March 23, 2017 | Author: Sachin Dhiman | Category: N/A
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ICS 01.100.30; 91.080.40 ISBN 0-626-10274-X
SABS 0144*
*This standard references other standards
Edition 2
1995
SOUTH AFRICAN STANDARD
Code of practice
Detailing of steel reinforcement for concrete
Published by THE SOUTH AFRICAN BUREAU OF STANDARDS
Gr 19
SABS 0144 Ed. 2
SABS 0144
ICS 01.100.30; 91.080.40
Ed. 2
SOUTH AFRICAN BUREAU OF STANDARDS CODE OF PRACTICE DETAILING OF STEEL REINFORCEMENT FOR CONCRETE
Obtainable from the South African Bureau of Standards Private Bag X191 Pretoria Republic of South Africa 0001 Telephone Fax E-mail Website
: (012) 428-7911 : (012) 344-1568 :
[email protected] : http://www.sabs.co.za
COPYRIGHT RESERVED Printed in the Republic of South Africa by the South African Bureau of Standards
SABS 0144 Ed. 2
Acknowledgement The South African Bureau of Standards wishes to acknowledge the valuable assistance received from the SAICE (Structural Division) Concrete Committee.
Notice This standard was approved in accordance with SABS procedures on 24 April 1995. NOTE 1 In terms of the Standards Act, 1993 (Act 29 of 1993), no person shall claim or declare that he or any other person complied with an SABS standard unless a) such claim or declaration is true and accurate in all material respects, and b) the identity of the person on whose authority such claim or declaration is made, is clear. NOTE 2 It is recommended that authorities who wish to incorporate any part of this standard into any legislation in the manner intended by section 31 of the Act consult the SABS regarding the implications.
This standard will be revised when necessary in order to keep abreast of progress. Comment will be welcome and will be considered when the standard is revised.
Foreword This second edition (first revision) cancels and replaces SABS 0144:1978. Annexes A, B, C, D and E are for information only.
Attention is drawn to the normative references given in clause 2 of this standard. These references are indispensable for the application of this standard.
ISBN 0-626-10274-X
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SABS 0144 Ed. 2
Introduction This standard is intended to cover all types of reinforced concrete. Some specialized structures, such as silos and reservoirs, are not mentioned specifically, but the general principles apply. The methods set out in the standard are derived from South African practice as evolved over a period of 50 years. They are used by consulting engineers and reinforcement suppliers, and represent a good standard of detailing. The provisions set out are not mandatory, but are intended as a guide to normal procedures. The object of the standard is to present those methods that will save time and effort in the drawing office and at the same time facilitate placing of reinforcement and communication with the construction site, and reduce the likelihood of errors. NOTE – The drawings contained in this standard have been derived from various sources, and do not necessarily comply with the ISO requirements for drawings. The way in which the drawings have been done, is therefore not prescriptive.
In writing the standard, it has been found impossible to separate design considerations from detailing rules because of their interdependence. To avoid confusion, therefore, the reasons for some of the rules have been included. The standard is intended to be in accordance with the provisions of SABS 0100-1 but note has been taken of overriding recommendations in other similar modern standards (ACI1), CEB-FIP2), Australian, British, German) and recent research findings. Adjustments based on the experience of members of the committee who prepared this standard have also been made. It must be emphasized that with the new limit-state approach, the stress in the reinforcement under normal or even self-weight load conditions is considerably higher than was usual. As a result, good detailing has become extremely important.
1) ACI: American Concrete Institute. 2) CEB-FIP: Comité Européen du Béton – Fédération Internationale de la Précontrainte.
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SABS 0144 Ed. 2
Contents Acknowledgement
Page . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii
Notice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii Committee . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix 1
Scope
2
Normative references . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
3
Detailing considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 3.10
4
2 2 2 3 3 3 3 3 4 4
Placing drawings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Referencing of bars and placing instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Revisions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Preferred spacing of reinforcement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Scheduling of bar reinforcement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9
6
General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bending schedules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Placing and wiring in position . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Support of reinforcement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Preassembly of cages and mats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Concreting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Openings, pockets, other trades and services . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Measurement of quantities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Economical use of reinforcement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Detailing of reinforcement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 4.1 4.2 4.3 4.4
5
.................................................................. 1
General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Paper sizes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Title panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Numbering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Drawing and dimensioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bending details . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cutting and bending tolerances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Methods of expressing quantities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Combined placing drawings and bending schedules . . . . . . . . . . . . . . . . . . . . . . .
General requirements for all components 6.1 6.2 6.3 6.4 6.5
12 12 12 13 13 14 14 14 15
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Cover to reinforcement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The maintenance of cover and position of reinforcing bars . . . . . . . . . . . . . . . . . . Splicing of reinforcing bars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bends and anchorages for reinforcing bars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bundling of bars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15 16 21 23 24
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SABS 0144 Ed. 2
Contents (continued) Page 7
Component detailing – Beams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 7.9 7.10 7.11 7.12 7.13 7.14 7.15 7.16
8
25 25 25 28 33 40 41 43 43 44 48 48 52 52 53 57
Component detailing – Slabs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 8.1 8.2 8.3 8.4 8.5 8.6 8.7 8.8 8.9 8.10 8.11 8.12
9
Numbering of beams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Types of detail . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Preferred methods of detailing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Practical requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Stirrups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Beams of depth exceeding 750 mm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Intersections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Maintaining bars in position . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Minimum reinforcement requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Curtailment of bars in beams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bent-up bars for shear reinforcement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Corbels and halving joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Splicing of tension bars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Prefabrication of beam cages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Corners and cranked beams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Deep beams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Minimum reinforcement in slabs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Spacing of bars in slabs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Diameters of bars in slabs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Scheduling of steel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Maintenance of position of steel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Openings and corners in slabs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cantilever slabs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Curtailment of top tension reinforcement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Corner reinforcement in two-way slabs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Slabs of other types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Flat slabs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
61 61 62 63 63 63 64 66 71 71 71 71
Component detailing – Columns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 9.1 9.2 9.3 9.4 9.5 9.6
General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Detailing method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Main reinforcement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Stirrups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Splicing of column reinforcement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Large change in column size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
75 75 75 78 82 84
10 Component detailing – Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 10.1 10.2 10.3 10.4 10.5 10.6 10.7
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General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Detailing methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Reinforced and plain concrete walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Kickers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cranking of vertical bars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Layers of reinforcement in thin walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Layers of reinforcement in thicker walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
84 84 84 84 84 87 87
SABS 0144 Ed. 2
Contents (continued) Page 10.8 10.9 10.10 10.11 10.12 10.13 10.14 10.15 10.16 10.17 10.18 10.19 10.20
Prefabrication of reinforcement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Vertical stages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Clips . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pockets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Splices at top of wall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Splices to slabs and beams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Walls with nominal reinforcement or plain concrete walls . . . . . . . . . . . . . . . . . . . Walls in which the required area of vertical reinforcement exceeds 0,4 % of the plan area of concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Walls constructed by means of sliding or climbing shuttering . . . . . . . . . . . . . . . . Retaining walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Walls, other than retaining walls, contributing significantly to horizontal stability of a structure, for example tank walls, silo walls, shear walls, core walls . . . . . . . Walls with corners subject to horizontal bending . . . . . . . . . . . . . . . . . . . . . . . . . . Walls subject to bending forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
88 88 88 88 90 91 92 92 92 93 96 97 98
11 Component detailing – Foundations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 11.1 11.2 11.3 11.4 11.5 11.6 11.7 11.8 11.9
Detailing methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Main reinforcement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Combined bases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pile caps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Raft foundations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Wall foundations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Machine foundations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Strap beams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Column starter bars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
99 99 102 103 103 103 103 103 105
12 Staircases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 12.1 12.2
Diagrammatic details . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 Re-entrant corners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
13 Welded steel mesh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110 13.1 13.2 13.3 13.4 13.5 13.6 13.7 13.8
Use of mesh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Types of mesh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mesh placing drawings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Scheduling of mesh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bending of mesh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Galvanized mesh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Lapping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
110 110 110 112 114 118 118 118
14 Detailing with respect to aqueous liquid retaining structures . . . . . . . . . . . . . . . . . . . . . . . 120 14.1 14.2 14.3 14.4 14.5
General principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Causes of cracking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Detailing to minimize effects of cracking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cover . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
120 120 120 123 123
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SABS 0144 Ed. 2
Contents (concluded) Page 15 Detailing of steel reinforcement for post-tensioned concrete slabs . . . . . . . . . . . . . . . . . . 125 15.1 15.2 15.3 15.4 15.5 15.6
General principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Causes of cracking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Detailing to minimize effects of cracking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tendon profiling and positioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cover . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
125 125 125 127 128 129
Annexes A Shape codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130 B Additional information on corners and cranked beams . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 B.1 B.2 B.3 B.4 B.5 B.6 B.7 B.8 B.9
Changes in angle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Methods of reinforcing opening corners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Methods of improving strength of opening corners . . . . . . . . . . . . . . . . . . . . . . . . . Reinforcement less than 1 % . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Reinforcement more than 1 % . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Looped reinforcement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Junction of beams and columns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cranked beams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Closing corners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
131 132 133 135 135 135 136 137 139
C Steel reinforcement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140 C.1 C.2 C.3 C.4
Steel bars for concrete reinforcement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Size and availability of steel bars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Deformations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Welded steel mesh for concrete reinforcement . . . . . . . . . . . . . . . . . . . . . . . . . . .
140 140 140 141
D Table of bond and lap lengths for fully stressed bars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142 E Tables of the area and mass of reinforcing bars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143
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SABS 0144 Ed. 2
Committee SABS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
VJ Woodlock (Chairman) AT Brownhill (Standards writer) E Coetzee (Committee clerk)
Concrete Society of South Africa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
M McEwan
CSIR Boutek . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
BG Lunt
Department of Public Works and Land Affairs . . . . . . . . . . . . . . . . . . . . . . . .
CJ Jacobs MG Knoetze
Eskom . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
BP Hill DF van Tonder
Institute of Concrete Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
J Kellerman
Metricomp Programmes (Pty) Limited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
SG Stoch
Natal Provincial Administration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
D Le Voy
Portland Cement Institute . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
GRH Grieve P Taylor
South African Property Owners' Association . . . . . . . . . . . . . . . . . . . . . . . . .
KM Wood
South African Reinforced Concrete Engineers' Association . . . . . . . . . . . . .
B Doyle GJG Griffiths
The South African Association of Consulting Engineers . . . . . . . . . . . . . . . .
RJ Snowden C Vidulich
The South African Institution of Civil Engineers . . . . . . . . . . . . . . . . . . . . . . .
AE Goldstein RS Stamm MF Yawitch
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SABS 0144 Ed. 2 Blank
x
CODE OF PRACTICE
SABS 0144 Edition 2
Detailing of steel reinforcement for concrete
1 Scope 1.1 This standard recommends methods for detailing steel reinforcement for concrete and is applicable to most reinforced concrete. 1.2 The detailer is not expected to make decisions based on design aspects and should always seek instructions from the designer if there is any doubt as to methods of detailing. NOTES 1 In this standard, stirrups and ties are measured externally. 2 The word "rebar" (meaning "reinforcing bar") is being used overseas and it is possible that in time it will become common usage in this country. 3 The attention of users of this standard is drawn to annex A, recommended shape codes, annex B, additional information on corners and cranked beams, annex C, details of steel reinforcement, annex D, a table of bond and lap lengths for fully stressed bars and annex E, tables of area and mass of reinforcing bars.
2 Normative references The following standards contain provisions which, through reference in this text, constitute provisions of this standard. All standards are subject to revision and, since any reference to a standard is deemed to be a reference to the latest edition of that standard, parties to agreements based on this standard are encouraged to take steps to ensure the use of the most recent editions of the standards indicated below. Information on currently valid national and international standards can be obtained from the South African Bureau of Standards. BS 8007, Code of practice for design of concrete structures for retaining aqueous liquids. SABS 82, Bending dimensions of bars for concrete reinforcement. SABS 920, Steel bars for concrete reinforcement. SABS 1024, Welded steel fabric for reinforcement of concrete. SABS 0100-1, The structural use of concrete – Part 1: Design. SABS 0100-2, The structural use of concrete – Part 2: Materials and execution of work. SABS 0143, Building drawing practice.
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SABS 0144 Ed. 2
3 Detailing considerations 3.1 General In preparing drawings and bending schedules, bear the following factors in mind: a) the designer's design requirements; b) that the quantity, location, and cover of steel reinforcement should be simply, correctly and clearly shown; c) that the placing drawings and bending schedules should be adequately cross-referenced, easily read and capable of easy checking in the drawing office and on site; d) that it should be possible to locate a detail readily, should a query arise; e) that one detailer should be able to take over from another with a minimum of delay and supervision; f) the cutting and bending of the reinforcement; g) the sequence of the placing and wiring in position of reinforcement; h) maintaining the position of reinforcement; i) the preassembly of cages; j) the effects of the concreting operation; k) the accommodation of other trades and services; l) the measurement of quantities; m) economy in the use of steel; and
n) the position of construction joints.
3.2 Design The designer should ensure that the detailer is informed of special considerations for secondary stresses caused by items such as (but not limited to) support conditions, shrinkage, temperature variations, bursting effects of laps and splices, and stress concentrations arising from hooks and bends.
3.3 Bending schedules Prepare bending schedules on standard size sheets that are small enough to facilitate handling by clerical, fabrication and placing personnel. Ensure that bending details are simple and easy to read. Large structural units should be broken up into components as dictated by construction joints or into readily identifiable units such as "Floor", "North (East/South/West) wall", "Roof at level xxxx", etc. So compile the schedules that delivery of the required reinforcing for each component can be effected without the need to abstract from schedules. Ensure that the system of bar-referencing is coherent and systematic, and lends itself to easy identification and to use in computer systems.
2
SABS 0144 Ed. 2 3.4 Placing and wiring in position Ensure that drawings are simple, pictorially clear and adequately detailed to enable the steel fixer to place bars where required. Avoid crowding drawings with information by detailing by components. Ensure that reinforcing steel that connects elements to be cast at different times is so detailed that it is included with that portion to be cast first, for example splice bars for columns, and continuity reinforcing for beams and slabs to be cast in portions. If the order of casting is not clear, use suitable cross-references to detail splices in one of the sections. Where the complexity of the detail is such that an out-of-the-ordinary sequence is required to place the reinforcement, ensure that the sequence is shown on the detail. Give consideration to detailing reinforcement that occurs in different layers (for example top and bottom steel in slabs, and near and far face steel in walls), on separate views if the readability can be improved by reducing the crowding of information.
3.5 Support of reinforcement 3.5.1 Reinforcement that is placed at cover distances from formwork will be maintained in position by suitable lifting or spacer units provided for in the main specification. Ensure that adequate space is allowed for such units by the correct dimensioning of stirrups and clips, taking required tolerances into consideration. 3.5.2 Top reinforcement in slabs and other components could become displaced as a result of its own mass or by construction traffic normally expected before or during the placement of concrete. Provide bracing bars or stools (or both) of suitable rigidity and at suitable spacings with or without supporting bars of a similar nature, to make it difficult for the reinforcement to be displaced. This is particularly important where the spacing of bars is so close as to make it difficult or inconvenient to avoid standing on the reinforcement. Bear in mind that the contractor could raise an objection regarding the adequacy of the stools provided.
3.6 Preassembly of cages and mats In components such as columns, foundations, beams and walls, give consideration (when dictated by specific requirements or to allow the economic use of reinforcement) to so detailing reinforcement that it can be conveniently preassembled (see 7.14) before it is placed in position. Ensure that assembled units are sturdy enough to stand up to handling, erection and construction loads, and that they are not too heavy to be lifted by the men or equipment available for the work.
3.7 Concreting Ensure that the reinforcement is so spaced as to allow the placing and the efficient consolidation of the concrete.
3.8 Openings, pockets, other trades and services Consider holes and openings of significant proportions as permanent features of the structure and detail the reinforcement to suit. Do not use detailing instructions such as "cut to suit on site" (see 17.4.4 of SABS 0143). Take note of the positions of down pipes (especially inlets and outlets), sleeves, pipes and electrical conduits, whether shown on the structural layout or not. To avoid site difficulties, show them on the reinforcement details where necessary.
3
SABS 0144 Ed. 2
Figure 1
3.9 Measurement of quantities It is important to be able to compute the mass of steel used at any stage in a contract. Bending schedules prepared in accordance with 3.3 will assist in meeting this requirement. Ensure that placing drawings and bending schedules are adequately cross-referenced and that all revisions are suitably recorded. If, in the case of a revision, there is any possibility of doubt regarding the alteration, prepare separate schedules showing only the revision, with adequate cross-referencing. (For methods of expressing quantities, see 5.8.)
3.10 Economical use of reinforcement Economy in the use of reinforcement can be achieved if both the type of steel used and the labour involved in cutting, bending and placing are considered. When considering the types of steel, bear the following in mind: a) that where high tensile steel (HT) is used instead of mild steel (MS), considerable savings can be achieved; NOTE – The consent of the designer should be obtained before MS is substituted for HT.
b) that for stirrups, the difference in the bend radii of high tensile and mild steel should be considered with regard to the effect that the larger radius required for high tensile bars will have on the position of corner bars and the resultant reduction in the available space for other bars; and c) that reinforcement costs can be reduced: 1) when larger diameter bars are used, since fewer bars would be required; this also saves labour costs; 2) by the use of maximum lengths (stock lengths) up to 13 m; and 3) possibly by the use of mechanical splices (instead of lapped splices) for larger diameter bars. Labour costs could be further reduced by the minimum usage of bends in bars, reducing the number of bars and providing clear unambiguous reinforcement details.
4
SABS 0144 Ed. 2
4 Detailing of reinforcement 4.1 Placing drawings 4.1.1 Paper sizes Prepare reinforcement placing details on sheets of size A0 or smaller. Combined placing drawings and reinforcement bending schedules (see 5.9) should preferably be on sheets of size A3 or A4. Alternatively, larger sheets may be used, provided that they are so subdivided that they can be cut down to A3 or A4 size for use in the workshop or on site.
4.1.2 Title panel To facilitate reference when prints are filed or folded, place the title panel in the bottom right-hand corner of the sheet. 4.1.2.1 In the title panel, put the following information: a) the drawing number and the revision suffix; b) the project number; c) the scale, the date of drawing, and the names or initials of the persons who design, draw and check the drawing; d) the project title; e) the drawing title; and f) the name, address and telephone number of the organization. 4.1.2.2 In the title panel or in a notes panel, put the following information: a) the revision details, including the date; b) the reinforcement cover; and c) the reinforcement abbreviations. Update the revision suffix each time the drawing is issued after revision.
5
SABS 0144 Ed. 2 4.1.3 Drawings and details Draw bars in thick lines to ensure that they stand out clearly in relation to structural outline and dimension lines (see SABS 0143). The recommended methods of indicating bars are shown in figure 2, and either method may be used. Bars with right angle bends are not normally shown with a radius.
Figure 2 Ensure that, for ease of understanding, details are clear and legible and that the different bars in an arrangement are shown diagrammatically and in correct relationship with one another (see figure 3).
Figure 3 Give enough information to enable the bars to be correctly placed, including any dimensions that are required to position ends of bars; these dimensions should be given from a fixed object, such as a side shutter. When bars are superimposed on others of different lengths, indicate the ends of the bars by means of the bar mark (see figure 4). On all placing drawings, indicate clearly the numbers of the related bending schedules. If drawings are to be reduced for issue by photocopy methods, the reduction should not be such as would impair the readability.
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SABS 0144 Ed. 2
Figure 4
4.1.4 Numbering of components Ensure that each component, such as a slab, panel, beam, column and foundation, has a unique distinguishing number or other identification, irrespective of whether reinforcement details are identical in two or more components; for example identical panels could be numbered A1, A2, etc.
4.2 Referencing of bars and placing instructions 4.2.1 Identification and labels When referencing bars, consider the identification labels or tickets. The labels or tickets are attached to the bars after they have been cut to length and remain on the bars until they are ready to be placed in position. For positive identification at each stage, give the following information so as to enable the correct generation of labels or tickets:
7
SABS 0144 Ed. 2 Type/size
Mark
Number of
Length
Bending
x
x
x
x
Sorting on site
x
x
x
Component/ location
x
It can thus be seen that the bar mark need not be unique; every beam can have an A bar.
4.2.2 Placing and bar notation When bars are to be placed in position, the essential information required is the number of bars in the set, the type and size, the mark, the spacing, the location, and, if needed, comment. Typical examples of the way this information should be indicated on placing drawings are as follows: a) 14 Y16-08-200 T, which describes fourteen bars type Y of 16 mm diameter, mark 08 at 200 mm centres, in top of member (see figure 5); b) 25 R8-Q-150 B ABR, which describes twenty-five bars type R of 8 mm diameter, mark Q at 150 mm centres in bottom of member, with alternate bars reversed; and c) 7 Y16-09 and 7 Y16-10 ALT at 200, which describes seven bars type Y of 16 mm diameter, mark 09, and seven bars type Y of 16 mm diameter, mark 10, placed in order 09, 10, 09, 10, 09, 10, etc., the spacing between successive bars being 200 mm. Either of the methods shown in figure 5 may be used to show bar placing requirements.
Figure 5
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SABS 0144 Ed. 2 4.2.3 Type of steel Use the following symbols to refer to the type of steel (see SABS 920 and annex C) or steel mesh (see SABS 1024 and 13.2) to be used and, where necessary, give a more detailed description in the specification. R
= plain round mild steel bars of strength 250 MPa;
Y
= high yield deformed steel bars of strength 450 MPa;
Z
= types of steel not covered by R or Y; and
SM = standard mesh ) high tensile wire of strength 485 MPa. DM = design mesh ) Explain the meaning of Z in the specification, on the drawings and in the schedules. Detail bars of symbol Z on separate schedules. Give the symbols and the types of reinforcement on the bar bending schedules. NOTE – Unless specifically noted otherwise, different types of steel may be used in the same member.
4.2.4 Size of bars Show the size of bars, i.e. the nominal diameter, in millimetres, as follows: 8, 10, 12, 16, 20, 25, 32, 40 or 50. NOTE – Y8 reinforcement is generally unavailable but high tensile wire of diameter 8 mm is commonly available.
4.2.5 Bar marks NOTE – The bar size is not part of the bar mark.
4.2.5.1 The bar mark could consist of one of the following: a) a two-digit number in the range 01 to 99, with or without a letter prefix or suffix, for example B25 or 87K; b) a three-digit number in the range 001 to 999; c) a letter in the range A to Z or a pair of letters, AB to AZ; and NOTE – Avoid the use of lowercase letters, since they are easily confused with numbers, and do not use I or O.
d) a letter or letters as in (c) above, followed by a single-digit number, for example K5 and AL9. 4.2.5.2 No bar mark should consist of more than three characters. Ensure that prefixes or suffixes of letters or numbers that are used to describe the location of the bars or to describe any other function are not included in the bar mark. An example of a system that uses the bar mark to describe the bar location is given in table 1. 4.2.5.3 When detailing by components, it is convenient to start scheduling each component with, say, mark "A" and to rely on a component marking system to distinguish the bars on site, i.e. the same mark may be used in different components on the same drawing or bending schedule.
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SABS 0144 Ed. 2 Table 1 — Location method of bar marking 1
2
3
Location in component
Number
Letter
01 to 29
A to F
Horizontal bars in foundations, pile caps, beams, and slabs – top
30 to 49
G to L & T (omit I)
Shaped bars in beams and, e.g., shear bars
50 to 59
U to Y
Stirrups
60 to 79
S, S1, etc.
80 to 99
M to P (omit O)
Vertical bars in columns and walls Stairs Horizontal bars in foundations, pile caps, beams, and slabs – bottom
Horizontal bars in walls Spacer bars Bars other than above NOTE – Where the allocated numbers are insufficient, use 30A, 30B, 30C, etc., or G1, G2, G3, etc.
4.2.6 Symbols — Location or comment Ensure that the location or comment relating to the placing of a bar is not ambiguous. Use only the symbols listed below: ABR
= alternate bars reversed
ALT
= alternately
B
= bottom
B1
= lowest of the bottom layers
B2
= second lowest of the bottom layers
B3
= third lowest of the bottom layers
CHC
= continuous high chair
EF
= each face
EW
= each way
FF NF
= far face ) Ensure that the direction of viewing is made clear on the key plan = near face )
HC
= high chair
HOR
= horizontal
NTS
= not to scale
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SABS 0144 Ed. 2 STG
= staggered
T
= top
T1
= highest of the top layers
T2
= second highest of the top layers
T3
= third highest of the top layers
TOG
= together
VER
= vertical
Examples of the use of some symbols are given in figure 6.
Figure 6
4.3 Revisions Ensure that revisions are so made that confusion, omissions and double delivery can be avoided. When it becomes necessary to revise a previously issued placing drawing or bending schedule, do so by crossing out (but not erasing) the letters and figures that are to be changed. Show the new
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SABS 0144 Ed. 2 figures/letters and a revision letter set in a triangle adjacent to the correction. (This revision letter is not necessarily related to one on a corresponding drawing or bending schedule, though it could, by coincidence, sometimes be the same.) Ensure that, on any revised placing drawing, the number(s) of the relevant revised schedule(s) is/are clearly stated, and vice versa.
4.4 Preferred spacing of reinforcement The preferred spacings of reinforcement are from 75 mm to 200 mm, in increments of 25 mm, and from 200 mm upwards, in increments of 50 mm (see 7.4.1 and 8.3.5).
5 Scheduling of bar reinforcement 5.1 General Scheduling is the operation of listing the size, type, length and bending details for each bar (or sheet of welded mesh) detailed on the placing drawings for the purpose of cutting, bending and bundling the bars for dispatch to site. A recommended reinforcing bar schedule format is given in SABS 82 and in figure 56, where the shape code columns may be omitted. A recommended schedule format for welded mesh is shown in figure 89.
5.2 Paper sizes Schedules should be on sheets of size A3 or A4 and should be of one size only for any one job. The sheets should have a clear margin of at least 10 mm all round to allow for filing, and for registration errors during printing. Where sheets of size A0 or A1 are used, ensure that they are so subdivided that they can be cut down to A3 or A4 size for use in the workshop or on site.
5.3 Title panel To facilitate reference when prints are filed or folded, place the title panel in the bottom right-hand corner of the sheet.
5.3.1 In the title panel, put the following information: a) the schedule number and the revision suffix; b) the project number; c) the reference drawing number; d) the date of the schedule and the names or initials of the persons who design, draw and check the schedule; e) the project title; f) the sheet title and the section; and g) the name, address and telephone number of the consulting engineer.
5.3.2 In the title panel or in a notes panel, put the following information: a) the revision details, including the date; b) the reinforcement cover;
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SABS 0144 Ed. 2 c) the reinforcement type; d) the reinforcement abbreviations; and e) the reinforcement masses, if required. Update the revision suffix each time the drawing is issued after revision.
5.4 Numbering Ensure that the schedules have simple consecutive numbers and that they are cross-referenced to the related placing drawing or key plan. (Similarly, ensure that the bending schedule numbers are shown on the placing drawing or key plan.) Ensure that each schedule refers to one drawing only and to one specific section of the job and component (foundation, column or beam). For large projects, the schedule number may also incorporate the section identification, for example 1075/FF/27, which indicates job No. 1075, first floor slab, sheet No. 27. (Ensure that the sheet number in this example, i.e. 27, is not used for any other sheet in the same project.) This facilitates grouping and identification. Avoid such terms as "page number" or "sheet 2 of 14", which can be confusing.
5.5 Drawing and dimensioning Ensure that bar shapes and dimensions are clear and unambiguous. Dimension obtuse or acute angles for bends by using either offsets or slopes, whichever is more important. Because of the radii, there is no point on the bar that can be identified as a "corner". Calculate the slope length as the distance between intersection of the projections of the OUTER bar lines as seen in elevation, measured parallel to the slope, as follows:
Only use overall dimensions where slopes are not critical but the overall dimensions are critical. Otherwise show the slope, even if it means using a non-standard bar, but ensure that the overall dimension is not critical. Avoid details where both slope and overall dimension are critical. Where it is unavoidable to do so, mark the drawing to indicate critical dimensions. Indicate dimensions as follows:
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SABS 0144 Ed. 2
In the case of a bar that has multiple critical dimensions, it is advisable that a dimensioned section of the component that shows the bar be included with the schedule, to enable the fabricator to draw the section and check the bar for fit.
5.6 Bending details Use the bar shapes shown in SABS 82 and in annex A.
5.7 Cutting and bending tolerances The tolerance on a dimension of a bar should be the applicable value shown in table 1 of SABS 82.
5.8 Methods of expressing quantities Express the quantity of steel reinforcement generally as follows: a) bar reinforcement: the total mass, in kilograms, for each separate bar diameter for each type of steel; and b) welded steel mesh: in the case of 1) standard mesh (SM), the gross area, in square metres, of each mesh of the same reference number (see SABS 1024), and 2) design mesh (DM), the mass, in kilograms.
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SABS 0144 Ed. 2 NOTES 1 It is desirable but not essential to show the quantity of reinforcement on bending schedules. 2 The exact requirements for expressing quantities of reinforcement will often be prescribed by the "standard methods of measurement" pertaining to a particular construction contract. In such cases, this can take precedence over (a) and (b) above.
5.9 Combined placing drawings and bending schedules It is strongly recommended that placing details and bending schedules that relate to one component appear on the same drawing. Standardized exploded forms of placing diagrams have been developed that serve equally well as bending schedules. The use of such techniques facilitates the work of the detailer, the bender, the reinforcement placer, the checker and the contractor, and reduces considerably the work in the drawing office. If complicated details necessitate more specific description than is normally provided, make special sketches or drawings, done to scale, on the same size drawing sheets. In such cases, provide a key plan that locates and identifies the components. All the principles set out with regard to placing drawings (see 4.1) and bending schedules apply to the combined placing and bending schedules.
6 General requirements for all components 6.1 Cover to reinforcement 6.1.1 Nominal cover Nominal cover is the dimension used in the design. Ensure that it is indicated on the reinforcement drawings. This cover is to the outside steel (for example, in beams and columns, it is to the outside of the stirrup). The extent of the nominal cover should be the highest value determined on the basis of the following: a) the size of the reinforcement (The cover to any bar should be at least equal to the diameter of the bar or, in the case of a bundle of three or four bars, at least equal to the diameter of the equivalent single bar (see 6.5 for information on bundling).); b) the degree and nature of exposure of the finished structure (The cover required to protect the reinforcement from corrosion is reduced if higher quality concrete is used.); and c) the fire rating of the structure, i.e. the protection required to prevent excessive temperature increase in the reinforcement during a fire.
6.1.2 Cover required for various exposure conditions The cover for particular conditions of exposure is given in SABS 0100-2.
6.1.3 Special cover If surface treatment of the concrete is required, for example to produce a bush-hammered or exposed aggregate finish, ensure that the cover is increased by the expected effective depth of the treatment. Additional cover might also be needed if chases are formed in the concrete surface, and porous aggregates, such as slag, are used or if low-density concrete is specified.
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SABS 0144 Ed. 2 6.1.4 Cover for fire protection 6.1.4.1 Values for fire resistance of various components are given in SABS 0100-1. 6.1.4.2 Other factors that should be considered in relation to fire protection are as follows: a) cover for fire protection that has a thickness exceeding 30 mm might have to be bound in with wire mesh; b) special plasters can be used to reduce the cover that would otherwise be required; c) careful attention should be given to special type floors (see tables 45 and 46 of SABS 0100-1); d) the cover for beams can be reduced if there is more than one layer of steel (see SABS 0100-1); and e) in low-rise buildings of high fire risk, it is necessary to establish the required fire rating.
6.1.5 Bar dimensions When determining the dimensions on the bending schedule in cases where reinforcement is to fit between two concrete faces, use the values for deductions given in column 5 of table 2. The recommended deductions apply to reinforced concrete construction where the tolerances on the size of the member are as specified in column 4 of table 2. Where tolerances are in excess of these, increase the values of the deductions accordingly. Table 2 — Deductions from bar dimensions Dimensions in millimetres 1
2
Distance between concrete faces
Type of bar
0 - 1 000 1 001 - 2 000 Over 2 000 Any length
3
4 Tolerances
Reinforcement
5 Deductions
Formwork
Total1)
Stirrups and other bent bars
+5 +5 -10 +5 -25
±5 ±5 ± 10
10 10 15
Straight bars
± 25
± 10
35
1) Based on limit of each "plus" tolerance (see 5.7).
6.2 The maintenance of cover and position of reinforcing bars 6.2.1 General Steel reinforcement should be properly supported or stayed in order to ensure that correct cover and position are maintained during the placing of concrete.
16
SABS 0144 Ed. 2 6.2.2 Spacing of supports 6.2.2.1 Horizontal bars The spacing of supports for horizontal bars should conform to the appropriate values given in table 3. Table 3 — Spacing of supports for horizontal bars Dimensions in millimetres 1 Nominal diameter of bars 8 10 and 12 16 and 20 25 and 32
2
3
Minimum spacing of supports High tensile steel 500 600 1 200 1 800
Mild steel 400 500 1 000 1 500
6.2.2.2 Vertical bars Support bars at the vertical forces of components in at least two positions over both width and height, the positions being not more than 1 m apart in the case of bars of nominal diameter up to 12 mm and 1,5 m apart in the case of bars of nominal diameter 16 mm and more.
6.2.3 Methods of support The cover and position of bars should be maintained by the use of a) bar supports and cover blocks, and b) steel stools and high chairs.
6.2.4 Bar supports and cover blocks Bar supports and cover blocks are not usually of height exceeding 75 mm. A number of types are available and the choice of the one to be used depends largely on whether the reinforcement is to bear on the device or lean against it. In the latter case, the device should be positively attached to a vertical or horizontal bar or to the formwork, to ensure that it is not displaced during the erection of reinforcing steel or formwork or during the placing of concrete. Ring-type cover devices should be used to support column bars. Cover devices can be made of mortar, fibre cement, plastics or steel. Considerations that affect the choice of the type to be used (other than steel) are given in table 4. Mortar cover blocks for bottom bars are often made on site and could contain a projecting wire with which to attach the steel bar being supported. The mortar cover blocks should be dense and made from a 1:1 cement and coarse sand mix and cured for seven days; they should be of thickness at least 20 mm and should be placed under the upper layer of a bottom reinforcement mat. Plastics devices should be strong enough to withstand crushing.
17
SABS 0144 Ed. 2 Table 4 — Suitability of different types of cover device 1
2
3
4
5
6
Consideration Appearance of finished concrete
Weathering of finished concrete
Fire resistance
Steam curing
Corrosion of reinforcement
Mortar blocks
NS
WC
S
S
S
Rings of mortar
WC
S
S
S
S
Fibre-cement blocks
Type of device
WC
WC
S
S
S
Plastics rings1)
S
WC
WC
S
WC
Plastics chairs1)
S
WC
WC
S
WC
Key: S = suitable; WC = suitable with care; and NS = not suitable. 1) Care should be taken in the choice of the shape of the spacer.
6.2.5 Steel stools and high chairs 6.2.5.1 General Steel stools and high chairs are used to support the top reinforcement of suspended slabs and foundations. Determine the height of the supports from the cover required and from the diameter of bars used, and specify the height in multiples of 10 mm. 6.2.5.2 Steel stools Steel stools should be bent to shape code 83 (see annex A). They are detailed and priced as reinforcement. The dimensions of steel stools should conform to the appropriate values given in table 5. Table 5 — Size of steel stools 1
2
3
4
Diameter of stools Feature of stools
Height range, mm Top length, mm, max. Length of feet, mm1) Bars supported
mm 10
12
16
100 - 300 300 100 2
310 - 500 450 150 2 or 3
510 - 1 000 600 250 2 or 3
1) When the stools are supported on the bottom reinforcement, the length of the feet are to be equal to 1,5 times the bar spacing plus 100 mm (see figure 7).
In general, specify stools to support the lower layer of the top mat, two bars at a time and at the spacing recommended in 6.2.2. Depending on the diameter and spacing of the bars in the lower layer of the top mat, one or two lines of bars may be left unsupported (see figure 7). In this event, ensure that the lower layer of the top mat is well tied to the upper supported reinforcement. It may be acceptable for stools to stand on the formwork or foundation blinding direct, but where this is not permitted, the feet of the stools may be
18
SABS 0144 Ed. 2 extended and the height adjusted to allow them to be supported on the bottom reinforcement, two bars at a time. Care should then be taken to ensure that the cover devices to the bottom reinforcement are of adequate strength to support the extra mass.
Figure 7 6.2.5.3 High chairs (HC) High chairs are factory made and support one bar at a time (see figure 8). They stand on the formwork or blinding direct, and the legs may, if so required, be fitted with plastics ferrules (paint is not satisfactory). Positioning and spacing follow the same rules as for bottom cover devices. High chairs are not reinforcement items and are measured separately.
19
SABS 0144 Ed. 2
Figure 8 6.2.5.4 Continuous high chairs (CHC) Continuous high chairs are usually of length at least 2 m. The diameter of the top bars and the diameter and spacing of the legs will vary according to heights and details of design (see table 6), and for this reason, continuous high chairs are usually specified by height and are paid for by length. They are not scheduled as reinforcement. The chair legs stand on formwork or blinding direct and may, if so required, be fitted with plastics ferrules. Continuous high chairs of acceptable strength can be made from bar reinforcement by welding (see figure 9). Table 6 — Dimensions of continuous high chairs Dimensions in millimetres 1
2
3 Dimension
Features of continuous high chairs
Height range 80-150
160-200
8 10 400 10 2
10 10 400 10 2
Diameter of leg Top bar diameter Spacing of legs Height increment Length of chair
Figure 9
20
SABS 0144 Ed. 2 6.3 Splicing of reinforcing bars 6.3.1 General Splicing is the method of transferring force from one bar to another. Methods of splicing include lapping, welding, and mechanical means.
6.3.2 Lapping splices 6.3.2.1 The following are two methods of lap splicing: a) placing or cranking one bar next to the other with a lap of a bond length (see figure 10 and 7.13.3); and NOTE – Cranking of bars should be avoided as far as possible since it causes bursting forces and tends to induce cracking.
Figure 10 b) butting two bars and providing a splicing bar to cover the butting point over a bond length on each side. With the use of this method, in a series of adjacent bars, butts can be provided at points that are at least a bond length apart. A single splicing bar extending over all the butting points is then provided (see figure 11).
21
SABS 0144 Ed. 2
Figure 11 6.3.2.2 Where bars are in tension, the question of crack control has to be considered and the maximum distance between the bars on either side of a spliced bar should not exceed 300 mm for reinforcement of nominal tensile strength 250 MPa, or 180 mm for reinforcement of nominal tensile strength 450 MPa (see figure 11). Outer corner bars of beams should generally be spliced in positions of least stress. Where such a splice is essential, so place the nearest effective bar that the distance between its outer face and the corner does not exceed 150 mm for mild steel (MS) reinforcement or 90 mm for high tensile (HT) steel reinforcement (see SABS 0100-1 and figure 11). Because cracks induced by sudden changes in section can induce premature shear failure and because laps induce bursting forces in the concrete, not more than the greater of one bar and one-fifth of the steel area should be lapped or stopped off at any one section except at ends of beams, and splices should be staggered by at least one bond length.
6.3.3 Welded splices Welded splices are not generally recommended but, if required, should be carried out in accordance with an appropriate specification (see SABS 0100-1). High tensile steel reinforcing bars that comply with SABS 920 (appendix D) are not weldable unless especially so specified.
6.3.4 Mechanical splices There are a number of types of mechanical splices available, all of which use sleeves or devices that fit over bars to be joined. When the use of mechanical splices is being considered, specialist advice should be obtained and the splice detailed accordingly.
22
SABS 0144 Ed. 2 6.4 Bends and anchorages for reinforcing bars 6.4.1 Standard radii The minimum standard internal radii for bends in reinforcing bars and for anchorages at the ends of reinforcing bars are two bar diameters for mild steel bars and three bar diameters for high tensile steel bars.
6.4.2 Large radius bends Where larger than standard radii are required to control bearing stresses such as for bent-up bars in beams or slabs and for bars that are to be continuous around corners in connections between beams and columns, and at junctions of retaining walls and foundations, each bar should be bent around a former to a radius of at least 7,5 times the nominal diameter of the bar. Large diameter highly stressed bars in poor concrete will require a larger radius. (See also 7.11.3.) Generally, reinforcement fabricators use formers of the following sizes for bending bars of nominal diameter: a) 8 mm and 10 mm: a former of radius 100 mm; b) 12 mm: a former of radius 150 mm; c) 16 mm and 20 mm: a former of radius 200 mm; and d) 25 mm and 32 mm: a former of radius 250 mm. Formers of larger radii are not generally available.
6.4.3 Bar scheduling Ensure that the required radius of bend is clearly indicated on bending schedules. In the case of bars that are to be bent to standard shapes, insert on each bar line a suitable note calling attention to any special radii (see SABS 82).
6.4.4 Effective anchorage values of hooks and bends The effective value of an anchorage at the end of a bar, measured from the start of the curve of the bend or hook (see figure 12) to four diameters beyond the curve, is the lesser of 24 bar diameters and, a) in the case of a bend, four times the internal radius of the bend, and b) in the case of a hook, eight times the internal radius of the hook.
23
SABS 0144 Ed. 2
Figure 12
6.5 Bundling of bars 6.5.1 General Bundled bars are groups of two, three or four bars that are tied together and that are in contact side by side (see figure 15).
6.5.2 Advantages Because bundled bars provide more reinforcement in less space than do single bars, it is possible to reinforce a member more heavily and still get good compaction of concrete. In this way, beam widths can often be reduced, with a corresponding saving in cost.
6.5.3 Disadvantages 6.5.3.1 The bond strength of a bundle is less than the sum of the bond strengths of the individual bars. This is owing to the smaller perimeter in contact with the concrete, and to the bursting forces developed, which are a function of the total force transferred by bond. 6.5.3.2 Because of the effect referred to in 6.5.3.1, cover should be increased to that required for a single bar of the same cross-sectional area as that of bundled bars. The bond reduction factors given in SABS 0100-1 and other standards take these effects into account. 6.5.3.3 Not more than one bar at a time in bundled bars may be curtailed or spliced, except at the end of a beam. Ensure that a full lap (tension or compression) is provided between points of curtailment or splicing.
24
SABS 0144 Ed. 2 6.5.4 Columns Unless patented splices are used, the bundling of bars in columns is not recommended, since all joints have to be staggered at 40 bar diameters. However, even when patented splices are used, the necessary staggering of splices makes assembly difficult and prefabrication impossible. It is recommended, therefore, that a splint splice be provided for each joint or, alternatively, that an additional bar be provided for each bundle.
7 Component detailing — Beams NOTE – This clause deals generally with the detailing of beams for which the assumption that plane sections remain plane in bending applies. Empirical rules for the detailing of stirrups and longitudinal side bars in beams of depth exceeding 750 mm, are given in 7.6. These beams are not to be confused with deep beams for which the above assumption does not apply and which are not covered in SABS 0100-1. Guidelines for the design of deep beams are given in annex D of SABS 0100-1. Recommendations for the detailing of deep beams are given in 7.16.
7.1 Numbering of beams Number all beams with unique numbers, even if they are otherwise identical. A recommended system is as follows: starting in one corner of the structure, number the beams in one direction from 1 up to 100, and number the beams at right angles to those, starting from 101. If there are more than 100 beams in one direction, start numbering the beams at right angles at 201 or 301, etc.
7.2 Types of detail There are two main types of detailing for beams that have shear reinforcement, namely with stirrups only and with bent-up bars and stirrups. Although bent-up bars used for top and bottom reinforcement in continuous beams are economical, where special anchorage lengths have to be detailed, stirrups are more economical and easier to bend and fix. Bent-up bars are hardly ever used in building construction.
7.3 Preferred methods of detailing 7.3.1 General Beams can be detailed by means of exploded views or by full detailed elevations which should be drawn to scale. These methods are often used for civil engineering structures. (See also 7.3.2.) 7.3.1.1 Exploded views In an exploded view, show the main bars in their relative positions diagrammatically but not necessarily to scale. Place top bars towards the top of the diagram, and straight bottom bars towards the bottom of the diagram. Insert stirrup-placing details below the information that relates to longitudinal bars (see figure 13). 7.3.1.2 Types of exploded views Two types of exploded view detailing that could be used are as follows: a) the placing drawing is combined with bending information; the same reinforcement schedule is used for bending and for placing the reinforcement (see figures 13 and 14); and b) the placing drawing is separate from the bending schedule. (For building construction, they are often printed on the same sheet of paper.) In either case, ensure that the order of scheduling is the same as the order of representation of the bars (from top to bottom – see figures 13 and 14).
25
SABS 0144 Ed. 2
Figure 13
26
SABS 0144 Ed. 2
Figure 14
27
SABS 0144 Ed. 2 7.3.2 Drawing to scale Whether or not drawing to scale is necessary will depend on the complexity of the detailing and the skill and experience of the detailer. However, in the case of beams of length exceeding 12 m, beams that have more than two types of bent-up bars, cranked beams, and non-prismatic beams, consider detailing exploded views to scale.
7.3.3 Identification Indicate and identify beam supports, for example column 36A, and give dimensions and the clear span between consecutive supports. Give the identification of adjacent beams where continuity occurs. Bar marks should start from 01 or A for each beam, depending on whether a numerical or an alphabetical system is used (see 4.2.5). Alternatively, a location system of numbering may be used, but this too should start afresh for each beam, for example bottom bars may be marked 01, 02, 03, etc., and stirrups 60, 61, etc., or A, B, C, etc., and S, S1, etc. (see table 1). Ensure that an adequate number of sections is drawn to facilitate the wiring of reinforcement in position. The sections should show the reinforcement cages at critical points along the length of the beam. It is not necessary to show the outline of the concrete unless this is needed to clarify the placing requirements, but it is desirable where features such as nibs occur. Dimension the position of the starts or ends of bars and stirrups from the face of the support, or from the centre-line of beams or columns. Show continuity bars consistently on the same side of all beams, usually on the right-hand side. Bars detailed elsewhere, that project into the beam, should be shown as a heavy broken line, and a note should be given on the drawing.
7.4 Practical requirements 7.4.1 Minimum spacing Recommendations for minimum spacing (and cover for normal exposure) of bars in beams are given in table 7 and in figure 15. For beams that have one layer of reinforcement, the arrangement with the use of pairs of bars enables the greatest number of bars to be used. The numbers of bars given in the table are the maximum numbers and might have to be considerably reduced at intersections. The numbers given for bundles in the table refer to the bars in the bottom layer only. An odd number given for pairs or bundles indicates that there is not enough room for an extra pair or bundle and only one bar can be fitted in, for example the number 5 in column 7 or column 10 of table 7 means two sets of two bars and one single bar.
7.4.2 Maximum spacing In order to control crack widths, the clear distance between bars should not exceed 300 mm for reinforcement of tensile strength 250 MPa and 125 mm for reinforcement of tensile strength 450 MPa in the top of the beam at continuous supports, and 175 mm for reinforcement of tensile strength 450 MPa in the bottom of the beam (see SABS 0100-1).
28
SABS 0144 Ed. 2 Table 7 — Beam reinforcement, maximum number of bars per layer Dimensions in millimetres 1 Beam width
2 Bar dia.
3
4
5
Outside dimensions of stirrups
6
7
8
Number of bottom bars per layer (maximum)
9
10
11
12
Number of top bars per layer (maximum)
13
14
Spacing of bars
Single
Pairs
Bundles
Single
Pairs
Bundles
Single
Pairs
Bundles
Single
Pairs
Bundles
100 100 100 80
100 100 80 60
1 1 1 1
2 0 0 0
2 0 0 0
0 0 0 0
0 0 0 0
0 0 0 0
30 30 30 32
35 35 35 45
40 40 43 55
150
16 20 25 32
100 100 100 100
200
16 20 25 32
150 150 150 150
150 150 150 130
150 150 130 110
2 2 2 2
2 2 2 2
2 2 2 0
1 1 1 10
0 0 0 0
0 0 0 0
30 30 30 32
35 35 35 45
40 40 43 55
220
16 20 25 32
170 170 170 170
170 170 170 150
170 170 150 130
2 2 2 2
4 3 3 2
3 3 2 2
2 2 1 1
2 2 0 0
2 2 0 0
30 30 30 32
35 35 35 45
40 40 43 55
250
16 20 25 32
200 200 200 200
200 200 200 180
200 200 180 160
3 3 3 2
4 4 4 2
4 4 3 2
2 2 2 2
4 3 2 0
4 3 2 0
30 30 30 32
35 35 35 45
40 40 43 55
300
16 20 25 32
250 250 250 250
250 250 250 250
250 250 230 210
4 4 3 3
6 5 3 3
6 5 4 3
3 3 3 2
5 4 4 3
5 4 3 2
30 30 30 32
35 35 35 45
40 40 43 55
330
16 20 25 32
280 280 280 280
280 280 280 260
280 280 260 240
5 4 4 3
6 6 5 4
6 6 4 3
4 4 3 3
6 5 4 3
6 5 4 3
30 30 30 32
35 35 35 45
40 40 43 55
350
16 20 25 32
300 300 300 300
300 300 300 280
300 300 280 260
5 5 4 4
7 6 6 4
6 6 5 4
5 4 4 3
6 6 5 4
6 6 4 3
30 30 30 32
35 35 35 45
40 40 43 55
400
16 20 25 32
350 350 350 350
350 350 350 350
350 350 350 310
6 6 5 5
8 8 7 5
8 7 6 4
6 5 5 4
8 7 6 4
8 6 6 4
30 30 30 32
35 35 35 45
40 40 43 55
450
16 20 25 32
400 400 400 400
400 400 400 380
400 400 380 360
7 7 6 5
10 9 8 6
10 8 7 5
7 6 5 5
9 8 7 6
9 8 6 5
30 30 30 32
35 35 35 45
40 40 43 55
500
16 20 25 32
450 450 450 450
450 450 450 430
450 450 430 410
8 8 7 6
12 10 9 7
10 10 8 6
8 7 6 5
10 10 8 6
10 9 8 6
30 30 30 32
35 35 35 45
40 40 43 55
550
16 20 25 32
500 500 500 500
500 500 500 480
500 500 480 460
9 9 8 7
12 12 10 8
12 11 9 7
9 8 7 6
12 10 10 7
12 10 8 6
30 30 30 32
35 35 35 45
40 40 43 55
600
16 20 25 32
550 550 550 550
550 550 550 530
550 550 530 510
10 10 9 7
14 12 11 8
14 12 10 8
10 9 8 7
14 12 10 8
13 12 10 7
30 30 30 32
35 35 35 45
40 40 43 55
650
16 20 25 32
600 600 600 600
600 600 600 580
600 600 580 560
11 11 10 8
16 14 12 10
14 13 11 8
11 10 9 8
15 13 12 9
14 12 10 8
30 30 30 32
35 35 35 45
40 40 43 55
29
SABS 0144 Ed. 2 Table 7 (concluded) Dimensions in millimetres 1 Beam width
2 Bar dia.
3
4
5
Outside dimensions of stirrups
6
7
8
Number of bottom bars per layer (maximum)
9
10
11
12
Number of top bars per layer (maximum)
13
14
Spacing of bars
Single
Pairs
Bundles
Single
Pairs
Bundles
Single
Pairs
Bundles
Single
Pairs
Bundles
650 650 650 630
650 650 630 610
12 11 10 9
17 15 14 10
16 14 12 9
12 11 10 8
16 14 12 10
16 14 12 9
30 30 30 32
35 35 35 45
40 40 43 55
700
16 20 25 32
650 650 650 650
750
16 20 25 32
700 700 700 700
700 700 700 680
700 700 680 660
14 12 11 10
18 16 14 11
18 16 13 10
13 12 11 9
18 16 14 10
17 15 12 10
30 30 30 32
35 35 35 45
40 40 43 55
800
16 20 25 32
750 750 750 750
750 750 750 730
750 750 730 710
15 13 12 10
20 18 16 12
18 16 14 11
14 13 12 10
19 17 15 12
18 16 14 10
30 30 30 32
35 35 35 45
40 40 43 55
850
16 20 25 32
800 800 800 800
800 800 800 780
800 800 780 760
16 14 13 11
22 19 17 13
20 18 15 12
15 14 12 11
20 18 16 12
20 18 14 11
30 30 30 32
35 35 35 45
40 40 43 55
900
16 20 25 32
850 850 850 850
850 850 850 830
850 850 830 810
17 15 14 12
22 20 18 14
22 19 16 12
16 15 13 11
22 20 17 13
21 18 16 12
30 30 30 32
35 35 35 45
40 40 43 55
950
16 20 25 32
900 900 900 900
900 900 900 880
900 900 880 860
18 16 15 13
24 22 19 14
22 20 17 13
17 16 14 12
24 21 18 14
22 20 16 13
30 30 30 32
35 35 35 45
40 40 43 55
1 000
16 20 25 32
950 950 950 950
950 950 950 930
950 950 930 910
19 17 16 13
26 23 20 16
24 22 18 14
18 17 15 13
25 22 20 15
24 21 18 14
30 30 30 32
35 35 35 45
40 40 43 55
NOTES 1
The parameters used to calculate the table are as follows:
a) minimum clear space allowed between bars (with the use of 20 mm or 25 mm aggregate): single bars : 30 mm or effective diameter; pairs of bars: 35 mm or effective diameter ( dia. × 2 ); 3 bar bundles : 40 mm or effective diameter ( dia. × 3 ); b) side cover to main bars is greater of (25 mm + stirrup diameter) and effective diameter – fire or corrosion risk could require an increase; c) 100 mm allowance for vibrator (top bars only) – could be reduced if small vibrator is available; and d) 10 % of diameter allowed for ribs and 10 mm tolerance on stirrups. 2
30
Allowance should be made in bottom cover if pairs or bundles are used. Radius of three times stirrup diameter allowed for corner bars (bottom only) stirrup dia. 10 mm.
SABS 0144 Ed. 2
Figure 15
31
SABS 0144 Ed. 2 7.4.3 Spacing of top reinforcement at supports for concrete placing 7.4.3.1 Top reinforcement at columns or beam intersections should have a clear space of width at least 100 mm for the placing of concrete and to permit compaction with a vibrator (see figure 16). 7.4.3.2 Where the thickness of a slab that is supported by a beam is sufficient and the stirrup spacing is at least 100 mm, it is possible to insert a vibrator at the side of the beam (see figure 17), and in this case, for beams of width less than 900 mm, it is not necessary to leave the space required in terms of 7.4.3.1. Table 7 can be used for such cases, but make allowance for the space occupied by stirrup carrier bars. 7.4.3.3 In order to obtain enough space for the insertion of a vibrator, some tension zone continuity bars could be placed in the slab. Although this helps to reduce cracking in the slab caused by the flexure of the beams, this should not, however, be done without the consent of the designer, who should consider the ability of the slab to transfer shear forces.
Figure 16
Figure 17
7.4.4 Bond Tests have shown that top bars in beams have a lower bond strength than bottom bars. This is largely because of better compaction in the bottom section and because of settlement of the concrete after compaction. Tech. corr. 2 1997
Annex D gives required bond lengths for different grades of concrete and reinforcement. These lengths should be increased for top bars, a suggested value for the increase being 50 % for top bars of nominal diameter exceeding 20 mm.
32
SABS 0144 Ed. 2 If additional anchorage is required, use square bends in preference to round hooks, since square bends interfere less with the placing of steel and concrete. Where such additional anchorage is required and in the absence of other instructions from the designer, the radius of the right angle bend should not be less than 7,5 bar diameters.
7.4.5 Side cover To reduce the possibility of spalling of the concrete because of compressive stresses in the bend (apart from the requirements for corrosion and fire protection), place tension bars that have bends of radius at least three bar diameters from the side face.
7.5 Stirrups 7.5.1 Diameter and spacing Stirrups should generally all be of the same diameter, their spacing being varied to suit design requirements. Spacing should preferably be in 25 mm increments from 75 mm to 150 mm and in 50 mm increments above 150 mm (see table 8). Table 8 — Cross-sectional area of stirrups at various spacings 1
2
3
4
5
6
7
8
9
10
11
12
13
450
500
Cross-sectional area of stirrups
Stirrup type
Nom. dia. of bar
Stirrup spacing
mm
mm
mm2
75
100
125
150
200
250
300
350
400
Single (2 legs)
8 10 12 16
1 340 2 094 3 015 5 361
1 005 1 570 2 261 4 021
804 1 256 1 809 3 216
670 1 047 1 507 2 680
502 785 1 130 2 010
402 628 904 1 608
335 523 753 1 340
287 448 646 1 148
251 392 565 1 005
223 349 502 893
201 314 452 804
Double (4 legs)
8 10 12 16
2 680 4 188 6 031 10 723
2 010 3 141 4 523 8 042
1 608 2 513 3 619 6 433
1 340 2 094 3 015 5 361
1 005 1 570 2 261 4 021
804 1 256 1 809 3 216
670 1 047 1 507 2 680
574 897 1 292 2 297
502 785 1 130 2 010
446 698 1 005 1 787
402 628 904 1 608
Triple (6 legs)
8 10 12 16
4 021 6 283 9 047 16 084
3 015 4 712 6 785 12 063
2 412 3 769 5 428 9 650
2 010 3 141 4 523 8 042
1 507 2 356 3 392 6 031
1 206 1 884 2 714 4 825
1 005 1 570 2 261 4 021
861 1 346 1 938 3 446
753 1 178 1 696 3 015
670 1 047 1 507 2 680
603 942 1 357 2 412
7.5.2 Types of stirrups 7.5.2.1 Open stirrups Use open stirrups with clips where beam reinforcement is to be assembled in position and where closed stirrups are not required by the designer for resisting torsion. (Normal practice is to use one clip at every second stirrup or set of stirrups, or at 600 mm centres, whichever is the lesser spacing.) In regions of hogging moment where there is heavy reinforcement (reinforcing equivalent to more than three Y32 top bars), use clips at every stirrup. In regions of heavy shear (exceeding 1,2 MPa) where more than two legs of stirrups are used at a section, use clips at every stirrup group. Stirrups that have the tops bent outwards (such as shape code 53) have a considerably reduced capacity where anchored in thin slabs.
33
SABS 0144 Ed. 2 Open stirrups with or without clips (as in shape codes 72 and either 35 or 85) should always be detailed and drawn as follows:
Clips of the same diameter as the main steel should be provided at every stirrup position in cases where there is no top slab steel. 7.5.2.2 Closed stirrups Use closed stirrups (shape code 74) where so required by the designer, for resisting torsion. 7.5.2.3 Multiple stirrups Use double or multiple stirrups as instructed by the designer or where restraint against the buckling of bars in compression is required. If there is any doubt regarding bars being in compression, consult the designer. Multiple stirrups should also be used where they are required to control splitting forces associated with high bond stresses at the ends of main bars or at splices or laps in main bars. This applies where the equivalent of more than one Y32 bar is stopped off or spliced (see 7.13.4). 7.5.2.4 Bars in compression Because the rules for stirrups where reinforcing steel is in compression are the same as those for columns (see 9.4.1 and 9.4.2), provide stirrups such that the legs are at centre-to-centre spacing not exceeding: a) 300 mm across the beam; and b) the lesser of 12 times the diameter of the smallest bar included in the tying and 300 mm along the beam. Stirrups used for tying bars in compression should have a diameter not less than one-quarter of the diameter of the largest bar included in the tying. So arrange stirrups that every alternate bar or group of bars in the outer layer of reinforcement is restrained by a stirrup with an included bend angle that does not exceed 135°. If any unrestrained bar is separated from a restrained bar by a clear distance that exceeds 150 mm then such unrestrained bar shall also be restrained as above.
7.5.3 Transverse spacing of stirrups The transverse spacing of vertical legs should not exceed 0,75 times the effective depth of the beam.
34
SABS 0144 Ed. 2 Where multiple stirrups are used, especially in wide beams, one of the stirrups should cover the full width of the cage (see figure 18).
Figure 18
7.5.4 Force not applied to top of beam Where a load is applied to the bottom or side of a beam (for example where one beam frames into another), ensure that there is sufficient suspension or "hang-up" reinforcement in the form of stirrups to transfer the force to the top of the beam. If the load is large, bent-up bars can be used instead of, or as well as, stirrups (see figure 19).
Figure 19
7.5.5 Beam of varying depth Detail stirrup sizes individually where beams have varying depths and a range of stirrup sizes has to be detailed. The number of different stirrup sizes can be reduced by using concertina stirrups (see figure 20) with the legs lapped at least one bond length (see annex D). The difference between the lengths of successive groups should be at least 50 mm. In order to maintain the size of the member, use stirrups of shape code 72 or 60 at centre-to-centre distances of at least 1 000 mm.
35
SABS 0144 Ed. 2 Ensure that concertina stirrups are adequately stiffened with clips. Schedule the reinforcement as shown in figure 21.
Figure 20
36
SABS 0144 Ed. 2
Dimensions in millimetres
Figure 21
37
SABS 0144 Ed. 2 7.5.6 Effect of intersection on stirrup sizes Ensure that stirrup sizes take into account the width at beam-column intersections, the depth and top and bottom cover at beam-beam intersections, and the size and cover of slab reinforcement. Where beam-beam intersections result in the beam top steel's being too low to support the slab top steel at the correct level, provide stools to support the slab reinforcement.
7.5.7 Minimum stirrup requirements If the maximum shear stress in the beam exceeds half of the permissible value, the ratio of the total area of all the legs of the stirrups in a given length to the plan area of the web over the same length, expressed as a percentage, should be at least 0,12 % for high tensile steel stirrups, or 0,2 % for mild steel stirrups. Where the shear stress in the beam nowhere exceeds half of the permissible value, it is recommended that the percentages be not less than 0,12 % and 0,1 % respectively. Guidance on minimum stirrup requirements is given in tables 9, 10, 11 and 12.
7.5.8 Anchorage A stirrup is considered to be effectively anchored if it has a standard bend around a bar of at least its own diameter. Table 9 — Minimum stirrup requirements — Percentage 0,12 % — Minimum spacing 0,75d Dimensions in millimetres 1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
800
850
900
950
1 000
Type, size and spacing of stirrups Width of beam
Depth of beams 250
300
350
400
450
500
550
600
650
150
Y8S 140
Y8S 180
Y8S 200
Y8S 250
Y8S 300
Y8S 300
Y8S 350
Y8S 400
Y8S 150
Y10S Y10S Y10S Y12S Y12S Y12S 150 500 550 600 600 600
Y12S 600
200
Y8S 140
Y8S 180
Y8S 200
Y8S 250
Y8S 300
Y8S 300
Y8S 350
Y8S 400
Y8S 400
Y10S Y10S Y10S Y12S Y12S Y12S 450 500 550 600 600 600
Y12S 600
250
Y8S 140
Y8S 180
Y8S 200
Y8S 250
Y8S 300
Y8S 300
Y8S 300
Y8S 300
Y8S 300
Y10S Y10S Y10S Y12S Y12S Y12S 150 500 500 600 600 600
Y12S 600
300
Y8D 140
Y8D 180
Y8S 200
Y8S 250
Y8S 250
Y8S 250
Y8S 250
Y8S 250
Y10S Y10S Y10S Y10S Y12S Y12S Y12S 400 400 400 400 600 600 600
Y12S 600
350
Y8D 140
Y8D 180
Y8D 200
Y8S 200
Y8S 200
Y8S 200
Y10S Y10S Y10S Y10S Y10S Y10S Y12S Y12S Y12S 350 350 350 350 350 350 500 500 500
Y12S 500
400
Y8D 140
Y8D 180
Y8D 200
Y8D 250
Y8S 200
Y10S Y10S Y10S Y10S Y10S Y10S Y10S Y12S Y12S Y12S 300 300 300 300 300 300 300 450 450 450
Y12S 450
450
Y8D 140
Y8D 180
Y8D 200
Y8D 250
Y8D 300
Y8D 300
Y10S Y10S Y10S Y10S Y10S Y10S Y12S Y12S Y12S 250 250 250 250 250 250 400 400 400
Y12S 400
500
Y8D 140
Y8D 180
Y8D 200
Y8D 250
Y8D 300
Y8D 300
Y8D 300
Y12S 350
NOTES 1 Y8 bars are not always available. 2 S: Single (2 legs) D: Double (4 legs).
38
700
750
Y10S Y10S Y10S Y10S Y10S Y12S Y12S Y12S 250 250 250 250 250 350 350 350
SABS 0144 Ed. 2 Table 10 — Minimum stirrup requirements — Percentage 0,2 % — Minimum spacing 0,75d Dimensions in millimetres 1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
800
850
900
950
1 000
Type, size and spacing of stirrups Width of beam
Depth of beams 250
300
350
400
450
500
550
600
650
700
750
150
R8S 140
R8S 180
R8S 200
R8S 250
R8S 300
R8S 300
R8S 300
R8S 300
R8S 300
R10S R10S R10S R12S R12S R12S 150 500 500 600 600 600
R12S 600
200
R8S 140
R8S 180
R8S 200
R8S 250
R8S 250
R8S 250
R8S 250
R10S R10S R10S R10S R10S R12S R12S R12S 350 350 350 350 350 550 550 550
R12S 550
250
R8S 140
R8S 180
R8S 200
R8S 200
R8S 200
R10S 300
R10S 300
R10S R10S R10S R10S R10S R12S R12S R12S 300 300 300 300 300 450 450 450
R12S 450
300
R8D 140
R8D 180
R8S 160
R10S R10S 250 250
R10S 250
R10S 250
R10S R10S R10S R10S R10S R12S R12S R12S 250 250 250 250 250 350 350 350
R12S 350
350
R8D 140
R8D 180
R8D 200
R10S R10S 200 200
R10S 200
R10S 200
R10S R10S R10S R10S R10S R12S R12S R12S 200 200 200 200 200 300 300 300
R12S 300
400
R8D 140
R8D 180
R8D 200
R8D 250
R10S 180
R10S 180
R10S 180
R10S R10S R10S R10S R10S R12S R12S R12S 180 180 180 180 180 250 250 250
R12S 250
450
R8D 140
R8D 180
R8D 200
R8D 200
R8D 200
R8D 200
R10S 160
R10S R10S R10S R10S R10S R12S R12S R12S 140 160 160 160 160 250 250 250
R12S 250
500
R8D 140
R8D 180
R8D 200
R8D 200
R8D 200
R10D 300
R10D 300
R10S R10S R10S R10S R10S R12S R12S R12S 140 140 140 140 140 200 200 200
R12S 200
NOTE – S: Single (2 legs) D: Double (4 legs).
Table 11 — Minimum stirrup requirements — Percentage 0,06 % — Minimum spacing 1,00d Dimensions in millimetres 1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
800
850
900
950
1 000
Type, size and spacing of stirrups Width of beam
Depth of beams 250
300
350
400
450
500
550
600
650
150
Y8S 200
Y8S 250
Y8S 300
Y8S 350
Y8S 400
Y8S 450
Y8S 500
Y8S 550
Y8S 600
Y10S Y10S Y10S Y12S Y12S Y12S 600 600 600 600 600 600
700
750
Y12S 600
200
Y8S 200
Y8S 250
Y8S 300
Y8S 350
Y8S 400
Y8S 450
Y8S 500
Y8S 550
Y8S 600
Y10S Y10S Y10S Y12S Y12S Y12S 600 600 600 600 600 600
Y12S 600
250
Y8S 200
Y8S 250
Y8S 300
Y8S 350
Y8S 400
Y8S 450
Y8S 500
Y8S 550
Y8S 600
Y10S Y10S Y10S Y12S Y12S Y12S 600 600 600 600 600 600
Y12S 600
300
Y8S 200
Y8S 250
Y8S 300
Y8S 350
Y8S 400
Y8S 450
Y8S 500
Y8S 550
Y8S 550
Y10S Y10S Y10S Y12S Y12S Y12S 600 600 600 600 600 600
Y12S 600
350
Y8D 200
Y8S 250
Y8S 300
Y8S 350
Y8S 400
Y8S 450
Y8S 450
Y8S 450
Y8S 450
Y10S Y10S Y10S Y12S Y12S Y12S 600 600 600 600 600 600
Y12S 600
400
Y8D 200
Y8D 250
Y8S 300
Y8S 350
Y8S 400
Y8S 400
Y8S 400
Y8S 400
Y8S 400
Y10S Y10S Y10S Y12S Y12S Y12S 600 600 600 600 600 600
Y12S 600
450
Y8D 200
Y8D 250
Y8D 300
Y8S 350
Y8S 350
Y8S 350
Y8S 350
Y8S 350
Y10S Y10S Y10S Y10S Y12S Y12S Y12S 550 550 550 550 600 600 600
Y12S 600
500
Y8D 200
Y8D 250
Y8D 300
Y8D 350
Y8S 350
Y8S 300
Y8S 300
Y10S Y10S Y10S Y10S Y10S Y12S Y12S Y12S 500 500 500 500 500 600 600 600
Y12S 600
NOTES 1 Y8 bars are not always available. 2 S: Single (2 legs) D: Double (4 legs).
39
SABS 0144 Ed. 2 Table 12 — Minimum stirrup requirements — Percentage 0,1 % — Minimum spacing 1,00d Dimensions in millimetres 1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
800
850
900
950
1 000
Type, size and spacing of stirrups Width of beam
Depth of beams 250
300
350
400
450
500
550
600
650
700
750
150
R8S 200
R8S 250
R8S 300
R8S 350
R8S 400
R8S 450
R8S 500
R8S 550
R8S 600
R10S R10S R10S R12S R12S R12S 600 600 600 600 600 600
R12S 600
200
R8S 200
R8S 250
R8S 300
R8S 350
R8S 400
R8S 450
R8S 500
R8S 500
R8S 500
R10S R10S R10S R12S R12S R12S 600 600 600 600 600 600
R12S 600
250
R8S 200
R8S 250
R8S 300
R8S 350
R8S 400
R8S 400
R8S 400
R8S 400
R8S 400
R10S R10S R10S R12S R12S R12S 600 600 600 600 600 600
R12S 600
300
R8S 200
R8S 250
R8S 300
R8S 300
R8S 300
R8S 300
R8S 300
R10S R10S R10S R10S R10S R12S R12S R12S 500 500 500 500 500 600 600 600
R12S 600
350
R8S 200
R8S 250
R8S 250
R8S 250
R8S 250
R10S R10S R10S R10S R10S R10S R10S R12S R12S R12S 400 400 400 400 400 400 400 600 600 600
R12S 600
400
R8D 200
R8D 250
R8S 250
R8S 250
R10S R10S R10S R10S R10S R10S R10S R10S R12S R12S R12S 350 350 350 350 350 350 350 350 550 550 550
R12S 550
450
R8D 200
R8D 250
R8D 300
R10S R10S R10S R10S R10S R10S R10S R10S R10S R12S R12S R12S 300 300 300 300 300 300 300 300 300 500 500 500
R12S 500
500
R8D 200
R8D 250
R8D 300
R8D 350
R12S 450
R10S R10S R10S R10S R10S R10S R10S R10S R12S R12S R12S 300 300 300 300 300 300 300 300 450 450 450
NOTE – S: Single (2 legs) D: Double (4 legs).
7.6 Beams of depth exceeding 750 mm 7.6.1 Stirrups for deep beams To stiffen the legs of stirrups for deep beams against buckling during construction, tie clips to the legs and horizontal bars. Space the clips horizontally at every second or third stirrup, subject to a maximum space of 600 mm, and vertically at alternate intersections of horizontal bars (see figure 22).
Figure 22
40
SABS 0144 Ed. 2 7.6.2 Longitudinal side bars In beams of depth exceeding 750 mm, provide longitudinal bars over two-thirds of the depth from the tension face (the top of the beam at supports of continuous beams and the bottom of the beam for span moments). Place these bars near the side faces and not more than 250 mm apart. The diameter of the bars (in millimetres) should be at least s . b/fy where s
is the spacing, in millimetres;
b
is the beam width, in millimetres; and
fy is the characteristic strength of the steel, in megapascals. The minimum diameters that should be used, derived from the formula, are given in table 13 for steel of tensile strength 450 MPa. At the non-continuous end of a beam, provide U-bars to correspond with the side bars. (See also 7.7.1.) Table 13 — Minimum diameters of longitudinal side bars (450 MPa) Dimensions in millimetres 1
2
3
4
5
6
7
8
9
10
11
Minimum diameter of longitudinal side bars Bar spacing 250 200 150
Beam width 250
300
350
400
500
600
700
800
900
1 000
12 10 10
12 12 10
16 12 10
16 12 12
16 16 12
20 16 16
20 20 16
20 20 16
25 20 20
25 20 20
7.7 Intersections 7.7.1 Beam-column At beam-column intersections, ensure that the main beam bars avoid the main column bars. If splice bars are used (as in figure 23), the beam cages may be prefabricated (see 7.14) and the splice bars placed in position after the beam reinforcement has been dropped into place. Note, however, that this detail requires more reinforcement because of the additional lap.
41
SABS 0144 Ed. 2
Figure 23 If beams do not frame into a column on all four sides to approximately the full width of the column, ensure that stirrups are provided in the column for the full depth of the beam or, alternatively, that special U-bars are detailed with the beam, to restrain the column bars from buckling and to strengthen the concrete in compression. This is especially important where the slab and beam concrete is of a weaker grade than the column concrete. In general, it is advisable to supply U-bars at the noncontinuous ends of beams of depth exceeding 600 mm.
7.7.2 Beam-beam 7.7.2.1 General Ensure that, at beam-beam intersections, reinforcement is so arranged that layers in mutually perpendicular beams are at different levels. 7.7.2.2 Top steel It is good practice, for the following reasons, to pass the secondary beam steel over the main beam steel:
42
SABS 0144 Ed. 2 a) the secondary beam steel is usually of smaller diameter and requires less cover; and b) the secondary beam top reinforcement is available to act as a support for the slab top reinforcement. Where the main beam is very heavily stressed, however, it might be more economical to pass the main beam steel over the secondary reinforcement. Whichever method is adopted, it is considered good practice to keep the top steel in each beam at constant level, for instance in the case of beams of constant depth, make all the stirrups the same size. 7.7.2.3 Bottom steel To accommodate bottom bars, it is common practice to make secondary beams shallower than main beams, even if only by 50 mm (see figure 24). When beam soffits are at the same level, the secondary beam steel should pass over the main beam steel. Unless the secondary beam span is short, bars of diameter less than 25 mm may be draped (see figure 25). Cranking of bottom bars is usually unnecessary. NOTE – If the secondary beam span is short, draped bars might not sag enough to reach their correct position.
Figure 24
Figure 25
7.8 Maintaining bars in position (see also section 6) 7.8.1 Spacer bars Spacer bars required to separate layers of reinforcement are scheduled and measured.
7.8.2 Carrier bars Ensure that top bars that act as stirrup carriers are extended to the face of the beam support. Do not curtail light carrier bars on the assumption that the main top tension reinforcement over the supports will support the stirrups.
7.9 Minimum reinforcement requirements 7.9.1 Bottom bars Bottom bars should be at least 2 R12 or 2 Y10 and should constitute at least 0,25 % of the crosssectional area of the beam if of mild steel, or 0,15 % if of high tensile steel.
43
SABS 0144 Ed. 2 7.9.2 Top bars Top carrier bars (i.e. top bars not at supports) should be at least equivalent to the greatest of the following: a) 2 R10 or 2 Y8 (if available) (see 4.2.4); b) 0,15 % of the cross-sectional area of the beam if of mild steel or 0,10 % if of high tensile steel; and c) the reinforcement required by the design for hogging moments. The diameter of stirrup carrier bars should be at least equal to that of the heaviest stirrup.
7.9.3 Side bars Bars provided at the sides of a deep beam (see 7.6.2) should be at least equivalent to Y10.
7.10 Curtailment of bars in beams 7.10.1 General The following recommendations do not take high bond stresses into account. Where bond stresses are high, it might not be possible to curtail bars where they are no longer required for tension. If, however, in a series of continuous beams, the spans are equal or do not differ by more than 15 %, and the characteristic live load does not exceed the characteristic self-weight load for substantially uniform loading, bars can be curtailed with the use of the simplified rules given in 7.10.5. If these conditions are not met, bending moment envelopes should be provided by the designer. It should be noted that the use of envelopes enables economies to be made in reinforcement. Where bundled bars are used, individual bars in bundles should not be curtailed at spacings closer than 40 bar diameters, except at the supports of beams.
7.10.2 Bending moment envelope 7.10.2.1 If a bending moment envelope is available: a) bars in tension should extend by at least an anchorage length (see annex D) from the point at which they are fully stressed, for example for the first bar to be curtailed, the point of full stress, in the case of hogging reinforcement, will be at the face of the support. The remaining bars should be considered fully stressed at the point at which any curtailed bar is no longer needed (see figure 26); and b) bars should extend by at least the greater of one beam depth and 12 bar diameters beyond the point at which the continuing bars can resist the moment (see figure 26). 7.10.2.2 A bar should not be stopped in a tension zone unless: a) it also extends by a tension lap from the point at which it is no longer needed; or b) the continuing bars provide double the area required; or c) the shear capacity of the section is greater than twice the shear force actually present. 7.10.2.3 If the shear diagram is not available, ensure that either 7.10.2.2(a) or 7.10.2.2(b) is complied with.
44
SABS 0144 Ed. 2
Figure 26
7.10.3 Cut-off points 7.10.3.1 As it is undesirable to curtail more than one bar at any point, do not stop more than 20 % of the reinforcement at any point when more than one bar is curtailed. 7.10.3.2 Cut-off points should be separated by at least a tension bond length. 7.10.3.3 When deciding on cut-off points, make allowance for placing errors. Errors are less likely to occur if bars are detailed symmetrically, especially in end spans where bottom reinforcement is needed towards the non-continuous end. There is a tendency for fixers to place bars symmetrically.
7.10.4 Anchoring bottom reinforcement In the case of continuous beams, at least 30 % of the midspan reinforcement, other than bottom reinforcement that serves as compression reinforcement, should be taken 12 bar diameters beyond the centre-line of the support, and bottom reinforcement that serves as compression reinforcement should extend by at least a compression bond length into the support. In the case of simply supported beams and the non-continuous end of end spans of continuous beams, anchor the reinforcement at the supports by means of one of the following (see also the note below): a) an effective anchorage of 12 bar diameters beyond the centre-line of the support (no hook or bend should begin before the centre-line); b) an effective anchorage of 12 bar diameters plus half the beam effective depth from the face of the support (no hook or bend should begin at a distance from the face of the support equal to more than one-half of the beam depth); and
45
SABS 0144 Ed. 2 c) if the bond stress is less than half that permissible, a straight length of bar extending for a distance beyond the centre-line of the support equal to the greater of one-third of the width of the support and 30 mm. NOTE – As the conditions for anchoring given in (c) above will not often be susceptible to checking, ensure that, if (c) is applied, one of the other means is also applied.
7.10.5 Simplified rules for beams NOTE – In this subclause, L is the effective span: i.e. the lesser of a) the clear span plus the effective depth, and b) the distance from centre-line to centre-line of the supports.
7.10.5.1 Simply supported beams (see figure 27) At least 50 % of the tension reinforcement at midspan of a simply supported beam should extend to the supports and have an effective anchorage (see 7.10.4), at least 25 % should extend to within 0,08L of the support centre-line, and the rest should extend to within 0,15L of the support centre-line. 7.10.5.2 Cantilever beams At least 50 % of the tension reinforcement of a cantilever beam should extend to the end of the cantilever (and be turned down for bond where necessary) and the rest should extend to a distance (from the face of the support) of the greater of 0,5L and 45 bar diameters. The extent of curtailment of tie back bars should be determined by the designer. 7.10.5.3 Continuous beams (see figure 27) 7.10.5.3.1 At least 20 % of the top reinforcement in tension over the supports of a continuous beam should be made effectively continuous through the spans. Of the remainder, half should extend to a point at least 0,25L from the face of the support, and the other half to a point at least 0,15L from the face of the support, but no bar should stop at a point less than 45 bar diameters from the face of the support. 7.10.5.3.2 At least 30 % of the bottom reinforcement in tension at midspan should extend to the supports. Half the remainder should extend to points within 0,2L of the centre-line of interior supports. The remaining 35 % should extend to within 0,1L of the centre-line of supports. 7.10.5.3.3 At a non-continuous end, 50 % of the tension reinforcement should extend to the supports and terminate in an effective anchorage as in 7.10.5.1 above and the remainder should extend to within 0,05L of the centre-line of the support. 7.10.5.4 Continuous beams of which spans differ by not more than 15 % NOTE – In this subclause, L is the greater of the effective span and the adjacent span on the other side of the support in the case of top bars, and L is the effective span in the case of bottom bars.
7.10.5.4.1 Of the top reinforcement in tension over supports, at least 33 % in short spans adjacent to long spans, and at least 20 % in all other cases, should be made continuous over the whole span. Of the remainder, half should extend to a point at least 0,3L from the face of the support, and the other half to a point at least 0,2L from the face of the support. No bar should extend by less than a tension bond length from the face of a support. 7.10.5.4.2 At least 33 % of the bottom reinforcement in tension at midspan (at least 50 % in the case of simply supported ends, where the detailing should be as in 7.10.5.1) should extend to the supports. For interior spans, half of the remainder should extend to a point that is within 0,1L of the centre-line of supports and the remaining third to a point that is within 0,2L of the centre-line of supports.
46
SABS 0144 Ed. 2
Figure 27
47
SABS 0144 Ed. 2 7.11 Bent-up bars for shear reinforcement 7.11.1 First bend Start the top of the first bend not more than 0,5d from the face of the support, and space subsequent bends at distances apart equal to 0,75d (or less if so required by the design).
7.11.2 Anchorage length Measure the anchorage length from the top bend. Annex D gives bond lengths (as recommended in SABS 0100-1) for the shear, compressive and tensile stresses permitted in mild steel and deformed bars of tensile strength 450 MPa. Wherever possible, give top bars an increased bond length (see 7.4.4).
7.11.3 Bend diameter To reduce concrete compressive stresses at the bends, bends of radius at least 7,5 bar diameters are required. It is not, however, generally practicable to bend to radii exceeding 250 mm. Where the side cover to a bar is less than 3 bar diameters, the radius of the bend should be at least 10 bar diameters. If the radius of a bend in a fully stressed bar is less than 10 bar diameters, the side cover should be more than 3 bar diameters. Additional clips or stirrups should be provided to prevent lateral splitting at splices.
7.12 Corbels and halving joints 7.12.1 Corbels A corbel is a short cantilever beam in which the principal load is applied in such a way that the distance between the line of action of the load and the face of the supporting member is less than 0,6d and the depth at the outer face of the bearing exceeds one-half of the effective depth at the face of the supporting member.
7.12.2 Main reinforcement The main tension reinforcement in a corbel should be not less than 0,4 % and not more than 1,3 % of the section at the face of the supporting member and should be adequately anchored. Anchor the reinforcement at the front face of the corbel either by welding it to a transverse bar of equal strength or by bending back the bars to form loops; in either case, the bearing area of the load should not project beyond the straight portion of the bars that form the main tension reinforcement (see figures 28 and 29). NOTE – The limitation on reinforcement percentages is due to the limited number of tests results available.
48
SABS 0144 Ed. 2
Figure 28
Figure 29
7.12.3 Horizontal force When a corbel is required to resist a horizontal force in the direction H applied to the bearing plate (see figure 28) because of shrinkage or temperature changes, provide additional reinforcement to transmit this force in its entirety. This reinforcement should be welded to the bearing plate and adequately anchored within the supporting member.
7.12.4 Shear reinforcement Provide shear reinforcement in the form of horizontal stirrups distributed in the upper two-thirds of the effective depth of the corbel at the column face. This reinforcement should have an area of at least one-half of the area of the main tension reinforcement and should be adequately anchored (see figure 30).
49
SABS 0144 Ed. 2
Figure 30
7.12.5 Halving joints Several recommended bar arrangements for halving joints are to be found in literature covering practice in the United Kingdom, the United States of America and Germany. Figure 31 shows three arrangements, each of which has its advantages, disadvantages and special requirements.
50
SABS 0144 Ed. 2
Figure 31
51
SABS 0144 Ed. 2 7.13 Splicing of tension bars (see also 6.3) 7.13.1 Lap splices Whenever possible, lap splices should be staggered by one bond length (see annex D).
7.13.2 Maximum number of bars spliced Because cracks induced at sudden changes of section can cause premature shear failure, and because of bursting forces at lap splices (see 7.13.4), do not stop or lap more than the greater of one bar and one-fifth of the total steel area, at any one section except at the ends of beams, or where top reinforcement is stopped off in a region of compression.
7.13.3 Cranks at splices Splicing bars by lapping is not desirable if it is necessary to crank one of the bars (see figure 10), since this makes bending and placing more difficult. It is preferable to butt the bars to be spliced, and to provide additional lapping reinforcement. If several bars are to be spliced in a beam, provide one or more additional bars (see figure 11). The length of lap required is given in annex D, but some codes require appreciably greater lap length. Note that the length for a lap splice is 25 % greater than that for a tension bond.
7.13.4 Bursting forces Because lap splices induce bursting forces in the concrete, increase the shear capacity in the region of the splice by adding, over the length of the lap, additional stirrups of area equal to about half the area of the bars being spliced.
7.13.5 Crack control Where spliced bars are butted, crack control is important. Therefore, the distance between bars on either side of the spliced bars should not exceed the appropriate value given in figure 11. As this is especially important where corner bars are spliced, the lapping bar should be as close as possible to the spliced bar (see 6.3.2.2).
7.14 Prefabrication of beam cages In order to facilitate the prefabrication of beam cages, longitudinal bars may be stopped at the faces of supports. In such cases, ensure that equivalent splices are provided for the top and bottom steel and for the middle bars if they are assisting in resisting shear or torsion (see figure 23). It should be noted that the arrangement shown in figure 23 requires an additional mass of reinforcement because of the extra splices, and also that great care is needed on site to ensure that the splices are placed in the correct position.
52
SABS 0144 Ed. 2 7.15 Corners and cranked beams 7.15.1 General Recommendations are given on various methods of reinforcing corners (for additional information see annex B). Closing corners present no great problem, but opening corners require careful detailing (see figures 32 and 33).
Figure 32
Figure 33
7.15.2 90° opening corners with not more than 1 % reinforcement Where the amount of reinforcement in the beam is equal to or less than 1 %, detail the reinforcement as shown in figure 34 or figure 35, the splay steel being equal to 50 % of the main steel.
53
SABS 0144 Ed. 2
Figure 34
Figure 35
7.15.3 90° opening corners with more than 1 % reinforcement If the area of reinforcement exceeds 1 %, provide transverse steel as well as splay steel as in figure 36. (The use of a splay is also strongly recommended.)
Figure 36
54
SABS 0144 Ed. 2 7.15.4 Cranked beams The recommended methods of detailing are shown in figures 37, 38 and 39.
Figure 37
Figure 38
Figure 39
55
SABS 0144 Ed. 2 7.15.5 Beam and column junction Where a column extends above a beam, bend the beam top reinforcement down into the column but if it is necessary to bend the bars up, detail additional steel as in figure 40.
Figure 40
7.15.6 Closing corners At closing corners, provide adequate radii (equal to at least 7,5 bar diameters) and some additional reinforcement as in figure 41.
Figure 41
56
SABS 0144 Ed. 2 7.16 Deep beams 7.16.1 Simply supported deep beam on two supports 7.16.1.1 Longitudinal reinforcement The main longitudinal reinforcement corresponding to the ties considered in the design model should be uniformly distributed over a depth, measured from the lower face of the beam, of the lesser of 0,12H U and 0,12L (figure 42) where L
is the design span;
H is the total height of the beam; H U is equal to H – C – d /2 where C is the cover to the top bar; and d is the diameter of the top bar. The longitudinal reinforcement should be fully extended from one support to the other. At supports, the anchorage should be obtained by bending the bars up, by using horizontal hooks or U-loops or by anchorage plates, unless the length between the centre of support and the end of the beam exceeds the anchorage length (see SABS 0100-1).
Figure 42
57
SABS 0144 Ed. 2 Attention is drawn to the importance of providing small diameter bars in order to limit the width and development of cracks under service load and to facilitate anchorage at the supports. It is of particular importance that these anchorages be adequate. Tests show that insufficient anchorage leads to rupture under considerably smaller loads than those that could be expected from the other characteristics of the beam. Anchorage achieved by vertical hooks is to be avoided since it tends to promote cracking in the anchorage zone. 7.16.1.2 Detailing of the shear reinforcement 7.16.1.2.1 Direct loading (the load is applied at the top of the beam) Under direct loading, the shear reinforcement can be made of a light mesh of orthogonal reinforcement, consisting of horizontal stirrups surrounded by vertical stirrups. The total percentage of the bars in each direction should not be less than 0,2 % (0,1 % in each face). 7.16.1.2.2 Suspended loading (the load is applied at the bottom of the beam) Under suspended loading, the orthogonal mesh described in 7.16.1.2.1 should be supplemented by introducing additional stirrups to transmit the total load between its point of application and the level corresponding to the lesser of H U and L. These stirrups should surround the bars of the lower reinforcement and be extended over a depth equal to the lesser of H U and L (see figure 43). Near the supports, the height of the stirrups may be slightly reduced (by about 20 %).
Figure 43 7.16.1.2.3 Indirect loading (or indirect supports) Indirect loading corresponds to a load applied over the total depth of the beam by means of a transverse perpendicular wall or by a column of large cross-section, which is extended down to the lower part of the beam.
58
SABS 0144 Ed. 2 According to the chosen design model, the force transmitted to the beam should be resisted by additional reinforcement (suspension reinforcement) made: a) either of vertical stirrups extended without cut-off, near the common volume, over a length equal to the lesser of H U and L (see figure 44(a)); or b) by bent-up bars that resist about 60 % of the load, placed symmetrically to the line of action of the load, and by complementary stirrups (see figure 44(b)).
Figure 44
59
SABS 0144 Ed. 2 7.16.2 Continuous deep beams 7.16.2.1 In the span (i.e. the positive moment area) Subclause 7.16.1 applies for the main reinforcement and also for the shear reinforcement in the span of a continuous deep beam. 7.16.2.2 Over the supports For the main horizontal tensile reinforcement over the supports, the following applies: a) a fraction 1 L & 1 2 H
in the range 1 < L < 3 of the total required cross-sectional area of reinforceH
ment should be placed in the upper strip which extends to the lesser of 0,2H and 0,2L (see figure 45); b) the remaining cross-sectional area should be uniformly distributed within the lower strip just below, which extends to 0,6H or 0,6L (see figure 45); and c) one bar in two may be stopped symmetrically at a distance from each face of the support equal to 0,4H or 0,4L. Where H > L, supplementary longitudinal reinforcement should be placed near the upper face of the beam. The arrangement of the reinforcement in the tensile zones over the support should be such as to control the cracking to acceptable limits since, in these regions, the maximum elastic tensile stresses occur. It is particularly important to ensure the correct behaviour of these zones, since they lie in the path of the stress lines from the loads to the supports; hence the forces to which they are subjected are inescapable and can only be resisted by proper design of the structure. It is important that the state of stress near the supports be studied, because of the considerable intensity of shear and normal stresses that occur simultaneously in horizontal and vertical planes.
Figure 45
60
SABS 0144 Ed. 2 Attention is drawn to the extreme sensitivity of continuous deep beams to the various phenomena produced by displacement of the supports. In the elastic range, even small displacements of the supports can completely change the stress distribution and even reverse the direction of the stresses. The satisfactory behaviour of existing deep beams, most of which have been conceived without rigorously taking into account differential displacement of supports (elastic and plastic deformations of supports, shrinkage, foundation settlements, etc.) proves the possibilities of adaptation of the structure beyond the elastic range. Nevertheless, in order to avoid increasing the probability of cracking and the risk of destruction of the beam, it is necessary to reduce as far as possible all causes that can produce differential settlements.
7.16.3 Concentrated loads In very deep beams, concentrated loads applied on the centre-line of the supports produce, in vertical planes, compressive or tensile stresses which cannot be neglected. The distribution of these stresses is similar to the diffusion of prestressing forces in the anchorage zone.
8 Component detailing — Slabs NOTE – The attention of users of this clause is drawn to the following publications: Report No. 2 on the design of pre-stressed concrete flat slabs by the Joint Structural Division of SAICE and ISE, and British Concrete Society Technical Report No. 43 on post-tensioned concrete floors – Design Handbook.
8.1 General In general, detail slabs in plan only, using diagrammatic representation; show the bars as if they fall towards the top of the drawing, or to the left of the drawing (see figures 5 and 53). It is good practice to detail top and bottom bars separately (see 3.4) and where any complication occurs, to include sections.
8.2 Minimum reinforcement in slabs 8.2.1 Main steel The area of the main tension reinforcement in a solid slab and at continuous supports should be at least 0,13 % of the cross-sectional area of the slab, based on the effective depth of the slab if high tensile deformed steel is used or at least 0,24 % if round mild steel is used.
8.2.2 Secondary steel The area of the secondary reinforcement at right angles to the main reinforcement should be at least 0,13 % of the cross-sectional area of the slab, based on the total depth of the slab if high tensile deformed steel is used or at least 0,24 % if round mild steel is used. Where there is top and bottom reinforcement, the area of secondary reinforcement should be the greater of 0,06 % of the cross-sectional area of slab and one-quarter of the main steel.
8.2.3 Edges of slabs The area of the steel that is parallel to the supports in the edge strips of two-way slabs should be at least equal to the applicable values given in 8.2.1 and 8.2.2. (Where torsion reinforcement is added, include this in the area computed.)
61
SABS 0144 Ed. 2 Where reinforcement is curtailed, the sum of the top and bottom steel areas, at right angles to the support, should be at least equal to the applicable values given in 8.2.1 and 8.2.2.
8.2.4 Special cases Where a slab is restrained from shrinking (for example a slab restrained by concrete walls and a base cast in rough rock) or where a slab is exposed to repetitive temperature changes or to severe weather conditions, the minima given in 8.2.1 to 8.2.3 might be considered by the designer to be too low, whereas in a slab that is deeper than structurally necessary, and is free to shrink, the minima might be considered excessive. Where a slab constitutes the flange of a beam, the designer should specify his requirements for transmitting horizontal shear.
8.2.5 Ribbed and coffered slabs — Topping The topping steel in ribbed slabs could be provided by sheets of mesh reinforcement, of crosssectional area in each direction of at least 0,12 % of the gross cross-sectional area of the topping, lapped by at least 60 wire diameters.
8.2.6 Ribbed and coffered slabs — Ribs With the exception of stirrup requirements, the minimum reinforcement is as for beams. If the shear stress is less than the permissible value, no stirrups are required.
8.3 Spacing of bars in slabs 8.3.1 Maximum spacing of main tension reinforcement in solid slabs — High tensile steel (450 MPa) 8.3.1.1 For a slab of thickness not exceeding 200 mm, the maximum permissible spacing is twice the effective depth plus the bar diameter. 8.3.1.2 For a slab of thickness exceeding 200 mm, the maximum permissible spacing is the appropriate value given in table 14. Table 14 — Maximum spacing of bars (450 MPa) in slabs of thickness exceeding 200 mm 1
2
3
4
5
6
7
Maximum spacing mm Position of reinforcement
Amount of tension reinforcement %, gross
Span Support
62
Up to 0,5
0,6
0,7
0,8
0,9
1,0
350 300
300 250
250 200
250 200
200 175
175 150
SABS 0144 Ed. 2 8.3.2 Maximum spacing of main tension reinforcement in solid slabs — Other types of steel Use the spacing recommended in SABS 0100-1.
8.3.3 Spacing of secondary steel — Temperature, shrinkage and distribution steel The spacing of secondary steel should not exceed five times the effective depth of the slab.
8.3.4 Spacing of topping steel in voided slabs The spacing of topping steel in voided slabs in each direction should not exceed half the centre-tocentre distance between the ribs and should be such that there are at least two bars between adjacent ribs.
8.3.5 Preferred spacing of bars in slabs When possible, adopt the following spacings (in millimetres): 75; 100; 125; 150; 175; 200; 250; 300; 350; 400; 450 and 500.
8.3.6 Spacing of bars where curtailment occurs The spacing of top and bottom steel on either side of a curtailed bar in a slab other than a cantilever slab should not exceed the lesser of twice the spacing required in terms of 8.3.1 or 8.3.2 (as relevant) and five times the effective depth. The spacing of bars going to the end of a cantilever slab, whether or not curtailment occurs, should not exceed the permissible maximum given in 8.3.1 or 8.3.2 (as relevant).
8.4 Diameters of bars in slabs The diameter of main tension reinforcement should normally not exceed 15 % of the slab thickness. For practical purposes, however, it is preferable to use bars of 10 mm or more as main top tension steel, unless welded mesh is being used. In cantilevers of length 1 200 mm or more, the use of bars at least equivalent to Y12 bars is recommended.
8.5 Scheduling of steel Ensure that all reinforcement is scheduled in specific lengths, for example 50 of 12 m (not 600 m cut to suit on site).
8.6 Maintenance of position of steel 8.6.1 Cover requirements Ensure that the cover requirements are stated on the placing drawing (see 6.1).
8.6.2 Maintenance of cover See 6.2 for recommendations on the maintenance of cover and for details of cover devices for bottom steel (see 6.2.4) and of stools and chairs for top steel (see 6.2.5).
63
SABS 0144 Ed. 2 8.7 Openings and corners in slabs 8.7.1 Normal trimming reinforcement Where no special loading or vibration conditions occur, the following general rules for trimming reinforcement can be followed: a) half of the steel intersected by the hole is detailed to lie on each side of the opening; b) additional bars are placed in the line of the hole if the space thus created exceeds the permissible spacing; and c) diagonal stitching bars (see figure 46) are put across the corners of rectangular holes or so placed as to frame circular holes. They should be placed at both the top and the bottom if the thickness of the slab exceeds 150 mm. The diameter of these bars should be the same as that of the larger of the slab bars, and their length should be about 80 bar diameters.
Figure 46
64
SABS 0144 Ed. 2 8.7.2 Corners in slabs Re-entrant corners should also have additional corner stitching bars as for holes (see 8.7.1). Where the slab is restrained against horizontal movements (caused by shrinkage, creep or temperature) by walls, stiff beams, or friction, place extra steel and diagonal bars across such corners to reduce the crack sizes (see figure 47).
Figure 47
65
SABS 0144 Ed. 2 8.8 Cantilever slabs 8.8.1 Support to top tension steel Support the top steel of cantilever slabs at spacings (for stools and chairs) generally about 10 bar diameters less than those recommended in 6.2.2 and ensure that a row of stools or chairs supports every bar close to the face(s) of the member that supports the cantilever (see figure 48). The bending of the main bars should be such that they contribute to the supporting of the steel, bars that extend to the end should have square returns (shape code 38) and in the return there should be two fixing bars, one at the top and one at the bottom. Unless adequate stools are provided, each curtailed bar should have a cranked bend (shape code 41 or 42) and should have a top fixing bar at the crank (see figure 48).
Figure 48
8.8.2 Curtailment of cantilever bars Curtailed bars should extend by at least 20 bar diameters beyond the point at which they would be terminated for structural purposes (see figure 48).
8.8.3 Secondary steel So design and detail bottom steel that it is at right angles to the support that carries construction loading in the propped condition. The total area of top and bottom distribution steel parallel to the face(s) of the support should be between 0,25 % and 0,4 % of the gross cross-sectional area, depending on the length of the slab between joints, the degree of end restraint by corners and the degree of exposure to temperature changes, for example a cantilever slab in a north facing location requires more distribution steel than does one in a shaded south facing position.
66
SABS 0144 Ed. 2 8.8.4 Ends of cantilever slabs Schedule main cantilever bars to go right to the ends of the slab, both next to the construction joint and at the free end, and add an extra bar at each end. Extra distribution steel is required at corners of cantilevers at both the top and the bottom to distribute induced cracks (see figure 49). Where the end of a cantilever is supported by a wall (or similar structure), ensure that the bottom steel is adequate to accept possible reverse moments (see figure 49).
Figure 49
8.8.5 Tie-backs and counterweights to cantilevers 8.8.5.1 In slab Ensure that the support of cantilever bars in the slab from which the cantilever springs is provided in accordance with the same rules as those that apply to the cantilever itself (see 8.8.1). 8.8.5.2 Bottom of beams Ensure that, when a cantilever slab is at the bottom of a beam (see figure 50), the design of the stirrups in the beam provides for moment, shear, hanging tension and, if necessary, torsion. If possible, when detailing this steel, provide for the placing of the beam steel without the necessity of the threading of the main beam steel through the cantilever anchorage loops. Note the special difficulty induced by bent-up bars in the beam steel. NOTES 1 See the alternative arrangements shown in figure 50 and also the principles applicable to opening corner details in retaining walls and in beams given in 10.19 and 7.15, respectively. 2 Curtailed bars that go to the back of a beam could drift out of position during concrete casting. 3 Hairpin type bars should be related to the horizontal stirrup spacing and this could cause difficulties.
67
SABS 0144 Ed. 2
Figure 50
68
SABS 0144 Ed. 2 8.8.5.3 Top of beams Where the weathering step is 30 mm or less, crank the bars at a slope not exceeding 1 in 6 (see figure 51(a)). Ensure that the combination of top bars and stirrups is such as to provide the required restraints. Note that if a bar is laced over and under the beam bars, it is fully restrained, provided that the beam top bars are heavy enough and a stirrup is within 50 mm of the bar. If the bar is not so laced, so detail the steel as to ensure effective anchorage against bursting (see figure 51).
Figure 51
69
SABS 0144 Ed. 2 8.8.6 Cantilevers around corners Ensure that, at a corner of a cantilever slab, the detailing is such that tie-back loading and the deflections that arise from this arrangement are accounted for. If "fan" type detailing is used, take care to avoid congestion (see figure 52). Take particular care with drainage inlets.
Figure 52
70
SABS 0144 Ed. 2 8.9 Curtailment of top tension reinforcement 8.9.1 Two-way slabs The cut-off points of the top tension reinforcement depend upon the load distribution assumed in the analysis and should be given by the designer.
8.9.2 One-way slabs The recommendations that cover the curtailment of top tension reinforcement in beams apply also to continuous one-way slabs (see 7.10).
8.10 Corner reinforcement in two-way slabs Recommendations regarding torsion reinforcement required in the corners of restrained slabs when the main reinforcement is concentrated in central strips are given in SABS 0100-1. It is common practice to keep the reinforcement uniform for the entire width of the slab. If this method is adopted, schedule the bars to start not more than one space away from the edge of the support. If this is done for both top and bottom steel, extra torsion reinforcement will not be required for slabs that are continuous at one or two edges. Slabs that are discontinuous at both edges will require extra top steel in the corners.
8.11 Slabs of other types 8.11.1 Composite slabs In slabs of prestressed concrete or in slabs that have steel or similar ribs, the area of the topping steel in each direction should be at least 0,12 % of the gross cross-section. Check with the designer to ascertain the steelwork necessary for adequate shear connection.
8.11.2 Ribbed or voided slabs Ensure that at least 50 % of the total main tension reinforcement in the ribs is carried through at the bottom onto the bearing and anchored (see 7.10.4).
8.12 Flat slabs 8.12.1 General rules Rules for the arrangement of reinforcement in flat slabs are given in SABS 0100-1 and a diagrammatic interpretation of these is given in figure 53. Where temperature differentials are possible and for consideration of shear, it is recommended that at least one-half of the bottom steel in slab and column strips be anchored effectively.
71
SABS 0144 Ed. 2
Figure 53
72
SABS 0144 Ed. 2 8.12.2 Reinforcement of mushroom heads Mushroom heads are normally cast with the columns and the detail of the reinforcement should be such that the steel for the head can be formed into a separate cage (see figure 54). NOTE – The designer should determine the amount of steel required in the mushroom head to control cracks arising from the out-of-balance moments.
Figure 54
73
SABS 0144 Ed. 2 8.12.3 Shear reinforcement at column heads and dropped panels The best method of providing bar shear reinforcement for slabs at column heads is to use beam cages in one direction and bars in the other direction, wired to the cages (see figure 55).
Figure 55
74
SABS 0144 Ed. 2
9 Component detailing — Columns 9.1 General A column is a vertical structural element the greater lateral dimension of which is not more than four times the lesser.
9.2 Detailing method Detail columns by means of exploded views. Show the levels of the bottom and the top of the column (at top of slab or beam or upstand beams). Indicate on the reinforcement detail the positions of all intermediate beams. Show each bar mark once and provide adequate sections showing all main bars and the arrangement of stirrups (see figure 56). Consider carefully the effect of kickers on levels (see 10.4). Note that reinforcement for columns is very often preassembled and details should allow for this (see 3.6).
9.3 Main reinforcement 9.3.1 General The main reinforcement (the longitudinal bars) should consist of mild steel or high tensile steel bars of diameter at least 12 mm. Generally they are used singly, but the use of bundles and pairs is permissible (see 6.5.4). Place a longitudinal bar (or bundle) in each corner of the section. Unless there are bending moment considerations, arrange the main reinforcement symmetrically. Ensure that asymmetrical arrangements are carefully detailed and orientated to avoid errors in placing.
9.3.2 Maximum or minimum amount of reinforcement The assessment of the maximum or minimum amount of reinforcement is a function of the design. From a practical point of view (handling of the cage, arrangement of splicing, etc.), the area of reinforcement should be between 0,5 % and 3 % (maximum 6 % at splice). Where more than 3 % is used, take special care because congestion can create problems. Where congestion occurs, consider the use of mechanical splices (see 6.3.4).
9.3.3 Maximum spacing of main bars The spacing between main bars should not exceed the lesser of twice the least dimension of the column and 400 mm.
9.3.4 Minimum spacing of main bars For practical reasons, the spacing between the main bars should be at least 80 mm, measured centreto-centre if not bundled, or 100 mm clear between bundles.
75
SABS 0144 Ed. 2
Figure 56
76
SABS 0144 Ed. 2 9.3.5 Number of main bars 9.3.5.1 Figure 57 gives a guide to the number of bars if bundling is not used and also indicates typical bar arrangements.
Figure 57
77
SABS 0144 Ed. 2 9.3.5.2 The use of bars restrained direct by stirrups (see 9.4.1.1) alternating with loose bars gives adequate access for vibrators (see figure 58). Dimensions in millimetres
Figure 58
9.4 Stirrups 9.4.1 Horizontal configuration 9.4.1.1 So arrange stirrups as to contain all of the corner bars and to restrain each bar effectively. A bar is considered to be effectively restrained in the horizontal plane if it is: a) enclosed by a stirrup of internal angle not exceeding 135°; b) between two bars, each restrained as in (a) above, and at a centre-to-centre distance not exceeding 150 mm from each such bar; c) enclosed by helical stirrups; or d) surrounded on all four sides by beams or slabs or both. 9.4.1.2 Stirrups of rectangular columns should generally be closed and hooks should be square (shape code 60). Avoid the use of shape code 81 for column stirrups. Dimension stirrups and clips externally. 9.4.1.3 To facilitate placing and compacting of concrete, stirrups should as far as possible leave the centres of the columns free of crossing steel. Provide for, and show on sections, built-in items such as rainwater pipes and particularly inlets and outlets (see figure 56).
9.4.2 Vertical spacing of stirrups Ensure that the horizontal restraints of a bar are not further apart vertically than the least of the following: a) the lesser lateral dimension of the column; b) 12 times the diameter of the smallest longitudinal bar; and c) 300 mm.
78
SABS 0144 Ed. 2 9.4.3 Diameter of stirrups Ensure that the diameter of each stirrup is at least 0,25 times the diameter of the largest longitudinal bar and at least 0,01 times the average of the cross-sectional dimensions of the column. Subject to design requirements, the nominal diameter of bars for stirrups should normally be 8 mm, 10 mm or 12 mm.
9.4.4 Edge column stirrups Where columns are not restrained at a floor (see figures 59 and 60), provide horizontal reinforcement clips, open stirrups or U-bars. This reinforcement is best detailed with the beam. If the concrete mix in the floor is of a lower grade than that in the columns, check for possible requirements for extra steel, particularly in edge columns.
Figure 59
79
SABS 0144 Ed. 2 9.4.5 Temporary fixing stirrups Provide at least two temporary fixing stirrups to hold splices in position (see figure 60) or to stiffen helically bound columns during fabrication, and ensure that such stirrups are detailed and scheduled. NOTE – If columns are detailed as in figure 62, a note should be included in the detail, alerting the fixer to the fact that the stirrups above the floor may not be removed.
Figure 60
80
SABS 0144 Ed. 2 9.4.6 Large columns Where the reinforcement for very wide columns is to be fabricated in separate cages and erected in sections, it should be held together by bars of diameter 12 mm, at double the stirrup spacing (see figure 61).
Figure 61
81
SABS 0144 Ed. 2 9.5 Splicing of column reinforcement 9.5.1 General Splicing is normally accomplished by the lapping of bars. The lengths of laps in the main bars should, unless otherwise required by the designer, comply with the applicable values given in annex D. The bottoms of bars are normally at floor level unless concrete kickers are permitted.
9.5.2 Continuity of column bars The continuity of column bars can be achieved by: a) so continuing the bars that they lap with the bars of the upper columns either: 1) with the lower bars cranked into a position inside the upper bars (see figure 62(c)); or 2) with the upper bars cranked into a position inside the lower bars (see figure 62(a)); NOTE – In case (1) above, double sets of stirrups or additional stirrups are required to restrain the crank when the height of set exceeds the depth of the relevant intersecting and restraining member. Where there is an adequate restraining member, the slope of crank should not exceed 1: 6 (see figure 62(b)). In case (2) above, a double set of restraining stirrups is required at the crank (see figure 60) and the crank slope should not exceed 1:10.
b) terminating all or some of the bars below floor level and introducing separate splices to start the column above; NOTE – Where the relative displacement of the column faces exceeds 100 mm, this principle should be applied (see figure 62(d)).
c) using mechanical splices (see 6.3.4) to a specification approved by the designer; d) using welded splices (see 6.3.3) to a specification approved by the designer.
82
SABS 0144 Ed. 2
Figure 62
83
SABS 0144 Ed. 2 9.6 Large change in column size Where a large reduction in column size occurs, the upper column could require more steel than the lower column and additional splices could be required.
10 Component detailing — Walls 10.1 General A wall is a vertical structural element the greater lateral dimension of which is more than four times the lesser.
10.2 Detailing methods Detail walls in panels or sections to suit the construction procedure (see figures 63 and 64). They may be detailed on elevations or diagrammatically as in the case of slabs (see 8.1).
10.3 Reinforced and plain concrete walls 10.3.1 For a wall to be considered as a reinforced concrete wall, the area of vertical reinforcement should be at least 0,4 % of the plan area of the wall.
10.3.2 A wall that has less reinforcement than that specified in 10.3.1 is considered as a wall with nominal reinforcement, or as a plain concrete wall. A plain concrete wall could require a certain minimum area of reinforcement (see 10.14). NOTE – For fire resistance purposes, unless the vertical reinforcement content of a reinforced concrete wall is at least 1 %, the wall is classified as a plain concrete wall.
10.4 Kickers It is not common practice to provide kickers in building construction but it is common in civil engineering construction. If kickers are used, the required lap in the reinforcement should be provided above the kicker.
10.5 Cranking of vertical bars Do not crank vertical bars except where the wall changes in section. Heavy corner bars might, however, have to be cranked.
84
SABS 0144 Ed. 2
Figure 63
85
SABS 0144 Ed. 2
Figure 64
86
SABS 0144 Ed. 2 10.6 Layers of reinforcement in thin walls Ensure that the reinforcement is detailed in such a way that the concrete can be thoroughly compacted. For walls of thickness not exceeding 170 mm, where the insertion of a vibrator could lead to difficulties, a single layer of vertical and horizontal bars may be provided at the centre of the wall and an external vibrator may be used (see figure 65(a)).
10.7 Layers of reinforcement in thicker walls For walls of thickness exceeding 170 mm but less than or equal to 220 mm and also for walls of thickness exceeding 220 mm but that have a reinforcement content greater than nominal, provide two layers of reinforcement in both the vertical and the horizontal directions, the former layer being placed on the inside of the latter (see figure 65(b)). Provide clips to restrain the vertical bars against buckling or displacement prior to and during the construction of the wall. The bending, spacing and size of the clips should be in accordance with the requirements relating to stirrups in columns (see 9.4). In walls of thickness exceeding 220 mm and that have nominal reinforcement, horizontal steel can be placed inside the vertical steel to reduce the possibility of the coarse aggregate's being "hung up" on the horizontal bars (see figure 65(c)). However, in this case ensure that sufficient space is left between the inner layers in order to allow for the placing and vibration of the concrete. This space should be the greater of at least 100 mm and at least 75 mm greater than the largest size aggregate. The alternative method of placing horizontal steel inside vertical steel also applies to retaining walls (see 10.17).
Figure 65
87
SABS 0144 Ed. 2 10.8 Prefabrication of reinforcement Reinforcing mats should be prefabricated wherever possible. This can be achieved by any of the following methods: a) the detailing of mats as reinforcement for walls, with loose splice bars provided at corners, columns and counterforts (this enables the contractor to erect complete wall sections); b) the detailing at intervals along the wall of stiff "column cages", with the remaining horizontal and vertical bars placed in between (this method involves more site work than does (a) above but is often quicker than erecting the whole wall reinforcement in situ); and c) the use of large cages as described in 9.4.6. NOTE – The substitution of welded mesh for the reinforcement described in (a) and (b) above is often beneficial. See table 15 for available and transportable mesh sheet and roll sizes.
10.9 Vertical stages Walls should be detailed in vertical stages (lifts) to suit construction. The height of a stage should generally not exceed 6 m. Vertical reinforcement should have a diameter of at least 10 mm for stages of height not exceeding 3,5 m. A diameter of at least 12 mm should be used for stages of height up to 6 m, and also for reinforcement in "column cages". Where mesh is used as in 10.8, the size of wire may be less than 10 mm if "column cages", as described in 10.8(b), are provided.
10.10 Clips Provide clips to maintain the spacing of bars and space them at a maximum centre-to-centre distance of 1 m in each direction. Detail the clips (which are best detailed as shape code 35 or 85) to connect the two inner layers of steel (see figure 64 and see also 10.15 for heavily reinforced walls).
10.11 Pockets 10.11.1 Small pockets A small pocket to be left in a wall can be formed by means of expanded polystyrene that should be anchored to prevent it from floating. If the wall is to support a beam or a slab, insert one or more reinforcing bars into the polystyrene block (see figure 66), to ensure a strong, rigid splice connection. Ensure that the width of the pocket exceeds the length of the bend at the end of the future splice bar (see figure 66).
10.11.2 Large pockets A large pocket can be formed by means of timber. Slope the top of the pocket to facilitate concreting operations (see figure 66).
88
SABS 0144 Ed. 2
Figure 66
89
SABS 0144 Ed. 2 10.12 Splices at top of wall Where a slab is to be cast at the top of a wall, detail the continuity steel into the top of the slab with the wall reinforcement: a) if Y10 or lighter, as straight bars to be bent into the slab (see figure 67(a)); and b) if heavier than Y10, as L bars extending at least a lap length below the soffit of the slab (see annex D and figure 67(b)). Alternatively, use the double U-bar detail shown in figure 67(c).
Figure 67
90
SABS 0144 Ed. 2 10.13 Splices to slabs and beams Where a section of wall is common with a slab or beam and is cast as part of the slab or beam, detail, with the wall, any splices that are required to be cast into the wall and cross-reference them on the slab or beam reinforcing details. Where the wall is to be cast through, the connection with the slab or beam can be achieved by means of: a) pockets of sufficient depth to ensure adequate bond of reinforcement (see 10.11); or b) a rebate in the wall, with splice bars bent into the rebate in the wall and later bent out (see figure 68). It is normally preferable to provide pockets, since the rebending of reinforcing bars usually causes them to kink. Also, the level of the rebate is critical, since a small inaccuracy in levels will cause a considerable weakening in the connection, whereas an out-of-level pocket can easily be enlarged. Bars larger than Y10 or R16 should not be detailed to be bent, but mild steel bars are recommended if bending is unavoidable. If greater strength is required, welded or mechanical splices can be used (see 6.3.3 and 6.3.4).
Figure 68
91
SABS 0144 Ed. 2 10.14 Walls with nominal reinforcement or plain concrete walls 10.14.1 Reinforcement could be required: a) to control tension caused by eccentricity or horizontal forces; b) to distribute vertical loads; or c) to control shrinkage and temperature cracking.
10.14.2 In those areas where reinforcement is required, provide high tensile steel reinforcement in accordance with the following: a) except as recommended in (b) below, so distribute steel in both faces together that, in walls of thickness not exceeding 400 mm, there is a total of at least 0,25 % vertically and at least 0,2 % horizontally of the cross-sectional area of the concrete, both reducing linearly (for thickness exceeding 400 mm) to 0,12 % at 800 mm, after which the areas of reinforcement, both vertically and horizontally, remain constant at 480 mm2 per metre of face; b) for external walls and walls exposed to the weather, provide steel of area at least 0,25 % of the cross-sectional area of the concrete in the exposed face, both vertically and horizontally, up to a maximum of 480 mm2 per metre of face; c) ensure that the spacing of vertical and horizontal reinforcement does not exceed two wall thicknesses, subject to a maximum of 500 mm; and d) provide reinforcement as trimming around openings (see 8.7).
10.15 Walls in which the required area of vertical reinforcement exceeds 0,4 % of the plan area of concrete 10.15.1 The spacing of vertical and horizontal reinforcement should not exceed two wall thicknesses, subject to a maximum of 500 mm. 10.15.2 Ensure that clips are provided for vertical bars at a horizontal spacing not exceeding two wall thicknesses. 10.15.3 The vertical bars are placed inside the horizontal bars. 10.15.4 Vertical bars that are not fully restrained are placed within a centre-to-centre distance of 200 mm from a bar that is fully restrained. 10.15.5 Vertical spacing of clips should not exceed the lesser of 15 times the diameter of the vertical reinforcement and 300 mm. 10.15.6 Preferably, clips of shape code 85, alternately reversed, should be used.
10.16 Walls constructed by means of sliding or climbing shuttering Detailing of walls that are to be constructed by sliding or climbing shuttering is affected by construction techniques that are often unique to the system involved. These techniques, for example, include the use of jacking rods and spacers, are reliant on casting cycles, have separation problems and depend upon a variety of factors that require special detailing and should therefore be planned in conjunction with the contractor. In general, connections to slabs and beams are by means of chases or pockets (or both), since it is not generally feasible to leave splice bars protruding from the walls. Tolerances are such that it is very difficult to ensure that splice bars are fixed at the correct level. Splice bars that
92
SABS 0144 Ed. 2 are to be bent out should therefore be not larger than Y10 or R16. If heavier splices are required and it is not possible to provide pockets of adequate size, consider the use of mechanical splices or casting in anchored steel plates of adequate size to allow for tolerances, to which splice bars can be welded (see figure 69). When sliding shuttering is used for walls, vertical splices should preferably be staggered to ease placing problems and to prevent the displacement of reinforcement during sliding. Placing details should call attention to the adequate wiring together of upper and lower reinforcement.
Figure 69
10.17 Retaining walls There are different types of retaining walls, for example cantilever walls with L, T and reversed L bases, counterforted walls, crib walls and propped and semi-propped walls, each one requiring its own individual reinforcing technique (see figures 70 to 73). However, the same general principles apply to all, the more important of which are as follows: a) so detail the reinforcement as to keep the placing as simple as possible and to minimize difficulties on site, which are often compounded by the conditions under which the work is carried out. In particular, walls should be detailed to suit the method of construction; b) so arrange the distribution of reinforcement (which is governed by design) as to allow for adequate continuity, and stagger laps to avoid abrupt termination of reinforcement; c) carefully control the cover to reinforcement on faces adjacent to earth. This applies especially to faces where concrete is to be cast against excavation, for example in footings where the use of blinding is recommended; d) so detail expansion joints in the walls as to ensure that relative movements of contiguous sections are minimized by the transfer of shear across joints; e) ensure that, at joints, detailing caters for the incorporation of water-bars when required; f) extra reinforcement could be required to meet additional stresses induced by heavy earth compaction and by shrinkage in the wall against the restraint of such compacted earth, especially between counterforts;
93
SABS 0144 Ed. 2 g) provide an area of reinforcement in the compression face of the wall (both vertically and horizontally) of 0,12 % to 0,25 % of the plan area of the wall, depending on exposure. This reinforcement (indicated by a dotted line in figures 70 to 72) facilitates the maintenance in position of main bars during concreting; h) take account of the reduction of effectiveness of reinforcing at corners, especially at re-entrant or opening corners. The inclusion of fillets and splay bars in the case of reversed L bases is recommended; i) in the case of cantilever walls, place the vertical reinforcement in the outer layer to take maximum advantage of the available lever arm; j) ensure that provision is made for the structure above or beyond the wall, where the required information relating to the continuity of the reinforcing has to be provided; k) the radius of bends for the main tensile bars is critical and should be at least 7,5 bar diameters; and l) if problems are encountered in the accommodation of bars at the intersection of the base and wall, consider reducing the bar diameters and increasing the member thickness.
Figure 70
94
SABS 0144 Ed. 2
Figure 71
Figure 72
95
SABS 0144 Ed. 2
Figure 73
10.18 Walls, other than retaining walls, contributing significantly to horizontal stability of a structure, for example tank walls, silo walls, shear walls, core walls Each component requires individual detailing, depending on the relevant design criteria. Generally, however, the methods recommended in the preceding subclauses apply. Because of the effect of horizontal and bursting forces, pay careful attention to the horizontal reinforcement, in particular to bond and lap lengths, lap positions and the staggering of laps, distribution of reinforcement and cover.
96
SABS 0144 Ed. 2 10.19 Walls with corners subject to horizontal bending 10.19.1 Attention is drawn to the fact that the formwork arrangements can affect the reinforcement
details.
10.19.2 A distinction should be made between: a) opening L corners; b) closing L corners; and c) T junctions.
10.19.3 In the case of opening corners, detail the steel as indicated in figure 74 or 75, use diagonal bars equal in area to half that of the main reinforcement and incorporate splays wherever possible (see annex B). NOTE – Vertical U-bars could clash unless detailed to have different heights.
Figure 74
Figure 75
10.19.4 In the case of closing corners, provide an external L bar (see figure 76). Alternatively, use the arrangement recommended above for opening L corners, except that no splay bars are required.
97
SABS 0144 Ed. 2 10.19.5 In the case of T-junctions, use the arrangement shown in figure 77.
Figure 76
Figure 77
10.20 Walls subject to bending forces In the case of walls that will be subjected to bending forces, apply the rules for minimum amounts of reinforcement and for spacing that apply to slabs (see 8.2.3, 8.2.4 and 8.3).
98
SABS 0144 Ed. 2
11 Component detailing — Foundations 11.1 Detailing methods Foundations should normally be detailed diagrammatically in a) plan (see figure 78), or b) elevation (see figure 79). In the case of (a) above, provide a diagrammatic plan that shows the location of the foundation reinforcement as for slabs, and also provide a plan of the starter bars and stirrups, as for columns. Column and wall starter bars and the foundation reinforcement are to be shown on the same placing drawing. In the case of (b) above, provide a diagrammatic elevation that shows the location of the foundation reinforcement, as for beams. NOTE – Cover requirements for foundations are more stringent than for other elements (see 6.1.2).
11.2 Main reinforcement 11.2.1 Minimum diameters For all types of foundations, the diameter of reinforcement other than mesh should be at least 10 mm.
11.2.2 Minimum areas If the projection of the foundation beyond the face of the column or wall exceeds two-thirds of the depth of the foundation, ensure that the foundation is reinforced. The area of high tensile steel reinforcement should be at least 0,1 % of the foundation area in both directions. In the case of continuous foundations where control of shrinkage is important, increase this value in the longitudinal direction to at least 0,25 % of the area of the foundation.
11.2.3 Anchorage It is normal practice to provide at least a nominal square bend (shape code 35) at each end of the main reinforcement. However, in small or shallow foundations, or where high founding pressures develop, the bend length might have to be increased for anchorage purposes.
99
SABS 0144 Ed. 2
Figure 78
100
SABS 0144 Ed. 2
Figure 79
101
SABS 0144 Ed. 2 11.2.4 Columns on edges of foundations To prevent a corbel-type failure (i.e. a shear failure along an inclined plane) if a column is located on the edge of a foundation, it is advisable to provide horizontal U-bars around the starter bar cage, these bars being designed for every such column (see figure 80).
Figure 80
11.3 Combined bases For combined bases, detail both the longitudinal and transverse bars in accordance with the recommendations for beams (see clause 7), but apply more rigorous cover requirements (see 6.1.2).
102
SABS 0144 Ed. 2 11.4 Pile caps Relatively high stresses (especially punching shear and bursting) are normally generated in pile caps because of the high localized forces involved. Depending upon the spacing and layout of the pile group and the thickness of the pile cap, the reinforcement is placed in a combination of a "banded" arrangement (i.e. the reinforcement is concentrated over the piles direct) and a uniformly distributed grid. Provide tension bond lengths at both ends of main bars past the outer edges of the piles. Mechanical anchorage of bars can be incorporated, where advantageous, by the positioning of heavy bars at the inside of bends. Square bends should be held in position vertically by two or three horizontal stirrups of diameter at least 12 mm. Because of difficulties in assembly, closed stirrups should normally not be used in the vertical plane. Detailing should be flexible to allow for the large tolerances inherent in pile construction (i.e. allow generous laps and tolerances).
11.5 Raft foundations For raft foundations, detail both the longitudinal and transverse bars generally in accordance with the rules for slabs and beams. (See also the recommendations regarding cover and stools in 6.1 and 6.2.) In the case of large raft foundations, special consideration might have to be given to the means of support and the maintenance of stability of the top reinforcement.
11.6 Wall foundations 11.6.1 Axially loaded walls Detail foundations and starter bars in the same way as column bases. Starters are commonly in the form of U-bars.
11.6.2 Walls with transverse bending Apply the relevant recommendations given in 10.17 for retaining walls.
11.7 Machine foundations Take special note of the machine maker's specifications. Vibration waves induce tension stresses. Such stresses can occur in unusual directions and places. Therefore ensure that all bond lengths, laps and steel areas are generous.
11.8 Strap beams Because of the high localized loadings involved, the anchorage of the main top reinforcement in a strap beam is critical. Consideration of the possibility of a corbel-type failure as described in 11.2.4 is important and special reinforcement might be needed to prevent its happening. Ensure that the radius of the bend of the top bar is large enough to prevent overstressing of the concrete. For maximum economy, curtail the top steel towards the counterbalancing base. Pay special attention to the problem of accommodation of the reinforcement in the region where the column projects from the base and the resultant difficulties associated with the placing of concrete. Take care to ensure that the main top bars can be fixed, since it is common for the base to be constructed against unexcavated material or against an adjacent structure so preventing the threading in of a top bar that has a return bend at the bottom of its vertical leg. For the method of detailing, see figure 81.
103
SABS 0144 Ed. 2
Figure 81
104
SABS 0144 Ed. 2 11.9 Column starter bars 11.9.1 General Detail column starters generally in accordance with the rules for columns, with due allowance for increased cover underground (see 6.1.2 and 9.5). The number of starter bars need not be the same as the number of column bars (subject to 9.3.3 and 9.3.4).
11.9.2 Positioning Ensure that starter bars are so positioned as to allow the column cage to fit into or over the starter cage (see figure 82). Clearly indicate the relative positions of starter bars and main column reinforcement on the detailing drawings. Take special care where congestion of reinforcement occurs (i.e. if the area of the starter bars is 2 % or more of the area of the column) or where the arrangement of the bars is not symmetrical. Ensure that bars are caged rigidly enough to enable them to retain their shape and position during concreting.
Figure 82
11.9.3 Lengths of starter bars So detail the vertical starter bars as to ensure that a full bond length is provided into the base (see annex D for bond lengths). The effectiveness of a bar in compression that is further than
105
SABS 0144 Ed. 2 approximately four bar diameters beyond the bend is limited. In shallow bases, special details are required to provide the necessary bond. The length of the starter bar projecting into the column should be at least equal to the value for the appropriate bond length given in annex D. Ensure that each vertical bar has a square bend on the bottom to assist in site placing, except in the case of an extremely deep base where the starters can be suspended in position, in which case it is essential to provide adequate support. Where a square bend is provided, the length of the bend should be at least 100 mm or enough to enable the bar to rest on the base mat when so required, and to be tied to the foundation reinforcement. Alternatively, U-bars could be used for starters.
11.9.4 Stirrups Ensure that there are at least three stirrups to maintain starter bars in position. The stirrups can be spaced at 300 mm within the foundation, since the foundation provides adequate restraint, but ensure that temporary stirrups above the base suit the requirements of the column detail (see 9.4). As they interfere with the subsequent positioning of the main cage, it is essential that the temporary stirrups be removed after the base has been cast. Ensure also that the size of the starter cage allows for the specified bending and placing tolerances.
11.9.5 Columns with large moments If the columns will be subjected to predominating moments, the bars can be crossed (see figure 83).
Figure 83
106
SABS 0144 Ed. 2
12 Staircases 12.1 Diagrammatic details Staircases are normally detailed diagrammatically in plan or section. This is best done by arranging the placing detail and bending schedule adjacent to each other on one sheet (see figure 84). Soffits for flights of stairs are often not erected at the same time as floors. In such cases, detail stair splices from floor landings and intermediate landings up and down into the flight, and so dimension their positions that they can be correctly wired into position. The detail should suit construction joints. Two types of stairs are shown diagrammatically detailed in figures 85 and 86, as follows: a) the flight spanning from inner edge to inner edge of landings (figure 85); and b) the flight, together with its landings, spanning from outer edge to outer edge of landings (figure 86).
12.2 Re-entrant corners When tensions in bars meeting at a corner produce a resultant force resisted only by the concrete cover, the bars should be crossed over and anchored on either side of the crossover by a bond length adequate for the stresses in the bars (see bars D and E in figure 84). NOTE – Where the percentage of steel exceeds 0,5 %, refer to corners and cranked beams (see 7.15).
107
SABS 0144 Ed. 2
Figure 84
108
SABS 0144 Ed. 2
..... Figure 85
Figure 86
109
SABS 0144 Ed. 2
13 Welded steel mesh 13.1 Use of mesh Welded steel mesh is generally used for slabs on fill and in roads. It is also used for suspended slabs, walls in buildings, culverts, retaining walls and in any component for which a suitable mesh is obtainable. Major advantages are that site placing time is reduced and good bond characteristics are obtained.
13.2 Types of mesh There are two types of mesh available: a) the standard range in sheets or rolls, as set out in table 15; and b) design mesh, where requirements for wire sizes and spacings could be varied and staggers and bent shapes introduced. Manufacturers might be able to supply mesh of varying sizes and spacings. Wires can be plain or indented. When in doubt as to the best approach, consult a manufacturer before proceeding with details.
13.3 Specifications The requirements for steel mesh are given in annex C and in SABS 1024.
110
6,3 5,6 4,0
4,0 4,0 4,0
312 246 126
042 042 042
1) See SABS 1024. The reference number is the nominal mass of the mesh, in kilograms per square metre × 100. 2) These meshes are also available in standard rolls of 60 m × 2,4 m, but see also 13.5.6.
NOTE – The standard sheet size of all mesh is 6 m × 2,4 m.
300 300 300
2,45 1,93 1,00
0,33 0,33 0,33
1,22 0,96 0,96
2,78 2,26 1,33
4,33 3,41 2,89
100 100 100
6,3 5,6 5,6
3,11 2,45 1,93
2782) 2262) 1332)
7,1 6,3 5,6
156 123 123
100 100 100
433 3412) 2892) 396 312 246
7,72 6,55 5,17 1,55 1,55 1,22 6,17 5,00 3,95 197 197 156
786 636 503
7,1 7,1 6,3
10,0 9,0 8,0
200 200 200
100 100 100
772 655 517 200 200 200
3,11 2,45 1,93 1,00 1,55 11,22 0,96 0,50 1,55 1,22 0,96 0,50
197 156 123 063
197 156 123 063
7,1 6,3 5,6 4,0
7,1 6,3 5,6 4,0
200 200 200 200
6,17 5,00 3,95 3,08 2,50 1,97
3,08 2,50 1,97
393 318 251
393 318 251
200 200 200 200
10,0 9,0 8,0
311 2452) 1932) 1002)
10,0 9,0 8,0
200 200 200
200 200 200
kg/m2
Cross
Longitudinal
Cross
Longitudinal
Total nominal mass per unit area
10
617 500 395
Cross
kg/m2
9
mm2/m of width
8 Nominal mass of wires per unit area
7
Nominal cross-sectional area of wires
6
Cross
Longitudinal
mm
5
mm
4 Nominal diameter of wires
3
Centre-to-centre spacing of wires
2
Longitudinal
Mesh reference1)
1
Table 15 — Standard meshes (see also annex C)
SABS 0144 Ed. 2
111
SABS 0144 Ed. 2 13.4 Mesh placing drawings 13.4.1 Slabs To indicate the placing of sheets in position, represent each sheet on the plan layout by a single-line rectangle with one diagonal line on which the sheet mark is shown (see figure 87). The size of the rectangle is the overall size of the sheet, and, since the sheets normally overlap, so do the rectangles. The lap should be dimensioned or stated in the notes. Where a sheet might be placed the wrong way round (e.g. a square sheet with longitudinal wires and cross-wires of different diameters), show the direction, diameter and spacing of the longitudinal wires on the sheet concerned. The direction of the longitudinal bars is indicated by the symbol:
.
So detail sheets that a minimum number of layers occur at laps and at the intersection of sheet corners. Show the sheet placing sequence to achieve this. The detail is best achieved by using overhangs (flying ends) or loose bars. To avoid confusion, show top and bottom mesh on separate layouts. Top mesh marks should be prefixed by the letter T, and bottom by the letter B. Bear in mind that bottom mesh is generally placed before, and top mesh after, the electrical contractor has positioned his conduit. In two-way slabs where both dimensions exceed the maximum width of the available sheets, in order to avoid lapping of mesh in one direction, use two layers so placed that the main longitudinal wires of each layer are at right angles to each other (see figure 87). Do not use draped sheets except in the topping of ribbed slabs where the centre-to-centre distance between ribs does not exceed 1,2 m (see figure 88).
13.4.2 Walls and other components Show mesh for walls and other components in plan or elevation by a rectangle and diagonal line as in figure 87. Use separate layouts for mesh in different faces if the arrangement of the sheets in the faces is different.
13.4.3 Mesh as stirrups for column and beam cages The assembly details of mesh as stirrups for column and beam cages are normally incorporated in a combined assembly/bending schedule on a component basis.
112
SABS 0144 Ed. 2
..
Figure 87
Figure 88
113
SABS 0144 Ed. 2 13.5 Scheduling of mesh Examples of schedules for mesh are given in figure 89.
13.5.1 Tolerances Manufacturers' tolerances on sheet and roll sizes are ± 25 mm on lengths and widths not exceeding 6 m, and ± 5 % in all other cases.
13.5.2 Drawings Where possible, do not list mesh on the same schedule as bar reinforcement. Where mesh and bars occur in a single component (for example slabs with holes to be stitched; column and beam cages), the schedule should cover all the reinforcing steel for the component. It is to be noted that mesh and reinforcing bars are often fabricated in different workshops.
114
SABS 0144 Ed. 2
Figure 89
115
SABS 0144 Ed. 2 13.5.3 Standard mesh (see table 15) Ensure that the following information is given on each schedule that covers standard mesh: a) the number of sheets; b) the length of the longitudinal wires; c) the length of the cross-wires; d) whether in sheets or in rolls (see also 13.5.5 and 13.5.6); and e) whether the wires are to be plain round or indented. NOTE – Indented wire is available down to a nominal diameter of 5,6 mm.
13.5.4 Non-standard mesh (see figure 90) Ensure that the following information is given on each schedule that covers non-standard mesh: a) the number of sheets; b) the diameter, number and spacing of wires in direction L; c) the diameter, number and spacing of wires in direction B; NOTES 1 Wires in direction L can be spaced in steps of 50 mm from a minimum spacing of 100 mm. 2 Wires in direction B can be spaced in steps of 50 mm from 100 mm to 300 mm. 3 Spacing can vary in both directions within any one sheet such that the spacing is either the normal value or twice the normal value. 4 The diameter of the larger of the wires should not normally exceed twice that of the smaller.
d) the length of the wires in direction L; e) the length of the wires in direction B; NOTES 1 Dimension B should not exceed 2,4 m. 2 It is recommended that dimensions L and B be exact multiples of the relevant spacing, since sheets of these dimensions are the most economical to produce.
f) whether in sheets or in rolls (see also 13.5.6); g) whether the wires are to be plain round or indented; NOTE – Indented wire is available down to a nominal diameter of 5,6 mm.
h) whether the ends are to be staggered or not, and, if relevant, the extent of the stagger; and NOTE – Wires should be staggered in direction L only.
116
SABS 0144 Ed. 2 i) the overhang (flying ends). NOTE – Unless otherwise specified, the wire ends will project by one-half of the spacing module beyond the outer intersection wire. This projection is referred to as "overhang". Ensure that any overhang that is specified is in 25 mm steps and is at least 25 mm. At laps, specify enough overhang to avoid clashing of transverse bars and also to achieve adequate bond.
Figure 90
13.5.5 Sheet size Because of transportation and handling difficulties, sheets should not exceed a final width of 2,4 m and an overall length of 6 m. Manufacturers might be able to supply wider and longer sheets.
13.5.6 Rolls Heavy mesh that has main wires of diameter exceeding 5,6 mm should not be ordered in roll form since it is difficult to lay flat after unrolling. In general, the use of rolls causes problems in straightening and rolls should therefore be specified with caution (see table 15).
117
SABS 0144 Ed. 2 13.6 Bending of mesh 13.6.1 Preferred shapes Because of the volume they occupy, do not bend mesh sheets into large, hollow core shapes. For transportation purposes, L-shaped or V-shaped sheets can be nested. Column cages have their bars inserted in the yard and are therefore suitable for transporting. Beam cages can be assembled in two ways: a) as open stirrups, the clips being added on site (and the cages delivered nested); and b) as closed cages with bars in position, designed to fit clear between column faces, the splice bars being added on site (see figure 23).
13.6.2 Permissible shapes Mesh can be bent in one direction only and should be bent only to simple shapes. As bending of mesh is a factory operation, do not specify site bending. Shapes that could be used are the following (see annex A): shape codes 34; 35; 37; 38; 41; 45; 48; 49; 52 (open); 54; 55; 60; 73. The length of a bend or of a hook is normally at least 100 mm.
13.6.3 Limitations of bending The maximum width of the average bending machine is 5 m. Bending on the weld is permissible, provided that the cross-wire is inside the bend. For other positions of the bend relative to adjacent cross-wires, where the cross-wire is within 100 mm of the bend, consult the manufacturers. Closed shapes such as shape code 60 are not always practicable but this should be checked with the supplier. For any U-shape, the parallel legs of the U should not be closer than 100 mm.
13.7 Galvanized mesh It may be desirable to use galvanized mesh in precast work. Before specifying it, check the size limitations of the galvanizing plant and also whether passivation of the zinc will be necessary.
13.8 Lapping Use the same lap distances as for reinforcing bars, with no reduction in the bond distance for the cross-wires. The lap distance will normally not be less than the cross-wire spacing. Do not lap mesh at points of maximum stress. Nominal reinforcement to control cracking should have full tension laps (see table 16 for bond and lap distances).
118
4
1 2 3
43
20
28
30
40
40
36
30
34
46
20
30
36
40
54
20
42
38
40
30
44
or 25 d + 150 mm, or 300 mm, whichever is the greatest.
-
-
-
-
-
-
140
170
220
150
180
230
4,0
4
160
190
240
170
200
260
200
240
300
210
250
320
180
210
270
190
230
290
230
260
340
240
280
370
6,3
200
240
310
210
260
330
260
300
380
270
310
410
7,1
mm
220
270
340
240
290
370
290
340
430
300
350
460
8
Diameter of mesh wire
11
360
420
540
380
440
580
250
310
390
270
320
410
280
340
430
300
360
460
36
42
54
38
44
58
44
52
68
47
56
72
Length required (in diameters)1)
Plain wire or bars
10
10
Indented wire or bars
320
380
490
340
400
520
9
9
-
-
-
-
-
-
300
300
300
300
300
300
4,0
12
13
14
15
300
300
300
300
300
320
300
300
380
300
310
400
5,6
16
310
310
310
310
310
370
310
330
430
310
350
450
6,3
330
330
380
330
330
410
330
370
480
330
400
510
7,1
mm
350
350
430
350
350
460
350
420
540
380
450
580
8
Diameter of mesh wire
mm
8
mm
7 Minimum lap length
6 Minimum bond length
5,6
5
Figures for "length required (in diameters)" have been rounded off, as have equivalent bond and lap lengths derived from those values. The table is based on mesh of characteristic strength 450 MPa except for link reinforcement, which has a characteristic strength of 425 MPa. The mesh is assumed to be of a) smooth round bars or wire, or b) indented round bars or wire (25 % increase in bond stress). No reduction in bond lengths has been allowed for in the table for the anchorage values of bends and hooks. (These values are given in 6.4.4.)
NOTES
1)
Shear (mesh in the form of stirrups)
Tension
Shear (mesh in the form of stirrups)
58
30
Length required (in diameters)1)
3
20
Concrete class
Stress classification
Tension
2
1
Table 16 — Minimum bond and lap lengths for fully stressed mesh
380
380
490
380
400
520
400
470
610
420
500
650
9
17
400
420
540
400
440
580
440
520
630
470
560
720
10
18
SABS 0144 Ed. 2
119
SABS 0144 Ed. 2
14 Detailing with respect to aqueous liquid retaining structures 14.1 General principles In addition to all normal requirements, aqueous liquid retaining structures should be designed to have a low probability of leakage. Great care needs to be taken with detailing, to ensure that dense solid concrete can be placed. Any congestion of steel that prevents this should be avoided. The specification and detailing of all expansion, contraction and construction joints are necessary to prevent leakage at joints and special attention should be given to intersections of joints.
14.2 Causes of cracking 14.2.1 In immature concrete Setting of concrete is associated with a rise in temperature caused by cement hydration. With a subsequent fall in temperature, the concrete shrinks, setting up internal tensions in concrete where freedom of movement is restrained, leading to cracking in the hardened concrete structure. Further shrinkage takes place as the concrete dries out, adding to the internal tensions.
14.2.2 In mature concrete 14.2.2.1 Loading of the structure causes tensile stresses because of bending or axial tension. 14.2.2.2 Temperature and moisture changes, both seasonal and diurnal, can cause additional tensile stresses.
14.2.3 Other causes Other causes of cracking include a) any abrupt change in thickness of structure, b) free ends of reinforcement within a structure, c) re-entrant corners in elements such as the slab and the walls, and d) penetrations through structure by pipes and access hatches.
14.3 Detailing to minimize effects of cracking 14.3.1 Minimum reinforcement Direct tension cracking caused by thermal and shrinkage movement differs radically from the mechanism that causes flexural cracking. After the formation of the initial crack, all further cracks are influenced by the reinforcement. Provided that the reinforcement across the cracks does not yield, the contraction of the concrete at both sides of the crack is restrained by the reinforcement.
120
SABS 0144 Ed. 2 BS 8007 recommends the minimum cross-sectional area of reinforcement to ensure that the steel does not yield at a crack, as being 0,35 % using grade 450 steel or 0,64 % using grade 250 steel based on 35 MPa concrete. Where closely spaced movement joints (typically at 5 m to 6 m centres) allow for complete freedom of movement, this minimum steel can be reduced to two-thirds of the above figure. Note that freedom of movement can differ in different directions. If reinforcement does not yield, the crack width is a function of the diameter of bar and the total amount of steel. Therefore, unless small diameter bars at close centres are used, more steel than the above minimum might be necessary. The amount of steel mentioned above is related to a "surface zone" and only the surface zone needs to be reinforced. For definition of surface zones, see figures 91 and 92. In walls of thickness less than 200 mm, the minimum steel for both zones can be placed in one layer.
14.3.2 Reinforcement to counter the effects of external loading Reinforcement size, spacing and cover will be specified by the designer, taking into account the loads and design crack widths. The detailer should be aware that ultimate anchorage bond stresses for horizontal bars in direct tension according to BS 8007 are 0,7 times the values obtained for nonaqueous liquid retaining structures. The bond and lap lengths required will be 1,43 times the values in annex D for bars stressed to the maximum allowable. In order to maintain small crack widths, the designer might have worked to lower stresses in the steel than the maximum allowable, in which case some lesser anchorage and lap lengths could be applicable. The detailer should agree with the designer what lap and anchorage lengths are applicable.
14.3.3 Openings and corners in slab or walls The rules applicable to openings should be modified by allowing 1,5 times as much trimming steel as that given in 8.7. Care should be taken in thin walls, to ensure that diagonally placed bars do not interfere with the placement of concrete in the very critical position below openings. If the diagonal bars cannot be placed without interfering with concreting, use additional framing steel parallel to the sides of the opening. Stagger discontinuous trimming bars to avoid causing a stress raiser where all bars stop at one position.
Figure 91
121
SABS 0144 Ed. 2
Figure 92
14.3.4 Junctions of walls with other walls or with floor slabs Junctions of walls with other walls or with floor slabs are typically opening corners and normally occur at the most highly stressed places in the wall. The detail of figure 74 or 75 is to be used, depending on the reinforcement layout of the member in which the starter bars are to be anchored. In all cases, bars should be anchored as deeply as possible into the anchoring structure. Therefore, in a junction of two walls with vertical bars placed inside horizontal bars, the detail of figure 74 is preferable while with vertical bars placed outside of horizontal bars, the detail of figure 75 is preferable. The detail of figure 77 is acceptable only in the case where the horizontal steel in the through-wall is placed outside the vertical steel. If the through-wall horizontal steel is inside the vertical steel, then a detail using vertical U-bars for the intersecting wall starters is preferable. Starter bars for walls off floor slabs are different in the two orthogonal directions, depending on the relative positions of the floor slab reinforcement to enable starter bars to be anchored in the bottom layer of the slab reinforcement. All of the above give rise to stress raisers at the end of the starters and splicing bars. Consideration should be given to staggering laps by half of the lap length, to reduce the effect of the stress raiser.
122
SABS 0144 Ed. 2 14.4 Cover The nominal cover of concrete for all steel, including stirrups, link, sheathing and spacers, should not normally be less than 40 mm. Greater cover might be needed at a face in contact with aggressive soils or if subject to erosion or abrasion. In thin sections where it is not possible to achieve a 40 mm cover, a higher cement content or special reinforcement should be used.
14.5 Joints The position of all joints, whether movement or construction joints, is to be shown on the drawings.
14.5.1 Construction joints Full structural continuity is assumed in design at a construction joint. Reinforcement across the joint is fully continuous, and cracking at the joint is controlled by the use of reinforcement. Vertical joints should be cast against stop ends. The concrete in the earlier pour should be properly prepared prior to casting of the later pour in accordance with the requirements of BS 8007. It is not necessary to incorporate waterstops in properly constructed joints but these should be considered where supervision of construction cannot be guaranteed.
14.5.2 Movement joints Typical movement joints are shown in figure 93. The details of interconnections of different types of waterstops at joint junctions should be clearly indicated on the drawings.
123
SABS 0144 Ed. 2
Figure 93
124
SABS 0144 Ed. 2
15 Detailing of steel reinforcement for post-tensioned concrete slabs 15.1 General principles Post-tensioned concrete slabs can comprise either concrete slab panels supported on walls or beams or concrete flat slabs supported on columns. In both cases, the normal requirements for reinforcement detailing apply, the principal differences being: a) the relatively small amount of reinforcement required; b) the thinness of slabs relative to spans; c) the importance of accurately profiling post-tensioning tendons and the requirement of maintaining them in position; and d) the detailing at post-tensioning anchors to counteract bursting forces.
15.2 Causes of cracking The causes of cracking in post-tensioned concrete slabs are similar to those outlined in 14.2. Further causes of cracking are as follows: a) greater likelihood of cracking in immature concrete because of low amounts of reinforcement; b) restraint cracking arising from the restraint to movement offered by a stiff vertical support structure under the action of both shrinkage, creep, temperature and elastic shortening; NOTE – The effects of elastic shortening can be largely eliminated by disconnecting the slab from rigid vertical supports during stressing of the slabs.
c) cracking arising from the termination of post-tensioning tendons at positions internally in the slabs; and d) cracking owing to concentrated forces at anchorages.
15.3 Detailing to minimize effects of cracking 15.3.1 Minimum reinforcement for flexure Minimum reinforcement is specified by the designer to counter the effects of tensile stresses that are in excess of the tensile capacity of the concrete, particularly in zones of peak tensile stress such as the negative moment regions over column supports. The limits of concrete tensile stress and the corresponding areas of reinforcement required are specified in the relevant codes of practice. In addition, some codes of practice specify minimum areas of reinforce-ment to counteract the possibility of catastrophic collapse arising from the loss, from whatever cause, of post-tensioning tendons.
15.3.2 Reinforcement for shrinkage In post-tensioned flat slabs, tendons are provided in both directions and will override the normal minimum percentage of reinforcement required for counteracting shrinkage and thermal stresses.
125
SABS 0144 Ed. 2 Consequently, minimum levels of reinforcement or mesh (or both) provided in post-tensioned slabs are frequently below 0,12 % unless otherwise required, as mentioned in 15.3.1.
15.3.3 Shear reinforcement Shear reinforcement is frequently required in post-tensioned flat slabs at internal and external column positions. It most often takes the form of stirrup reinforcement, which should be carefully detailed and positioned in a manner similar to that for shear reinforcement in reinforced concrete slabs. Structural steel cruciform beams, specially welded reinforcement cages or patented type shear reinforcement studs recently developed in the USA, are sometimes also used for shear reinforcement purposes at column heads. Careful detailing is particularly necessary because of the presence of post-tensioning tendons and the occurrence of anchorages at external column supports (see figure 94).
Figure 94
126
SABS 0144 Ed. 2 15.3.4 Reinforcement at external anchorages Reinforcement is required at external anchorages, to withstand localized bursting forces. The recommended minimum amounts and distribution of the reinforcement are illustrated in figure 95. This is the recommendation of the Post-tensioning Institute in the USA and has been derived from tests. NOTE – In figure 94, detailers should check that the detail is consistent with specialist design.
Figure 95
15.4 Tendon profiling and positioning Tendon profiling is a detailing function in that tendons are supported on reinforcement stools similar to stools used for reinforced concrete. Accurate detailing of stools is necessary for the following reasons: a) accurate maintenance of the profile is critical for realizing the assumptions made in design; b) the difficulty of profiling and retaining the tendon in position within the depth of a thin slab; and c) the tendency for tendons to be disturbed during the concreting process. Stools are more effective when designed and detailed to be anchored to the bottom mat of reinforcement.
127
SABS 0144 Ed. 2 In post-tensioned flat slabs, tendons are invariably banded in one direction and distributed evenly in the other. This positioning of tendons should also be considered by the reinforcement detailer. See figure 96.
Figure 96
15.5 Cover The requirements of minimum cover for reinforcement and tendons are the same as those applicable to reinforced concrete for both corrosion and fire protection. The inter-relationship of draping tendons in two directions together with fixing reinforcement in two directions should be considered. A recommended fixing system is illustrated in figure 97, where the lower-most tendon is fixed in the B2 layer and the uppermost tendon is in a third layer above it. Similar layering applies in the areas of top reinforcement.
128
SABS 0144 Ed. 2
Figure 97
15.6 Joints Specifying and detailing of control joints and construction joints are necessary because of the greater sophistication of the system and its corresponding lesser degree of flexibility in construction operations.
129
SABS 0144 Ed. 2
Annex A
(informative)
Shape codes
130
SABS 0144 Ed. 2
Annex B (informative)
Additional information on corners and cranked beams B.1 Changes in angle Because a change in direction of a force requires the application of an equilibrating force, special attention is required in detailing changes in angle in members (see figures 32 and 33). It can be seen that, in the case of an opening corner, the forces needed for equilibrium cause tension across the member (see figure 32), whereas in the case of closing corners, compression is caused (see figure 33). Concrete is able to resist compressive stresses, but even in the case of closing corners, the compressive stresses could be excessive and the radii of tension bars should be at least 7,5 bar diameters. Tests have shown that the strength of opening corners can be very low. This is owing to the fact that some common details do not provide for the equilibrium of the joint, and even where the primary forces are taken care of, secondary stresses can cause premature failure. Figure B.1 shows that, for an elastic model, tensile stresses tend to cause splitting in two places as shown in figure B.2. Tests on reinforced specimens have shown similar cracks. To prevent failure, it is therefore necessary to provide reinforcement across the cracks.
Figure B.1
131
SABS 0144 Ed. 2
Figure B.2
B.2 Methods of reinforcing opening corners Figure B.3 shows four methods of reinforcing opening corners. Figure B.3(a) shows a standard method of reinforcing square corners. This method is, however, only 40 % efficient; in other words, the joint will fail at a load of less than 40 % of the load that will cause the member to fail. The method shown in figure B.3(b) is not much better. A slightly better method of reinforcing square corners than that shown in figure B.3(c) is the use of several tie bars as in figure 36. However, it can be seen that, unless a splay is provided, the cover at the corner becomes very small for a reasonable radius of bar.
132
SABS 0144 Ed. 2
Figure B.3
B.3 Methods of improving strength of opening corners There are three methods of improving the strength of opening corners, it being necessary to use more than one method in certain cases. The methods are: a) the provision of additional splay reinforcement as in figure B.4; b) the provision of additional splay reinforcement as in (a) above, and a splay corner (see figure B.6); and c) the provision of extra reinforcement across the corner as in figure B.5. The methods shown in figure 35 and in figure B.6 have been strongly recommended by Swedish authors, the splay steel area being one-half of the main steel area.
133
SABS 0144 Ed. 2
Figure B.4
Figure B.5
Figure B.6
134
SABS 0144 Ed. 2
B.4 Reinforcement less than 1 % Where the area of reinforcement is less than 1 % of the beam area, the use of a detail as shown in figure 34 (the splay steel being equal in area to 50 % of the main steel) is probably quite adequate.
B.5 Reinforcement more than 1 % If the area of reinforcement is more than 1 % of the beam area, transverse steel as well as splay steel should be provided, and the provision of a splay is very desirable.
B.6 Looped reinforcement Where U-bar reinforcement is used, as in figure 36, it should be noted that very high crushing stresses inside the loop can cause premature failure. The CEB-FIP recommendations state that the radius of the loop be not less than (0,35 + 0,70 Db/Da) Fy/Fcu × Db (see figure B.7) where Db
is the bar diameter, in millimetres;
Da
is the distance from the plane of the loop to the surface, in millimetres;
Fy
is the characteristic steel strength, in megapascals; and
Fcu
is the concrete cube strength, in megapascals.
For a class 25 concrete with a 50 mm cover, the required diameters of loops are given in table B.1. Table B.1 — Required loop diameters Dimensions in millimetres 1
2
Bar diameter
Loop diameter
20 25 32 40
455 600 920 1 310
NOTE – Class 25 concrete, 50 mm cover.
135
SABS 0144 Ed. 2
Figure B.7
B.7 Junction of beams and columns B.7.1 Single junction A junction of a single beam with a column can be considered as a combination of an opening corner and a closing corner. For this reason, the detail shown in figure B.8 is poor since it is similar to that shown in figure B.3(b), which is quite inefficient. If it is essential to use this detail, extra steel should be provided (see figure 40). If the steel is bent down, care should be taken. A full tension lap bond length should be provided below the end of the curved section, and below half-beam depth, especially at haunches of portal frames (see figure B.9).
Figure B.8
136
SABS 0144 Ed. 2
Figure B.9
B.7.2 Double junction At a double junction of beams with columns, it is common practice to carry the beam steel through and not to bend it down into the columns. This is perfectly satisfactory when the characteristic live load does not exceed the characteristic self-weight load. However, where considerable moments (say more than 33 % of the total) are transmitted into the columns, it might be necessary to bend reinforcement from the column into the beam (see figure B.10). Because the bars pass through the column, this requires very careful detailing.
Figure B.10
B.8 Cranked beams B.8.1 Deflection angle less than 30° Where the deflection angle at a corner is less than 30°, the method of detailing should be as shown in figure B.11.
137
SABS 0144 Ed. 2 To make placing of reinforcement easier, it is common practice to use an odd number of bars on one side and an even number of bars on the other side. Conditions at the corner are such that the compressive forces in the beams are not balanced, and therefore stirrups should be provided to balance, say, 50 % of the resolved force. The total area of stirrups required is then equal to the main steel area multiplied by sin (A/2), where A is the deflection angle.
Figure B.11
B.8.2 Deflection angle between 30° and 45° Where the deflection angle is between 30° and 45°, a splay with splay reinforcement should be used, as for 90° corners (see figure 37). However, in such a detail, the congestion of the reinforcement at the corner is considerable. For this reason, the detail shown in figure B.12 could be considered, but this detail can be dangerous if the stirrup reinforcement is displaced or inadequately bonded. It should be noted that the stirrups at the corner are required to take all the force component from the main reinforcement and that the cover at the corner is reduced because of the large radius of the reinforcement. Because the stirrups in figure B.12 could be difficult to hold in position during concreting, it might be better to use the detail shown in figure 38. Here the stress condition at the corner is less severe than for figure B.12 because the stirrups are smaller, and bond is less of a problem. There is no problem with cover, and the dimensioning of the stirrups is easier.
Figure B.12
138
SABS 0144 Ed. 2 B.8.3 Deflection angle between 40° and 90° Where deflection angles are between 40° and 90°, the detail used for 90° corners can be used. The recommended detail is a splay with stirrups and splay reinforcement (see figure 36).
B.9 Closing corners Although closing corners are stronger than opening corners, main tension bars should have adequate radii to reduce compressive stresses. In addition, extra reinforcement should be supplied in the corners where the stirrups of the beam and column are stopped off (see figure 41). If stresses are high, steel should be provided across the potential crack which runs from the inside of the bend in the reinforcement, as shown in figure B.13. The section should be checked to ensure that the steel can be accommodated.
Figure B.13
139
SABS 0144 Ed. 2
Annex C (informative)
Steel reinforcement C.1 Steel bars for concrete reinforcement (see also SABS 920) C.1.1 Mild steel Hot rolled mild steel bars of plain round cross-section, minimum yield stress 250 MPa. The yield stress of the bar should not exceed 400 MPa. Hot rolled mild steel deformed bars (not generally available), of minimum yield stress as above.
C.1.2 High tensile steel Hot rolled high tensile steel deformed bars, of minimum yield stress 450 MPa, or of a minimum 0,20 % proof stress. The ultimate tensile strength of the bar should be at least 15 % greater than the yield stress or 0,2 % proof stress determined by the test.
C.2 Size and availability of steel bars C.2.1 Generally available ex stock Round mild steel: 8 mm, 10 mm, 12 mm, 16 mm, 20 mm, 25 mm, 32 mm. High tensile steel deformed bars (450 MPa): 10 mm, 12 mm, 16 mm, 20 mm, 25 mm, 32 mm.
C.2.2 Available but not generally held in stock Round mild steel: 6 mm, 40 mm, 50 mm. High tensile steel: 8 mm wire (that does not comply with SABS 920).
C.2.3 Length The maximum length of reinforcing bars available ex stock is 13 m.
C.3 Deformations C.3.1 High tensile steel deformed bars manufactured in South Africa have the following patterns: a) two diametrically opposite longitudinal ribs, with "herring bone" pattern deformations on either side of the ribs; and b) two diametrically opposite longitudinal ribs in a spiral form, with inclined deformations in the same direction on either side of the ribs (cold twisted bars).
140
SABS 0144 Ed. 2 C.3.2 Mild steel deformed bars manufactured in South Africa have the following patterns: a) two diametrically opposite longitudinal ribs, with inclined deformations in the same direction on either side of the ribs; and b) herring bone pattern as in C.3.1(a). NOTE – Mild steel bars can also be patterned. Deformations are not necessarily indicative of high tensile steel.
C.4 Welded steel mesh for concrete reinforcement (see also SABS 1024) C.4.1 Proof stress and tensile strength When tested in accordance with 6.2.2(a) of SABS 1024, the proof stress (at 0,43 % total elongation under load) of the wires in the mesh should be at least 485 MPa and the tensile strength should be at least 510 MPa. In addition, either the tensile strength should be at least 5 % higher than the yield stress recorded during the tensile strength test or the elongation should be at least 12 % when measured on a gauge length of 5,65 So , where So is the initial cross-sectional area of the test piece.
C.4.2 Indented wire Indentations should be as described in BS 4482, Hard drawn mild steel wire for the reinforcement of concrete.
141
142
Compression
Tension
Compression
31
27
24
20
46
39
37
29
33
29
26
22
30
40
20
25
30
40
20
25
30
40
29
40
25
34
30
20
39
25
9
10
8
10
175 215
210 260
235 290
265 330
230 290
290 365
315 390
365 455
160 195
190 235
215 265
245 305
235 290
270 340
315 395
360 445
12
260
310
350
395
345
435
470
545
235
285
320
365
350
405
470
535
345
415
465
525
460
580
625
725
315
375
425
485
465
540
630
715
16
mm
430
520
580
655
575
725
780
910
390
470
530
610
580
675
785
890
20
Diameter of bars
25
625
750
845
970
925
1 080
1 255
535
645
725
820
720
910
975
685
830
925
1 050
920
1 160
1 245
1 135 1 450
490
585
660
760
720
845
980
1 115 1 425
32
11
12
13
14
16
17
18
27
33
36
41
43
55
59
68
25
30
33
38
38
44
51
58
Length required (in diameters) 8
3001)
1)
410 360 325 3001)
3001) 3001) 3001)
430
545
585
330
345
435
470
545
680
3001)
3001) 300
380 330
305
375
440
510
580
10
3001)
300
355
410
465
20
25
320
390
435
495
515
655
700
32
390
470
530
610
600
705
490
585
660
760
750
610
735
825
950
940
880 1 100
430
520
580
655
690
535
645
720
670
810
900
820 1 025
860 1 075
870 1 090 1 360
935 1 165 1 460
855
1 035
1 155
1 310
1 375
1 740
1 865
2 175
780
940
1 060
1 215
1 200
1 05
815 1 020 1 275 1 630
925 1 160 1 450 1 850
16
820 1 090 1 360 1 700
3001)
355
400
455
450
530
615
695
12
mm
Diameter of bars
19
Technical corrigendum 1, Dec. 1995 15
1 The values of lap lengths for top bars are valid for elements of depth exceeding 300 mm (see table 24 of SABS 0100-1). 2 In the case when concrete cover is less than twice the bar size, 4.11.6.6.3 (increased lap lengths) of SABS 0100-1 applies. 3 Extra stirrups might be required for laps in compression (see 4.11.4.5.1 of SABS 0100-1).
NOTES
1) The minimum required value.
Plain round mild steel (250 MPa)
High yield deformed steel (450 MPa)
Tension
8
mm
7
mm
6 Lap lengths for top bars and compression laps
5
Anchorage and lap lengths for bottom bars
Length required (in diameters)
45
Concrete class
Stress classification
Steel type
4
20
3
2
1
Table D.1 — Minimum bond and lap lengths for fully stressed bars
SABS 0144 Ed. 2 (Technical corrigendum December 1995)
(informative)
Annex D
Table of bond and lap lengths for fully stressed bars
SABS 0144 Ed. 2 (Technical corrigendum June 1998)
Annex E (informative)
Tables of the area and mass of reinforcing bars Table E.1 — Area 1
2
3
4
5
6
7
8
Tech. corr. 3 1998
9
10
11
12
13
300
350
400
450
500
Area of steel per metre mm2
Bar diameter
Bar spacing
mm
mm 75
100
125
150
175
200
250
8 10 12
672 1 048 1 508
503 785 1 131
402 628 908
336 524 754
288 488 646
251 393 565
201 314 452
168 262 377
144 244 323
126 196 283
112 175 251
101 157 226
16 20 25 32
2 680 4 188 6 344 10 724
2 011 3 142 4 909 8 042
1 608 2 514 3 926 6 434
1 340 2 094 3 272 5 362
1 148 1 796 2 804 4 596
1 005 1 571 2 454 4 021
804 1 257 1 963 3 217
670 1 047 1 636 2 681
574 898 1 402 2 298
503 785 1 227 2 011
447 698 1 091 1 787
402 628 982 1 608
8 & 10 10 & 12 12 & 16
860 1 276 2 096
644 958 1 571
516 766 1 256
430 638 1 048
368 548 898
322 479 785
258 383 628
215 319 524
184 274 449
161 240 393
143 213 349
129 192 314
16 & 20 20 & 25 25 & 32
3 436 5 368 8 636
2 576 4 025 6 476
2 060 3 220 5 180
1 718 2 684 4 318
1 472 2 300 3 700
1 288 2 013 3 238
1 030 1 610 2 590
859 1 342 2 159
736 1 150 1 850
644 1 006 1 619
572 894 1 439
515 805 1 295
Table E.2 — Mass and area 1
2
3
4
5
6
7
Bar diameter
Mass per unit length
mm
kg/m 1
2
3
4
5
8 10 12
0,395 0,617 0,888
50 79 113
101 157 226
151 236 339
201 314 452
251 393 565
16 20 25
1,58 2,47 3,85
201 314 491
402 628 982
603 942 1 473
804 1 257 1 963
32 49 50
6,31 9,86 15,40
804 1 257 1 963
1 608 2 513 3 927
2 413 3 770 5 890
3 217 5 027 7 854
8
9
10
6
7
8
302 471 679
352 550 792
402 628 905
1 005 1 571 2 454
1 206 1 885 2 945
1 407 2 199 3 436
1 608 2 513 3 927
4 021 6 283 9 817
4 825 7 540 11 781
5 630 8 796 13 744
6 434 10 052 15 708
Area mm2 Number of bars
sabs pta (pdf)
143
