to the shear and bending condition of a tie crossing an open cavity. Masonry walls are relatively stiff and as a result horizontal deflections at failure due to lateral wind loads will usually be only a few millimetres. The ability of a tie to accept and transfer load depends on its axial stiffness as well as strength.
Vertical twist ties provide the highest ability to trans mit lateral loads . However, they are unnecessa rily strong in tension and not very flexible and should not be spec ified wh ere large differentia l movements are expected to tak e place between the leaves, or whe re large adjust men ts are likely to be needed during construction. At the other end of the scale , butterfly wire ties are relatively weak in compression and are proba bly more ideally suited to low rise buildings up to two storeys or 11 m in height when used at the standard spac ings recommended in BS 5628 : Part 1 (Ref. 6).
Table 6.1 Characteristic strengths of wall ties used as panel supports (from Table 8, BS 5628: Part 1) Type
CharaetensllC strengths Of tee engaged in dOvetail sJots set: In structw"al ccoceie TenSIOn kN
She ar kN
40
5.0
30
45
35
4.0
Dove tail slo t types of ees (al Ga lvan ized or sta inless sleellrshlail anchors 3mm thick , 17mm min . width in 1.25mm thick galvanized or stainless steerSlol , 150mm long , set In structural concrele (b) Galva nized or stainless steer fishtail anchors 2mm IhiCk, 17mm min . width, in 2mm thick galvanIZed or stai nless steel sots
1SOmm long. set in structural concrete Ie) Copper fisht ail anchOrs 3mm thICk, 17mm min. Width In 1.2Smmcopper slots. 150mm long . set In structural concrete
Cha raaensllC loads in ties embedded in mortar
Shear·
Tensoon
"""., _nabon
Mortar deSign8tlOfl (I) a ndl_'
(.)
IN)
(i). (i1) or (iii)
~
..
"""'"
desig nahon (i),( ii)
(iii)
(i¥l
Cavlty walf tlest
kN
kN
kN
kN
kN
kN
kN
(a) W ire bunerfly ty pe : Zinc coa ted mild stee l or stainless steel
30
2.5
20
z.o
0.3
0 .3
-
(b) Ve rtical twi st type : Zinc coa ted mild stee l or bronze or stain less stee l
50
4.0
25
35
5.0
40
Z.5
(e) Do ub le triang le type : Zinc coated mi ld steel or bro nze or stainless steer
50
40
2.5
3.0
1.25
1.25
-
• Apphc a tNe only to cases where shear exrsts between clos ely abunlng surfaces . e .g . wher e Int ernal walls abut exte rnal wall s or to fie the two leaves 01a collar tolnted wall . They dO not apply to the shear resistance 01a tie crossing an open cavity. • • Prov id ing the open cavity ISnot greater than 75mm.
t See as 12-'3 : 1978 . No le : Bu«_r1ly II •• nol re<:omm.nded for olher then low ri s. buildings.
44
Table 6.2
Selection of ties (from Table 9(b) BS 5628 : Part 3) Type 01tie in BS 1243
Cavitywidth
mm Increasing strength
Increasingflexibility and sound insulation
I
150 or less
Vertical twist Double triangle
75 or less
Butterfly
75 or less
Table 6.3 Spacing of ties ' (Table 6 BS 5628 Pt. 1) Leal thickness
Cavity width
Spacing of ties
Horizontally
Number ct ues
Vertically
per square metre
mm
mm
mm
mm
Less than 90
50 ·7 5
450
450
4.9
90 or more
50-150
900
450
2 .5
The partialsafetyfactorlor matenal strength ( IX m) 01 wa ll lies should be 3.0. When considering the probable effects of misuse
or accidental damage. this value may be halved . The partial safety factor applied 10 wind loads ( IX f) when considering the stabilityof laterally loaded wall panels. whose removal would in no way affectthe stabilityof the remaining structure, should be 1.2.
"Additionalties should be provided within 225mm of all openings at max, 300mm vertical centres.
-
Butterfly wire ties are therefor e not recomm ended for cladding panels in medium and high rise buildings. They should be used only at the discretion of an engineer or suitably qual ified designer. Double-triangle wire ties seem to offer the most suitable combination of both co mpressive strength and the ability to accommodate vertical and horizontal differential movem ents . As with ali wire type ties incorporated In high rise build ings , the numb er of tieslm 2 required should be verified by an engineer or suitably qua lified designer. For example, consider a multi-storey building 50m long x 15m wide x 35m high (approx. equivale nt to t o storeys) located in a smali town or on the outskirts of a large city situated in the North of England. The wind pressures are calculated as foliows to CP3 Ch.V : Part 2: (Ref. 18). Basic wind speed V = 46 mls Topography factor S, = 1.0 (Area 3. Class A) Ground roughne ss S2 = 1.03 (H > 35m ) factor Statistical factor S3 = 1.0 (50 yr. exposure) Design wind speed V. = 46 x 1.0 x 1.03 x 1.0 = 47.4 mls
Dynamic pressure q = 0.613V. = 0.613 x 47.4 = 1.38 kN/m' 1000 1000 Table 7 (Ref. 18): 3/2 < h!w < 6 & 3/2 < IIW < 4 Max. external pressure coefficient Cpe = +0.80 also high local suction coefficient Cpe = - 1.20. Apply ing a part ial safety factor " f = 1.2 for cladding panels maximum compressionforce = (0.8 x 1.38) x 1.20 = 1.32 kN and max. tension force = (1.20 x 1.38) x 1.20 = 1.99 kN . Assuming a 1:1:6 mortar and " m = 3.0 , the quantity of ties requi red for each type is summarised in the table below: Strength (kN)
Type
No. ties
Spacing
1m'
(mm) H xV
Tension Compression Double Triangle
1.3
0 .42
3.2
600)( 450
Vertical Twist
1.3
1.3
1.5
900x 450
45
The above spacings do not take into account the additional tying requirements around the sides of openings orto the perimeter of the wall panel. They also represent the sort of spacings that can be expected for the worst case, i.e. wall panels to the top storey. The spacings of the double triangle type tiescan be gradualty increased as one moves down the height of the building but must not exceed the maximum permitted spacings of 900mm horizontally and 450mm vertically. Fog. 6.6 divides the British Isles into four zones and suggests typical spac i"lls for allernative types of cavity wall ties In single storey and medium to high rise buildings. A number of manufacturers are producing alternative cavity wall tie designs. Each should be assessed on its own merit taking into account structural performance as proven under acceptable test procedures.
6.4 FRAME TIES The selection of a suitable frame tie is very important in terms of both structural performance and ability to accommodate differential movements. Fig. 6.3 shows some typical examples of frame ties commonly available today. Frame ties tend to be manufactured out of strip metal nominally 20mm wide x 2 or 3mm thick by 150mm long , and tend to create similar problems to those posed by the vertical twist cavity ties , i.e. insufficient fleXibility to accommodate thermal and moisture movements. Some of the addrtional precautions necessary, particularly to accommodate vertical andlor horizontal movement, are outlined in Fig. 6.4.(a) and (b). Fig. 6.5 shows some alternative frametie designs which, whilst not being as strong in compression nevertheless are much better for accommodating differential vertical and horizontal movements. Frame ties are not covered by a relevant British Standard, but BS 5628: Part 1 stipulates that where ties are required to transmit compression, provided that any gap between the wall and the supporting structure is not greater than 75mm , the characteristic strengths given in Table 6.1 may be used . Other important functions of the frame tie are:(i) Durability. (ii) Resistance to the passage of water particularly wrth frame ties directly between external brickwork and steel frame, i.e. incorporate an adequate drip .
(iii) Profile suitable for minimising tendency to collect mortar droppings.
6.5 METHODS OF FIXING WALL PANEL RESTRAINTTIES TO STEEL FRAMES Fig. 6.7 indicates a number of alternative methods for connecting wall ties , restraining an external wall panel against lateral wind loads to a frame. The range of fixings available is listed below:a. Bolted connection - main disadvantage is the lack of suitable tolerance on sening out unless the holes are either drilled on site as the work proceeds or vertically slotted in the fabrication shop to accommodate any minor deviations in the bed joint positions. Holes drilled on site are very expensive. Under no circumstances should wall ties be bent to suit the brickwork coursing. b. Self drilling and self tapping screws normally used to fix metal roof decking to steel purlins. They can be installed in a single high speed operation in steel up to 20mm thICk without the need for drilling a pilot hole . Wall panel restraint ties up to 3mm thick can be accommodated. c. Shot fired nails - main advantage is the speed at which the fixing is made. However there are definite drawbacks such as correct cartridge selection, and the experience of the operator using the gun . One common problem is insufficient penetration of the nail allowing free movement of the wall panel tie between the steel web or flange and the head of the nail. It is recommended that a shot fired or power actuated fastener should only be used in shear and compression. Unless adequate site supervision is provided. they are not suited for use with a tie in tension. d. Proprietary and slotted frame tieschannels, positioned vertically or horizontally, may be either welded or bolted to the steel web or flange in the fabrication shop . The slotted frame ties can then be inserted into the channels as the masonry proceeds on site . The cost of this type of fixing can be relatively expensive when compared to either (b) or (c) and may be vulnerable to transportation damage.
46
Table 6.4 Su itability 01 alternative IIxlngs lor wall panel restraint t ies to steel Irame. Type 01 fixing
Nut and bolt
Sell drill an d tap screw
Tension
Shear
./ ./
./
K
Shot fired nails Tie in channel surface fixed to beam/co lum n
./ ./
Tie in channel cast into concrete
./ ./ ./
1.
./
No test date availab le. Spacings giv en in tables to Figu re 6 .6 are based on an ass umed capacity 015 0% of the values scecneopn Tabl e 8, 5628 : Part 1: 1985 10allo w for de-bond ing ol lie and effect s of lever arm produ ced by gap betwee n brickwork and steel frame.
as
e.
Proprietary dovetail slots and ties cast into the edge of an insitu rein forced concrete floo r or concrete casing to a perimete r floor beam. Table 6.4 summarises the suitability of the alte rnative typ e s ollixing normail y used.
6.6 MASONRY PANELS CONTAINING OPENINGS
--
Very litt le experimental data is avai lable on the performance of wail pa nels containing ope nings. BS 5628 : Part 3 (Ref . 6) provides some Simple rules for buildings up to and incl uding lour storeys. These are set out below:"Wails should be free Irom doo rs, windows etc . un less either: (i) intermediate supports are provided , or (ii) the total area of such openings is not greater than 10% of the appropriate max imum area give n in Table 8 or 25% of the actual area of wa il, whichever is the lesser, and no ope ning less than half its maximum dimension from the edg e of the wail . . ." As with most simplilied gu idelines. the designer may lind these a little restr icti ve and for
ope nings whose size and location wit hin a pan el are not cove red by the cod e, an alternative approac h wiil be necessary. BS 5628 : Part 3 Ap pe ndi x D suggests
two options:(i)
Div ide the pan el into sub-pane ls and then design each part in accordance with the rule s given in the code. An obvious dr awback of this method is that line loads on the free edge o f a pan el are not cate red for in the code. Th is p rob iem can be ove rco me using Jo hansen's yield line theory which enables bend ing moment coeff icien ts to be ca lculated for pan els with line load s. Wh ile thi s theo ry is not strict ly appl ica ble to masonry pan el s. good co rrelatio n with exper ime ntal results has been obtained for pan el s without open ings. (ii) As with lin e load s. Johansen's yie ld line theory can be app lied for obtain ing the bending moments in wail pan els with ' smail" openi ngs . Wh at constitutes a ' smail" open ing is dependent upo n a number of factors and the design er should ass ess each individual wall panel on its own meri ts, ta king into account bot h the size and di sposition o f ail openings .
47
Figure 6.1 DETAILS PROVIDING SIMPLE AND FIXED VERTICAL LATERAL SUPPORT.
/
/
/
/
/
/
/'
j. b'
/'
/
(ii)
(i)
(iii)
(a) Fixed vert ical support conditions.
>
(ii)
(i)
(iii)
(b) Simple vertica l support conditions.
48
Figure 6.2 DETAILS PROVIDING SIMPLE AND FIXED HORIZONTAL LATERAL SUPPORT.
D.p.c. material
Dp.c. formed from 2 or3 courses of dp.c. clay bricks to BS 3921: 1985.
must be capable ofresisting !texural bending " stresses.
Ground level. (ii)
(i)
(i) & (ii) Not to be used with porta l frames since the wall is required to be free to rotate at d .p.c. level as the portal frame sways. Therefore use simple support shown below.
V
I IX I"
rY
Inner leaf -~+V-:lk-;-'-- lied to channel cast into !toar slab.
~
/
/ /
,
:..
~
iX :'>(
Outer brick teaf lied to !toar beam.
SOft joint.
Sliding anchor with lies into brick and blocJ
(iv)
(iii) (a) Fixed ho ri zo ntal su pport cond it ions.
Smooth dp.c. Movement joint.
-
-P"'T- h.:~,;.--
(i) Suitable for portal frame.
(ii) (b) Simple horizontal support cond it ions.
49
Figure 6.3 TYPICAL EXAMPLES OF FRAME TI ES.
(a)
(b)
(e)
(e)
(d)
(f)
(9)
50
Figure 6.4(a) DETAILS TO ACCOMMODATE VERTICAL AND/OR HORIZONTAL MOVEMENT.
Channel welded orboiled to lleb 01 standIion
al 450 vertJcal cis. max.
Channel boiled to flange
al 450cIS. max.
Channel bolted through vertJcally slotted holes In flange 0' stanchion using countersunk bolts.
Ie cki-bonr1ed using plastic sleeve Of proptietaJY cki-txJncIlng agenl to allawhorizon/illmovemenl 01masonry. te alsoI"", to move vertically In channel.
Note:Whenusing flexible ties the amountofvertical movement should be limited toavoidrain water penetrating the outer leaf andcoming into contact with the steel frame. Alternatively the ties can be installed sloping down towards the outer leaf.
rles ffxed to llange wilh selldrilling sell lapping ancholS at450vertical
cts.max.
Shot firedlixlngnot acceptable when In
tension.
De-txJncIing ollie alkJws horizon/ill movemenl 01 masonry
--
ne ffxerJ to web withselfdrillingsell tapping anchors orshot firing at 450 verticat ers. max.
,
Y
tI"
Flexible liealkJws movemenl in vertJcal and horizon/ill directions.
51
Figure 6.4{b) DETAILSTO ACCOMMODATE VERTICAL AND/OR HORIZONTAL MOVEMENT.
t
M iId_._ _
to_
beammax.
450ett
»>:
Note :When using flex ible nes the amount at vertical movement should be lim ited to avoid ra in water pen etrating the outer leaf and coming into contact with the steel fra me. Alternatively the ties can be installed sloping down towards the o uter lea f.
52
Figure 6.5 ALTERNATIVE NON-STANDARD FRAMETIE DESIGNS FOR INCREASED FLEXIBILITY.
Courtesyot Harris and Edgar Ltd.
53
Noles 10 Fi gure 6.6 1. Cavity wall tie spacing based on a 3.0m wide x 3 .5m high panel in a 10 storey building 50m long x 15m wide , ground roughness Category 2, Class A. 2. Assuming that only the inner leaf is tied to the frame . Additional cavity ties must be provided around the perimeter of the panel at these spacings in order to stiffen the edge of the panel. 3. Assuming one row of ties at floor level per panel. 4. Cavity wall tie spacing based on a 3.0m wide x 6.0m high panel in a single storeybuilding 30m long x 10m wide , ground roughness Category 2, Class B. Main frames at 6.0m centres with splitter posts positioned midway between main frames . 5. Spacing doe s not conform with blockwork construction. Options are:(i) Use fishtail anchors debonded to allow in-plane movement of the masonry. (ii) Increase spacing to 225mm and tie both the brickwork and blockwork leaves to the frame . TIes to be staggered vertically. (iii) Alter cavity wall cons truction to two leaves of brickwork, the inner leaf tied to the frame at 150mm centres. 6. Double triangular ties can be used at these spacings whether in tension or com pression. 7. Fishtail anchors can be used at these spacings.whether in tension , compression or shear . 8. Additio nal ties provided around perimeter of panel at same centres as floor and column pane l. 9. Additional ties should be provided within 225mm of all open ings at 225mm vertical and horizontal
centres.
54
Figure 6.6 TYPICAL SPACINGS OF DOUBLE TRIANGULAR AND VERTICAL TWIST CAVITY TIES AND PANEL RESTRAINTTIES IN SINGLE STOREY AND MEDIUM TO HIGH RISE BUILDINGS.
Panel Restraint Ties to Frame Wind Zones Medium to High Rise Buildings - Max. Height 10 Storeys (35m) Panel restraint ties'
cavity waJIlies' •
Wi""
,~ .
450
450
-
-
......
-
,--
10100' 1-1
Do,bIe
VertICal
triangular
twist
l> 38
9OOx 450
90011450
2 l> 42
750. 450
90011450
225
450
450
450
3
l> 46
600 x 4 50
900 III 450
225
450
225
450
4
l> 52
450 II 4 50
900 x 450
225
450
225
450
II
(ms- ' )
1
--
..... .
+ ,- ,
Tocolumns
450
,
450
Single Storey Build ings - Max. Heigh t to Eaves 6.0m
_.
Panel restraint ties'
cavity waft ties' x
W'""
V.-
-
......
10coIumn&lsplinef post . .
-
-
..... .
Toeavesbeam H
-
v (ms-'j
Double triang ular
1
l> 38
900 x 450
900 x 450
2
l> 42
900 x 450
900 x 450
225
450
450
450
3
l> 46
900 x 450
90011450
225
450
225
450
4
»
450 x 450
900 x 450
150'
225
225
450
52
twist
225
F""'''' 7 450
450
"lIhIu 7
450
55
Agure 6.7 METHODS OF FIXING FRAME TIES TO THE MAIN STRUCTURE.
(a) Channe l cast into compos ite floor slab.
(b) Channel surface fixed to composite floor slab using expanding bolt.
(c) Channel welded to web or flange of stanchion.
(d) Channe l bolted through slotted holes in web or flange of stanchion using countersunk bolts.
(e) Tie fixed to stanchion using self drilling self tapping anchors or shot fired nails . Note: Shot fired fi xi ng not acceptable In tension.
56
IJ
LIST OF
REFERENCES 1. 2. 3. 4. 5. 6.
7. 8. 9. 10. 11. 12. 13. 14. 15. 16.
17. 18. 19.
20. 21 .
22. 23 . 24. 25 . 26. 27. 28.
BS 5606 : 1978 "Code of Practice for Acc uracy in B u ild i n g ~ BS 6093: 1981 "Cod e 01 Practice for the Des ign of Joints and Jointing in Building Oonstrucnon" BOA De sign Note 3 "Brickwork Dimensions Tables" - Hargreaves T. BS 3921 : 1985 "Specilication lor Clay Bricks" CIRI A Technical Note 113 "A Suggested Design Procedure lor Accuracy in Building ~ BS 5628 : Part 1: 1985 "Structural Use of Unreinlorced Masonry': Part 2 : 1985 "Structural Use of Reinforced and Prestressed Masonry': Part 3 : 1985 "Materials and Components. Design and Workmansh ip~ DO 93 : 1984 "Method s for Assessing Exposure to Wind-driven Ra in~ CP 121: Part 1: 1973 (wijhdrawnj "Brick and Block Masonry': BRE Report "Driving Rain Index" BRE Digest 236 "Cavity lnsulation" BRE Digest 277 "Bum-in Cavity Wa ll Insulation for Housing~ BOA Des ign Note 7 "Brickwork Durabil i~ Hard ing J. R. and Sm ith R. A. BS 1243: 1978 "Spec ifica tion for Metal Ties for Cavity Wall Con struction" BS 729 : 1971 "Hot Dip Galvanized Coatings on Iron and Steel Art icle s~ BSC Publica tion "Steelwork in Cavity Walls~ PO 8484 : 1979 "Commentary on Corrosion at Bimetallic Contacts and its Alleviarion" BS 6213 : 1982 "Guide to the Selee1ion 01 Constructional Sealants" CP 3 Chapter V: Part 2 : 1972 "Basic Data lor the Design 01 BUildings - Wind Loads. "Fire and Steel Construction - An Introd uction to the Fire Protection of Steel" - D. A. Ellio t. "Fire Protee1ion for Structural Steel in Bu ild ings~ ASFPCM/Constrado . BS 5250: 1975 "Cod e 01 Bas ic Data lor th e Des ign 01 BUildings : the Control 01 Condensation in Dwellings~ 6229 : 1982 "Code of Practice for Flat Rools with Continuously Supported Cove rings~ BS 5950 : Part 1: 1985 "Code of Practice lor Des ign in Simp le and Con tinuous Construction : Hot Rolled See1ions~ BS 5950: Part 2: 1985 "Spec ification lor Mat erials . Fabrication and Eree1ion : Hot-Rolled secuons: BS 4 : Part 1: 1960 "Structu ral Stee l See1ions: Specilication for Hot-Rotted See1ions~ BRE Publication "Performance Specifications for Wall Ties~ R. C . De Vek ey. BS 187 : 1978 "Specifica tion for Calcium Silicate (Sand lime and Flintlime ) B ricks~ BOA Design Gu ide "Designing for Brickwork Movement~ Morton J.
as
-57
The Brick DewIopment Association _side House Winkfield Windsor Berbhire 5L4 20X rei Winkfield Row 10344) 885651
British Steel Corporation B5C General Steels Structural Divi sion - 5ectlons
p.o. Box24 , Steel House Redcar, CJeveland. T5 10SOL Telephone: 0042 474242
