IRC 87-1984 Falsework for Road Bridges

8/12/2019 IRC 87-1984 Falsework for Road Bridges

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IRC i 87-1984

GUIDELINES F OR THE DESIGNAND

ERECTION OF F LSEWORKFOR

ROAD BRIDGES

THE INDI N ROADS CONGRESS996


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IRC 87 1984

GUIDE LINES FOR THE DESIGNND. ERECTION OF F LSEWORKOR

RO D BRIDGES

ublished yTHE INDIAN ROADS CONGRESS

Jamnagar House, Shahjahan Road,New Delhi-110 011

1996Price Rs. 36

Plus packing postage)


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IRC : 87-1984First Published March, 1984Reprinted : August, 1996

Rights of Publication and of Translation are reserved

Printed at M/s. Sagar Printers and ~ l i s h e r sNew Delhi-110003 1000 cop1es)

Clause NoIntroductionI Scope2. Definitions3. Materials

3.1. Genera)

CONTENTS

3.2. Specifications for Materi als3.3. New Materi als3.4. Formwork Accessories3.5. Form Coatings or Release Agents and Sealantsfor Formwork

4. Design

5.6.

4.1. General4.2. Loads4.3. Permissibl e Stresses4.4. Overturning4.5. Deflection Limits4.6. , Analysis4. 7. Lateral and Diagonal Bracings4.8. Shores4.9. Proprietary Items4.10. Foundation of Faisework4.11. Special requirements for Prestressed Concrete4.12. Commo n Deficiencies in designPlans

Site Operations6. I. General6.2. Erection6.3. Concreting Operations and Application of Loads6.4. Removal of Forrnwork

IRC: 87 1984

Page No.

24

588899

103

1414145

151916171718

18189

2122


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IRC: 8 7 1 9 ~ 4 .6.5. Precautions for Special Structures6.6. Re-use and Maintenance of Formwork6.7. Check for Workmanship

7. Special Formwork7.1. Slip Forms7.2. TravelHng For ms7.3. Extreme Weather Condition

8. Trusses or Girders used as FalseworkAppendix 1 : Information to be supplied bymanufacturers of proprietary systems .. Appendix : Typical connec,tion details offalsework

2324242626267

2728

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IRC : 87-1984

GUIDELINES FOR THE DESIGN AND ERECTIONOF FALSEWORK FOR ROAD BRIDGES

INTRODUCTIONThe draft of the Guide1ines for the Design and Erection ofFalse work for Road Bridges was prepared by a Subcommittee(personnel given below) of the Bridges Committee and was .finalisedby them in their meetings held on the 23rd, 24th and 25th November, 1978. The draft of the Guidelines were approved by theBridges Commi ttee in their meetings held o n the 12th 13thFebruary 29th 30th December, 1981 and 6th March 1982.

G. Venkatesu1uS.C. MotwaniK.D. BaliT.S. ChandrasekharG.S. IyerD.N. KhuranaG.C. MathurN.Y. MeraniA.D. NarainK. Suryanarayana RaoP.S. SandhawaliaJ.S. Sodhi

... Convenor... Member SecretaryRep. of M,s. Gammon (India)Ltd. (S.R. Sivaswamy)Rep. of U.P.S.B.C. Ltd.(Brijendra Singh)Rep. of Mfs. Indian Plywood.Manufacturing Co., Ltd.Bombay (Lt. Col. G.B. Singh)Rep. of N.B.C.C. (A.I. Ibrahim)Rep. of C.A.I. (T.M. Menon)

Director General (Road Development)and Addl Secretaryto the Govt. of India Ex-officio.These guidelines were approved by the Executive Committeein their meeting held on 21st -July 1983 and by the Councilin their108th meeting held at Pondicherry on 21st August, 1983 subjectto the condition that the comments made thereon should be takeninto consideration by the Member-Secretary an d the Convenor ofthe Bridges Committee and they were authorised to make any

changes considered necessary in light of the comments made by themembers of the Council. The comments of the members of theCouncil were again considere d by the Bridges Committee in theirmeeting held at New Delhi on 16 th December 1983 and theguidelines were finalised for publication.1. SCOPE

These guidelines apply to the design, fabrication, erection andstripping of falsework built from mostly structural materials andused as temporary structures for supporting most type of permanentconcrete bridge structures.1


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IRC: 87 1984The guidelines prescribe only the minimum requirements andare to be supplemented by design judgement andexperience.

2. DEFINITIONSFor the purpose of these guidelines, the following definitions

shall apply :2.1. Base PlateA device used to transfer the vertical load from a structuralmember to its foundation. or foundation structure element in such away as to distribute the load2.2. Bay LengthThe distance between the centre lines of two adjacent shores.2.3. BlindingA layer of lean concrete 50 to 100 mm thick, put down onsoil to seal it and provide a clean bed for construction work.2.4. BracingThe system of members (diagonal and horizontal) which actsin compression or tension and stiffens a frame against defo rmation.2.5. Coupler or ClampA device for connecting together the component parts oftubular shores and bracings.2.6. Dead LoadThe self weight of a member being designed or analysed.2. 7. FalseworkThe total temporary structure system including the formworkfor the permanent structure during erection and until it becomesself supporting.2.8. ForkheadA U -shaped housingto take joists or stringers.

2 9 ~ FormworkjFormsA part of the falsework used as mould for the poured con

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IRC: 87 1984crete. t consists of the sheeting and its immediate supporting orstiffening members.

2.10. FrameA fabricated principal unit of falsework made from timber orsteel (tubular or rolled steel sections).2.11. Grade StressThe appropriate safe-working st ress level of timber.2.12. Guard Rail or Hand RailA ho_rizontal rail secured to uprights and erected along theexposed S J ~ e s of. scaffolds to prevent persons from falling off anedge or losmg their balance.2.13. LiftThe height of concrete formed and cast in one pour.2.14. Load Bearing MemberAny component of a structure which is directly subje cted toload.2.15. Prop/ShoreIndividual vertical or inclined member used to support loads.2.16. Resb lring or Reproppiog

. . A system used during the construction operation in which theongmal shores are removed and replaced in a planned sequence toavoid any damage to partially cured concrete. 2.17. Scaffold/ScaffoldingAny t e m p o r ~ y elevated platform and its supporting structureused for supportmg workmen or matenals or bothand in thecontext of these guidelines is deemed to comprise wooden or steelmembers. t includes similarly constructed means of access andegress.2.18. ShimA thin piece, usually, of wood, metal or stone used for adjust-ing the formwork.


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IRC : 87-19842.19. Shock LoadThe load imparted to.a structure due to impact of material.2.20. Sill or Sole PlateA footing or bearing (usually of wood) which distributes the

vertical shoring loads to the ground or slab below.2.21. StrutA member in compression.2.22. StudA vertical or horizontal stiffener fixed to the back of the form

sheeting.2.23. Superimposed Load or Imposed LoadAny load that a member is required to support in addition toits own self weight. t includes loads such as that of concrete,forming material, falsework material, workmen, equipment andwind forces, etc. 2.24. TierA unit or frame or shore erected one above another in a

vertical direction.2.25. TransomA cross beam or horizontal scaffold tube.2.26. WedgeA piece of strong timber or metal which tapers in its. lengthand is used to adjust elevation or line to tighten or release formwork. Folding wedges comprise a pair of wedges laid one above

the other with thick ends apart.2.27. YokeIn a vertical slip form, a yoke in the form of inverted Uwhich carries the wall forms and is itself carried and. raised by a

jack or a screw arrangement.3. MATERIALS

3 1. GeneralThe permitted materials for falsework in the context

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IRC; 87-1984of these guidelines are timber, steel, plywood, concrete andmasonry.

3.2. Specification for Materials. All the. m a t e r i ~ s shaH conform to the specified quality

c o n s ~ s t a n t wtth the mtended purpose and actual site conditions asapplicable. .Where materials or components and their uses arecovered by existing IS or IRC Standards as shown n Table 1 o n f ~ r m i t y w i ~ h them s ~ j e c t to the satisfaction of supplementaryreqmrements, If any, ansing out of these guidelines shall beensured.

TABLE 1

Material Principal use Minimum size

(l) 2) 3)

(a) Timber i) Form,shoring andscaffolding

ii) Form fordeck soffit,beam sidesand other vertical surfaces 25 mm

i i i) Beam soffi.t 50 rnmCoJumn sides. 30.mmiv) Props 75 x 100 mmv) BalJies forshoresfor bracings 100mm dia75 mm dia

ISpecification Remarksand designdata sources

4) 5)

IS : 883 Soft woods ofpartially seasonedstock arerecommended forformwork sincefully dried timberswells excessivelywhen it becomeswet and greentimber will dryout and warpduring hotweather.

-do--do--do

-do-

*IS : 883 Code of Practice for Use of Structural Timber in Building.5


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IRC : 87-1984 IRC : 87-1984(1) (2) (3) (4) 5) (1) (2) (3) (4) (5)

Form work com-(b) Ply- Forms and 6mm IS : 4990** Plywood ponents such aswood Form linings provides large plates, prop,Sheeting and area of joint frames, accesso-panels 12mm free smooth ries and trestles, etc.concrete surface, (iv) Clamps/ IS:2750@@. easy in handling, Couplers forlight weight, tubularfiexibiHty of use, centeringcapacity to with- (d) A_Jumi- Light.weight Manufac-stand hot and mum panels and turer scold c1iinates,.no A Joys forming systems datashrinkage shoring andcupping or falseworktwisting, high (e) Fibre Precast concrete Manufac- This material is aresistance to Glass construction turer s glass fibre rein-impact load and and architectural data forced plasticvibration, as of concrete product, exceJJentbonding. cast concretereusability. surfaces can be(c) Steel i) Sheet Plate Fo.rms and Form IS:226+ Steel forms can moulded to anyshape without -linings 3,15 mm IS:2062* stand repetitive joints or seems.with form IS:961@ use. (f) Precast 37 mmvibrators IS:l?77 -dO- - concrete(ii) RoUed Form s.upports IS:961@ Steel framing and (g) Asbes- Column forms UsuaHy left inSections and shoring IS:226+ bracing can be tos and duct formers position andtubes framing, shoring IS:l161** used in conjunc- cement provides theIS:1977 tion with timber finished surfaceIS:2062* and plywood (h) Lami- Circular column Manufac-panel system. nated forms, formers turer s(i) angles pres:;ed for small ducts data50x50x6mm paper,

ii) flats tubes50x6 min (Card(iii) tubes Board)40mmdia i) Hard Form panels and o~ o m i n l bore board G.I.Jiningwith wall with minimum 12 mmthickness lining thick4.05 mm j) Plastics; Formliners o

(iii) Proprietary Forms can be Design data to be Polyete.; fo r decora tiveSystems obtained for obtained from rene, concreteround, square the manufacturer Polyeth-rectangular or of the proprietary elene,Polyvin-polygonal shapes. syst_ems. ylchlo-ride**IS 4990 Specification for Plywood for Concrete Shuttering :work. (k) Rubber Form lining o+IS 226 Specification for Structural Steel (Standard Quality) and void*IS 2062 Specification for Struc tural Steel (Welding Quality) forms@IS 961 Specification for Structural Steel (High Quality) @@ IS: 2750 Specification for Steel Scaffoldings.IS 1977 Specification for Struct ural Steel (High Steel)**IS 1161 Specification for Tubes for Structural purposes. ote : The sizes given in Table 1 are only indicatice of the minimum require-ments and shaU be derived from the actual detailed design.6 7


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IRC : 87-19843 3. New MaterialsSeveral new materials like aluminimn alloys, fibre gl?.ss,asbestos cement, plastics at;Id rubber, etc, are n o ~ available w b t ~ hcan be used for false work. As these matenals are not yet mcommon use it shall not be interpreted to exclude tbe use of any

such m t e r i ~ l s which can meet quality and safety requirements forthe work. In the designs in which these new materials are used,the manufacturer s specifications and data shall be adopted aftertests are conducted on them to verify the parameters, if necessary.3.4. Formwork Accessories

. For the d ~ s i g n of form ties, form anchors and form hangerspermissible stress shall c o n f ~ r m to the r_elevant standards as well asdesign data based on test evtdence pubhsh.ed by t h ~ manufacturers.3 4.1. Form. ties: A for n t i ~ is a tensile unit adopted forholding concrete forms against the active pressure of ~ e s h l y placedplastic concrete.. Form ties. are also manufactured part pro-

prietary system. 3.4.2. Form anchors: Form anchors are devices used in-thesecuring of formwork to previously placed < o n c n ~ t ~ of aqequatestrength. The devices normally e m e d ~ e d m the concreteduring placement. Actual load carrymg capacity of. the anchorsdepends on the strength of c_oncrete in which they are embedded,the area of contact between the concrete and anchor and the depthof embedment. Manufacturers.also publish design data .and. estinformation to assist in the selectton of proper form anchor devtces.3.4.3. Form hangers: Forni hangers are often. tised to sus

pend formwork from a supporting structure.3.5. Form Coatings or Release Agents and Sealants for Formwork

3.5.1. Form coatings: Form coatings or sealants are usuallyapplied to contact surface e i t h ~ r d ~ r i n g manufacture or in the fieldto serve one or more of the followmg purposes:(a) to sealthe contact surface and-joints fr om intrusion of moisture orJoss of moisture and cement slurry.(b) to a]ter the texture of the contact surface.(c) to improve the durability of the contact surface.(d) to f ~ c i l i t a t e release of form from concrete during stripping.3.5.2. Release agents: Form release agents are applied toform contact suifaces to prevent bond and thus facilitate stripping.

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IRC : 87-1984They may be applied permanently to form materials duringmanufacture or in the field or may be applied to the form beforeeach use. The release agents shall be checked for compatibilitywith form surfaces, p lastic c oncrete including admixtures andrequirements for the application of further materials to theha.rdened concrete.. They shall be kept off construction jointssurfaces and reinforcing steel by applying before the reinforcementis laid. Care shall be taken to ..,,Isure that excessive application ofrelease agent does not cause staining of concrete surface or retardcuring. Where exposed aggregate work or other type of concretesurface finish is desired, release agents may be designed suitably.

3.5.3. Manufacture r s recommendations: Manufacturer s recommendations shall be followed in the use of coatings, sealants andrelease agents, but independent investigation of their performanceis recommended before use.3.5.4. Form insulation: These are usually used for prote-ction of concrete n cold weather. These shall be used as permanufacturer s recommendations.3.5.5. Sealants: In order to get smooth concrete surfacefinish and prevent escape of cement slurry, use of laminated tarpaper or similar sealant can be permitted.

3.5.6. Laminated tar paper (craft paper): These are mostlyused to give a smooth surface and to prevent leakage of cementslurry. These shaH be used as per manufacturer s recommen-dations.4. DESIGN

4.1. General4.1.1. Falsework shall be designed to meet the requirementsof the permanent structure, taking into account the actual

conditions of materials, environment and site conditions. Methodsof easy dismant(:lling and erection shall be catered for.4.1.2. Falsework may be designed in accordance withrelevant IRC Codes in force for design of permanent structuresunless otherwise mentioned herein.4. 1.3. Careful attention shall be paid to the detailing ofconnections and function with a view to avoid gross errors leadingto significant damage or failure. t shall be ensured that local

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IRC : 87-1984failures do not lead to progressive collapse involving the entirestructure.

4.2. Loads4. 2.1. False work shall be designed to cater for the vertical,horizontal and other loads as specified in the subsequent c l a ~ s e s4.2.2. Vertical loads: Vertical loads sbali comprise (a) Deadload, and (b) Superimposed load.4.2.2. I Dead load

a) Dead load shaH inc lude the self weights of the falsework structuresincluding formwork.b) Any ancilliary temporary work connected to and supported by thefalsework structure.c) Permanent structure supported by the falsework.

Self weights shall be determined a c c o r ~ n g to clause 205 ofIRC:6 except for the following items for which the unit weightsgiv,en in clause 4.2.2.1.1. shall apply.4. 2.2.1.1. The following unit weights shall be adopted in the

absence of actual measurements:a) Wet concrete including reinforcementb) Timbe r soft wood)

... 26 KN/m1

... 6 KNjm 3c) Formwork sheeting main and secondary bearers) ... Actual weightd) Scaffold tube ... 45 jm

For falsework composed of scaffold tube fittings, the additional weight of fittings may be estimated for by increasing the selfweight of the vertical and horizontal members by 15 per cent.Similarly, in the case of falsework built with fabricated frames,the additional weight of fittings may be estimated at 5 per cent ofthe total weight of the frames and bracings.4.2.2.2. Superimposed loads4.2.2.2.1. Superimposed loads shall include the following :(a) Construction personnel

(b) Plant and equipment including the impact .and surgeSpecial consideration shall be given to items of plant which causevibration and to the effect on form work of external bolt on vibrators and prestressing equipment. Large horizontal forces may10

IRC : 87 1984develop in pumped c.oncrete pipe runs though surcharge will usuallybe smaller. The pipes s ~ l l be a d e q u ~ t e l y anchored, specially atbends and the effect of blowmg out the hoe shall also be considered.

c) Stacking of meterials- his normally occurs from storage of o l l o w pots a n ~ r ~ i n f ? r c e m e n t on the formwork prior toconcretmg. If there IS hkehhooJ that formwork will be used forsubstantial storage of material, this shall be designed for andclearly indicated on the drawings.(d) Surcharge on concrete-This is of particular importancewhen _formwork has been designed to carry thin slabs of concrete, as t s common practice initially to deposit the concrete nheaps.e) Impact due to deposition of concrete-This can be due tothe deJ?osition of concrete from over-head skips, but has generallya ~ o c a l mfluence. Where formwork is p:utic ularly susceptible tothts type of over-load, and even greater general superimposed

l o a ~ s shal.l b: used. However, deflection is frequently the rulingdestgr cntena and a temporary over load which causes only tem-porary excess deflection may be permissible.

f) Prestressing loads- The forces and deformation of thec o n c r e t ~ associated with prestressing are often transferred to thesupportmg falsework. Allowance shall be made in the falseworkdesign to accommodate either the force or the movement involved.

4.2.2.2.2. Uniforrilally distributed J o ~ d of 3.6 kNJm2 of theforms a ~ e a r n a ~ be assumed to cater for the superimposed loadsexcept m specified cases where actual estimation of individualelements shall be done. 4.2.3. Lateral loads : The lateral loads shall comprise :

a) Lateral pressure of fresh concreteb} EnvhtJnmentaJ loadsc) Miscellaneous

4.2.3 I. Lateral pressure of fresh concrete4.2.3.1.1. The factors effecting lateral pressure on forms are:(a) Density of concrete-Denser concrete increases thehydrostatic pressure.


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IRC: 87 19844.3.3. lrt case of reusable components in steel, timber etc.the values of permissible stresses shall be reduced if necessary,considering the number of reuses and the actual degree ofdeterioration. 4.4. Over-turningFactor of safety against o v e r ~ t u r n i n g shall be taken as 1.33.4.5. Deflection LimitsIn general, the deflection of members in form work is limitedby the tolerances specified for permanent works. In general, thecalculated deflection of unsupported areas of form faces shall notexceed 3 mm or 0.003 of the span whichever is least.4.6. Analysis4.6.1. Load transfer systems : The system which transfer s th eloads to the false work shall be exa mined to ensure that all possiblechanges in the conditions of load transfer are provided for. Rela-tive deflections between the permanent structure and the falseworkincluding settlement of the foundations may cause high local concentrations of load.Adjustable or non-adjustable distance pieces, including jacksand similar devices are often used to transfer loads. In case ofscrew jacks its capacity shall be checked for a minimnm of 3 percent of the vertical load acting horizontally at top of jack.4.6.2. Statical redundancy : Statical redundancy or indeter-minacy shall be allowed for in the design, wherever applicable.4.6.3. Connections : Eccent ric loading and/or partial conti- nuity in structural members can be caused by the t r a n ~ f e r ofsecondary moments through semi-pinned joints and connections forbracing. This applies particularly to falsework constructed ofscaffold tubes or similar members.4.6.4. Special loading conditions : The design or sequence of

construction the p e ~ z n a n e n t structure may give rise to special,or unusual loadmg conditiOns on the falsework. Where this is soit shall be i ~ d i c a t e d clearly. by the d e s i g ~ e r of such permanent. works so that Jt may be taken mto account m the design of thefalsework. 4.6.5. Reversal of loading : Reversal of moments and stresses may occur during erection and dismantling of the falseworkand shall be accounted for in the design.

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IRC: 87 19844. 7. . ~ a t e r a l and Diagonal Br.acings4.7. I. Diagonal bracings in both the longitudinal and lateraldirections shall connect the shores or props of the upper and lowerbays of the falsework at splice or jojnt as the case may be.

i) The bottom horizontal bracing shaH be within 600 mm . of thebottom. (ii) Top horizo ntal bracing shaU be within 600 mm from top.iii) i n t e r n ~ e d i a t e horizontal bracings shaH be designed to suit thedes1gn reqUirements. .

(iv) The diagonal bracings sball be at slope between 30 and .60 to thehorizontal. 4. 7.2. The falsework system shall be designed to trans fer alllateral loads to the ground or to completed construction of adequ-ate strength and stiffness already in place n such a manner as to

e n s ~ r e safety at times. Diagonal bracing must be provided inverttcal and honzontal planes where required to provide Stiffnessand to prevent buckling of individual members A laterally bracedsystem sha11 be anchored to ensure stability. Diagonal bracingmust be capable of resisting the overturning moment.4.8. Shores4.8. I. All shores shaJJ have a firm bearing. Inclin ed shoresshall be braced securely against slipping or sliding. The bearin gend.s of shores shall be c.ut square. and have a tight fit and splices.Splices shaiJ be secure agamst bendmg and buckling. Connectio nsof shore ~ e a d s o other framing shall be adequate to prevent theshores from falling out when reverse bending causes upwarddeflection of the forms.

. 4.8.2. Timber shores, where used, shall meet the followingrequuements :(a) The numbe of splicings in any shore shall be kept to the minimum.The rnatchmg ends of shores to be spJiced shallbe cut square forproper seating. As far as practicable, loca tions of splices s h ~ u l dbe staggered(b) The minimum sizes of timber used for splicing shall be 450 mm x75 mmx40mm.(c) All splice fastening shall be adequate.(d) Metal splice pieces of adequate size may be used in place of timber.(e) Lap spJices shall be prohibit ed.

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IRC : 87-19844.9. Proprietary ItemsWhen proprietary forms, shoring or components are used,the manufacturers' recommendations for safe working loads shallbe supported by data sheets and test reports for components byan approved testing organisation. Necessary details required tobe furnished by the manufacturer are given in Appendix ].4.1 0. Foundation of Falsework4.10.1. Purpose of foundations : Where the falsework restson ground, or with permanent construction at ground level, it isnecessary to distribute the loading from the falsework into thesoil or works below in a reliably safe distributive manner tocontrol within acceptable limits any total or differential settle-ments. The details of the site conditions and the safe bearingpressures for use in the design shall form part of design briefs.4.1 0.2. Falsework supported on foundations of the permanentconstruction : Where the vertical loads from the falsework aretransferred to the ground, a check shall be made that the groundcan safely receive the loading. In some instances, tbe loads may

be carried into pile caps or foundation bases. The use of parts ofthe foundation of the permanent works as a foundation for thefalsework shall minimize the possibility of settlement at thosepoints. When p a r ~ of the falsework is s u p p ~ r t e ~ on s u ~ h f o u n ~ a -tions and the remamder of the falsework dtstnbutes tts loadmgdirectly to the ground, the possibilities of the differential settlementsshall be considered.4.10.3. Falsework supported on permanent construction aboveoround level : Where it s intended to support the falsework onpermanent constr1:1ction, t is essent ial to. determine l i m i a t ~ o n s , ifany, which the des1gn of permanent works 1mposes on the mc1denceand distribution of load from the falsework. It is essential todetermine the strength of the permanent works to receive loadingbased on the rate of gain of strength and maturity of concrete in

the structure.4.10.4. Falsework supported on the ground: The loads fromthe falsework shall be applied to the ground through. distributionmembers which may be of timber, steel base plate occasionallyprecast to ensure p r o p ~ ~ e d d _ e d in contact with the ground.T.he alignment of these d1stnbutwn members must be controlledso that the shores of the falsework system are centrally placed,on the member. These ground distribution members shall not

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IRC : 87-1984us ually be subjec t to critical stre sses, but such a possibility shallnot be overlooked.

4.10.5. Foundation supports comprising piles or other deepground insertions shall be designed and installed to specific designsand drawings. The settlement characteristics of these measureswill need to be evaluated. Where there is a likelihood of thefoundation becoming flooded, precautions shall be taken to directsuch flood wa ters away from the area and the installed foundationsto safely withstand the dire.ct and indirect consequences of suchflooding including scour, undermining or weakening of groundstrata.

4.11. Special Requirements for Prestressed Concrete4.11.1. The structural designer shall indicate special requirements, if any, for prestressed construction. Where required, it maybe necessary to provide appropriate means of lowering or remov-ing the form work before full prestress is applied to preventdamage due to upward deflection of resilient formwork.

11.2. The restraint to shrinkage of concrete shall be keptto a minimum and the hogging of members due to prestressingforce and the elastic deformation of formwork or falsework shall beconsidered in the design and removal of the formwork.

4.12. Common Deficiencies in DesignSome avoidabie common design deficiencies lead ing or contributing to failure, are :(a) Lack of sufficient aJJowance in design for special loads.(b) Inadequate shoring or reshoring.(c) Improper positioning of shores at different levels where highfaJsework is involved. This may create reverse bending.(d) Inadequat e provisions (especially where beam hangers are used) toprevent rotation or twisting of beam forms, particularly when slabsframe into them on only one side or slabs of unequal spans frame

into beams.(e) Inadequate provision against upiift.(f) Insufficient allowance for unsymmetr ical or eccentric loading dueto placement sequence.g) Inauequate design of form ties or clamps.

(h) Inadequate protection against scour, where applicable, and(i) Poor foundat ion conditionsof site not accounted for in design.j) Lack of proper adjustment of shims and wedges during-concreting.

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IRC : 87-19845. PLANS

5.1. Falsework plans shall include the followinginformation:(a) Design assumpti ons-All major design values and loading conditions shaH be shown on these drawings. They include assumedvalues of superimposed load, rate of placement, mass of movingequipment which may be o p ~ r t e d on formwork; foundation pressures, c m b e r ~ d i g r m s and other pertinent information, if applicable.(b) Types of materials, sizes, lengths and connection details.(c) Sequence of removal of forms and shores.(d) Anchors, form ties, shores and braces.(e) Field adjustment of the form during placing of concrete.(f) Working scaffolds and gangways.(g) Weepholes, vibr ator holes, or access doors for inspecti on and placing of concrete.(h) Construction joints, expansion joints.(i) Sequence of concrete placements and minimum/maximum eiapsedtime between adjacent placements.j) Chamfer strips or grade strips for exposed corners and constructionjoints.

{k Foundat ion details for falsework.(I) Special provisions such as protect ion from flood water, ice anddebris at stream crossings.

(m) Form coatings and release agents.(n) Means of obtaining specified concrete.(o) Location of box outs, pipes, ducts, conduits and miscellaneousinserts in the concrete, attached to or penetrating the forms.(p) Location and spacing of rubber pads where shutter vibrations areused.

6. SITE OPERATIONS6. l. General6.1.1. The site operations are broadly divided into theoperations of erection of falsework, concreting (applications ofloads) and dismantling of falsework. 6.1.2. Proper coordination and communication betweenthe design, construction and supervision agencies shall be ensuredin respect of all aspects of formwork at site.6.1.3. The preparation and erection of falseworkjformworkrequires the same skill and attention to details as that of thepermanent structure. Falsework shall always be regarded as astructure in its own right, the stability of which at all stages of

8

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IRC : 87-1984construction is permanent for safety of the permanent structure as well as the personnel working at site.

6.1.4. Constant emphasis shall be laid upon attention todetails. It is possible that the omission of a bolt or ineffectivefixing of securing devices or the failure to tighten up an item pro-perly, may lead to local instability which might place the wholestructure in jeopardy. The checking ofwork done shall be painstaking and thor ough while at the same time the workmanshipshould e meticulous. Care and time spent in erection connot besubstituted by checks and supervision at a later stage.

6.1.5. The required standards of workmanship shall betaught to the less experienced workmen and they shall be madeto realise the importance of this. The supervisory staff shall, fortheir part demand ~ i l required standards of workmanship at everystage. -6.2. ErectionThe following points require particular attention duringerection :

{i) Check whether the assumed design loads and sequences are com. patible with the actual conditionsat site.{ii) The field practice follows the working drawings/inst ructions fromthe ~ a d e s i g n e r Any changes found necessary shall be effected inconsultation with all concerned.(iii) Check immediately before loading that the formwork has notdeteriorated and is still in accordance with the design.{iv) Check the adequacy of the foundations for the formwork in respectof bearing capacity and settlement characteristics. (v) Suitable precautions as necessary to guard against excessive storageof materials on a recently formed deck before this is self-supportingare taken.

(vi) Partial formwork shall not be left in place without proper support.{vii) Whet her the wedges are of sufficient height to allow raising theforms to the required position after any settlement/elastic shorteningof the prop occurs. Wedges should be used only at one end of aprop.(viii) For night construction, adequate. lighting facilities with electricwire:> duly protected and insulated shall be provided.(ix) All construct ion equipments like cranes, hoists etc. shaH only beoperated by experienced staff.(x) No distribution member shaH be set or bedded into ground which is frozen.

(xi) No distribution member shall be founded over groun d which has19


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IRC : 87-1984previously been excavated locally and backfilled without properprecautions.

(xii) Edges subject to erosion such as the edges of slopes and terracesshall be protected against eroding forces.(xiii) Any rock outcrop s, 9uried tocks or obstructions which are uncovered and not indicated on the drawings shall.be reported to the designer as they can result in differential settlements.(xiv) All foundation members set in the ground to distribute the loads

from the vertical members shaH be set level.(xv) Splicing of timber shall be done with the help of MS bolts and nuts.Nail joints, if unavoidable, shall be properly designed. (xvi) In respect of proprietary components, the manufacturer s recommendations shall be rigidly adhered to.

(xvii) Where mud falsework is to be used for minor bridges and culverts,following precautions shall be observed:(a) The earthen bed shaJJ be properly compacted to eliminate settlements.(b) The contact surface between the falsework and the concreteshall be made water proof by suitable. means.(c) Proper berm and retaining arrangement/s lope shalJ be providedat ends of raised earth.(d) Piers shall be enveloped by earth on both sides to avoidunbalanced earth pressure from one side only.

6.2.2. Props supporting fromwork .having out of plumb alignment and runners locate d eccentric in prop heads seriously reducetheir load carrying capacity even. iii propri etary systems. Propsshall be checked for verticality by plumbing and props in each roweyeing through the remainders.Prop riet ary form work support. system shall specify safe working loads and factors of safety at specified tolerance s. They shallindicate whether the information given is based on the yield or onthe collapse value of the unit and whether the values given arebased on calculations or actual tests. The recommended safeworking loads shall not apply to any . prop in . defective conditio nor to any prop erected outside the specified tolerances. Factor of

safety for the first use shall not be less than 2 and may be increased suitably for subsequent use.Normal tolerances shall be such that no runner shall beplaced with its centre-line more than 25 mm eccentric tQ the centreof the prop head and/or no prop shall be erected :more than lf I in 40) out of plumb. In case any of the (ollowing defects arenoticed, prop may be set aside, discarded or returned to workshopsor depots for attention or s,crap : .

2

tRC: 871984(i) A tub e with a bend, crease or any noticeable lack of straightness.

(ii) A tube with more than superficial corrosion.(iii) A bent head or base plate.(iv) An incorrect or damaged correcting pin.

are:6.3. Concreting Operations and the Application of Loads6.3.1. Points for check before and during these operations(i) Wh ether proper permission to commence the placement of concretehas been accorded ?

(ii) Whether the reinforcement and falsework have been checked ?(iii) Whether the forms are clean and free from wood-shavings, grit etc ?(iv) Whether form oil has been applied ? Form oil should be avoidedfor concrete surfaces on which plastering is to be done; on suchsurfaces, whitewash s desirable. f form oil is applied; it should bechecked that form oil is not applied or splashed carelessly on thereinforcement or prestressing tendon and anchorages.(v) Where camber has been provided, the free (t op) surface of theconcrete should never be finished fiat but should also be camberedto the same extent as the form.

(vi) Whether all forms are mortar tight ?(vii) Whether the sequence and rate of concreting, that is, of placement isas per the design brief?

(viii) Whether all precaution s have been taken to prevent accidental impactand scouring/flooding of foundations ?(ix) Whether adequate precautions have been taken to keep unne-cessarymaterials away from the falsework ?(x) Whether adequate access ramps etc. i n the correct positions havebeen provided for the smooth flow of men, materials and machines ?

(xi) Whether the forms are in the correct position in space and adequately braced to remain there and the forms are dimensiona)Jy accurateto produce finished concrete of the required dimensions ?(xii) The props and bracings shall be watched during the placement ofconcrete and its vibration and any members which may tend to workloose or wedges which shift should be attend ed to. An agreedsystem of communication between the man below and the man in

charge of concreting operations should be established so that concreting can be stopped instantly if at all it becomes necessary to do so.(xiii) Platforms for the movement of workers and mechanised concretebuggies (used in large works) shaH be separate and should not placeload upon the reinforcing steel. If this is unavoidable, steel chairsshall be placed under the reinforcement at adequate spacing toprevent deformation of the reinforcement.(xiv) Arrangements for field adjustments and constant inspections offorms, shores and foundations during placing of concrete both bysupervising as well as constru ction agency to be ensured to stop

21


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JRC : 87-1984leaks, tightening wedges, and clamps, to adjust shores and for timelyaction against disturbances, etc).

6.4. Removal of Formwork6.4 1. Forms shall not be struck off until the concrete hasreached a strength at least twice the stress to which the concretemay be subjected at the time of removal of form work. The

strength referred to shall be that of concrete using the same cementand aggregates with the same proportions and cured under conditions of temperature and moisture similar to those existing on thework Where possible, the formwork shall be left longer as itwould assist the curing. Proper precautions ishall be taken toallow for the decrease in the rate of hardening of concrete thatoccurs during cold weather.ote : In normal circumstances and where ordinary Portlandcement is used, forms may generally be removed afterthe expiry of the following peroids :

(a) Walls, columns and vertical 24 to 48 hours as may be decided byfaces of all struct ural) the Engineer-in-Charge.members.(b) Slabs (props left under )(c) Beams and arches soffits(Props left under)(d) Removal of props underslabs(e) Removal of props underbeams and arches

3 days7 days7 14 days14 21 days

For other cements, the stripping time recommended forordinary Portland cement may be suitably modified.Note 2 : The number of props left under , their sizes and disposition shall besuch as to be able to safely carry the fuJJ dead load of the slab, beamor arch, as the case may be, toget her with any live load likely tooccur during curing or further construction.

6.4.2. Falsework shall be gradualJy and uniformly loweredin such a manner so as to avoid any shock or vibration or injurious,stresses in any part of the structure.6.4.3. Immediately after removal of the formwork, theconcrete shall be carefully inspected. Defects, if any, shall bemade good as soon as practicable.6.4.4. Where the side shutters also support the flange of the

22

IRC: 87 1984T-Beam, such shutters shall be removed only after the flangeconcrete attains sufficient maturity.

6.4.5. For prestressed units, the side forms shall be releasedas early as possible after 9 hours, but within 24 hours, at the latest,and the soffit forms shall permit without restraint deformation ofthe member w ~ n .prestress is applied. Form supports and soffitforms for cast-m-sttu members shall not be removed until sufficientprestress has been applied to carry the dead load, any formworksupported by the member and anticipated construction loads.

6 4.6. All fromwork shall be removed without .impact or. h o ~ k hkely. to damage the concrete. Removal operations shall beearned out m proper sequence so that the structure is not subjectedto excessive or eccentric loads. Soffit fromwork shall not beall? Yed, to fall to th e leve l below (a practi ce known as crashstnkmg) but shall be lowered in a controJJed manner to preventprobable damage to structure as well as formwork.6.4.7. Where the shape of the member is such that the formwork had re-entrant angles, the form work shall be removed as soonas possible after the concrete has set to avoid shrinkage cracks dueto the restraint.

. 6.4.8. Where internal metal parts are permitted, they orthen removable parts shall be extracted without causing anydamage to the concrete and remaining holes filled with mortar.No permanently embedded metal part shall have less than 25 mmcover to the finished concrete surface.6.4.9. Premature release of props to allow soffit formworkto removed, followed by replacement of the props, is normallyadvisable only when careful control can be exercised. Suchprocedures shall be .effectively supervised and subject to theapproval of the Engmeer responstble for the design of thestructure.6.5. Precautions for Special Structures6.5.1. Prestressed concrete structures : The falsework shall beso arranged as to ensure no stress reversal in the permanentmember on prestressing. The foundati on shall be adequate for theloads expected to be transferred on prestressing.The falsework shall be set at a highe r level to allow fordeflection and shortening of the end supports.

23


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IRC: 87-19846.5.2. Arch s ~ p e r s t r u t u r e : The sequenee of erection andremoval of centering shall be as per the design. Normally wedgesshould be struck in pairs from the crown outwards to the springings.,loosening them gradually without shock to the arch rings.6.5.3. Marine works : Due provision shall be made forcatering to forces specific to marin e environments such as tides,

waves, adverse wind conditions, etc. Timber shuttering or falsework which are likely to be affected by marine borers shal l beavoided and if at all used for very short periods shall be inspectedand the material examined at close intervals to detect the presenceof these borers.The formwork materials shall be protected aganist corrosion.The frequency of inspection shall be suitably increased.6.5.4. Composite construction : Falsework of memberswhich are parts of a composite construction shall be erected withdue care to ensure proper bearing, rigidity and lightness, to preventsettlement or deflections beyond allowable limits. Wedges, shims,jacks, etc. should be provided so as to permit adjustment if requiredduring concreting, 6.5.5. For special structures requiring complicated formworkof the type not already used, it may be desirable to test a mock-upof the scheme to ensure satisfactory results.6.6. Re-use and Maintenance of FormworkThe number of reuses of formwork is entirely the responsibility of the contractor subject to the condition that it continues toproduce the specified result. Forms which are to be reused shallbe carefully cleaned and properly repaired between uses. Concreteor mortar film sticking to the form face or the joining surfaces shallbe completely removed after each use. When not required forimmediate reuse, the formwork materials shall be properly stored.Wooden components in particular shall be protected from adverse

weather conditions during storage. Metal components shall becleaned and painted periodically. Threaded parts shall be oiled/greased after thorough cleaning and removal of dirt or slurry. Freemovement of the telescopic components shall be ensured byperiodic cleaning/oiling.6.7. Check for Workmanship6. 7.1. Checking shall be thorou gh and records of checkscarried out should be maintained for important works. Checks

24

IRC : 87-1984should be made at critical stages of erection and it is suggested thatchecking be done when:

a) the foundation for the falsework is prepared and before verticalmembers are erected,b) the falsework structure has attained a height of one and a half timesits least plan dimension,c) the falsework reaches the level of support of formwork, andd) immediately before the loads are applied,

6.7.2. Checking shall be timely and shall never be hurriedup. Such checking shall be based on a system concept with checklists suitably standardised. The check list in general s h ~ l l cater tothe following functional areas: i) The structure is in accordance with the detailed drawings;ii) The structural dimensions are within agreed tolerances;iii) The foundatiOI;IS are adequate and fully bedded;iv) The verticals are true;v) Bracings a[}d ties are provided and properJy connected;

vi) The compone nt materials are free from defects;vii) The planned sequence of concreting is fully understood and appreciated, including placement of concrete in layers;

viii) Facilities shall be provided to the safety supervis or in exercising hisnormal functions; . . . . ix) The falsewo rk shall . be maint aine d in a serviceable state .until rendered redundant by the maturity of the concrete; .x) In case the timber posts need to be spliced are the ends made squareto abut against each other;xi) Is the splicing done with timbe r plates and using proper nuts andbolts?

xii) Are suitable cleats provided at crossings or junctions of any twomembers.?xiii) Are proper lateral supports of scantlings given to the vertical facesof the webs of beams ?xiv) Is every individual beam supported independentl y right up tothe ground level ?

. xv) Whether weep holes or vibrator holes, clean out hQl e s and temporary openings for placing concrete up to height of opening aridinspection windows are provided ?xvi) Whether safe scaffold platform is available for workmen to reachforms? .

xvii) Whether fittings for form vibrat ors are provided ?xviii) Whether adequat e lighting arrangements have been made, ifrequired? and

25


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IRC : 87-1984xix) Whether requirements of safety regulations have been met with atthe working area ?

7. SPECIAL FORMWORK7 1. Slipforms7.1.1. General : Slipform s can be used for vertical structures,such as beams, piers and wells etc. These.forms are usually movedby jacks riding on steel rods or pipes embedded in or attached tothe hardened concrete. The movement of forms may be continuous process until the structure is .completed or in a phasedsequence of finite placements.Slipforms shall be designed, constructed and the slidingoperations carried out under the supervision ofpersons experiencedin slipform work.Jacking rods or pipes may be left in place or withdrawn asconditions permit.The design of the yokes must provide for adequate clearanceto instal horizontal reinforcing bars and embedments in their

correct locations prior to concreting.Forms shall be of about one nietre height and may be oftimber, plywood or steel. Special care must be taken in buildingthe forms and arranging the jacks so that the forms will drawstraight without twist.Forms shall be conitructed with a slight batter so that theywill be self-clearing as they slide. A range of 6 tnm to 8 mm in aheight of 1 m of form is indicative of current practice.7.1.2. Sliding operations : The sliding speed is determinedby the rate of setting and hardening of the freshly placed concrete,the rate at which the concrete can be supplied, placed andcompacted, and the rate at which reinforcement steel be

supplied and fixed. When using . ordinary Portland cement, theaverage sliding speed is in the range of 150 mm - 300 mm perhour;Alignment and plumbness of the structure shall be checkedat the beginning and at least once in eight h o u ~ s of operation.7.2. TraveUing Forms7.2.1. Travellin g forms consist of formwork mounted on

26

IRC : 87-1984moveable frames or scaffolding called travellers. After the purposeof the formwork is served at one section of the structure, theforms are released and moved along the structure to the next sec..;tion tobe concreted.

7.2.2. Travelling forms are suitable for many types ofbridges particularly where a number of repetitions are involved.These forms can be used both for members of constant crosssection and variable cross section.

7 2.3. Each set of forms and travellers shall be designed forthe particular job. Forms are attached to the traveller moun edon wheels, skids, etc. Jacks are generally used for deshuttenngand for adjustment to profile at the next section.7 2.4. Tra veiling cantilever formwork for cantilever bridgesis a particular example of use of travelling forms for bridge deckconstruction. Such formworks, because of their importance .andlarge loads involved, are designed with the same care as that for apermanent structure.7.2.5. Cantilever formwork eliminates falsework altogether.

The deck is constructed as a series of segments progressivelycantilevering out of the pier. The forms are suspended from astructural frame anchored to the already concreted segment ofthe deck and cantilevering out to sustain t he forms for the nextsegment.7.2.6. The canti lever forms shaJI be so arranged as to facilitate continuous concreting of the entire segment in .one operation.Necessary provision shall be made to enable adjustments in profileto cater to the camber requirements of the bridge deck.7 3. Extreme Weather ConditionsFalseworkfFormwork in extreme weather conditions shallrequire supplemental design and specification dependin g upon the

necessity in each case which are outside the purview of theseguidelines.8. TRUSSES OR GIRDERS USED AS FALSEWORK

The design criteria, the permissible stresses and deflection_limitsshall conform to those specified in IRC : 24.

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IRC : 87-1984Appendix ](Clause 4.9)

INFORMATION TO BE SUPPLIED BY MANUFACTURERSOF PROPRIETARY SYSTEMS

A-1. GeneralA-1.1. The information which the manufacturer is requiredto supply shall be in such detail as to obviate unsafe use of theequipment due to the intention of the manufacturer not havingbeen made clear or due to wrong assumptions on the part of theuser.A-1.2. The user shall refer u n ~ s u l problem or problemsof erection/assembly not in keeping with the intended use of theequipment, to the manufacturer of the equipment.A-2. Information requiredA-2.1. The manufacturers of proprietary systems shallsupply the following information:(a) Description of basic functions of equipment.(b) List of items of equipment available, giving range of sizes, spans andsuch like, with manufacturer s identification numbe rs or other

r e f ~ r e n c e s . .(c) Tpe basis on which the safe working loads have been determinedand whether the. factor of safety given applies to collapse or yield .

. (d) Whether the supplier s data are based on c l c u l ~ t i o n s or t.ests. Thisshall be clearly state d a s there may wide variations betweenresults obtained by eithe r method. . .(e) Instructions for use and. maintenance; .including any .points whichrequire special attention during erection, especia1ly where safety .jsconcerned.f) Detailed dimensional information, as follows :

(i) Overall dimensions and depths and widths of members.(ii) L ine drawings inc1uding perspectives and photographs showingnormal uses.

(iii) Self weight.(iv) Full dimensions of connections and any special positioningarrangements.(v) Sizes of members, including tube diameters and thicknesses ofmaterial. .

(vi) Any permane nt camber built in to the equipment.(vii) Sizes of holes and dimensions giving their positions.

28

g) Data relating to strength of equipment as follows :(i) Average failure loads as determined by tests.

IRC: 87-1984

(ii) Recommended maximum working loads for various conditionsof use.(iii) Working resistance moments derived from tests.(iv) Working she ar capacities derived from tests.(v) Recommended factors of safety used in assessing recommendedloads and deflections based ori test results.(vi) Deflections under load together with recommended pre-camberand limiting deflections.

(vii) If working loads depend . on calculations, working stressesshould be stated. If deflections depend on theoretical momentsof inertia or equivalent moments of inertia rather than tests,this should be noted.(viii) Information on the design .of sway bracing against wind andother horizontal loadings.

(ix) Allowable loading relating to maximum extension of basesandjor heads.

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TYPICAL CONNE TIO

Fillets c h a m f ; ~ s e r t e d formallow gr somettmesb out t ehind feath o mfiltrateand so f ered edgeshave to ~ r m b a ~ fins whi he repatred c

9 ~ o u t t i g h tb o t ~ t s achieved.crampin ,actiOn bet g~ o r d s andeenIntegra) filJet

N DETAILS OF AppendixFORMWORK

Groutfins

SKETCH NO 3)

SKETCH NO 4)31

IRC: 81 1984

Staggerin facilitate 8.J?t;tts toformworktgtdtty of

Foldingwith wedgesh squares oulders


20/22

IRC: 87-1984

(SKETCH NO 5)

SKETCH No. 6)

Typical d struts b e ~ i l s ofrunners ~ ~ n gJ againstocks

Jute. or ruused as gask er packinggrout l e a k a g ~ t s to prev:ent

Rebate nforms toallowtight Joint

_ j

Typical suppo tarrange rincr ments formed struts

Ground

Typicalarrangement ofoffsetm formwork

Typ cal arran-gement ofincr anmed shore


21/22

JRC : 87-1984

Placing of runner in a forkhead

Wedges

SKETCH NO 11)

34

Slope ternced to receivetimber sole plates

/

IRC : 871984

//

Base details on slopes

SKETCH NO. 1235

Concrete or othersimilar hard material

SolePI ates


22/22

IRC: 87-1984

Section

Timber bearer

ElevationBracing to be parallel to ground line

Position of bottommost horizontal bracingSKETCH NO. 13)Forkhead

. - -~ ----- ---=-_;;;;.--- --- _::::: - = ::; --=- - . ___..:::::::.---.:--. -----=-------=:::..-__ ________ :;. .:.;:;--:::::. ._ 0~ ~- . :::= === = = :-.::::---- --Timber wedge cut

to correct angle

Forkhead detail at inclined deckSKETCH NO. 14

36

Documents

IRC 87-1984 Falsework for Road Bridges