1、BRITISH STANDARD BS 7973-2:2001 Spacers and chairs for steel reinforcement and their specification Part 2: Fixing and application of spacers and chairs and tying of reinforcement ICS 77.140.99 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAWBS 7973-2:2001 This British Standard,
2、 having been prepared under the direction of the Standards Policy and Strategy Committee for Building and Civil Engineering, was published under the authority of the Standards Policy and Strategy Committee and comes into effect on 16 October 2001 16 October 2001 The following BSI references relate t
3、o the work on this standard: Committee reference B/525/2 Draft for comment 00/104696 DC ISBN 0 580 38557 4 Committees responsible for this British Standard The preparation of this British Standard was entrusted by Technical Committee B/525, Building and civil engineering structures, to Subcommittee
4、B/525/2, Structural use of concrete, upon which the following bodies were represented: Association of Consulting Engineers British Cement Association British Precast Concrete Federation Ltd. Building Research Establishment Concrete Society Ltd. Department of the Environment, Transport and the Region
5、s (Construction Directorate) Department of the Environment, Transport and the Regions (Highways Agency) Institution of Civil Engineers Institution of Structural Engineers UK Steel Association Amendments issued since publication Amd. No. Date CommentsBS 7973-2:2001 BSI 16 October 2001 i Contents Page
6、 Committees responsible Inside front cover Foreword ii 1S c o p e 1 2 Normative references 1 3T e r m s a n d d e f i n i t i o n s 1 4 Designations and symbols 1 5 Tying of steel reinforcement 2 6 General requirements for spacers and chairs 2 7 Spacers and chair categories and applications 3 8 Spac
7、ing of spacers and chairs 3 Bibliography 16 Figure 1 Spacers for bottom reinforcement in slabs 4 Figure 2 Continuous chairs for top reinforcement in slabs with bottom reinforcement 5 Figure 3 Chairs for top reinforcement in slabs without bottom reinforcement 6 Figure 4 Circular chairs for top reinfo
8、rcement in slabs with bottom reinforcement 7 Figure 5 Spacers for slab edges 9 Figure 6 Spacers for ribbed slabs 10 Figure 7 Spacers for beams 12 Figure 8 Spacers for columns 13 Figure 9 Continuous chairs for walls 15 Table 1 Applications for spacers and chairs in terms of category 3BS 7973-2:2001 i
9、i BSI 16 October 2001 Foreword This British Standard has been prepared by Technical Committee B/525/2. It is the first edition of the standard. Until now the inadequate manufacture and use of spacers and chairs and method of tying has been a major cause of misplaced steel reinforcement resulting in
10、decreased durability of reinforced concrete. In November 1989 the Concrete Society published Spacers for reinforced concrete (CS101) 1 providing recommendations for achieving cover but until now no British Standard has existed. All British Standards for reinforced concrete design and construction (e
11、.g. BS 8110-1, BS 5400-7 and BS 8007) state that the nominal cover specified applies to all reinforcement including links. This British Standard gives standardized methods of achieving the specified nominal cover. It is based on the relevant parts of Concrete Society Report CS101 Spacers 1 published
12、 in November 1989 and was developed to be consistent with the Comit Euro-International du Bton Bulletin dInformation No. 201 Spacers, chairs and tying of steel reinforcement 2. It is imperative that chairs and spacers conforming to BS 7973-1 are applied in accordance with BS 7973-2. However, the nee
13、d to check cover before concrete placement and maintaining it whilst placing and compacting the concrete is extremely important. Where the specified cover cannot be achieved the instructions of the designer should be obtained. Abnormal loads, such as those exerted by construction plant, storage of m
14、aterials and heavy reinforcement cages, can overload spacers and chairs. Under abnormal load conditions adequate support is most suitably achieved using heavy (H) category line spacers at centres which depend on the exact size and nature of the load. A British Standard does not purport to include al
15、l necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii,
16、 pages 1 to 16, an inside back cover and a back cover. The BSI copyright notice displayed throughout this document indicates when the document was last issued.BS 7973-2:2001 BSI 16 October 2001 1 1 Scope This part of this British Standard specifies fixing and application requirements for spacers and
17、 chairs sufficient to achieve and maintain cover to reinforcement in in situ reinforced concrete members subject to normal construction loads. Application requirements include tying and spacing. This British Standard applies to all types of reinforcement conforming to BS 4449 and BS 4482 and some ty
18、pes of welded fabric conforming to BS 4483, supplied to the preferred shapes and tolerances given in BS 8666. Other important aspects such as clear and unambiguous detailing, the need to consider buildability, formwork tolerances and reinforcement are not specified. Standards of workmanship and supe
19、rvision are also outside the scope of this British Standard as is a means of resisting wind loads or enabling the lifting of prefabricated reinforcement cages. NOTE 1 Where appropriate, the basic principles can be applied to precast concrete or proprietary systems. NOTE 2 Straight reinforcement for
20、curvilinear members to be formed to a radius exceeding the maximum radius of bending given in BS 8666 may require extra tying and support to resist additional loads caused by the springing effect of the bars. 2 Normative references The following normative documents contain provisions which, through
21、reference in this text, constitute provisions of this part of this British Standard. For dated references, subsequent amendments to, or revisions of, any of these publications do not apply. For undated references, the latest edition of the publication referred to applies. BS 4449, Specification for
22、carbon steel bars for the reinforcement of concrete. BS 4482, Specification for cold reduced steel wire for the reinforcement of concrete. BS 4483, Specification of steel fabric for the reinforcement of concrete. BS 7973-1:2001, Spacers and chairs for steel reinforcement and their specification Part
23、 1: Product performance requirements. BS 8666, Specification for scheduling, dimensioning, bending and cutting of steel reinforcement for concrete. 3 Terms and definitions For the purposes of this British Standard the terms and definitions given in BS 7973-1 and the following apply. 3.1 tying wire w
24、ire used to fix reinforcement, spacers and chairs and which is normally 16 gauge black annealed wire NOTE Corrosion resistant wire of equal strength may, where considered appropriate, be used. 4 Designations and symbols The following designations and symbols are used throughout this British Standard
25、. c Cover or nominal cover (the nominal cover specified on the structural design drawings). d The nominal size of the bar nearest the surface of the concrete including links, used to determine the frequency of spacers along the bar to which they are fixed. For the spacing of chairs, d is the nominal
26、 size of the bar or wire that the chair is supporting. D The nominal size of the main bar.BS 7973-2:2001 2 BSI 16 October 2001 5 Tying of steel reinforcement 5.1 General 5.1.1 Reinforcement shall be tied together to prevent displacement of bars. The spacing of ties for slabs, beams, columns, foundat
27、ions and walls shall be in accordance with 5.2, 5.3, 5.4, 5.5 and 5.6. 5.1.2 Care shall be taken to ensure that projecting ends of tying wire do not encroach into the concrete cover. 5.2 Tying within slabs Perimeter bars shall be tied at every intersection. For bars up to and including 20 mm, altern
28、ate intersections shall be tied. Reinforcement at right angles to the edge of the slab shall be fixed by locating the bar with the specified end cover and tying it from that end inward. NOTE Where all bars are 25 mm or larger they may be tied at greater than alternate intersections but not exceeding
29、 50 times the size of the smallest bars. 5.3 Tying within beams Every intersection of a corner of a link with a longitudinal main bar shall be tied. Other bars within the links shall be tied at 50D centres. Where welded fabric is used as a link cage, it shall be tied at 50D centres to the main bars.
30、 Each set of multiple links shall be tied together. 5.4 Tying within columns Because of the importance of keeping the main vertical bars in their correct position, every intersection between vertical bars and links shall be tied. For link cages made of welded fabric the vertical wires shall be tied
31、at 50D centres to the main bars. Each set of multiple links shall be tied together. 5.5 Tying within foundations The horizontal part of starter bars shall be tied at every intersection with the foundation reinforcement at right angles to the starter bars and any bars parallel to it. The vertical par
32、t of the starter bar shall be tied at every intersection with any column links within the foundation. 5.6 Tying within walls Perimeter bars shall be tied at every intersection. For bars up to and including 20 mm, alternate intersections shall be tied. Reinforcement at right angles to the end of a wa
33、ll shall be fixed by locating the bar with the specified end cover and tying it from that end inward. NOTE Where all bars are 25 mm or larger they may be tied at greater alternate intersections but not exceeding 50 times the size of the smallest bars. 6 General requirements for spacers and chairs 6.
34、1 Cover shall be achieved by using factory made spacers and chairs manufactured according to BS 7973-1, to support and locate reinforcement during the construction of reinforced concrete elements. Reinforcement shall be adequately tied (see clause 5) together to prevent displacement of bars. The num
35、ber and position of spacers shall be as given in clause 8. 6.2 The requirements for beams and slabs shall apply to their equivalent foundation members, such as ground beams, ground slabs, strip footings, individual bases and pile caps, provided the reinforcement is supported off concrete blinding an
36、d is not subject to abnormal loads. 6.3 A spacer or chair shall maintain the reinforcement in the position specified on the structural design drawings during concrete placing and shall not significantly reduce the durability of the structure. 6.4 Spacers shall be fixed to the links, fabric or reinfo
37、rcement nearest the face of the concrete to which the cover is specified. 6.5 If coloured, textured, profiled or exposed aggregate finishes to the concrete are required, spacers shall be selected so that they do not disrupt the aesthetic appearance of the concrete. NOTE Where a concrete element has
38、only one face with a special finish, disruption of its appearance can be avoided by spacing the reinforcement off either the opposite face or by the use of chairs.BS 7973-2:2001 BSI 16 October 2001 3 6.6 Spacers with a suitable bearing area shall be used where cover is required between reinforcement
39、 and materials subject to indentation or puncture, such as some void formers, impermeable membranes and insulation materials. 6.7 When steel chairs are required to support reinforcement off an exposed face, the ends of each chair leg shall be encased in a protective tip, such as a closed plastics sl
40、eeve, for a distance of at least 40 mm. 7 Spacers and chair categories and applications Spacer and chair categories required for particular applications shall be in accordance with Table 1. Criteria for assessing the spacer category shall be in accordance with BS 7973-1:2001, Table 2. Table 1 Applic
41、ations for spacers and chairs in terms of category 8 Spacing of spacers and chairs 8.1 Spacers and chairs within slabs 8.1.1 Solid slabs 8.1.1.1 Bottom face All bar reinforcement nearest to the bottom face shall be supported by spacers at centres not exceeding 50d and not exceeding 1 000 mm. Spacers
42、 shall be staggered see Figure 1a). Fabric shall be supported by spacers at centres not exceeding 500 mm in two directions at right angles see Figure 1b). 8.1.1.2 Top face Top reinforcement shall always be supported off the bottom reinforcement where such reinforcement exists, by continuous chairs (
43、see Figure 2). Where there is no bottom reinforcement, the top reinforcement shall be supported from the formwork or blinding by the use of individual chairs at centres not exceeding 50d, fitted with protective tips, or by continuous chairs at centres not exceeding 50d resting on line spacers see Fi
44、gure 3a) and Figure 3b). In all cases, continuous chairs supporting individual bars shall provide a line of support to groups of adjacent bars at centres not exceeding 50d the size of bar they are supporting. The spacing of individual chairs shall not exceed 50d centres in both directions for indivi
45、dual bars, or 500 mm for welded fabric. Fabric shall be supported by continuous chairs at centres not exceeding 500 mm resting on line spacers, or by individual chairs at centres not exceeding 500 mm. Individual chairs shall be fitted with protective tips. Alternatively, top fabric shall be supporte
46、d off a bottom layer by 570 mm diameter circular chairs with their centres at each apex of an equilateral triangle of side 1 200 mm i.e. 1 200 mm centres in one direction and 1 040 mm in the direction at right angles and with rows staggered (see Figure 4). The ends of circular chairs shall be lapped
47、 at least 200 mm. Circular chairs shall not be used for foot traffic if either the main or the cross wires in the fabric they are supporting are less than 7 mm in size. Circular chairs shall each be tied at least twice to each of the bottom and top layers of fabric. For all fabrics the ties shall be
48、 placed wherever node points in the fabric and the chair coincide. NOTE These spacings are for A393 to A193 and B1131 to B385 fabric conforming to BS 4483. Spacer and chair category Application Light (L) To provide cover in vertical members to the reinforcement nearest the surface of the concrete or
49、 to horizontal reinforcement in small sections not subject to any foot traffic. Not suitable for reinforcement greater than 16 mm in size. Normal (N) To provide cover to reinforcement where the size of reinforcement is 20 mm or less. Heavy (H) To provide cover to reinforcement where the size of reinforcement is greater than 20 mm. Chairs (C) To support to the top reinforcement in slabs, so as to provide the required top cover or to separate layers of reinforcement.BS 7973-2:2001 4 BSI 16 October 2001 Dimensions in millimetres Figure 1
