CP 116 (1965), Precast Concrete Code of Practice

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BSI CP*116: ADD*% 70 1624669 0294989 3 m

BRITISH STANDARD CODE OF PRACTICE

LARG E-PAN EL STRUCTURES AND

STRUCTURAL CONNECTIONS IN

PRECAST CONCRETE Addendum No. I (1970) to

CP l i 6 : I965 and CP 116 : Part 2 : 1969 The structural use of precast concrete

THE COUNCIL FOR CODES OF PRACTICE BRITISH STANDARDS INSTITUTION

2 Park Street, London WIA 2BS - Copyright British Standards Institution Reproduced by IHS under license with BSI - Uncontrolled Copy Licensee=University of Hong Kong/5910986001

Not for Resale, 07/08/2005 01:57:54 MDTNo reproduction or networking permitted without license from IHS

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BSI CP*33b: ADD83 70 = Lb2Libb9 0294993 3 9

Addendum No. I (1970) lo CP 116

Addendum No. 1 (1970) to CP i I6 : 1965 and CP I I6 : Part 2 : 1969.

This Addendum has been prepared by a Committee convened by the Codes of Practice Committee for Building. It was published under the authority of the Executive Board on 26th November, 1970.

0 British Standards Institution.

SBN : 580 06275 9

This Addendum makes reference to the following British Standard and Code of Practice:

BS 916. Black bolts, screws and nuts, CP 116. The structural use of precast concrete.

British Standards and Codes of Practice are revised, when necessary, by the issue either of amendmettt slips or of revised editions. I t is important that users ascertaiti that they are in possession of the latest amendments or editions,

The following BSI references relaie to the work on this Code of Practice: Committee reference BLCP/35 Dran for comment 69/4327

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Copyright British Standards Institution Reproduced by IHS under license with BSI - Uncontrolled Copy Licensee=University of Hong Kong/5910986001


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B S I CPSLIIb: A D D * I I 7 0 Lb24bb9 0294990 T

Addendum No, 1 (1970) to C P 116

CODE DRAFTING COMMITTEE BLCP/35-PRECAST CONCRETE

(Secretariat: Institution of Striictriral Engineers) Mr. W. Hunter Rose (Chairman)

Mr. J. F. Bradford Mr. A. Marcham Mr. Brian Rhodes Mr. A. N. Sparke Mr. P. B. Kenyon Mr. D. T. Williams M r . A. J. Newman Mr. Andrew Short Mr. A. W. Hill Mr. J. D. McIntosh hlr. J. A. Derrington Mr. G. F. Eley Mr. A. H. Ferrier Dr. D. D. Matthews Mr. E. W. Bunn Mr. R. M. Silber

Mr. W. J. M. Haines Mr. W. S. Scott Prof. P. W. Abeles Mr. J. W. A. Ager Prof. R. H. Evans Mr. J. E. Guest Mr. R. A. D. Noble Mr. W. Hunter Rose J Mr. J. H. Garnham Wright Mr. R. C. Westbrook Mr. G. P. Mallett Dr. W. W. Chan Mr. J. Rodin

Mr. J. A. Loe Mr. Anthony Jones Mr. D. A. S. Lloyd Mr. R. I. Lancaster Mr. D. H. New

British Precast Corrcrete Federation

British Standards Itisiitrction British Steel Itidristry

Biiildiirg Research Station

Cemetit aiid Coiicrete Associatiori

Federation of C i d Eigineeriirg Cotitractors

Federation of Coiicrete Specialists

Greater London Coiiticil Incorporated Association of Arcliitects

Itistitutioti of Civil Etgitieers iiisti!iitioti of Mirnicipal Etrgbieers

arid Siirveyors

institiition of Strirchral Engineers

Ministry of Horisitg atid Local Govertirnent Ministry of Public Biiiidìirg and Works Ministry of Triirisport National Brrildiig Agency National Federation of Biiildittg Trades

Roud Research Laboratory Royal itistitrife o/’ Briiislì Arcliitects Royal Itistitrrtion of Charlered Srcrveyors

The Coiicreie Society

Eittplo)ers

The Committee is indebted to the following for valuablc assistance in connection with the Addendum:

Mr. A. P. Backler, Dr. E. W. Bennett, Mr. P. Burhouse, Mr. E. W. H. Gifford, Dr. F. W. Gifford, the late Mr. J. I<, Miles, Mr. G. Sonicrville and Mr, G . J . Zunz. IC----\

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B S I CP*KLLb: ADD*KL 7 0 1624667 029q992 3 rn

Addendum No. 1 (1970) to CP 116

CONTENTS

Foreword

901 a

902.

2. GROUP

903. 904.

905. 906. 907.

1. GENERAL

Introduction Misalignment and lack of plumb

Page 5

6 7

I: LARGE-PANEL STRUCTURES REQUIRED TO WITHSTAND ADDITIONAL LOADS OR THEIR EFFECTS

Stability requirements 7

Peripheral tie 9

Development of tie force I O

Horizontal connections between loadbearing walls and floors or roof 9

i nternal tie 10

3. GROUP II: OTHER LARGE-PANEL STRUCTURES

, 908. Design 11

4. SïRUCTURAI, CONNECTIONS

909. Connections 12 910. Continuity of reinforcement 13 91 1. Joints transmitting mainly compressive forces 15 912. Joints transmitting bcnding 16 91 3. Joints transniitting mainly sliear 16 914. Other types of cónnection 18 91 5 . Inspection 18

FIGURE

1. Example of corbel 19

This Addcnduni rcprcscnts a stiindrrd of g a d prncticc and tlicrcforr iitkcs llie furni of rcconinicnd;iliuns. Conipliancc witti il docs nut confer iinniuiiily froni relevant statutory and legal rcquircments.

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B S I CP*AILLb: ADDPAIL 70 M 162'4669 0294993 5 I

Addendum No. i (1970) to CP 116

BRITISH STANDARD CODE OF PRACTICE CP 116

THE STRUCTURAL USE OF PRECAST CONCRETE

ADDENDUM No. 1

STRUCTURAL CONNECTIONS IN PRECAST CONCRETE

LARGE-PANEL STRUCTURES AND

FOREWORD When CP 116, ' The structurai use of precast concrete I , was published in 1965, the Foreword stated :

' A sub-coinniittce has been set up to make a detailed study of connections in precast structural frames, and any reconimendations that can be made as a result of this sub-committee's work will be issued as addenda to the Code.'

When the work of this sub-coinmittee commenced, it was decided to include large loadbearing panel construction.

The Ministry of Housing and Local Government published Circular 62/68 in November 1968 dealing with flats constructed with precast concrete panels. The CP 116 committee is aware of this circular and of the notes published by the Institution of Structural Engineers giving guidance on the circular and also their paper ' Structural stability and the prevention of progressive collapse *, This addendum contains the recommendations of the cornmittee with respect to large precast concrete panels at the present time to deal with Recommendation 44 of the Ronan Point inquiry Report:

' A Code of Practice applicable specifically to large concrete panel construction should be prepared and published as a matter of urgency.' The cominittce has had uppermost in its mind the need to guard against

a chain reaction of faiiiircs following damagc to a small part of the structure due to an accidental loading not specifically considered in design, i.e. what has become known as progressive collapse, Thecoinmittee realises that not enough is known about the inagnitude and frequcncy of possible accidental loadings, such as explosive forccs, nor about the response of the structure to such loading. For the time being, therefore, and until thc necessary evidence becomes available, ihe committee has adopted the criteria contained in the Building (Fifth Arnend- ment) Regulations 1970.

The clause numbers in this addendum arc a continuation of the clause numbers in CP 116. Where cross reference. is made to clauses not forming part of

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the addendum, these clause numbers refer to clauses in CP 116, Values in this addendum Lire given in both SI and imperial units as this forms an addenduni fo both CP 116 : 1965 and CP 116 : Part 2 : 1969 (metric units). It supplements and extends these existing Codes, and it should not be used in isolation from the main Codes. In particular, Clause 909 replaces and extends Clause 346.

1. GENERAL

901. Introduction. This addenduni relates to structures which utilize precast loadbearing wall panels of not less than single-storey height. The iecommenda- tions apply particularly where floor and roof are also in concrete panel construction, but tlie principles should be taken to apply whereother types of floor and roof construction are used.

Clauses 909 to 916 also relate to connections in all types of precast concrete structures.

The stability of large-panel structures is normally obtained by arranging and joining floors and walls so that the floors can transmit load, or reactions to the walls which act as thin, deep buttresses and transmit these loads to the founda- tions. The choice of plan form is a most important consideration for eniuring stability and, as far as practicable, the various elements of a building should be arranged in such a way as to reduce lhe effect of any local accident.

The connections and critical sections of panels close to joints have to be designed to resist the worst combinations of shear, axial force and bending caused by vertical and horizontal loads. The detailed design of each critical section at a joint will determine whether there is full continuity, or whether there is a release of bending restraint without excessive reduction of resistance to shear and axial force. Where floor or roof units are designed as simply supported members, care should be taken that their shear resistance is adequate taking into account the effects of cracking due to restraint against rotation at the supports.

Large-panel structures have to be capable of withstanding safely the normal loadings specified for the type of structure concerned. In addition provision has to be made to accommodate local or general effects arising from constructional defects such as misalignment and lack of plumb and for which recommendations are given in Clause 902.

The recommendations given in Clause 903 to 908 inclusive dealing with the connections between units, the tying together of the structure, and the plan form of lhe building, aiin at enabling the structure to accommodate a limited amount of accidental loading which may occur as a result of causes such as construction loading, differential settlement of the supports, thermal movements, explosions, accidental impact, etc., which are not defined as normal loading. These accidental loadings may produce local damage, but the recommendations have as their objective the limitation of the extent of such damage to an acceptable risk. No

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B S I CP*L lb : ADD*% i 0 l b 2 4 6 6 9 0294995 9


structure can be expcctcd to be resistant to all the excessive loadings which could arise in cxtrcnic ciises.

Tlic prominence givcn i o such aims will depend inainly on the probable risk of a ha7ard occurring, and the coiiseqiicncc of fiiilurc. Two standards of strength are rcconiiiiendcd : iiaiiiely. that for large-panel striicliircs requiring special provisions foi addition:il accidciiial loads or their eíìècts (Group I) , for which rccoinnicndations iirc i i ide in Clauses 903 to 907 inclusivc; lind that for all other Iargc-piincl structurcs (Groiip I I ) , for which ilic recoinniciìdations of Clause 908 art: intended.

902. Misalignmcnt and Inck of pluniù. Misalignnieiit and lack of plumb produce clfccis which iirc both local and general. Tlic gcncral cffcct is to produce an ovcriiiriiing iiioiiicnt on tlie building. in addition io wind loading. The local cmects will influence the beliaviour of ihc joints and of tlie loadbearing panels. Both ilicsc cffccts should be takcii into account in design. I n calculating these cílècts, the beliavioiir of both tlic joint and tlie panel should be considered and tlic ecccntriciiies rclatcd to tlic tolerances iii nianufacture and ercction. Such tolcranccs should cover all aspects which are relevant to thcstability of the joint of the loodbcariiig panel. Paiicls should be checked for pluinb and alignment a t all Icvcls.

in ;he absence of firiii data the following allowances should be made: ( i ) li %'I; nim (0.47 d i ; in) out of plumb where I I isthc number of storeys; and (i) A niisaligniiicnt of 20 iiini (0.75 in) for thc purpose of calculating local

The perniissiblc stresses applicable to wind loading niay be adopted when

eccentricity across a joint between piinels.

assessing the stability of ilie structurc in flic light of these eíTccis.

2. GROUP I : LARGE-PANEL STRUCTURES REQLIRED *ro WITHSTAND ADDITIONAL ACCIDENTAL LOADS OR THEIR EFFECTS

903. Stiibility rcquirements. l i 1 addiiioii lo safely supporting all appropriate dcad, iniposcd and wind loads, buildings in this group should bc designed and constructcd so h i t if any oiic striictiirA iiicnibcr (otlicr than one purposely dcsigncd to resist iniiial daiiiiigc) wcrc considcrcd to Iiovc bccii reiiiovcd, tlic conscqucnt sirtictiiral failure would alfcci only LI sniall part of ilie building.

The structural pliin foriii of tlic building has it considerable cTTect on the :ibility of tlic building to iicccpt the loss of one iiiciiibci wiilioiit bccoiiiing scvercly damaged; in addition, the disposition of rciiiforcciiicni for tying iogethcr the building as ii wliolc has grcut infliiencc. I f thc recoiiiiiicndations givcn in Clauscs 904 to 907 arc followed, i t should not be ditìiculi to provide an xccpiablc building.

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Whcn asscssing how tlic building iiiiglit bcliavc iifier the loss of one tiieiiibcr (e.g. as a braced fraiiic, rigid fraiiic, bcaiii cantilever, etc.), accouiit iiiay b2 taken of any building coiiiponcnts, even those wliicli niay bc considcrcd to be non- loadbcaring under iioriiial conditions. 111 this assessiiient, tlie loading io bc considcrcd is the coiiibincd dead, iiiiposed and wind loads described below, and i f this indicates that structural damage would extciid beyond acceptable liiiiits, then the plan forin and/or tlie arrangciiicnt of tlic reinforcement should be niodified to ensure that structural failure is suitably restricted. The aniount of serious dainage acceptable in this contcxt should iiivolvc not more than 3 storcys nor aíìcct niore than 70 ni’ (750 fi2) or 15 ”/ó (whichever is thc least) of a!i arca masurcd horizontally, in cach storey aíïected.

Alicrnatively, damage need not be assuincd to be initiated by thc notional loss of a structural inember if it is capablc of sustaining a load of 34 kN/m2 (5 Ibf/in2) applied to i t from any dircction, siiiiultancously with and additional to the combined dead, iniposcd and wind loads described bclow, together with any load which would be transmitted to it from any immediately adjacent parts of the building, whether structural o r not, if these parts were subjected to a similar additional load applicd in the saiiic direction. Thc amount of load transmitted should iiot cxcecd the strcngtli of tlie adjaccnt paris nor the strength of thcir connections to thc structural nicinbcrs,

Thc extent of tlic part of n structural mcnibcr assunied to h e been initially rernovcd from a building and to have become wholly unserviceable should, in gcncral, bc takcn to be that part which is situatcd or spans between adjaccnt supports or bctwccn a support aiid an cxtreiiiity of tlic incmbcr. For particular types of structural incmbcr the extent of tlie portion rcnioved to be taken into account should be as follows: R e m : the clear span mcosurcd bctwccn adjacent supports or tlic length

of a cantilcver. Colirr>vi or pier: the clear height measured bctwccn adjacent lateral supports. Floor : thc arca included within ils lines of support and its titisupported

edges, if any, Notioniil lines of support niay be iakcn as straiglit lines between adjacent poiiits of support. Notional lines of support niay also be assuincd wlierc substantial partitions occur.

W«ll : the arca includcd within thc clcar Iiciglit nicasurcd betwccn tlic floors and its Icngtli bctwccn adjacent Intcr:il supports or betwccn a lateral support and a frec edgc or 2.25 times its hciglit, which - ever is the Icast. For the purpose of this dcîtnition of wall arca, a substantial partition* at right aiiglcs to the wall, providcd that i t is adcquatcly tied or bondcd to the wall, niay bc assunicd to be a latcral support lo that wull.

For the purposcs of this clause a subsinntiat partition mxy be taken as onc having an nvcragc w i g h t of iiol Icss Ilian I50 kglm2 (SO Ih/fiz).

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B S I CP*KLLb: ADD*L 7 0 i1624669 0294997 2


The arca of wuII or floor considcrcd to be icinovcd iiiay consist of more than one coiiipoiiciit. i t is rccoiiiiiicndcd thut in tlic case of a loadbearing flank wail in cross-wall construction tlic length of the wall section assunicd to have been reiiiowd should not bc Icss than tlic distance between adjaccnt lateral supportes, bctiicen it 1atcr;il support and a frce cdgc, or if [here arc no lateral supports, the cntirc Icngth of tlic flank wall.

Thc coiiibincd dead, iiiiposcd and witid loads referred to above sbould be takcn as:

( i ) tlic dead load, (i¡) one-third of the wind load, und

(iii) onc-third of the iniposcd load, except that (1) in the case of buildings or putts of buildings used predoiiiinantly for

storage, no reduction should be made, and (2) in tlie case of factory or workshop floors the load should not be

rcduccd bclow 490 kg/ni2 (100 Ib/ft2) on each floor.

Wlicrc structurcs arc designcd in accordance with this addenduin, debris loading nccd not nornxilly be takcn into account.

In coinplying vAli this clause, the design stresses for both steel and concrete may bc assumcd as 1.75 tiiiics thosc rcconimcndcd in Section 3, provided that, in the case of niild stccl, the incrcased design stress should not be taken as greater than 95 7; of tlie yield stress of the steel. Where interaction bctwccn ptccast units is assuimd îor bridging action, elfcctive stcel connections have to be provided betwen tlicsc units and care has to be taken to ensure that there is adequate shear rcsistancc in tlie vertical joints between wall panelS.

Rciiiforccment should be provided in every wall panel rcquired for stability and so arranged that the areu of vcrtical reinforcenicnt is not less than 0-1 % of the total horizontal crc,ss-scctional urca of the panel, and thc area of lateral reinforcciiiciit is not Icss than 0.1 :{ of thc total vertical cross-sectional area of the panel.

904. IioriLontal caniicctioiis betwcen loadbcaring walls and Iloors or roof. The steel coniicctioii ai the top and ut the bottoiii of all cxtcrniil loidbearing WIIIIS, or intcinal ioadbcaring \\ails having floors on one sidc only or having the floor on otic side spanning in a dilïcrcnt direction froiii that on the othcr side, should bc capable of resisting Iiurizoiital foiccs i n citlicr dircction at right anglcs to the wall equal t o 25 kN;iii* Iciigtli of joint (1700 Ibf/ft) at tlic top iind 13.5 kN/iiI* (850 Ibfift) at the bottoiii, without cscccding permissible strcsscs.

905. Pcriphcral tie. At cacli floor aiid roof level ¿in clïcctivcly uiiiiikxrupted pciiplicriil tic should be providcd. This tie should bc cap;ible of rcsiscing U

Thcse Figurcs relaie to a floor to cciling Iiciglit nut cxcceding 2-5 ni (8 fi) and should bc incrci1scil I I I proporiiirii for grciiirr Iieigliis.

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Addenduni No. 1 (1970) to CP 116

tensile force of 40 kN* (goo0 Ibf) without exceeding the permissible stress in the steel. The tie niay consist of:

( i ) steel reinforcement in the in situ horizontal external wall-to-floor joint; (2) steel reinforcement in the extcrnal wall close and parallel to the top edge

of the wall panels; (3) steel reinforcc,nent or prestressing tendons in an edge k a n i or in the

edge of the floor or roof construction within 1.2 in (4 fi) from the edge of. the building, or its general line where there are relatively small projections in the face.

Reinforcenieiit provided to resist dead, iiiiposcd and wind loading, or that needed to fiilfil the rcquircnients of Clauses 904 and 906, may form the whole or part of this tie.

At re-entrant corncrs, or at substantial changes in construction, care should be taken to ensure that.thc peripheral tie is adequately anchored into the adjacent floor or otherwise made effective.

906. ínternal tie. At each floor and roof Ievel,eíièctively uninterrupted ties should be provided in two directions at approximately right angles across the building and should be anchored to the peripheral reinforcement at both ends. Where openings occur in the floor and roof, care should be taken that the total tie force across the building is maintained,

The longitudinal (in the direction of spon) and transverse ties should be capable of resisting forces of 25 kN/m (1700 Ibf/ft) and 12.5 kN/m (850 Ibf/ft) respectively without exceeding the permissible stresses; where transverse ties are concentrated at a transverse wall the internal tic steel provided need be based only on a length equal to half of the longer of the floor spans supported by the wall. In buildings with two-way spanning slabs the tie forces in both directions should be equal to forces of 19 kN/m (1300 Ibf/ft) without exceeding the permissible stresses. Reinforcement provided for other purposes may be used for the internal ties.

907. Development of tie force. Except for units less than 1.2 m (4 fi) wide, till internal ties in the direction of the span should bc encased in the precast floor or roof units. Trmverse ties may be encased in the precast lloor or roof units or concentrated in the i n situ joints between units. Whenever ties are encaseù in the floor or roof unit, they should be adequately distributed to avoid out-of- balance eíTects on the units unless these clïccts are allowed for, and, except for units less than 1.2 m (4 ft) wide, at least two ties should be provided in the saille direction on each supported edge,

Where tics are encased in the precast floor or roof units, the tensile resistance between units niay be developed by nicihods allowed in Clause 910 except that the ties between units in the direction of the span should not be lapped at the

These figures relate to a floor to ceiling height not exceeding 2.5 m (8 ft) and should be increased in proportion for grcatcr heights,

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BSI CPrLLb: ADD*L 7 0 Lb24669 0294999 b


joint unless thc adcquacy of the lappcd joint can bc deiiionstratcd. In addition, tic-bars placcd i n tlic i n situ joints bctwccn uiiits slioiild not bc considered as lapping with thc rcinforccnicnt in thc units to form an ctkctivcly iinintcrruptcd tie.

Tics Iiavc to bc assunicd to bc fully tensioncd to within 25 mm ( i in) of the outside surface of a wdl which tlic tie is rcstraining against outward movcincnt. Tlic cificicncy of nicchanical anchorciges havc to bc dcterinincd by test. 'Whcn rcsistancc to tension is given by bond of the stccl bar to thc concrcie, an adcquatc bond length beyond tlic point of full tension has to bc provided,

Burs in thc in situ joints bctwccn units and bars at right anglcs to thc span niay bc lapped to forni cn'cctivcly unintcrruptcd tics but lapping should not bc used for anchoring internal tics to peripheral tics as required by Clausc 906 cxccpt for spccial rcasons to be justificd by the Engiiieer.

Whcre thc location of !lie tics is changed on plan, adequatc overlap should be providcd.

Wlicrc the plan foinis arc complex duc to re-entrants, change of span or other rcasons, adequatc tying togethcr should bc provided.

Where tie forces are developed by bond in in situ coiicrctc in joints, thc niain dimension of tlic in situ coiicrctc should be not less than:

( i ) 2 x bar size -1- 2 x nominal maximum size of aggrcgatc f 6 nim (0.25 in) for site bars lapping in an in situ joint.

(2) 1 x bar size -t. 2 :-: noininal maximum size of aggregatc -I- 6 mni (0.25 in) where a joint encloses a singlc site bar without laps.

Except for a nib at the bottom, thc width of a floor joint should preferably be not less than 35 inm (1% in) where units less than 1-2 ni (4 fi) wide are used and 60 mni (2.4 in) where wider floor units are used.

3. GROUP II : OTHER LARGE-PANEL STRUCTURES

908. Design. For thc design of ofhcr large-panel slructures, thc rccornnieiidations of Clauscs 901 and 902 arc appropriate and the rccoiiinicndations of Clauscs 904 to 907 inclusivc should be adhcred to, with the following modifications:

( I ) the tie forces specified in Clauses 904 to 906 may be halved; (2) tic bars placed in tlic in situ joint bctwcen floor units inay be considcrcd

as lapping with thc main reinforccnient in the units to form an utiintcrruptcd tic, providing the dinicnsions of the gap bctwccn and tliccdgc dciails of ihc units are designed to develop eíïcctivc bond (sec Clause 907);

(3) reinforcement forming tlic infcrnal tic niay bc placcd in'thc floor or roof units or concentrated at the joint, regardless of the width of the units (sec Clause 907);

(4) stccl between the foot of a loadbearing wall and thc supporting structurc need not bc provided where other structural methods sufice (sce Subclausc 9096).

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Addcndiiiii No. 1 (1970) to CP 1 I6

This claiisc tiitiy not iipply to singlc-stoïcy garages and likc structures wlicre adcquiitc nicans of ensuring stability arc provided.

4. STRUCTURAL CONNECTIONS

909. Conncctions a. G~*rrci.n/. Siibclauscs I ) to e of this clause follow closcly Cliiiisc 346 and give

gencral advice on tlic dcsign and construction of coiincctions. The remainder of this addcnduin givcs more detailed requircnients for particular types of connection. 4

h. S/rrtc/rii.al reqriii.enieri/.r, Tlie overall stability of the building, includiiig t tic sinbiliiy during tlic period of construction, should be considered wlieii designing and dctailing the connections. All nienibers should be adcquatcly tied togctlicr. Fiequciitly, the most scvere forces Lind stresses arc applied to precast units during the various stogcs of handling and construction. Tlie clkcts of these operaiions should bc carcfiilly studicd, particularly at seatings and bearings, to avoid spalling of cdgcs and corncrs which can Icad to instabilify and failure.

Coiincctioiis shoiild, howcver, where possible, he dcsigiicd in accordancc with thc gciicrally acccptcd thcorics applicable to reinforced concrete, prcstrcsscd concrcic or structural steel. Wlicrc, by tlie nature of the construction or inatcrial iiscd, siicli tlicorics arc not applicablc, the cniciency of the connection should be proven by tests and its usc justified by rcasoncd analysis of tlic tcst rcsulis. Care should be takcn to incliidc in tlie design the eíTccts of possiblc horizontal forces due to shrinkage or other causes and as far as possiblr: provision for niovcnicnt throughout the lifc of the building should be considered when designing and dctailing the coiincctions.

Dctailcd drawings of cach type of conncction shoiild be iiiade at thc design stage to a siiltìcicnt scolc to indicate the intcrrelation of ;ill parts of the coniicction. These tlctiiils should iillow for the eíTect of cuniulativc tolcranccs in diiiiciisions allowcd iindcr Clause 407 and in addition for ercctioii clearances in tlic iisscnibly and location of projccting parts. Where critical, thc :iCtüiil tolcroiiccs dlowcd by the dcsigiicr should be stiitcd on tlie drawings.

This iiiforiiiaiioii should bc avoilablc at tlic iiiiic of tciidcr. C. Prci/c,c/iorr. Coiiiiccíioiis slioiild bc dcsigncd 10 i1iiiiiit:iiii thc stmidiird of

protcciioii iigiiiist wciiilicr, lire and corrosion rcqiiircd foi' the rcniíiiiidcr of the siriici iirc.

d. íl/,i,<,<ri<ilrce. Wlicrc contiections arc io bc cq~osed. iticy should be so dcsigiicd tliiii tlic qii;iliiy of tippciirance icqiiircd for tlic iciiiaindcr of ilic striictiirc or building ciin bc iciidily :ichicved. This tiioy oftcii hc bcticr donc by ciiipliiisiriiig ratlier tt i i in by atlciiipiiig to coiiceíil tlie coniicctioiis.

c. Aí~i i i i$ ic / rrw, rr.ssertrb!y <ir id erectioii. klcthods oï iiianiifiiciiirc and erection I - LL



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Addcnduni No. 1 (1970) to CP I6

should be considered during design, and the following points should be given pnrticulnr attention:

( i ) V h r c projectitis burs or scctions arc reqiiircd, thcy sliould hc kept to a miniiiiiini and iiiade as simplc as possible. Tlic lengths of such projections should not bc iiiorc than ncccssary for security. .I

(2) Fragile fins and nibs should be avoic,ed. (3) Fixing devices should be located in concrete sections of adeqiiatc streiigth. (4) The prwticiibility of both casting and nssciiibly should be considered. ( 5 ) Specific instriictions shoiiid bc passki to the sitc, where necessary, on

the following: i Sequence of forming joint. I

Critical details and dimensions. e.g: accurate location required for a particular reinforcing bar or i i i i i t to tie left free to slide. Details of teiiiporary propping and ti. ic wlizii i t niay be rcinovcd. Description of general stability of s ‘y riicture with details of necessary

Degree to which uncompleted structurd niay proceed above the coinpletcd and matured section. Fiil1 details oî specialized iiiaterials. Tlic tolerances allowed for by the design,

temporary bracing. I

I (6 ) Most connections require tlie introduction of suitable jointing inaterial.

Suíììcient spacc should be allowed in the design for such iiintcrhl to ciisure that tlie propcr lilling of tlic joint is practicable.

910. Continuity of reinforcement

to ensiire continuity: a. Gvtrerd. The following jointing nicihods may be used for thc reinforcement

( I ) Lapping of bars. (2) Loop and dowel joints. (3) Sleeving. (4) Threading of bars. (5 ) Wclding of bats by splice or lap wclditig. ( 6 ) Any oilier iiiethod which Iias been proveil to bc sofe aiid priicticable by

1). Lqpiiv of 6 m : ~ The rcqiiireinciits for laps hi bars giveti in Clausc 315

Grori/pocke/. Tlic design should providc agoinst air locks diiririg groiitiiig. Siirnip.v. Tlic Iíippcd bnrs sliould be adcqu;itely eiicloscd by stirrups or

rcsiraiiicd by adjacent concrctc, c.g. as in joints bctwccii floor units. c. Loop « / i d dowljoi / i / , s . In loop and dowcl joints thc ritdiiis of tlw bend in

the loop lias to be sudi that tlic bearing stress docs not excecd tha t given in 13

independcot tests.

iippiy in ;iddition to tlic following design rules:

,



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BSI CP*&Lb: ADD*& 70 Lb24bb ï O295002 O

Addendum No. I (1970) to CP 116

Subclause 3155 Thc relativc position of tlic loops and the disposition of the dowcls should be arranged te ciisurc propcr transiiiission of thc load, without exccssivc displaccmcnt.

d. S/eevittg. ( i ) Two priiicipal types of slcevc jointing may be used: ( I ) Fillcd slccvcs capable of transmitting both tensilc and compressive

forces and uscd with advantagc in joining high-bond bars. ( 2 ) Slccvcs which align tlic acctirntcly square cut cnds of two successive

bars nicchanically to iallow the trnnsiiiissioii by end bearing, of coniptcssivc

( ¡ i ) ,4 /<\r t i tnm/. Tlic delitilcd dcsign of the slcevcs and the nicthod of iiiiiiiu1;1ctwc iind assciiibly should be such as to cnsurc that the cnds of the two bars can he accuriitely aligncd into the sleeve,

(iii) Cuircrvte cuwr. The concrete cover provided for ilic sleeve should be iioi Icss i h n that spccificd for iiornial reinforcemciit (Clause 3 IO). Additional light stirruping or otlicr encasing rciiiforcemcnt should be provided in the covcr whcrc slccvcs arc embedded i i i concrctc iiiadc with nori~ial aggregates, to cnsurc that the concrcfc covcr does not spall prcniaturcly in thc cvcnt of fire. No stich additional reinforcciiicnt nccd be provided for slccves cmbcdded in structural gradc lightwcight aggrcgatc concrete.

(iv) Ao/oryppe IC'SIS. Not Icss than thrce saiiiplcs of each type of slecve should be subjcctcd to loading tcsts to destruction, to deteriiiinc its loadbearing capacity and dcforniation undcr load.

e. Tlirecdirg. ( i ) ?'he following niethods may be used for joining threaded bars :

( I ) The threaded ciid of bars may he joined by left Iiandjright hand couplcrs. This type of tlircadcd connection requircs an cxccptional dcgrec of care and accuracy in iiianufacturc in view of the difficulty of cnsuring alignincnt.

(2) Onc set of bars iiiay be wclded to a steel platc which is drilled to rcccive the tlirciided cnds of the second set of bai's to be joined to the first sei. the ends of thc sccond set of bars k i n g held to ihc plaie by iiieaiis of nuts.

(¡i) Luckiirg c/erices. Wlierc fhcrc is ii risk of thc screwed coniicction working loosc. c.g. during vibration of i i i sitii concrctc. a locking dcvice should be incorporatcd. c.g. locknuts or spring washers.

(iii) Prorec/ioti. Girat care should be t;ikcii ;it all stugcs of triinsporiii- tioti, storagc iind erection to protcci the tlirciids froiii accidciitiìl daiiiiigc.

(iv) T l p e uf src~d. Thc use of tlircadcd coiincctioiis sliould'bc rcstrictcd to plain rouiid mild steel bars. Wlicrc tlicrc is diiliciilty in producing ti clcaii thrcad at thc cnd of a bar, siccl normally spcciíicd for black bolts (US 916 : 1953*. Clause 2) having ia niiniiiiuni tciisilc strcngili of 430 N/iiiiii2 (28 foiif/itP) sliotild be uscd.

forccs OiilY.

DS 916. ' Dlack bolis, s c r w s nnJ miis I.

14



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E S 1 CP*LLb: ADD*L i 0 Lb24bb9 0295003 2


(v) Design stresses. The structural design of the threaded joints should be based on the cross section of the bar at the root of the thread, the permissible stresses being as for reinforcemcnt generally. In the case of connections in tension, however, the permissible strcss of the steel should be that specified for bolts.

91 1. Joints transmitting mainly compressive forces a. Joi~irsfillcd with Ci situ coticrete or mortar. When joining walls the space

between adjacent wall panels should be capable of being properly filled by using normal standards of workmanship and supervision and therefore the filling inaterial and method of filling should be taken into account when sclecting its shape and size, The assembly instructions should contain definite information as to the stage during construction when the gap should be filled. The assembly instructions should form part of the design.

The strcngih of the concrete or mortar to be placed in situ should be taken into account in the design and stated. Where dry packed mortar is used as a

its consistency and waterlcement ratio are appropriate to tRe method of filling and compaction and that the cavity is completely filled.

Local stress concentrations due to surface irregularities or shims of too small an area should be avoided.

In the absence of more accurate information derived from a comprehensive programme of suitable tests, the area of concrete to be considered in calculating the strength of the joint may be either

( i ) the area of the in situ concrete ignoring the area of the intruding units; or (2) 75 %of thearea ofcontact between wall and joint, whichever is thegreater.

The area of contact should be assumed to be not greater than 90 % of the wall area. Only those parts of the precast units which are solid over the kar ing should be considered and the units should be properly bedded on concrete or inortar.

b. Direct bearitg connection. The contact surfaces should not contain excessive irregularities and the compressive stress in the contact area should not normally exceed 0.25 idw. Where the members to be joined are made of concretes differing in strength, then for purposes ofcnlculation the lower concrete strength is applicable. Higher stresses may be used where suitable measures are taken to prevent bursting of the concrete at the interface, e.g. the provision of steel bearing plates and/or additional enveloping or binding reinforcement at the column heads. Where stresses in excess of 0.5 itw are used, these should bejusti- fied by the results of loading tests specially designed for the purpose.

Direct bearing connections should not be used for wall to wall connections. Horizontal loading across direct bearing connections can reduce the load-

bearing capacity of the supporting nieinber considerably by causing prcmature splitting or shearing. Premature failure can be prevented by:

-

filling material it should comply with Clause 413, but care should be taken that 6

( I ) sliding bearings; 15

I -



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E S 1 CP*LLb: ADD*% 70 rn Lb24bb9 0295004 4


(2) transverse reinforcement in the form of binding or welded niesh; (3) continuity reinforcenient, provided to tie together the ends of two units

meeting over the supporting wall. Where, owing to large spans or other reasons, large rotations are likely to

occur at the end supports of íiexural members, suitable bearings capable of accommodating these rotations should be used.

912. Joints transmitting bending. Tlie design of structures consisting of precast concrete niciiibcrs is normally based on the assumption that the joints between thcse members are not capable of transmitting bending moments. Ai working loads, however, most joints have a measure of flexural stiffness, and unless this is taken into account in the design and suitable precautions are taken, unsightly

913. Joints transmitting mainly shear a. Corbels (see FI&. i). A corbel is a short cantilever beam in which the shear

span bears a ratio of less than 0-6 to the effective depth at the face of the supporting menibcr. Tlie bottom front edge is frequently chamfered and the depth of the chamfer should not exceed one-half of the overall depth at the face of the supporting nieinber.

The main tensile reinforcement in bending should be calculated in accordance with Clause 31 i or 3 13. The shear reinforcement should be- calculated in accordance with Clause 319, except that it should in no case be less than one-half of the main tensile reinforcement.

The main longitudinal reinforcement should be adequately anchored at the front face by welding to a crossbar of at least equal strength or by bending back the longitudinal bars, forming a loop. In either case the bearing area should not projcct to the front of the corbel beyond the straight portion of the niain reinforcement. The cross section of the main reinforcement should be not less than 0.4 % nor more than 1.3 % of the effective concrete section.

The shear reinforcement sli9uld consist of horizontal stirrups placed over tlic upper two thirds of the effective depth of the corbel. Where lhe corbel is - W g n e d to resist a stated horizontal force, additional reinforcement should be provided sufficient to transmit this force in its entirety. Where a corbel is designed to resist a stated vertical force only, additional reinforcement has to be providcd capable of resisting not less than 10 % of the vertical reaction taken to act as u horizontal force. The reinforcement should be welded to the bcaring plates if providcd and should be adequately anchored within the wall. The bcaring should satisfy the provisions of Subclause 91 IB.

6. Walls atrdJloors rratrsnriititrg drear. A joint niay be assuiiicd to transmit a shear forcc bctwccn panels, such as arises whcn a wall acts as a wind bracing wall or a floor acls as a wind girdcr, providing one of the following rcquircnicnts is satisfied:

i6

local failures niay rcsult (sec Clause 901). 1



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a

BSI CP*LLb: A D D x L 70 Lb24669 0295005 b =

Addenduni No. 1 (1970) to CP i16

( i ) Floor units transmitting shear in a horizontal plane should be re- strained to prevent their moving apart horizontally, and the joints between theni should be formed by grouting with a suitable concrete or mortar mix. No reinforcement need be provided in the joint, and the sides of the unit forming the joint may have the normal finishes given in Subclause 409b, when the calculated shear stress in the joint does not exceed 0-15 N/mm2 (21.8 Ibf/in2).

(2) No reinforcement need be provided in joints that are under coni- pression in all design conditions when the sides of the panels or units forming the joints comply with the finishes in Subclause 409d, and when the calculated shear stress in the joint does not exceed 0.30 N/mni* (43.5 Ibf/in*) (see Clause 91 ia).

(3) The shear stress calculated on the minimum root area of a castellated joint is less than the permissible shear stress in Table 3 (Clause 303). Separation of the panels normal to the joint should be prevented either by steel tics across the ends of the joint or by a compressive force normal to the joint under all loading conditions.

A taper is usually provided to the projccting keys of a castellated joint to ease the removal of formwork. To limit movcnients in the joint, this taper slioiild not be excessive.

(4) Reinforcement is provided to resist the entire shear force which does not exceed Q given by:

.

Q = pstArt tan + where pst -- permissible tensile stress in the reinforcement which should not exceed either i40 MN/m2 (20 o00 Ibf/in2) or the stress which can be developed by bond, Ast = cross-sectional area of the reinforcement which should be perpendicular to the cross section and properly anchored on both sides of the joint (reinforcement which is connected to other properly anchored reinforcement by one of the methods given in Clause 910 may itself be assumed to be properly anchored) and I$ = angle of internai friction; tan 4 can vary between 0-7 and 1.7 but the following value may be assumed: Smooth intcrfacc as in untreated construction joint (0.7). Roughened or castellated joint as defined in (i), (2 ) or (3) above without continuous in situ strips across the ends of the joint (1.4). Roughened or castellated joint as defined in (i), (2) or (3) abovr: with continuous in situ strips across thc ends of the joint (1.7).

Where the above expression is used in calculations to prove stability in the damaged state as required by Clause 908, a steel stress of 1 -ï5ps1 may bc assumed subject to a limiting shear stress on the joint of 5.5 MN/ni* (800 Ibf/in*).

( 5 ) The shear forci: across any joint undcr comprcssion does not excccd 17

w



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B S I CP*KL16: ADD*1 70 H 1624669 0295006 & H

Addciiduni No. I (1970) 1 0 CP 116

0.3 ian 4 tiiiies tlic coniprcssivc force norriiul i o itic joint whcrc tan 4 l ias !lie velues given iihovc. The \\hale shear force iiiay he assuilied io be resistcd by

i61 l i can be shown thai rcsisiancc to sliding of the joini is providcd by c Iter iiic;iiis for inïiaiicc shear displacciiicnis hci\vcet-i paiicls i i iay be I>rcscnied hy ilic rciiiforcciiicni in ihc i n situ joinis ~ICI'OSS ihc ends of ilie panels.

914. Other types of connection. Any oihcr type o f conncciioii tvliicli cai1 i-c sho\v i i io bc cqxihlc of ciirryiiig tlic loxis acting on i i niay he used. Aiiiongsi tliosc siiiiablc for rcsktiiig shcnr and flesurc are:

( I \ cLriincciionz wing siruciiiral siccl imcris: f 2 ) coiiiicciioiis iii:idc by prcsircssing iicrohi: (tic joiiii.

I h i i i ;idlicsitcs iiiay hc iiscd io forin joinis suhjccicrl :o conipressioii h i i ioi I O rcsisi icrision o r shear. Tlicy may not hv iiscd wlicre i l icy arc noi adeqiinicly I~ro~ccicd ;ig;iiiisi ilic cflects of fire.

915. Iiispectioii. A carcriil visual inspcciion of coniicciion prior i o concrciing i\ qxci;illy iiii1iori;irii.

rrictioil.



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BSI CP*LLb: ADD*L 70 E Lb24669 0295007- T - . h -

h iin tensile - reinforcement welded to cross bar or looped a s drawn

Addcndii in No. I (1970) IO CP I 16

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' I I I ' I I I I A

r I l

Fig. I . Example of corhel



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Documents

CP 116 (1965), Precast Concrete Code of Practice