1、BRITISH STANDARD BS 7973-1:2001 Spacers and chairs for steel reinforcement and their specification Part 1: Product performance requirements ICS 77.140.99 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAWBS 7973-1:2001 This British Standard, having been prepared under the directi
2、on of the Sector Policy and Strategy Committee for Building and Civil Engineering, was published under the authority of the Standards Policy and Strategy Committee on 16 October 2001 16 October 2001 The following BSI references relate to the work on this standard: Committee reference B/525/2 Draft f
3、or comment 00/104696 DC ISBN 0 580 38556 6 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 B/525/2, Structural use of concrete, upon which the following bo
4、dies 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 Regions (Construction Directorate) Department of the Environment, Tran
5、sport and the Regions (Highways Agency) Institution of Civil Engineers Institution of Structural Engineers UK Steel Association Amendments issued since publication Amd. No. Date CommentsBS 7973-1:2001 BSI 16 October 2001 i Contents Page Committees responsible Inside front cover Foreword ii 1S c o p
6、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 2 5 Spacers and chair categories and applications 3 6 General requirements for spacers and chairs 3 7D i m e n s i o n s 3 8 Stability 4 9 Load bearing capacity 6 10 Fixity 6 11 Marking 7 12 Inspection a
7、nd testing 8 Annex A (normative) Load testing 9 Bibliography 12 Figure 1 Geometrical requirements of clip-on spacers and wheel spacers 5 Figure 2 Isometric view of the fixity test for clip-on spacers 6 Figure A.1 Apparatus for load testing spacers 10 Figure A.2 Position of a wheel spacer for load te
8、sting 10 Figure A.3 Apparatus for point load testing chairs 11 Table 1 Applications for spacers and chairs in terms of category 3 Table 2 Point test load for spacers and chairs 7BS 7973-1:2001 ii BSI 16 October 2001 Foreword This British Standard has been prepared by Technical Committee B/525/2. It
9、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 decreased durability of reinforced concrete. In November 1989 the Concrete Society published Spacers for r
10、einforced 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.g. BS 8110-1, BS 5400-7 and BS 8007) state that the nominal cover specified applies to all reinforcement
11、including links. This British Standard gives standardized performance requirements for and methods of testing spacers and chairs. It is based on Concrete Society Report CS 101 “Spacers” 1 published in November 1989 and was developed to be consistent with the Comit Euro-International du Bton Bulletin
12、 dInformation No. 201 Spacers, chairs and tying of steel reinforcement 2. Performance and testing requirements are based on tests carried out on the capacity of spacers and chairs which have been available in the UK for many years and which have proved to be satisfactory in use. It is imperative tha
13、t chairs and spacers conforming to BS 7973-1 are applied in accordance with BS 7973-2. Abnormal loads, such as those exerted by construction plant, storage of materials and heavy reinforcement cages, can overload spacers and chairs. Under abnormal load conditions adequate support is most suitably ac
14、hieved using heavy (H) category line spacers at centres which depend on the exact size and nature of the load. Annex A is normative. A British Standard does not purport to include all necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compli
15、ance 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, pages 1 to 12, an inside back cover and a back cover. The BSI copyright notice displayed in this document indicates w
16、hen the document was last issued.BS 7973-1:2001 BSI 16 October 2001 1 1 Scope This part of this British Standard specifies product performance requirements for spacers and chairs sufficient to achieve and maintain cover to reinforcement in in situ reinforced concrete members subject to normal constr
17、uction loads when used in accordance with BS 7973-2. NOTE Where appropriate, the basic principles can be applied to precast concrete or proprietary systems. Product requirements for spacers and chairs include their dimensions, identification, point load strength, permanent deflection after loading,
18、stability and fixity. 2 Normative references The following normative documents contain provisions which, through 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 appl
19、y. For undated references, the latest edition of the publication referred to applies. BS 1881-108, Testing concrete Part 108: Method for making test cubes from fresh concrete. BS 1881-111, Testing concrete Part 111: Method of normal curing of test specimens (20 C method). BS 1881-116, Testing concre
20、te Part 116: Method for determination of compressive strength of concrete cubes. BS 4482, Specification for cold reduced steel wire for reinforcement of concrete. BS 4483, Steel fabric for the reinforcement of concrete. BS 7973-2, Spacers and chairs for steel reinforcement and their specification Pa
21、rt 2: Fixing and application of spacers and chairs and tying of reinforcement. BS 8110-1:1997, Structural use of concrete Part 1: Code of practice for design and construction. 3 Terms and definitions For the purposes of this British Standard the following terms and definitions apply. 3.1 cover dista
22、nce between the steel reinforcement and the nearest face of the concrete NOTE 1 Cover, or nominal cover, is the cover specified by the structural designer on the structural design drawings. NOTE 2 As the term “minimum cover” can be confused with “nominal cover”, it should not be used. 3.2 spacer com
23、ponent which is placed to maintain cover between the reinforcement and formwork or blinding and which provides cover or support for reinforcement at a single point on one or more faces of the formwork or blinding NOTE As stated in BS 8110-1:1997, Table 3.4, 15 mm cover spacers may only be used where
24、 the nominal maximum size of aggregate does not exceed 15 mm. 3.3 end spacer spacer designed to fit on the ends of reinforcement to provide end cover 3.4 line spacer spacer normally made of either plastics or cementitious bars, normally of constant cross-section, used to support horizontal layers of
25、 reinforcement or horizontal continuous steel chairs 3.5 rib spacer spacer used where there are no links within the ribs and which are designed to support one or more main bars in hollow pot, waffle, trough and ribbed slabs and to provide spacing between the sides of the hollow pot, waffle, trough a
26、nd rib formsBS 7973-1:2001 2 BSI 16 October 2001 3.6 wheel spacer spacer having a circular section, perpendicular to the bar to which it is attached, used for maintaining cover in vertical members to the reinforcement nearest the surface of the concrete 3.7 clip-on spacer spacer in which the clip ac
27、tion is an integral part of the design of the spacer NOTE A clip-on spacer is usually made of plastics. 3.8 wire-on spacer spacer that is attached to the bar by the use of tying wire NOTE Wire-on spacers are usually cementitious. 3.9 chair component in sizes of 50 mm to 300 mm normally manufactured
28、from steel wire conforming to BS 4482 commonly used to support top horizontal reinforcement or to separate vertical reinforcement in walls NOTE Chairs may be individual, continuous, or circular. Chair heights above 300 mm are normally scheduled using bent bar reinforcement. 3.10 individual chair cha
29、ir manufactured in standard heights of between 75 mm and 300 mm inclusive and used to support reinforcement at one point 3.11 continuous chair chair manufactured to provide a straight line of support at a uniform height normally in the range of 45300 mm NOTE Continuous chairs are generally available
30、 in continuous lengths of up to 2 000 mm. 3.12 circular chair steel chair delivered flat and formed into circles on site 3.13 welded fabric cross-over arrangement of longitudinal wires and cross wires that are welded together at the cross-over points in a shear resistant manner, conforming to BS 448
31、3 4 Designations and symbols The following designations and symbols are used throughout this British Standard. c Cover or nominal cover. 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
32、. For the spacing of chairs, d is the nominal size of the bar or wire that the chair is supporting. D The nominal size of the main bar.BS 7973-1:2001 BSI 16 October 2001 3 5 Spacers and chair categories and applications Spacer and chair categories required for particular applications shall be in acc
33、ordance with Table 1. Criteria for assessing the spacer category shall be in accordance with Table 2. Table 1 Applications for spacers and chairs in terms of category 6 General requirements for spacers and chairs 6.1 Materials of manufacture Spacers and chairs shall be manufactured from three basic
34、materials: plastics, cementitious material or steel wire. The material of manufacture shall have an equivalent durability when it is in place to that of the concrete itself. NOTE It is important that the spacer or chair does not cause any deterioration to the reinforcement or the concrete, including
35、 not allowing free passage of water to the reinforcement nor causing spalling of the finished face. 6.2 Requirements for non-cementitious spacers Non-cementitious spacers shall satisfy the condition that any cross-section perpendicular to the bar has at least 25 % voids within the enclosed perimeter
36、. 6.3 Requirements for cementitious spacers The mix used for cementitious spacers shall have a cube strength of at least 50 N/mm 2at 28 days when cast, cured and tested in accordance with BS 1881-108, BS 1881-111, and BS 1881-116 respectively. In accordance with BS 8110-1 concrete spacers shall not
37、be made on the construction site. 6.4 Requirements for steel chairs 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 sleeve, for a distance of at least 40 mm. Continuous and circula
38、r chairs shall comprise top and bottom wires of equal size and quality to which shall be welded transverse or lattice wires to space them. NOTE 1 If the chair is higher than 150 mm, strengthening may be required to meet the performance requirements of this British Standard. NOTE 2 The performance re
39、quirements of this British Standard are based on the use of 2 m lengths formed into circles of 570 mm diameter used to support the welded fabrics specified. 7 Dimensions 7.1 Preferred spacer and chair dimensions The standard range of spacers shall be for nominal covers from 15 mm to 75 mm in 5 mm in
40、crements. The standard range of chairs shall be for heights of 75 mm to 200 mm. NOTE As stated in BS 8110-1:1997, Table 3.4, 15 mm cover spacers may only be used where the nominal maximum size of aggregate does not exceed 15 mm. Spacer and chair category Application Light (L) To provide cover in ver
41、tical members to the reinforcement nearest the surface of the concrete or 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
42、 less. Heavy (H) To provide cover to reinforcement where the size of reinforcement is greater than 20 mm. Chairs (C) To support the top reinforcement in slabs, so as to provide the required top cover or to separate layers of reinforcement.BS 7973-1:2001 4 BSI 16 October 2001 7.2 Dimensional toleranc
43、es for spacers The tolerance on the spacer dimension providing the cover shall be 1 mm for covers/heights up to 75 mm and 2 mm for larger cover/heights over 75 mm. 7.3 Dimensional tolerances for chairs The tolerance on the chair dimensions providing the cover or the specified height shall be 2 mm. F
44、or continuous and circular chairs where the nominal cover dimension is provided by a longitudinal element any side-supporting element shall not protrude beyond the longitudinal element by more than 3mm. 7.4 Identification of the cover dimensions The nominal cover dimension of the spacer shall always
45、 be displayed on its packaging. Wherever possible, as part of the manufacturing process, the nominal cover dimension shall be indicated on the actual spacer. NOTE Single cover spacers are recommended. The maximum number of covers on each spacer shall be two with the value and orientation clearly mar
46、ked on the actual spacer. 7.5 Wire-on spacers The dimension of a wire-on spacer at its base shall be at least 20 mm measured in the direction of the bar which it is supporting and at least 0.75 of the cover dimension perpendicular to the bar. 7.6 Clip-on spacers As clip-on spacers have varying dimen
47、sional requirements relating to their fixity, they shall conform to clause 8. 7.7 Chairs 7.7.1 The distance between any two legs of an individual chair shall be not less than 0.5 of the specified height of the chair. 7.7.2 The distance between the two rows of supports of a continuous chair shall be
48、not less than 0.5 of the specified height of the chair. 8 Stability 8.1 The stability of a clip-on spacer, other than a clip-on wheel spacer, shall be provided by having a radius of rotation at least 5 mm greater than the required cover, both perpendicular and parallel to the line of the reinforcing
49、 bar to which it will be attached. NOTE The radius of rotation is illustrated in Figure 1. 8.2 Clip-on wheel spacers do not require a minimum radius of rotation perpendicular to the bar as stability is provided by the boss bearing length parallel to the bar which shall be greater than half of the required cover, as shown in Figure 1.BS 7973-1:2001 BSI 16 October 2001 5 Dimensions in millimetres Figure 1 Geometrical requirements of clip-on spacers and wheel spacers A at least c + 5 A at least c + 5 c c c c 5 5 5 B at least c + 5 At
