SANS1200GF - Prestressed Concrete

SABS 1200 G F - 1 9 8 4

A p p r o v e d by the CODNCIL O F THE SOUTH AFRICAN BUREAU O F ST'ANDAFDS on 6 J u n e 1984

SOUTH AFRICAN BUREAU OF STANDARDS

S'l'ANDAR13 I ZEE S P E C I F I CAT1 ON

for

C I V I L ENGINEERING CONSTRUCTION

GF : PRESTRESSED CONCRETE

O b t a i n a b l e from the S A BUIiEAU OF STANDARDS Pri-vate B a g X191 Pretor ia 0001 R e p u b l i c of South A f r i c a .

Telegrams : C o m p a r a t o r , Pretoria

Published and pr in ted i n the R e p u b l i c of South A f r i c a by the South A f r i c a n B u r e a u of Standards

Telex : 3-626-SA

ISBN 0-626-07011-2 G r 6

This eStandard is exclusively for use on one standalone PC. To access it from a file server or intranet constitutes a violation of SABS copyright rules. Note that only one printout of the standard may be made.

3 SABS 1200 GF-19R4 Prestressed concrete


CONTENTS

Page Number

5 5 5 5 5 5 5 5 5 5 6 6 6 6 6 6 6 6 6 6 6 7 7 7 7 7 7 7 7 7 7 7 7 8 8 8 8 9 9 9 9 9 9 9 9 9 10 10 10 10 10 10 10 10 10 10 10 11 11 11 11 11 11 11 11 11 11 11 11 12

14

Clause

1. 2. 2.1 2.2 2.3 2.4 2.4.1

3.1 3.2 3 . 3 3.4 3.5 3.6

4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8

5.1 5.2 5.3 5.4 5.4.1 5.4.2 5.4.3 5.4.4 5.4.5 5.5 5.5.1 5.5.2 5.5.3 5.5.4 5.5.5 5.5.6 5.5.7 5.5.8 5.6 5.7 5.7.1 5.7.2 5.7.3

6.1 6.2

7.1 7.2 7.2.1 7.2.2 7.2.3 7.2.4 7.3 7.3.1 7.3.2 7.3.3 7.3.4 7.4 7.4.1 7.4.2

8.1 8.1.1 8.1.2 8.2

3.

4.

5.

6.

7.

8.

APPENDIX A.

SCOPE ..................................................................... INTERPRETATIONS ........................................................... Supporting Specifications ................................................. Application ............................................................... Definitions ............................................................... Explanation of Terms ...................................................... Classes of structure ...................................................... MATERIALS ................................................................. General ................................................................... Grouting Materials ........................................................ Tendons ................................................................... Anchorages and Couplers ................................................... Sheaths ................................................................... PLANT ..................................................................... Ceneral ................................................................... Storage Capacity and Deteriorated Material

Tensioning Apparatus ...................................................... Attachment of Tendon to Tensioning Device ................................. Mixing Equipment for Grout ................................................ Casting Beds, Moulds, Formwork and Staging ................................ Handling, Lifting and Stacking Equipment ..................................

Safety Precautions ........................................................ Royalties .................................................................

................................

Pumping Equipment ......................................................... Mechanisms for Deflected Tendons .......................................... CONSTRUCTION .............................................................. General ................................................................... Tendons ................................................................... Surface condition ......................................................... Straightness .............................................................. Cutting ................................................................... Positioning of tendons and sheaths ........................................ Tensioning procedure ...................................................... Grouting of Sheaths ....................................................... General ................................................................... Sheaths ................................................................... Grout ..................................................................... Grout mix design .......................................................... Mixing .................................................................... Injection of grout ........................................................ Grouting during cold weather .............................................. Compressive strength of grout ............................................. Permanent Protection and Bonding of External Tendons ...................... Handling and Erection of Prestressed Units Handling, transportation and storage ...................................... Assembly and erection ..................................................... Forming structural connections ............................................ TOLERANCES ................................................................ General ................................................................... Prestressing .............................................................. TESTING ................................................................... General ................................................................... Load Tests on Individual Prestressed Units ................................ General ................................................................... Non-destructive (service) test ............................................ Destructive (ultimate) test ............................................... Special test .............................................................. Tests on Structures and Parts of Structures ............................... Age at test ............................................................... Test loads ................................................................ Measurements during tests ................................................. Acceptance criteria ....................................................... Tests on Grout ............................................................ Bleeding .................................................................. Compressive strength ......................................................

................................

MEASUREMENT AND PAYMENT ................................................... Measurement ............................................................... General ................................................................... Prestressing .............................................................. Scheduled Items ........................................................... ...........................................................................


5 SABS 1200 GF-1984 Prestressed concrete

SOUTH AFRICAN BUREAU OF STANDARDS STANDARDIZED SPECIFICATION

CIVIL ENGINEERING CONSTRUCTION


for

SCOPE 1.

1.1

2.

2.1

2.2

2.3

This specification covers requirements for prestressed concrete construction by means of pretensioning or post-tensioning. NOTE:

INTERPRETATIONS

SUPPORTING SPECIFICATIONS. Where this specification is required for a project, the following specifications shall, inter alia, form part of the contract document (NOTE: Items (b) and (c) below may or may not be bound in the document): a) Project specification; b) SABS 1200 A or sABs 1200 W. or SABS 1200 AH, as applicable; C) SABS 1200 G.

APPLICATION. This specification contains clauses that are generally applicable to prestressed concrete construction. Interpretations and variations of the specification are set out in Portion 2 of the project specification (see 2.1).

DEFINITIoPS. For the purposes of this specification the definitions and abbreviations given in the applicable of the specifications listed in 2.1 and the following definitions shall apply: Anchorage. A device comprising all the components and materials required to retain the force in a tendon and to transfer this force to the concrete. Characteristic strength. The manufacturer's guaranteed tensile strength of the prestressing steel below which not more than 5X of test results in a statistical population are expected to fall. Coil. One continuous length of finished strand or wire wound in closely packed concentric rings. Coupler. A device that is located at the interface of two stages of prestressing and that couples the tendons in the two stages. Fixture. An item such as a bolt, anchorage, bearing or the like, cast or grouted into concrete. Length of lay. Post-tensioning. its initial minimum specified strength. Prestress. Prestressed concrete. structural concrete in which effective internal stresses have been induced by means of tendons. Pretensioning. Pull-in. The elastic shortening of a tendon caused by movement of the tendon within the anchorage or coupler components due to seating and gripping action during or immediately after transfer. Sheath. A conduit that encloses a tendon and temporarily or permanently allows some movement between the tendon and the surrounding concrete. Strand. A number of wires of the same nominal diameter spun together in helical form round a core wire of slightly larger diameter. Tendon. A tensiooed element used in a concrete unit or structure to impart prestress to the concrete. (A tendon may consist of one or more bars, wires or strands.) Transfer. The action of transferring force from a tendon to the concrete. (It may cover work carried out both on the Site and also during the manufacture of prestressed concrete units.) Vent. An opening in a sheath that can be adjusted to control the release of air, the drainage of water or the injection or release of grout. Wire. R cold-drawn wire produced from a suitably treated hot-rolled rod. (The surface of a wire is initially smooth but the wire may subsequently be indented or crimped by a mechanical process and given a final stress-relieving treatment.)

The standards referred to in the specification are listed in Appendix A.

-

The longitudinal distance, or pitch, of one complete turn of a helix. A method of prestressing in which tendons are tensioned after the concrete has attained

The stress induced in concrete by tendons.

A method of prestressing in which tendons are tensioned before concrete is placed.

- -

2.4 EXPLANATION OF TERMS 2.4.1 Classes of Structure. A prestressed structure may, for the purpose of assessing its likely behaviour, be

classified as follows on the basis of the design limits placed on the flexural tensile stress:

Class 1 : No tensile stresses; Class 2 : Tensile stresses, but no visible cracking; Class 3 : Tensile stresses, but surface width of cracks do not exceed a) 0,l mm for members exposed to a particularly aggressive environment such as the very severe conditions defined in Subclause 2.4.1.4 of S M S 1200 G; and b) 0,2 mm for all other members. I

3.

3.1

3.2

MATERIALS

GENERAL. In addition to complying with the requirements of 3.2-3.6, materials shall comply with the relevant requirements of Clause 3 of SABS 1200 G.

GROUTING MATERIALS. a) Cement shall be ordinary portland cement or rapid-hardening portland cement complying with the relevant requirements of SABS 471;

Materials used for grouting shall comply with the following requirements:


S A W 1200 GF-1984 Prestressed concrete

6

3.3

3.4

3.5

3.6

4.

4.1

4.2

4.3

4.4

4.5

4.6

b) Ssnd shall comply with the requirements of SABS 1083 for sand fur concrete except that the grading shall be such that 100% passes through a 1,18 nun sieve; c) Ldmixtures shall not contain chlorides, nitrates, sulphicles or sulphites. When aluminium powder is used, the total expansion of the grout shall uot. exceed 10%.

TENDONS. Wire and strand shall comply with the applicable requirements of BS 5896. Bars shall be of cold-worked high tensile st.ee1 and shall comply with the requirements of BS 4406 for hot-rolled and processed bars. The characteristic strength of the steel shall be as specified in the project specification or, in the event of the Contractor electing to use, subject to approval, a steel with a different characteristic strength, the strength of the steel shall be such that the structural components in which the steel is to be employed perform in an approved manner the duty for which they were designed. In addition, steel to be bonded to the concrete as pretensioning reinforcement shall not be galvanized and shall be deformed either by indenting or crimping. The Contractor shall obtain from the manufacturer in respect of each consignment of steel tor tendons, a certificate stating the quality and the mechanical properties, and shall provide the Engineer with a COPY - ANCHORAGES AND COUPLERS. hnchorages and couplers shall comply with the requirements of BS 4447, and the Contractor shall provide the Engineer with the manufacturer's test certificate ( s ) as evidence that the anchorages and couplers do so comply.

SHEATHS. Sheaths for tendons shall be of an approved type that takes into account the design friction characteristics between sheath and tendon, and shall be of metal or of any other acceptable material. Except for vents (see 2.3) each sheath shall be mortar-tight and shall be sufficiently strong to prevent puncture, damage or excessive deformation during concreting operations. A sheath may be provided with a threaded entry to permit the use of a screwed connector from the grout pump (see 4.5). Where so directed, the Contractor shall submit samples of the sheaths that he proposes to USC.

STORAGE CAPACITY AND DETERIORATED MATERIAL. The storage capacity provided shall be adequate and shall comply with the requirements of Subclause 3.7 of SARS 1200 G. Storage of all prestressiny steel shall be above the ground and the steel shall be fully protected from the weather. Material that has deteriorated, become contaminated or been damaged shall not be used in the Works and shall be removed from the Site without delay.

Tendons shall consist of high tensile wire, strand or alloy steel bars.

PLANT

GENERAL. In addition to complying with the requirements of 4.2-4.8, plant and equipment (including formwork) shall comply with the relevant requirements of Clause 4 of SABS 1200 G.

TENSIONING APPARATUS. The tensioning apparatus shall be capable of applying to a tendon a controlled force than can be increased gradually and in such a way that no significant secondary stresses are induced in the teirdon, anchorage or concrete. The Contractor shall supply suitable hydraulic tensioning jacks which may be manually, mechanical ly or electrically operated. Each jack shall be so equipped that the force in the tendon during tensioiiing can be measured by direct-reading load cells or be obtained directly from pressure gauges fitted in the hydraulic system. Such measuring devices shall have an accuracy of 29% or better. A certified calibration chart showing the relationship between the measuring device readings and the force on the ram for both ascending and descending ram movements, shall be available on the Site. The Contractor shall maintain all tensioning jacks in good working order, and he shall ensure true and accurate readings by testing, calibrating and servicing the jacks before stressing each structure, or every 3 months during stressing operations for a structure, whichever is the more frequent. He shall provide the necessary facilities for measuring the elongation of each tendon to an accuracy of within 2% or 2 nun, whichever is the smaller value.

ATTACHMENT OF TENDON TO TENSIONING DEVICE. The Contractor shall provide safe and secure means for the attachment of each tendon to the jack or tensioning device.

MIXING EQUIPMENT FOR GROUT. The Contractor shall provide mixing equipment of a type that is capable of producing grout of a uniform and smooth consistency. a) sujtable screens for removing lumps and other foreign materials from the grout; b) facilities to enable high speed mixing to be carried out continuously for between 2 and 4 min ; and c) facilities for continuous agitation of the grout (by slow-speed mixing) while grouting is in progress.

PUMPING EQUIPMENT. The contractor shall provide grout pumping equipment that is capable of developing and maintaining a pressure.of at least 0,7 MPa. Each pump shall be fitted with a pressure gauge and with a controlling device that will effectively prevent the build-up of excessive pressure.

MECHANISMS FOR DEFLECTED TENDONS. The Contractor shall, where necessary, provide suitable mechanisms for so holding down or holding up tendons that frictional losses are minimized. In addition the said mechanism shall be such that a) for a single tendon, the deflector in contact with the tendon will have a radius of at least 50 times the tendon diameter in the case of a wire, or 10 times the tendon diameter in the case of a strand, and that the total angle of deflection will not exceed 15O; b) it will so effect the transfer of prestressing forces to the concrete and at the same time release the hold-down and hold-up forces, that any tensile stresses that develop in the concrete during the process do not exceed the permissible tensile stress limits associated with and normally accepted for concrete of the strength specified (see 5.4.5.1(k)).

The equipment shall incorporate

and


7 SiWS 1200 GF-1984 Prestressed concrete

4.7

4.8

5.

5.1

5.2

5.3

5..4 5.4.1

5.4.2

5.4.3 5.4.3.1

5.4.3.2

5.4.3.3

5.4.4 5.4.4.1

5.4.4.2

5.4.4.3

5.4.4.4

5.4.4.5

5.4.4.6

5.4.5 5.4.5.1

CASTING BEDS, MOUI.I)S, FORMWOIK AND STAGING. Casting beds shall be properly aligned and levelled. Moulds and formwork shall be such that the finished concrete surfaces are smooth and even and have true clean axrises. Formwork and staging shall be so designed that there will be no undue restraint on the elastic shortening of the concrete at the time of transfer of prestress.

HANDLING, LIFTING AND STACKING EQUIPMENT. The Contractor shall provide adequate equipment for so handling, lifting and stacking precast units that they are protected from permanent damage caused by stresses induced during handling or stacking, or by the use of slings, chains or hooks.

CONSTRUCTION

GENERAL. In addition to complying with the requirements of 5.2-5.7 the Contractor shall comply with the relevant requirements of Clause 5 of SABS 1200 G.

SAFETY PRECAUTIONS. The Contractor shall take particular precaution during and after tensioning to protect persons from injury and equipment from damaqe that may be caused by a sudden release of stored energy in the event of failure of any tendon or equipment.

ROYALTIES. Where applicable, the Contractor shall pay any royalties that may be due on whatever prestressing system is adopted and he shall indemnify the Employer against any claims that may arise from any infringement or alleged infringement of patents.

TENDONS Surface Condition. The Contractor shall ensure that all prestressing tendons and internal and external surfaces of sheaths are, at the time of incorporation of the tendons and sheaths in the structural unit, free from pitting, loose millscale, loose rust, paint and oil, grease, soap and other lubricants, and any other harmful matter. A tendon may be cleaned by wire brushing or by passing the tendon through a pressure box containing carborundum powder. Solvent solutions for cleaning shall not be used without the approval of the Engineer. Any prestressing steel or sheath which, in the opinion of the Engineer, is excessively rusty or otherwise unsuitable, shall be removed from the Site. Straightness a) Wire and strand. Wire and strand shall be in coils of diameter such that the curvature of the uricoiled wire or strand complies with the applicable requirements for curvature given in BS 5896. b) Bars. Prestressing bars, as delivered, shall be straight, except that where small adjustments will achieve straightness, such adjustments may be made by hand on Site under the supervision of the Engineer. Straightening of bars shall be carried out at ambient temperature. If the ambient temperature is less than 5OC, any heating required to raise the temperature of the bars above 5OC shall be done by means of steam or hot water. Bars that are bent in the threaded part shall be rejected. Cuttinq All cutting to length and trimming of ends shall be done by means of a) a high-speed abrasive cutting wheel, friction saw or any other mechanical method approved by the Engineer; or b) an oxy-acetylene cutting flame, excess oxygen being used to ensure a cutting rather than a melting action and the cutting being so done that neither the flame nor splashes come into contact with the anchorage or with other tendons. In the case of post-tensioning systems, cutting shall be done as specified in 5.4.3.1(a), the heating effect on the tendon being kept to a minimum and being such that the temperature of the tendon adjacent to the anchorage does not exceed 20OoC. The tendons or the elements of the tendons, as relevant, shall be cut or released in the order that will produce the least lateral eccentricity of prestress at any stage. Positioning of Tendons and Sheaths Subject to the tolerances permitted in terms of Clause 6 , tendons and sheaths shall be accurately located and their vertical and horizontal position maintained accurately as shown on the drawings. The assembly of post-tensioning tendons shall be done on raised platforms or tables that are fully protected from the weather. The Contractor shall use separate carriers for so supporting and fixing in position the tendons or the sheaths, as applicable, that they will not be displaced by heavy or prolonged vibration, pressure of the wet concrete, workmen or construction traffic. Tendons and sheaths shall not be supported or fixed by being welded to reinforcing steel. Carriers shall be so fabricated (by means of welding) and so located that they will not unnecessarily increase friction in tendons when the tendons are being tensioned. Sheaths shall be handled carefully to avoid their being damaged and in order to ensure that they retain their cross-section and profile. Joints in sheaths shall be securely taped to prevent penetration of the sheaths by concrete or laitance. Ends of sheaths shall be sealed and protected after the stressing and grouting operation. Tendons shall be clearly marked at each end so that extensions, slips or other movements that occur can be accurately measured. Tensioning Procedure General. The sequence of prestressing shall be such that the permissible stresses in the unit or structure, as specified in the prestressing force diagram given in the project specification or shown on the drawings, are not exceeded. The Contractor shall submit for approval a program indicating the sequence in which prestressing will be carried out, and shall obtain approval before commencing each tensioning operation. The Contractor shall, in respect of each tensioning operation, comply with the following requirements: a) Tensioning shall be carried out by personnel who are suitably qualified and under constant comwtent supervision. b) Immediately after concreting has been completed, the sheaths shall be flushed with water and the water expelled by compressed air.


S N ) S 1200 GF-1984 Prestressed concrete

E

5.4.5.2

5.5 5.5.1 5.5.1.1

5.5.1.2

5.5.1.3

5.5.2 5.5.2.1

5.5.2.2 5.5.3

c) llnless t h e s i d e s of a i ini t are outward s loping i n a d i r e c t i o n such t h a t u p l i f t w i l l not be impeded, s i d e forms s h a l l be removcd before the u n i t is s t r e s sed . d ) Tensioning s h a l l be so c a r r i e d out t h a t t he stress i n t he tendons increases gradual ly and a t a steady rate . e) While the ambient temperature is below OC, tensioning s h a l l not be c a r r i e d out without t h e apixoval of t h e Engineer. f ) Except where load cells a r e used, the Contractor s h a l l make allowance during s t r e s s i n g for f r i c t i m los ses i n t h e jack and i n t h e anchorage. g) Tendons s h a l l be s t r e s s e d t o t h e spec i f i ed force, and the Contractor s h a l l take s u f f i c i e n t measurements t o enable him t o complete a force-extension diayram. The Contractor s h a l l ensure t h a t t he measurement of extension is corrected f o r any pu l l - in of t he tendon occurring a t t h e non-jacking end, and f o r any s l ack i n the tendon. h) Where the f u l l stress cannot be a t t a i n e d i n a u n i t because of breakaqe, s l ippage or blockage of a sheath, and replacement o t h a t u n i t i s not p rac t i cab le , t h e Contractor s h a l l inform t h e Engineer a s to how he intends to r e c t i f y t h e f a u l t . The Contractor s h a l l not proceed with such r e c t i f i c a t i o n without the approval of the Engineer, and such approval s h a l l not r e l i e v e the Contractor of r e spons ib i l i t y f o r r e c t i f i c a t i o n of t he f a u l t . i) In the case of curved tendons, or tendons made up of a number of components, or tendons loaded i n s tages , t he Enqineer w i l l specify t h e order of loading and t h e magnitude of t h e load f o r each component of t he tendon. j) During the period between s t r e s s i n g t h e tendons and covering them with grout , concrete or o the r permanent protect ion, t he Contractor s h a l l e f f ec t ive ly p r o t e c t t h e tensioned tendons and t h e i r anchorages and sheaths from corrosion, and s h a l l plug the ends and ven t s of a l l such sheaths. k) In the case of post-tensioning, t h e tendons s h a l l not be s t r e s sed u n t i l t h e concrete s t r eng th has been found by v a l i d test r e s u l t s t o be a t least equal t o the spec i f i ed s t r eng th , when r e l evan t f o r t he s t age concerned. 1) In the case of pretensioning, t r a n s f e r s h a l l not take place u n t i l t h e concrete s t r eng th has been found by va l id test r e s u l t s to be a t least equal t o the spec i f i ed s t r eng th , when r e l evan t f o r t h e s t age concerned. m) The Contractor s h a l l keep records of every s t r e s s i n g operat ion and s h a l l d e l i v e r a copy of these records to the Engineer within 24 h of t h e completion of s t r e s s ing . Such records s h a l l include the da t e , t he coil number, t he s t r e s s i n g force, t he extension, t he u n i t number or pos i t i on , t h e concrete cube s t r eng th a t the time of s t r e s s i n g , and any o the r r e l evan t information. Final stage. The f i n a l s t age of tensioning w i l l be deemed t o have been s a t i s f a c t o r i l y accomplished when the tendons comply with a l l of t h e following requirements: a ) Each tendon s h a l l have been tensioned t o the required force; b ) The measured extension on individual tendons s h a l l be within 6% of t h e t h e o r e t i c a l extension; c) The average of t h e measured extensions of a l l t h e tendons i n a u n i t s h a l l no t deviate from the t h e o r e t i c a l extension by more than 3%; d ) The release or pul l - in , or both, as re levant , s h a l l , i n t he case of each tendon, be within 2 mm of t he designated value. Should any individual tendon o r group of tendons f a i l to comply with any of t he appl icable requirements of ( a ) - (d ) above, t he Contractor s h a l l i m e d i a t e l y advise t h e Engineer and ob ta in a ru l ing a s to the procedure to be followed. In the event of t h e f r i c t i o n of any tendon being too high, t h e Contractor may, sub jec t t o t h e approval of the Engineer and a f t e r having f i r s t re leased the tension i n t h e tendon, i n j e c t an approved water-soluble lub r i can t i n t o t h e sheath. The cos t of any remedial and co r rec t ive measures ( including the r e l ax ing and the retensioning of tendons) t h a t have been necessi ta ted by f a i l u r e of one or m o r e tendons t o comply with the requirements given above s h a l l be f o r t h e Contractor 's account. After the tensioning has been approved by the Engineer, t h e Contractor may c u t o f f t he p a r t of the tendons project ing beyond t h e anchorages. He may c u t t he p ro jec t ing p a r t of tendons before grouting is c a r r i e d o u t .

,

GROUTING OF SHEATIIS General When the sheaths of p re s t r e s sed concrete u n i t s are being grouted, t he Contractor s h a l l ensure t h a t a) the s t r e s sed tendons are protected, and b) an e f f i c i e n t bond is achieved between the s t r e s sed tendons and the concrete of t h e un i t . When sheaths a r e being grouted the Contractor s h a l l , i n order t o comply with t h e requirements given i n 5.5.1.1 above, e n s u r e t h a t a) e f f i c i e n t equipment is used; b ) workmanship is ca re fu l and supervision competent; c) t h e grout is mixed with a water/cement (w/c) rat io of between 0,38 and 0,43; d ) t h e grout to be in j ec t ed has good f l u i d i t y and low sedimentation (i.e. a l o w tendency t o bleed) i n the p l a s t i c s t a t e ; e) the grout develops acceptable d u r a b i l i t y and deiisi ty with l o w shrinkage i n the hardened state; f ) t h e grout forms an adequate bond with the tendons and t h e s i d e s of t h e sheaths; and 9 ) t h e methods adopted s h a l l be such t h a t they can be c a r r i e d out on the S i t e e f f e c t i v e l y and reasonably eas i ly . When so required by the Engineer, t he Contractor s h a l l undertake bleeding tests (see 7.4.1) or grouting tr ials, o r both. Sheaths The Contractor s h a l l provide and use a vent a t each crest i n the case of a p r o f i l e d sheath, and a t i n t e r v a l s of not more than 15 m, i n t h e case of a s t r a i g h t sheath. A l l sheaths s h a l l be thoroughly cleaned before grouting is c a r r i e d out. - Grout. An approved p l a s t i c i z e r s h a l l be used i n the grout. The grout s h a l l be such t h a t , when it is t e s t e d i n accordance with 7.4.1, bleeding does not exceed 2% a f t e r 3 h or 4% max. when bleeding is complete, and t h e bleed water s h a l l be re-absorbed f u l l y a f t e r 24 h.

I-


3 SABS 1200 GF-1984 Prestressed concrete

5.5.4

5.5.5

5.5.6

5.5.7

5.5.8

5.6

5.7 5.7.1 5.7.1.1

5.7.1.2

5.7.1.3

5.7.1.4 5.7.1.5 5.7.2 5.7.2.1

5.7.2.2

Grout Mix Design. At least one mnth before the commencement of grouting on the Site, tests shall be carried out to determine whether the grout complies with the requirements of this specification for fluidity, bleeding and strength. After a grout mix design that yields a grout complying with the said requirements has been agreed upon between the Contractor and the Engineer, the mix design shall not be altered unless trial mixes of any altered mix are made and tested and the written permission of the Engineer for use of the altered mix has been obtained. Mixing. When grout is mixed, water shall be added to the mixer first and then the cement. Only after the water and cement have been thoroughly mixed shall any admixture or sand be added. Mixing shall then he continued until a uniform consistency is obtained but, in any event, for at least 2 min. The w/c ratio of the mix shall be as low as possible within the range 0,35-0,s by mass, and the mix shall have the required fluidity. Injection of Grout. The Contractor shall carry out grouting as soon as practicable after the tendons have been stressed, but not before the stressing records have been approved. Grouting operations shall comply with the following requirements: a) The method of injectinq grout shall be continuous and slow enough to avoid segregation of the components of the grout and to ensure complete filling of the sheaths and complete encasement of the tendons. The pump suction intake shall at all times during the grouting operation be kept below the surface of the grout. b) The Contractor shall allow grout to flow successively from each intermediate vent and from the free end of a sheath until the consistency of the effluent grout is equivalent to that of the grout injected. He shall then close off the inlet opening firmly and close off intermediate vents, one after the other, following the direction of the flow. IIe shall carry out further injections as necessary to fill any cavities that are found. c) When injection of grout has been completed, the injection tube shall be sealed off under pressure which shall be maintained until the grout has set. d) Twenty-four hours after the injection of grout, the vents (if any) shall be opened, and any voids that may be present shall be filled with grout poured in under gravity.

Mixing shall not be done by hand.

Grouting during Cold Weather a) When the weather at the Site is cold, the Contractor shall keep accurate temperature records statina maximum and minimum air temperatures and the temperatures (at the time of grouting) of the units to be grouted. b) The Contractor shall not use any materials in which snow, frost or ice is present and he shall ensure that the sheaths and equipment are completely free of snow, frost and ice. c) Except where the unit is so heated as to maintain the temperature of the grout above 5OC for at least 48 h after the grout has been placed, the Contractor shall not place any grout when the temperature of the unit is below 5OC or is likely to fall below 5OC during the next 48 h . d) Except when the heating of sheaths is accompanied by a general external heating of the unit or structure, sheaths shall not be heated in any way. e) Grout materials shall be maintained at a temperature of at least 5OC. Compressive Strength of Grout. Cubes (of sides 100 mm) made of the grout used, and cured at a temperature of 22-25OC and a relative humidity of at least 90% for the first 24 h, and then kept in water at 22-25OC. shall have a compressive strength exceeding 20 MPa at 7 d . PERMANENT PROTECTION AND BONDING OF EXTERNAL TENDONS. After having been tensioned, external tendons in structures such as circular structures for water storage, shall receive permanent protection against mechanical damage and corrosion. Such tendons shall be so encased in a dense concrete, mortar or grout that acceptable durability and density with low shrinkage is developed in the hardened state and an adequate bond is formed with the tendons and with the parent concrete. The encasement material may be applied by means of compressed air or by any other means that can effectively and reasonably easily be used on Site. An approved plasticizer may be incorporated in the grout mix. When so required by the Engineer, the Contractor shall undertake preliminary tests on the encasement materials he proposes to use, to obtain a mix design that will yield a concrete, mortar or grout complying with the requirements for durability, density, shrinkage and bonding given above. After a mix design has been agreed upon by the Contractor and the Engineer, the design shall not be altered unless trial mixes have been made and tested, and the written permission of the Engineer for the use of the altered mix has been obtained. Protection and bonding of the tendons shall be effected within 7 d after final tensioninq of the tendon(s1, or as specified on the drawings, but shall not be undertaken without the prior approval of the Engineer. After the encasement or bonding has been completed the anchorages shall be encased in concrete or qrout, or completely coated with a corrosion-resistant material. The protection provided shall be such that it prevents the ingress of water and aggressive agents.

HANDLING AND ERECTION OF PRESTRESSED UNITS Elandling, Transportation and Storage Prestressed units shall not be removed from castinq beds until the units have been sufficientlv stressed to ensure that they resist, without permanent damage, all stresses induced during such movement. The position of lifting and supporting points, the method of lifting and the type of equipment and transport shall be subject to approval by the Engineer. The Contractor shall place legible and indelible identification, date, location and orientation marks on each unit, as and where necessary. Packing pieces shall be such that they do riot discolour or otherwise permanently damage the units. Units shall be so stacked that the accumulation of trapped water and dirt is prevented. Assembly and Erection General. The method of assemblv and erection agreed to with the Ensineer shall be strictly adhered to on Site. Immediately after a unit has been placed in position and before the lifting equipment is removed, temporary supports or temporary connections between units shall be provided as necessary. The final structural connections shall be completed as soon as is practicable. Temporary supports during construction. Temporary supports shall be so arranged and designed by the Contractor that account is taken of a) all construction loads (including wind loads) likely to be encountered during the completion of connections between any combination of precast and in-situ concrete structural units;


SABS 1200 GF-1984 Prestressed concrete

10

5.7.3

6.

6.1

6.2

7.

7.1

7.2 7.2.1

1.2.2

7.2.3

7.2.4

b) when appropriate, movements, includiug those due to shrinkage of concrete and to any tensioning; c) the need to prevent any local collapse from becoming progressive should a unit break accidentally and strike against another during erection; d) proper finishing and curing of any in-situ concrete, mortar or grout. Temporary supports shall not be removed or released until adequate strength has been attained in the in-situ portion of the structural connections. Forming Structural Connections. a) ensure that he has obtained the Engineer's approval of a unit before commencing the structural connection; b) inspect each structural connection to ensure that it complies with the design requirements set out in the project specification; c) ensure that each precast unit is free from irregularities of such size and shape as may lead to damage caused by stress concentrations; d) ensure that the contact surfaces of each precast unit have been suitably prepared to achieve the specified bond between the precast and in-situ concrete, or to enable the specified frictional resistance to be developed at a bearing; e) pay particular attention to 1) checking that the location of reinforcement and structural steel sections in the ends of precast units are within the specified tolerances, and 2 ) the introduction of any additional reinforcement needed to complete a connection; f) carry out the packing of connections in accordance with the assembly instructions; 9) when connections between units, particularly the horizontal joints between successive vertical lifts, are load-bearing and are to be packed with mortar or concrete, carry out tests to ensure that the material for the connections is suitable for the purpose and that the proposed method of filling will result in solid joints; and h) ensure that the composition and w/c ratio of in-situ concrete or mortar used in any connection is as specified, and that in-situ material is thoroughly compacted. No expanding agent shall be used without the prior approval of the Engineer.

TOLERANCES

GENERAL. The relevant tolerances specified in Clause 6 of SABS 1200 G shall apply, in addition to those specified in 6.2.

PRESTRESSING. Prestressing tendons shall be placed and maintained in position within the limits of the following permissible deviations:

and

The Contractor shall

Permissible deviation, mm Degree of accuracy

..-- _ I I - 11 - 111 .I a) In the direction of the width of the unit Units of width up to 200 mm .................................. + 10 * * - * Units of width over 200 mm ................................... * + 20 b) In the direction of the depth of the unit Units of depth up to 500 nun .................................. + 5 Units of depth over 500 mm

* As stated in the project specification, if required.

TESTING

GENERAL In addition to the relevant tests for concrete given in Clause 7 of SABS 1200 G, units, structures and grout sha l l , when so required (see 7.2.1). be subjected to the appropriate of the tests given in 7.2-7.4. The relevant test methods given in BS 5896 and BS 4486 shall apply to steel wire, strand and bars used for stressing.

- *

* * + D/ioo but not ................................... - more than 25

LOAD TESTS ON INDIVIDUAL PRESTRESSED UNITS General. hhere so required in terms of the project specification and scheduled, the Contractor shall carry out the applicable of the tests given in 7.2.2-7.2.4. In every case the test loads shall be applied and removed incrementally. Non-destructive (Service) Test. The unit shall be supported at its designed points of support and loaded for 5 min with a load equal to the sum of the characteristic dead load plus 1.25 times the characteristic imposed load. The deflection shall then be recorded. The maximum deflection measured after application of the load shall conform to the applicable requirements of the project specification. The recovery shall be measured 5 min after the removal of the applied load and, thereafter, the load shall be re-imposed. The percentage recovery after the second loading shall be not less than that after the first loading and not less than 90% of the deflection recorded during the second loading. A t no time during the test shall there be, in the opinion of the Engineer and in the light of a reasonable interpretation of relevant data, any sign of weakness or faulty construction in the unit(s) under test. Destructive (Ultimate) Test. The unit shall be supported at its design points of support and loaded to its ultimate design load. The unit shall not fail within 15 min after the application of the test load. A deflection exceeding 1/40 of the span will be regarded as failure of the unit. Special Test. For very large units or units not readily amenable to the tests specified in 7.2.2 and 7.2.3 (such as columns, the precast parts of composite beams, and units designed for continuity or fixity), the testing arrangements shall be agreed upon between the Contractor and the Engineer before such units are cast.


11 SABS 1200 GF-1984 Frestressed concrete

7.3 7.3.1

7.3.2

7.3.3

1.3.4

7.4 7.4.1

7.4.2

8.

8.1 8.1.1

8.1.2

TESTS ON STRUCTURES AND PARTS OF STRIJCTURES 3 e at Test. Where particular tests on structures or on parts of structures are required in terms of the project specification and are scheduled, the Contractor shall carry out the tests as soon as possible after the expiry of a period of 28 d that commences at the time of the placing of the concrete. When a test is required for a reason other than that the quality of the concrete in the structure has to be assessed, the test may be carried out earlier than the end of the said 28 d period, provided that the concrete has already reached its specified strength. When prestressed concrete is tested, allowance shall be made for the fact that the effective prestress at the time of testing will be greater than the value that will prevail during the working life of the structure. Test Loads. a) The test loads to be applied for the determination of the limit states of deflection and local damage shall be the characteristic dead and imposed loads. When the ultimate limit state is being considered, the test load maintained for a period of 24 h shall be the greater of 1) the sum of the characteristic dead load and 1,25 times the characteristic imposed load, and 2) 1,125 times the sum of the characteristic dead and imposed loads. Should any part of the characteristic dead load not be in position on the structure, compensating loads shall be added as necessary. b) Where only part of a structure is to be tested, special precautions shall be taken to ensure that all the units actually under test are subjected to the full test load, proper allowance being made for load sharing between units. Measurements during Tests. Measurements of deflection and crack width shall be taken immediately aftrr the application of each incremental load. In the case of the 24 h sustained load test, measurement of deflection and crack width shall be taken at the end of the 24 h period of loading, after removal of the load and after the 24 h recovery period. Sufficient measurements shall be taken to enable side effects to be taken into account. Acceptance Criteria. Subject to due allowance being made for the possible effects on a structure or part of a structure of variations in temperature and humidity during the period of the test, the following acceptance criteria shall apply: a) For Class 3 prestressed concrete structures, units that are intended to be exposed to very severe conditions, as defined in Subclause 2.4.1.4 of SABS 1200 G, the maximum width of any crack measured immediately on application of the test load for local damage shall not exceed 0,07 mm and, for all ot.her units, the width of any such crack shall not exceed 0,13 nun. For Class 1 and Class 2 prestressed concrete structures, no visible cracks shall occur on application of the test load for local damage. b) For units that are spanned between two supports, the deflection measured immediately after application of the test load for deflection shall not exceed 1/500 of the effective span. NOTE: Before cantilevered parts of structul-es are tested, the criteria for acceptance shall be agreed upon between the Contractor and the Engineer. c) If the maximum deflection in millimetres, occurring during a period of 24 h under the test load, is less than 4 0 L2/d, where L is the effective span in metres and d the overall depth of construction in millimetres, it is not necessary for the recovery to be measured and the criteria of (d) and (e) do not

d) If the maximum deflection is equal to or more than 40 L / d as given above and if, within 24 h of the removal of the test load for the ultimate limit state calculated in accordance with 7.3.2, a Class 3 prestressed concrete structure does not show a recovery of at least 75% of the maximum deflection that occurred during the 24 h under load, the loading shall be repeated. The structure will be regarded as having failed to pass the test if there is not a recovery of at least 75% of the maximum deflection that occurred during the second loading. e) If, within 24 h of the removal of the test load for the ultimate limit state calculated in accordance with 7.3.2, a Class 1 or Class 2 prestressed concrete structure does not show a recovery of at least R 5 % of the maximum deflection that occurred during the 24 h under load, the loading shall be repeated. The structure will be reyarded as having failed to pass the test if the recovery after the second loading is not at least 85% of the maximum deflection that occurred during the second loading.

TESTS ON GROUT Bleeding. A sample of the grout shall be placed in a covered graduated cylinder of diameter approximately 100 mm and fitted with a thermometer. The height of the grout in the cylinder shall be 100 nun. The temperature of the grout shall be kept at 20 2 2O C and bleeding shall be checked for compliance with 5.5.3. Compressive Strength. Grout shall be sampled in accordance with SABS Method 861 and tested in accordance with SABS Method 863 for compliance with 5.5.8.

MEASUREMENT AND PAYMENT

Test loads shall be applied incrementally and as follows: ~-

Temperature and weather conditions shall be recorded during the test.

2 apply.

MEASUREMENT General. Except as otherwise required in terms of 8.1.2 and 8.2, the terms of Clause 8 of SABS 120b G shall be applicable to prestressed concrete. Prestressing. Where prestressing is sufficiently detailed on the drawing or in the schedule, measurement will generally be by mass. Where different systems compete with one another at the tender stage, measurement may be made in terms of units that are the product of force and length or in terms of force units as specified in 8.2.7.1 and 8.2.7.2, respectively.



12

8.2 8.2.1

8.2.2

8.2.3

8.2.3.1

8.2.3.2

8.2.3.3

8.2.3.4

8.2.4

8.2.5

8.2.6

8.2.7 8.2.7.1

SCHEDULEI) ITEMS Establishing on Site, Maintenance and Dismantling of Pensioning Beds and Equipment .......... Unit: This item will he scheduled only where the Contractor is required to establish facilities on the Site as part of his temporary works for tensioning in-situ concrete. The rate shall cover the cost of setting up, operating, maintaining and, on completion of the work, dismantling the brds and equipment. Manufacture of Precast Prestressed Units .................................................... Unit: The dimensions or the drawing number of individual units will be stated. Separate items will be scheduled for different qualities of concrete and different types and sizes of units (small units of volume not exceeding 0.5 m3 of formed concrete will be grouped). The rate shall cover the cost of royalties, if any, of all material including concrete and reinforcinq and prestressing steel, of formwork and moulds, and of all labour and equipment required for mixing, placing, compacting, floating off, stressing, tenlporary stacking and curing. Casting of Prestresspd Units on Site (i.e. casting and tensioning of units in place in the structure or alongside the structure or on a casting bed on Site). Formwork, concrete and reinforcing steel. The provisions of SABS 1200 G shall apply to formwork, to concrete and, except as provided for in 8.2.3.3, to reinforcement. Supply and install sheathing and tendons (characteristic strength stated) .................. Unit: Separate items will be scheduled for tendons of different materials, cross-sections, types of construction, etc. The mass of tendons measured will include the mass of any loop or fan. The rate shall cover the cost of supplying sheathing complete with threaded inlets and with vents, of fixing the complete sheathinq to formwork, of supplying and making up tendons (including the cost of spacers and waste) and of threading the tendons through the sheaths. supply and install anchorages and couplers to suit tendons a) Anchorage at jacking end ................................................................. Unit: b) Anchorage at dead end .................................................................... Unit: c) Coupler at jacking end ................................................................... Unit: d) Coupler at dead end ...................................................................... Unit: The rate shall cover the cost of supplying, fabricating, storing, handling, protectinq, forming a recess for the anchorage and, when relevant, for the coupler, installing and fixing the complete anchorage assembly (including, when relevant, the coupler) to formwork, together with the cost of the reinforcement design for the whole anchorage zone and the cost of the helical reinforcement supplied a& part of the anchorage assembly. The rate for loop or fan anchorages shall exclude the cost of the length of tendon forming the loop or fan, which will be measured under 8.2.3.2. Post-tensioning and grouting of items supplied under 8.2.3.2 and 8.2.3.3 .................... Unit: Separate items will be scheduled for longitudinal, transverse and vertical tensioning. The rate shall cover the cost of a) royalties (if any, and if not already covered); b) site supervision and labour; c) plant and materials; d) prestressing of the unit by tensioning all or a few tendons at a time; e) anchoring off or coupling, or both; f) trimming of tendon ends; and 9) flushing out, grouting and making good the anchorage recesses. Erection and Building-in of Units ........................................................... Unit: The mass of each unit and details of connectioiis will be stated. Separate items will he scheduled for different sizes and different positions of units to be erected. The rate shall cover the cost of removal from temporary stacking, erection (including the cost of hoisting, scaffolding and temporary supports), building-in or fixing into position and construction of all structural connections. Miscellaneous Built-in Steelwork ............................................................ Unit: Separate items will be scheduled for different masses and sizes of miscellaneous built-in steelwork. The rate shall cover the cost of supplying and delivering (or taking delivery, as applicable), fixing into position and building into concrete the various items of steelwork. Special Tests ............................................................................... Unit: The sum shall cover the cost of complying with the requirements for tests stated in the project specification and in 7.2 or 7.3, as applicable. Alternatives to Suhclauses 8.2.3.2 and 8.2.3.3 supply and install sheathing and tendons .................................................... Unit: The unit, meganewton metre, will be calculated as the product of the characteristic strength in megapascals of the prestressing steel, the cross-sectional area of the tendon in square metres and the length of the tendon in metres between the faces of the anchorages. In the case of fan and loop anchorages the length of the tendon will include the length of tendon forming the loop or fan.

Sum

NO. OK m

t

NO. NO. NO. No.

No.

No.

ky or t

Sum

MN.m


13 SABS 1200 GF-1984 prestressed concrete

Separate items will be scheduled for tendons of different materials, cross-sections, characteristic strengths, types of construction, etc. The rate shall cover the cost of supplying sheathing complete with threaded inlets and with vents, fixing the complete sheathing to formwork, supplying and making up tendons (including the cost of spacers and waste) and threading the tendons through the sheaths. Supply and install anchorages and couplers to suit tendons

b) Anchorage at dead end .................................................................... IJnit: d) Coupler at dead end ...................................................................... Unit: The unit, meganewton, will be calculated as the product of the characteristic strength in megapascals of the prestressing steel and the cross-sectional area of the effectively anchored or coupled tendon in square metres. The rate shall cover the cost of fabricating, supplying, storing, handling, protecting, forming a recess for the anchorage and, when relevant, for the coupler, installing and fixing the complete anchorage assembly (including, when relevant the coupler) to formwork, together with the cost of the reinforcement design for the whole anchorage zone and the cost of helical reinforcement supplied as part of the anchorage assembly. The rate for loop or fan anchorages shall exclude the cost of the length of tendon forming the loop or fan.

8.2.7.2 a) Anchorage at jacking end ................................................................. Unit: c) Coupler at jacking end ................................................................... Unit:

MN MN MN MN



14

APPENDIX A. APPLICABLE STANDARDS

Reference is made to the applicable issues (see Subclause 2.2 of SABS 1200 A, SABS 1200 AA or SABS 1200 AH, as applicable) of the following standards:

BS 4447 BS 4486

BS 5896 SABS 471 SARS 1083 SABS 1200 A SAAS 1200 AA SABS 1200 AH SABS 1200 G

The performance of prestressing anchorages for post-tensioned construction Hot rolled and hot rolled and processed high tensile alloy steel bars for the prestressing of concrete High tensile steel wire and strand for the prestressing of concrete Portland cement (ordinary, rapid-hardening, and sulphate-resisting) Aggregates from natural sources Civil engineering construction: General Civil engineering construction: General (small works) Civil engineering construction: General (structural) Civil engineering construction: Concrete (structural)

SABS Methods 861 Sampling of freshly mixed concrete 863 Compressive strength of concrete (including making and curing of the test cubes)

ISBN 0-626-0701 1-2 sabc pia


Title page1. SCOPE 2. INTERPRETATIONS 3. MATERIALS 4. PLANT 5. CONSTRUCTION 5.1 GENERAL.5.2 SAFETY PRECAUTIONS5.3 ROYALTIES5.4 TENDONS 5.5 GROUTING OF SHEATHS5.6 PERMANENT PROTECTION AND BONDING OF EXTERNAL TENDONS5.7 HANDLING AND ERECTION OF PRESTRESSED UNITS

6. TOLERANCES 7. TESTING 7.1 GENERAL 7.2 LOAD TESTS ON INDIVIDUAL PRESTRESSED UNITS 7.3 TESTS ON STRUCTURES AND PARTS OF STRUCTURES 7.4 TESTS ON GROUT

8. MEASUREMENT AND PAYMENT 8.1 MEASUREMENT 8.2 SCHEDULED ITEMS

APPENDIX A - APPLICABLE STANDARDS Return to List of eStandards

SANS1200GF - Prestressed Concrete

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