SANS 10120-3 GF-1984 Code of practice for use with standardized specifications for civil engineering construction and contract documents Part 3 Guidance for design Section GF Prest.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 3 Section GF-3984 Prestressed concrete PART 3 : GUIDANCE FOR DESIGN SECTION GF CONTENTS Clause 1 . 1.1 1.2 1.2.1 1.3 1.3.1 1.3.2 1.3.3 2

4、 . 2.1 2.1.1 2.1.2 2.1.3 2.2 2.3 3 . 4 . 4.1 5 . Page Number . PRE-TENDER CONSIDERATIONS Investigations Administration Tolerances . Documentation Conditions of tender Drawings . Specifications DESIGN REQUIREMENTS . Design Experience . General . Sources of design inaccuracy Classes of structure Gener

5、al Quality . Protection and Bonding of External Tendons APPLICABILITY OF OTHER CODES TEST PROCEDURES . General . QUALITY CONTROL AND OTHER CONSIDERATIONS June 1984 Approved by the COUNCIL OF THE SOUTH AFRICAN BUREAU OF STANDARDS SABS 0120 : Part 3 Section GF-1984 Prestressed concrete SABS 1200 GF :

6、PRESTRESSED CONCRETE NOTE: The clause number(s) given at the beginning or after the heading of a clause is/are, unless otherwise stated, the number(s) of the relevant clause(s) of SABS 1200 GF. PRE-TENDER CONSIDERATIONS INVESTIGATIONS. Where the novelty of the design or other circumstances may warra

7、nt consideration of unusual or new prestressing techniques, research the market and technical literature thoroughly with a view to so framing a tender enquiry that realistic alternative offers can be submitted. ADHINISTRATION Tolerances. Ensure that. working drawings to be used by a manufacturer giv

8、e dimensions and permissible deviations as required by the engineer. DOCUMENTATION Conditions of Tender. Where the contractor is allowed to submit and use his own choice of prestressing system (subject to approval), provide him at the tender stage with such prestressing force diagrams as are necessa

9、ry to enable him to select the best system, tendon type, sizes and arrangement for the structure (see Subclause 3.2.2 of Section GF of Part 2 of the code), and require him to give details of the prestressing system offered. State also what details are required from the tenderer/contractor both at th

10、e tender stage and before work commences. Drawings Lifting details. Ensure that lifting details are practical and can be used safely, and are such that no damage will result from the use of the lifting equipment. Prestressing force diagram. Include in the document a prestressing force diagram to ena

11、ble the contractor to prepare and submit for approval a prestressing program (see Subclause 5.4.5.1 of SABS l200 GF). Specifications Points of support. In all cases, specify the points of support of prestressed units during storage, and ensure that these are so chosen as to prevent unacceptable perm

12、anent distortion of the units; supporting arrangements that permit minor settlements to occur without inducing stresses in the units are preferred; Tolerances a) Cost. While dimensional variations are inevitable, precast concrete units can be manufactured to comparatively small permissible deviation

13、s (PDs). Manufacturing to such small PDs, however, does significantly increase the cost of the units. b) Essentials. Specify small PDs only for those dimensions that are important to the correct assembly, performance and appearance of the structure, and ensure that these are as large as is practicab

14、le. Leave the PDs for other dimensions to the discretion of the manufacturer, but ensure that these are reasonable for the conditions of production and use. The manufacturer must, when requested, state these PDs. C) Consistency with adjoining components. Take care that the PDs for the units are cons

15、istent with any PD in the position and dimensions of adjoining components in the building. -. d) Impact of tolerance requirements on moulds. The PDs given in Clause 6 of SABS 1200 G“ are a general guide and, where more exact values are necessary, the PDs can be halved. However, restrict such reducti

16、ons to those dimensions of which the accuracy is important, as such small PDs will necessitate a very high standard of construction of moulds and closer than normal supervision and inspection at all stages of manufacture with consequent increased costs. In exceptional cases, it may be possible to re

17、duce certain PDs even further by means of specially designed moulds, but make such reductions with due discretion. c) Manufacturers advice. Obtain the manufacturers advice at the early design stages when very small PDS are likely to be required, as those which can be achieved in practice depend on a

18、 number of factors, including 1) the shape of the unit, particularly as this affects the rigidity of the mould; 2) the mould materials and the method of assembly; 3) the number of castings to be made from each mould; and 4) the position and shape of any projections through the moulded faces. f) Irre

19、gular units. Clearly define PDs for irregular, curved or specially shaped units by means of the project specification and the dimensions shown on drawings. g) Cumulative tolerances. Note particularly that tolerances can be cumulative, i.e. adjoining edges of two floor panel units nominally at the sa

20、me level can differ by the sum of the positive deviations on bow and thickness in one unit, and the same negative deviations in the next unit. h) Use plus and minus values. Where appropriate, give PDs as both plus and minus values on a specific dimension, rather than as a deviation from a maximum or

21、 minimum value and ensure that any working drawings to be used by a manufacturer give dimensions and PDs as required. i) Prestressed units a) In specifying POs take into account the creep, shrinkage, elastic shortening of the concrete, eccentricity of the steel and other significant factors. General

22、ly, the PDs given in Clause 6 of SABS 1200 G1) for length, cross-section, twist and flatness will apply until the stressing force is applied. b) By the use of appropriate factors applied to the method for the calculation of the deflection of beams given in Part I of SABS 0100). the camber of a unit

23、at a given age can be predicted. State this predicted camber and the age and other controlling conditions (e.g. if the unit is supported at the ends and subjected to self-weight only) on the drawings or in the project specification. Prestressing a dam wall. Where the project involves the tensioning

24、of a concrete dam wall, take suitable action in terms of Subclause 3.3.2 of Section GF of Part 2 of the code. 1) Concrete (structural) . 2) Structural use of concrete Part I : Design. SABS 0120 : Part 3 Section GF-1984 Prestressed concrete DESIGN REQUIREMENTS DESIGN EXPERIENCE General. Design of pre

25、stressed units must be done by a professional engineer experience6 in prestressing. Sources of Desiqn Inaccuracy (Subclause 5.4.5.1). In order to minimize design inaccuracy, take into account the problems encountered in the construction of prestressed concrete units as set out in Subclause 3.1.8 of

26、Section GF of Part 5 of the code. Classes of Structure (Subclause 2.4.1). Typically the following structures may be designed under each class: Class 1 : Nuclear and other structures where the presence of cracks could have disastrous effects; Class 2 : water-containing structures; class 3 : Bridges,

27、building frameworks and the like. GENERAL QUALITY. Ensure that precast units, whether of plain, reinforced or prestressed ccncrete, have been designed and manufactured in accordance with the applicable recommendations given in Part I of SABS 010o2), and that the quality of the material and the workm

28、anship are generally in accordance with the applicable requirements of SABS 1200 G1) and SABS 1200 GF. PROTECTION AND BONDING OF EXTERNAL TENDONS (Subclause 5.6). A tendon is considered as external when, after having been stressed and incorporated into the work but before it is protected, it is outs

29、ide the structure, as is the case when tendons are stressed around the outside of a concrete circular reservoir. The term “external tendon“ does not apply, for example, to the tendons of a floor comprising a series of precast beams that, although the beams are stressed with external tendons, are sub

30、sequently so concreted or so grouted that, in the finished floor, the prestressing tendons are contained in and adequately covered by the concrete or grout. Subclause 5.6 of SABS 1200 GF provides for the protection from mechanical damage and corrosion of external prestressing tendons k)y means of an

31、 encasement of dense concrete or dense mortar. (For fuller guidance on this subject, consult papers presented to the Sprayed Concrete Symposium of the Concrete Society of Southern Africa in June 1982 and, in particular, “Sprayed concrete and steel fibres“ by H P Spann. See also Subclause 3.1.12 of S

32、ection GF of Part 5 of the code.) Protection may also be provided by other materials that have adequate hardness and stability in the particular environment. In determining the type and quality of the material to be used for such encasement, give full consideration to differential movement between t

33、he structure arid the applied protection which may occur as a result of changes in load, stress, humidity or temperature, or as a result of creep, relaxation, drying or shrinkage. Where the protection to be applied is dense concrete or mortar that may develop undesirable cracking, use corrosion prot

34、ection that will remain unimpaired by differential movement. (See Subc.1ause 3.2.4 of Section GF of Part 2 of the co8e.j If it is required that external prestressing tendons be bonded to the structure, ac:hieve this by designing suitable reinforcement of the concrete encasement to the structure. APP

35、LICABILITY OF OTHER CODES Apply the relevant requirements of SABS 0100) to the design of prestressed concrete units. TEST PROCEDURES GENERAL. Apply the test procedures recommended in SABS 5150), except where otherwise specified in SABS 1200 GF or in the project specification. QUALITY CONTROL AND OTH

36、ER CONSIDERATIONS Apply the relevant recommendations of SABS 0157) to the design, process control and quality assurance aspects of prestressed concrete. A useful reference in this regard is Report on Prestressing Steel : 4. Principles of quality assurance with respect to prestressing steels.- l) See p.1. 2) See p.1. 3) Quality management systems. 4) Published for The Federation Internationale de la Precontrainte by the Cement and Concrete Association, Wexham Springs, Slough, England, in 1979. sabs pta