SANS 10120-5 GF-1984 Code of practice for use with standardized specifications for civil engineering construction and contract documents Part 5 Contract administration Section GF P.pdf

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1、 Collection of SANS standards in electronic format (PDF) 1. Copyright This standard is available to staff members of companies that have subscribed to the complete collection of SANS standards in accordance with a formal copyright agreement. This document may reside on a CENTRAL FILE SERVER or INTRA

2、NET SYSTEM only. Unless specific permission has been granted, this document MAY NOT be sent or given to staff members from other companies or organizations. Doing so would constitute a VIOLATION of SABS copyright rules. 2. Indemnity The South African Bureau of Standards accepts no liability for any

3、damage whatsoever than may result from the use of this material or the information contain therein, irrespective of the cause and quantum thereof. SABS 0120 : Part 5 Section GF-1984 Prestressed concrete Clause 1 . 1.1 2 . 2.1 2.2 3 . 3.1 3.1.1 3.1.2 3.1.3 3.1.4 3.1.5 3.1.6 3.1.7 3.1.8 3.1.9 3.1.10 3

4、.1.11 3.1.12 3.1.13 3.1.14 3.1.15 3.2 3.2.1 3.2.2 3.2.3 3.2.4 3.2.5 3.2.6 3.2.7 4 . PART 5 : CONTRACT ADMINISTRATION SECTION GF CONTENTS Page Number START OF CONSTRUCTION General . IMMEDIATELY AFTER THE HANDING OVER OF THE SITE General Samples DURING CONSTRUCTION et hods of Construction Handling and

5、 lifting Safety Application of loads Tensioning procedure . Post-tensioning Jacking friction losses . construction problems tha Grouting vents . . . . . may require adjustments in des . . . . . . . . sumptions . . Injection of grout . Grouting during cold weather . spraycrete storage . Projecting re

6、inforcement . Keeping stored units free of water . Administration Tendons Anchorages and couplers . Pressure gauges for measuring tensioning force Safety of stagings. etc post-tensioning to permit movement of units strength of grout . Handling and placing . QUALITY CONTROL AND OTHER CONSIDERATIONS J

7、une 1984 Approved by the COUNCIL OF THE SOUTH AFRICAN BUREAU OF STANDARDS SABS 0120 : Part 5 Section GF-1984 Prestressed concrete SABS 1200 GF : PRESTRESSED CONCRETE NOTE: The clause number(s) given at the beginning or after the heading of a clause is/are. otherwise stated, the number(s) of the rele

8、vant clause(s) of SABS 1200 GF. START OF CONSTRUCTION unless GENERAL. For the purposes of this part of the code, contract administration starts with instructions to the contractor to commence work as set out in Subclause 4.1 of Section 0. IMMEDIATELY AFTER THE HANDING OVER OF THE SITE GENERAG. The r

9、ecommendations of Section G should be applied, as relevant. SAMPLES. (Subclauses 3.4 and 3.5). The contractor should ascertain whether samples of anchorages or sheaths or both are required and if so, submit them without delay together with, in the case of anchorages, proof of satisfactory previous u

10、se. DURING CONSTRUCTION METHODS OF CONSTRUCTION Formork/Camber (Subclause 4.7). The specified vertical profile should be achieved by setting the formwork low or high as required, before concreting, to allow for changes in profile caused by deflection of formwork during concreting and by subsequent p

11、restressing and permanent loading. Unless already indicated on the drawings, details of the proposed profile should be calculated by the contractor and should be approved before construction commences. Observations should be made to determine whether the actual deflections correspond with the predic

12、ted deflections. If any significant discrepancies occur, the formwork settings for prestressed members still to be constructed should be adjusted accordingly. . - Handling (Subclause 4.8). Care should be taken to .avoid damage to units and adjoining structures during handling and lifting. Suitable p

13、recautions should be taken with regard to the following when prestressed units are transported: a) Distortion of the transporting vehicle; b) centrifugal force due to cornering; C) oscillation (a slim member might flex vertically or horizontally sufficiently to cause damage); d) the possibility of d

14、amage due to chafing. Safetv (Subclauses 5.2 and 5.4.1). In order to avoid costly delays and disruption of work due to a tendon failure, and for reasons of safety, when prestressing tendons have been stored on site for a prolonged period, the contractor should ensure by tests that the quality of the

15、 prestressing tendons has not been significantly impaired by corrosion, stress corrosion, loss of cross-sectional area or as a result of any mechanical damage. (See DD 81) .) Application of Loads (Subclauses 5.2 and 5.4.5). Transfer of prestressing force, whether partial or full, should be carried o

16、ut only after cube crushing tests have indicated an adequate concrete strength. Except where subsequent re-tensioning is to be applied, the prestressing of the concrete should be delayed as long as possible in order to minimize loss of tension due to concrete shrinkage and creep. In determining the

17、final jacking force and the resulting forces in the prestressing tendons, adequate and proper allowance should be made, in accordance with SABS 01002), for all factors that will contribute towards loss of prestress, for the prestressing system and for the properties of the prestressing steel being u

18、sed. Stressing of the tendons should be carried out with due care by experienced workmen and adequate steps taken to protect the workmen from injury. Proper records should be kept by the contractor of all stressing operations and, in the case of site stressing, a copy of the record (see Subclause 5.

19、4.5.1 (m) of SABS 1200 GF) , which should include wedge slip or slip-in measurements taken during anchoring, anchoring loads and extensions, should be handed to the engineer on each day during which stressing operations are carried out. The engineer will use these records and the prestressing force

20、diagram (see Subclause 5.4.5.1 of SABS 1200 GF) to check whether the tendons comply with the prestressing requirements. (See Subclause 3.2.2 of Section GF of Part 2 and Subclause 1.3.2.2 of Section GF of Part 3 of the code.) For factory stressing or for stressing remote from the works, copies of the

21、 stressing records should be furnished on demand. The engineer may order the contractor to cease any or all stressing operations where proper records are not being kept or where the operations are not being properly or safely carried out, and the contractor should take immediate steps to ensure that

22、, when the work is resumed, it is carried out to the satisfaction of the engineer. Tensioning Procedure (Subclause 5-4-51. A graph of stressing force or gauge readings should be plotted against expected tendon extensions before tensioning operations are commenced. The measured extensions should then

23、 be plotted on this graph as tensioning proceeds. Measurements of extensions should be regarded only as indirect indications of the tensioning force and as a check on that force. Calculations of extensions should be based on values of Youngs modulus provided by the contractor in terms of Subclause 3

24、.3 of SABS 1200 GF. Post-tensionin? (Subclauses 5.4.4 and 5.4.5) 3.1.6.1 In post-tensioning systems, tendons should preferably be inserted before concreting is carried out. 3.1.6.2 If the tendon is to be inserted after concreting, the contractor should dolly the sheath during the concreting process

25、to ensure a clear passage for the tendon. 3.1.6.3 Immediately after concreting, all sheaths should be flushed thoroughly with water. 3.1.6.4 Where anchorage of the prestressing tendons is achieved by means of friction grips or wedges and where no other slipping limitation is specified, the slip-in o

26、f each individual prestressing steel element, both during tensioning and after anchoring. should not exceed 10 mm. Tendons failing to conform to this limitation should be restressed. 1) BSI Draft for development - Recommendations for ground anchorages, published in 1982. 2) Structural use of concret

27、e. SABS 0120 : Part 5 Section GF-1984 Prestressed concrete The sequence of stressing should be as shown on the drawings or as specified and where not so shown or specified, should be such that lateral eccentricity of stress on any member is kept at a minimum. Where a tendon is cut back, a length of

28、tendon equal to at least one diameter of the tendon should be left projecting from the anchorage. Jacking Friction Losses (Subclause 5.4.5.1(f). A jack that has been calibrated against a proving ring has already had allowance made for jacking friction losses. Construction Problems that may require A

29、djustments in Design Assumptions (Subclause 5.4.5.1). There are three sources of design inaccuracy, as distinct from design error, that may be discovered during construction: a) The wobble factor. The wobble factor is the ratio between the friction loss in a tendon (due to kinks and irregularities t

30、hat are unavoidable in the relatively low mass sheath when it is stretched out. to receive the tendon) and the friction loss due to the sheath itself. Control of the wobble factor is in the hands of the contractor. If his tendon placing is bad, the wobble factor will be too high and if his tendon pl

31、acing is perfect (which is impassible) it will be too low. b) The co-efficient of friction. The control of the co-efficient of friction is also in the hands of the contractor and experience shows that the co-efficient is about 0,25 when the tendons and sheaths are in good condition. If a little rust

32、 is allowed to form the co-efficient of friction may rise to 0,3CI or more. C) Properties of steel tendons. The value of the Yungs modulus used in the design of the tendon may not be the same as that stated on the manufacturers test certificate. The contractor should by good workmanship, endeavour t

33、o avoid problems developing due to the factors referred to in (a) and (b) above. The information regarding the properties of the steel should become available in terms of Subclause 3.3 of SABS 1200 GF. Grouting Vents (Subclause 5.5.2). Grouting vents and extension pipes should be provided at each en

34、d of each sheath and should have a diameter of at least 10 m. In the case of long sheaths an& sheaths with high points along their length, additional vents with plug valves of similar diameter should be inserted at the most advantageous points for the purpose of bleeding air and water and of providi

35、ng additional grout injection points to ensure that the sheath is completely filled with grout. The end of each grouting pipe should be equipped with a plug valve or similar device capable of withstanding a grout pressure of 1 400 kPa without loss of water or air. Injection of Grout (Subclause 5.5.6

36、). Where grouting pipes are at different levels, the grout should be injected at the lowest vent. To prevent the formation of air-locks inside the sheath, grouting of each unit should be continuous. The grout to be injected should be continuously stirred during the grouting operation to prevent segr

37、egation taking place. Grouting during Cold Weather (Subclause 5.5.7). Special care should be taken when grouting is done during cold weather and allowance should be made for the fact that the temperature of a tendon rises much more slowly than does the air temperature. Spraycrete (Subclause 5.6). Sp

38、raycrete (i.e. sprayed concrete applied as shotcrete or by the gunite process) comprising an approved mix having a fineness modulus (FM) between 2.1 and 2.8 and a w/c ratio between 0,38 and 0,41, should be so applied that the hardened encasement forms a dense durable bond with the tendons and the pa

39、rent concrete and should comply with the applicable requirements of Subclause 5.6 of SABS 1200 GF. Storage (Subclause 5.7.1). When a stack of units in storage is fairly high, the units should be placed vertically above one another to minimize bending stresses in any unit. Projecting Reinforcement. W

40、here there is projecting reinforcement, precautions should be taken to prevent the formins of rust stains and to minimize efflorescence. Keeping Stored Units Free of Water. Units should be so stored that they are well drained and free of water as the freezing of trapped water can cause severe damage

41、. ADMINISTRATION Tendons (Subclause 3.3). In terms of BS 589fj3), the king or core wire should be of diameter at least 2% greater than that of the outer wires. This is necessary to prevent slipping because, when the tendon is stressed, there is no grip or anchorage holding the core wire. Anchorages

42、and Couplers (Subclause 3.4). In practice, typical grip efficiency of anchorages and couplers is of the order of 92%. Higher efficiency cannot be achieved with serrated wedge anchorage systems because use of such systems results in a drop in the actual breaking force of the tendon. Pressure Gauges f

43、or Measuring Tensioning Force (Subclause 4.2). Where a pressure gauge is sed for meas- uring the tensioning force in a tendon during tensioning, it should comply with BS 17804), be of diameter at least 150 mm and be so selected that it can be operated at between 50% and 90% of its full range. Provis

44、ion should be made in the system for a snubber or similar device to protect the gauge against sudden release of pressure, and also for a second gauge for use as a check. Safety of Stagings, etc. (Subclause 5.7.2.2). The contractor should ensure that he is fam:iliar with the requirements of the Facto

45、ries, Machinery and Building Work Act, 1941 (Act 22 of 1941) and with the regulations promulgated under the Act governing stagings, scaffolding, temporary works and lifting equipment. Post-tensioning to Permit Movement of Units (Subclause 5.4.5.1(k). In the case of post-tensioning, the contractor sh

46、ould be permitted to stress enough tendons to enable a unit to be moved from its casting bed. The minimum strength of concrete in this case should be 27 MPa, and permission to move the unit should be subject to the proviso that the tendons that have already been stressed, be restressed when the fina

47、l stressing is being done. Strength of Grout (Subclauses 5.5.8 and 7.4.2). A grout strength of 20 MPa at 7 d is generally accepted as the equivalent of 30 MPa at 28 d . Handling and Placing (Subclause 5.7.1). Where the contractor requests approval from the engineer for the movement of post-tensioned

48、 units from their casting beds before he has grouted the stressed tendons, he should adequately mark the grouted tendons so that possible slip can be observed. The contractor should realize that, should any slipping or damage occur, he will be responsible for replacing or restressing the affected te

49、ndon(s) as directed. He should ensure that no superimposed load is placed on such units without the permission of the engineer in writing. 4. QUALITY CONTROL AND OTHER CONSIDERATIONS 4.1 The relevant recommendations of SABS 0157) should be applied to the construction and erection of prestressed concrete. 3) High tensile steel wire and strand for prestressing of concrete. 4) Bourdon tube pressure and vacuum gauqes. 5) Quality management systems. ISBN 0626-07015-5