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AS 3600 Supplement 11994

Concrete structuresCommentary

(Supplement to AS 36001994)

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This Australian Standard was prepared by Committee BD/2, Concrete Structures. It

was approved on behalf of t he Council of St andards Australia on 27 July 1994 and

published on 10 October 1994.

The following interests are represented on Committee BD/2:

Association of Consulting Engineers, Australia

Australian Construction Services

Australian Federation of Construction Contractors

Australian Precast Concrete Manufacturers Association

AUSTROADS

Bureau of Steel Manufacturers of Australia

Cement and C oncrete Association of Australia

CSIRO, Division of Building, Construction and Engineering

Department of Public Works, N.S.W.

Hydro-electric Commission, Tas.

Institution of Engineers, Australia

Master Builders Construction and Housing Association, Australia

National Ash Association of Australasia

National Ready Mixed Concrete Association

Steel Reinforcement Institute of Australia

South Australian Department of Housing and Construction

University of Adelaide

University of New South Wales

University of Sydney

University of Technology, Sydney

Water BoardSydney, Illawarra and Blue Mountains

Review of Austr alia n Standa rds. To keep abreast of progress in industry, Australian Standards are subjectto periodic review and are kept up to date by the i ssue of amendments or new editions as necessary. It isimportant t herefore t hat Standards users ensure that they are i n possession of t he latest edition, and anyamendments thereto.

Full details of all Australian Standards and related publications wil l be found in t he Standards AustraliaCatalogue of Publications; this information is supplemented each month by the magazine The AustralianStandard, which subscribing members receive, and which gives details of new publications, new editionsand amendments, and of withdrawn Standards.

Suggestions for improvements t o Australian Standards, addressed to the head office of Standards Australia,are welcomed. Notification of any inaccuracy or ambiguity found in an Australian Standard should be made

without delay in order that the matter may be investigated and appropriate action taken.

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AS 3600 Supp11994

AS 3600 Supplement 11994

Concrete structuresCommentary

(Supplement to AS 36001994)

AS 3600 Supplement 1 first published in part asSAA M P28.C4 1975.

SAA MP28.C6 first published 1977.SAA MP28.C9 first published 1975.SAA MP28.C10 fi rst published 1975.SAA MP28.C11 fi rst published 1977.SAA MP28.C12 to C15 first published 1977.SAA MP28.C19 fi rst published 1978.SAA MP28.C21 fi rst published 1978.SAA MP28.C22 fi rst published 1978.SAA MP28.C23 fi rst published 1978.SAA MP28.C25 fi rst published 1978.SAA MP28.C26 fi rst published 1975.These Standards revised, amalgamated and redesignated

AS 3600 Supplement 11990.Second edition 1994.

Incorporating:Amdt 1 1996

PUBLISHED BY ST ANDARDS AUSTRALIA(STANDARDS ASSOCIATION OF AUSTRALIA)1 THE CRESCENT, HOMEBUSH, NSW 2140

ISBN 0 7262 9195 1

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AS 3600 Supp1 1994 2

PREFACE

This Commentary (AS 3600 Supplement 1) was prepared by Standards AustraliaCommittee on Concrete Structures and first published in 1990 to replace MP 28,

Commentary on AS 1480 Concrete Structures Code, which was w ithdrawn in January1991. While it is intended that it be read in conjunction with AS 3600, Concretestructures , it does not form an integral part of that Standard.

Objective The objective of this Commentary is

(a) to provide background reference material to the Clauses in the Standard;

(b) to indicate the origin of particular requirements;

(c) to indicate departures from previous practice; and

(d) to explain the application of certain Clauses.

The clause numbers and titles used in the Commentary are the same as those in AS 3600except that they are prefixed by the letter C. To avoid possible confusion between

Commentary and Standard clauses cross-referenced w ithin the text, Commentary clausesare referred to as Paragraph C ... in accordance with Standards Australia policy.

Gaps in the numerical sequence of Commentary Paragraphs indicate that either thetechnical requirements of the corresponding clauses in the Standard are essentially thesame as those previously given in AS 1480, Concrete Structures Code or AS 1481,Prestressed Concrete Code , or the committee considered that commentary on theseclauses was not needed.

Where appropriate, each Section of the Commentary concludes with a list of referenceswhich are cross-referenced numerically in the text, e.g. (Ref. 6) or (Refs 6, 7 and 8). Insome Sections additional references f or further reading, or as a lead to specialist literature,have also been listed.

As noted in the Preface to AS 3600, the Standard represents a comprehensive revision andamalgamation of AS 1480 and AS 1481. To put things in perspective, AS 1480 andAS 1481 largely dated back to 1973 and essentially represented the technology of the1960s. Since then there have been considerable advances in materials and constructiontechnology. Also, due to the increased application of computers to modelling andanalytical techniques, an improved understanding of both material and member behaviourin complete structures has been realized. More sophisticated analysis and designprocedures are now readily available to design-office staff via desktop computers, whilecomplex formulas can be quickly evaluated using electronic calculators.

While the Standard inevitably reflects the abovementioned changes, a considerable amountof material and concepts have been retained from AS 1480 and AS 1481, particularly in

those areas where the benefits of technical change seemed doubtful to the committee.However, in all such instances the opportunity was taken to edit retained requirements, inorder to remove ambiguities which in the past have led to conflicting interpretations.

Background to second edition

The background to the second edition of this Commentary is essentially the same as thatgiven in the P reface of the second edition of AS 3600, with respect to new and revisedreference S tandards. Furthermore, in agreeing to a second edition of the Standard ratherthan the usual green-slip amendments, the Committee also agreed that the samephilosophy should in addition apply to the Commentary so that consistency would bemaintained between corresponding editions of the two documents.

As the Commentary had not been amended since its publication, the opportunity was

taken to include improvements suggested in the interim by users, as well as theappropriate changes necessitated by the 1990 and 1994 amendments to AS 3600. All suchchanges are indicated by a single bar in the left-hand margin for the extent of the affectedtext or figure.

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3 AS 3600 Supp11994

Objective of second edition

The objective of the second edition is to provide a clean, updated version of theCommentary that is consistent with the second edition of AS 3600.

Like the Standard itself, this Commentary is neither an immutable nor a perfect document.

Suggestions for improvement to the Commentary, in either the content or extent of thatprovided, are therefore w elcomed by Standards Australia.

ACKNOWLEDGMENTS

Standards Australia wishes to acknowledge and thank the following members of BD/2 andits subcommittees w ho have contributed significantly to this Commentary.

Assoc. Prof. R Q BridgeMr B J CorcoranProf. K A FaulkesMr B J Ferguson

Dr I GilbertDr D GunasekeraMr H P IsaacsDr F S PitmanMr R J Potter

Prof. B V RanganMr W J Semple

Mr D J SmeeMr G C Verge

Dr P F WalshProf. R T WarnerMr A C WhittingMr P J Wyche

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AS 3600 Supp1 1994 4

CONTENTS

Page

SECTION C1 SCOPE AND GENERALC1.1 SCOPE AND APPLICATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

C1.2 REFERENCED DOCUMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

C1.3 INTERPRETATIONS AND USE OF ALTERNATIVE MATERIALS OR

MET HODS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

C1. 4 DE SIGN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

C1. 5 CONST RUC TI ON . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

C1. 6 DE FINI TI ONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

C1.7 NOTATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

SECTION C2 DESIGN REQUIREMENTS AND PROCEDURES

C2.1 DESIGN REQUIREMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19C2.3 DESIGN FOR STRENGTH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

C2.4 DESIGN FOR SERVICEABILITY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

C2.6 DESIGN FOR DURABILITY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

C2.7 DESIGN FOR FIRE RESISTANCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

C2.8 OTHER DESIGN REQUIREMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

SECTION C3 LOADS AND LOAD COMBINATIONS FOR STABILITY,

STRENGTH AND SERVICEABILITY

C3.1 LOADS AND OTHER ACTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

C3.2 LOAD COMBINATION FOR STABILITY DESIGN . . . . . . . . . . . . . . . . 24

C3.3 LOAD COMBINATIONS FOR STRENGTH DESIGN . . . . . . . . . . . . . . . 24

SECTION C4 DESIGN FOR DURABILITY

C4.1 APPLICATION OF SECTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

C4.2 DESIGN FOR DURABILITY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

C4.3 EXPOSURE CLASSIFICATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

C4.4 REQUIREMENTS FOR CONCRETE FOR EXPOSURE

CLASSIFICATIONS A1 AND A2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

C4.5 REQUIREMENTS FOR CONCRETE FOR EXPOSURE

CLASSIFICATIONS B1, B2 AND C . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

C4.6 REQUIREMENTS FOR CONCRETE FOR EXPOSURECLASSIFICATION U . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

C4.7 ADDITIONAL REQUIREMENTS FOR ABRASION . . . . . . . . . . . . . . . . 31

C4.8 ADDITIONAL REQUIREMENTS FOR FREEZING AND THAWING . . . . 31

C4.9 RESTRICTION ON CHEMICAL CONTENT IN CONCRETE . . . . . . . . . . 32

C4.10 REQUIREMENTS FOR COVER TO REINFO RCING STEEL AND

TENDONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

SECTION C5 DESIGN FOR FIRE RESISTANCE

C5.1 SCOPE OF SECTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

C5.2 DEFINITIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

C5.3 DESIGN REQUIREMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37C5.4 FIRE-RESISTANCE PERIODS FOR BEAMS . . . . . . . . . . . . . . . . . . . . . 38

C5.5 FIRE-RESISTANCE PERIODS FOR SLABS . . . . . . . . . . . . . . . . . . . . . 40

C5.6 FIRE-RESISTANCE PERIODS FOR COLUMNS . . . . . . . . . . . . . . . . . . 40

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C5.7 FIRE-RESISTANCE PERIODS FOR WALLS . . . . . . . . . . . . . . . . . . . . . 40

C5.8 FIRE-RESISTANCE PERIODS FROM FIRE TESTS . . . . . . . . . . . . . . . . 41

C5.9 CALCULATION OF FIRE TEST PERFORMANCE . . . . . . . . . . . . . . . . . 41

C5.10 INCREASE OF FIRE-RESISTANCE PERIODS BY USE OF

INSULATING MATERIALS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

SECTION C6 DESIGN PROPERTIES OF MATERIALS

C6.1 PROPERTIES OF CONCRETE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

C6.2 PROPERTIES OF REINFORCEMENT . . . . . . . . . . . . . . . . . . . . . . . . . . 51

C6.3 PROPERTIES OF TENDONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

C6.4 LOSS OF PRESTRESS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

SECTION C7 METHODS OF STRUCTURAL ANALYSIS

C7.1 METHODS OF ANALYSIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59C7.2 SIMPLIFIED METHOD FOR REINFORCED CONTINUOUS BEAMS

AND ONE-WAY SLABS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

C7.3 SIMPLIFIED METHOD FOR REINFORCED TWO-WAY SLABS

SUPPORTED ON FOUR SIDES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

C7.4 AND C7.5 TWO-WAY SLAB SYSTEMS . . . . . . . . . . . . . . . . . . . . . . . . . 60

C7.4 SIMPLIFIED METHOD FOR REINFORCED TWO-WAY SLAB

SYSTEMS HAVING MULTIPLE SPANS . . . . . . . . . . . . . . . . . . . . . . . . 61

C7.5 IDEALIZED FRAME METHOD FOR STRUCTURES INCORPORATING

TWO-WAY SLAB SYSTEMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

C7.6 LINEAR ELASTIC ANALYSIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

C7.7 ELASTIC ANALYSIS OF FRAMES INCORPORATING SECONDARYBENDING MOMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

C7.8 RIGOROUS STRUCTURAL ANALYSIS . . . . . . . . . . . . . . . . . . . . . . . . 65

C7.9 PLASTIC METHODS OF ANALYSIS FOR SLABS . . . . . . . . . . . . . . . . 65

SECTION C8 DESIGN OF BEAMS FOR STRENGTH AND SERVICEABILITY

C8.1 STRENGTH OF BEAMS IN BENDING . . . . . . . . . . . . . . . . . . . . . . . . . 67

C8.2 STRENGTH OF BEAMS IN SHEAR . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

C8.3 STRENGTH OF BEAMS IN TORSION . . . . . . . . . . . . . . . . . . . . . . . . . 79

C8.4 LONGITUDINALSHEAR IN BEAMS . . . . . . . . . . . . . . . . . . . . . . . . . . 80

C8.5 DEFLECTION OF BEAMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82C8.6 CRACK CONTROL OF BEAMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86

C8.7 VIBRATION OF BEAMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88

C8.8 T-BEAMS AND L-BEAMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88

C8.9 SLENDERNESS LIMITS FOR BEAMS . . . . . . . . . . . . . . . . . . . . . . . . . 88

SECTION C9 DESIGN OF SLABS FOR STRENGTH AND SERVICEABILITY

C9.1 STRENGTH OF SLABS IN BENDING . . . . . . . . . . . . . . . . . . . . . . . . . 92

C9.2 STRENGTH OF SLABS IN SHEAR . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93

C9.3 DEFLECTION OF SLABS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95

C9.4 CRACK CONTROL OF SLABS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

C9.5 VIBRATION OF SLABS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97C9.6 MOMENT RESISTING WIDTH FOR ONE-WAY SLABS SUPPORTING

POINT LOADS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

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SECTION C10 DESIGN OF COLUMNS FOR STRENGTH AND

SERVICEABILITY

C10.1 GENERAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

C10.2 DESIGN PROCEDURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100

C10.3 DESIGN OF SHORT COLUMNS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103

C10.4 DESIGN OF SLENDER COLUMNS . . . . . . . . . . . . . . . . . . . . . . . . . . . 103

C10.5 SLENDERNESS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107

C10.6 STRENGTH OF COLUMNS IN COMBINED BENDING AND

COMPRESSION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109

C10.7 REINFORCEMENT REQUIREMENTS FOR COLUMNS . . . . . . . . . . . . . 112

C10.8 TRANSMISSION OF AXIAL FORCE THROUGH FLOOR SYSTEMS . . . 113

SECTION C11 DESIGN OF WALLS

C11.1 APPLICATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116C11.2 DESIGN PROCEDURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116

C11.3 BRACING OF WALLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116

C11.4 SIMPLIFIED DESIGN METHOD FOR BRACED WALLS SUBJECTED

TO VERTICAL FORCES ONLY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116

C11.5 DESIGN OF WALLS FOR IN-PLANE HORIZONTAL FORCES . . . . . . . 116

C11.6 REINFORCEMENT REQUIREMENTS FOR WALLS . . . . . . . . . . . . . . . 118

SECTION 12 DESIGN OF NON-FLEXURAL MEMBERS, END ZONES

AND BEARING SURFACES

C12.1 DESIGN OF NON-FLEXURAL MEMBERS . . . . . . . . . . . . . . . . . . . . . . 119

C12.2 ANCHORAGE ZONES FOR PRESTRESSING ANCHORAGES . . . . . . . . 122C12.3 BEARING SURFACES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126

SECTION C13 STRESS DEVELOPMENT AND SPLICING OF

REINFORCEMENT AND TENDONS

C13.1 STRESS DEVELOPMENT IN REINFORCEMENT . . . . . . . . . . . . . . . . . 128

C13.2 SPLICING OF REINFORCEMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132

C13.3 STRESS DEVELOPMENT IN TENDONS . . . . . . . . . . . . . . . . . . . . . . . 133

C13.4 COUPLING OF TENDONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133

SECTION C14 JOINTS, EMBEDDED ITEMS, FIXINGS AND CONNECTIONSC14.1 DESIGNS OF JOINTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134

C14.2 EMBEDDED ITEMS AND HOLES IN CONCRETE . . . . . . . . . . . . . . . . 134

C14.3 REQUIREMENTS FOR FIXINGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134

SECTION C15 PLAIN CONCRETE MEMBERS

C15.1 APPLICATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135

C15.2 DESIGN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135

C15.3 STRENGTH IN BENDING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135

C15.4 STRENGTH IN SHEAR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135

C15.5 STRENGTH IN AXIAL COMPRESSION . . . . . . . . . . . . . . . . . . . . . . . . 135

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SECTION C16 CONCRETE PAVEMENTS, FLOORS AND

RESIDENTIAL FOOTINGS

C16.1 APPLICATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136

C16.2 ADDITIONAL DESIGN CONSIDERATIONS FOR PAVEMENTS AND

INDUSTRIAL AND COMMERCIAL FLOORS . . . . . . . . . . . . . . . . . . . . 136

C16.3 RESIDENTIAL FLOORS AND FOOTINGS . . . . . . . . . . . . . . . . . . . . . . 136

SECTION C17 LIQUID RETAINING STRUCTURES

C17.1 GENERAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137

SECTION C18 MARINE STRUCTURES

C18.1 APPLICATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138

C18.2 ADDITIONAL LOADS AND ACTIONS . . . . . . . . . . . . . . . . . . . . . . . . 138

C18.3 ADDITIONAL DURABILITY AND DESIGN REQUIREMENTS . . . . . . . 138

SECTION C19 MATERIAL AN D CONSTRUCTION REQUIREMENTS

C19.1 MATERIAL AND CONSTRUCTION REQUIREMENTS FOR

CONCRETE AND GROUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141

C19.2 MATERIALS AND CONSTRUCTION REQUIREMENTS FOR

REINFORCING STEEL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144

C19.3 MATERIAL AND CONSTRUCTION REQUIREMENTS FOR

PRESTRESSING DUCTS, ANCHORAGES AND TENDONS . . . . . . . . . . 145

C19.4 CONSTRUCTION REQUIREMENTS FOR JOINTS AND EMBEDDED

ITEMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147

C19.5 TOLERANCES FOR STRUCTURES AND MEMBERS . . . . . . . . . . . . . . 147

C19.6 FORMWORK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148

SECTION C20 TESTING AND ASSESSMENT FOR COMPLIANCE OF

CONCRETE SPECIFIED BY COMPRESSIVE STRENGTH

C20.1 GENERAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155

C20.2 MANUFACTURE OF CONCRETE . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155

C20.3 PROJECT ASSESSMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155

C20.4 PRINCIPLES FOR ASSESSMENT OF CONCRETE SPECIFIED BY

GRADE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156

C20.5 ALTERNATIVE ASSESSMENT METHODS . . . . . . . . . . . . . . . . . . . . . 156

C20.6 DEEMED TO COMPLY PROVISIONS . . . . . . . . . . . . . . . . . . . . . . . . . 156

SECTION C21 TESTING OF MEMBERS AND STRUCTURES

C21.1 PROOF TESTING OF BEAMS AND SLABS . . . . . . . . . . . . . . . . . . . . . 157

C21.2 PROTOTYPE TESTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157

C21.3 QUALITY CONTROL TESTING OF MANUFACTURED UNITS . . . . . . . 158

C21.4 TESTING FOR STRENGTH OF HARDENED CONCRETE IN PLACE . . . 158

APPENDIX CA ADDITIONAL REQUIREMENTS FOR STRUCTURES SUBJECT

TO SEISMIC ACTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160

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STANDARDS AUSTRALIA

Australian Standard

AS 3600 Supp 1

Concrete structuresCommentary (Supplement to AS 36001994)

S E C T I O N C 1 S C O P E A N D G E N E R A L

C1.1 SCOPE AND APPLICATION

C1.1.1 Scope The Standard sets out the minimum requirements for the design andconstruction of safe, serviceable and durable concrete structures. There may be otherrequirements, not covered by the Standard, which also have to be considered.

C1.1.2 Application A lower concrete strength limit of 20 MPa has been imposed, asstrength grades less than this are not considered suitable for structures.

An upper concrete strength limit of 50 MPa has been adopted, because much of theresearch on which the Standard is based involved concrete strengths at or below thisvalue. Nevertheless, higher strength concretes are being used in Australia and overseas(Refs. 1 and 2). The Standard may possibly be applied without change to concretes with28-day compressive strengths up to 65 MPa. However, beyond 50 MPa, concrete becomesincreasingly brittle in its structural behaviour and, as indicated in N ote 2, current detailingrequirements may be inadequate for ensuring the necessary elastic and ductile behaviourassumed in the various design Sections.

Concretes made from naturally occurring Australian coarse aggregates have surface-drydensities falling in the range 2100 kg/m3 to 2800 kg/m3. Lightweight structural concretesin Australia generally use naturally occurring sands combined with manufacturedlightweight aggregates, for which the surface-dry density is seldom less than 1800 kg/m3.Density limits for structural concretes have been set accordingly.

Design of road and pedestrian bridges is covered by the Austroads Bridge Design Code.

In the preparation of a Standard such as this, a certain level of knowledge and competenceof the majority of users must be assumed. As indicated by the Note, it was assumed thatthe predominant users of this Standard would be professionally qualified civil or structuralengineers experienced in the design of concrete structures, or equally qualified but lessexperienced persons working under their guidance. It is therefore intended that the

Standard be applied and interpreted primarily by such persons.

C1.2 REFERENCED DOCUMENTS The Standards listed in Appendix B are subjectto revision from time to time. A check should be made with Standards Australia as to thecurrency of any Standard referenced in the text.

C1.3 INTERPRETATIONS AND USE OF ALTERNATIVE MATERIALS ORMETHODS It is intended that where Committee Interpretations or Opinions are given,which may relate initially to particular projects but have general application, they will becollated and published in a separate document as Rulings, which will be updated on aregular basis. The Rulings will then form the basis f or future amendments or r evisions ofthe Standard or its Commentary and will be in line with similar Rulings applying to

other Australian Standards.

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The designer is usually required to seek approval from the appropriate A uthority, for theuse of alternative materials or methods. For example, fibre impregnated concrete m ay beused for members if it complies with the requirements of Section 2. However, the use ofsuch fibres would not mean that a relaxation of the requirements for conventionalreinforcement or tendons automatically follows (Refs 6 and 7).

C1 .4 D ESI GN The information applicable to most members may be shown in onlyone of the drawings, usually the first sheet, or cited in the project specification asappropriate (see Refs 4 and 5).

C1.5 CONSTRUCTION The extent of supervision and inspection depends on theimportance and complexity of the structure concerned.

Any structure which is either complex or contains tendons should be supervised by aperson responsible to a qualified engineer employed by the builder and experienced in thesupervision of comparable structures.

In addition, the works should be inspected at specified stages by a suitably qualified

person nominated by the building owner.

If there is any doubt regarding the design, or the interpretation of the documents, thesupervisor or inspector should refer the doubtful matter to the designer for resolution.

Suitable s ite records should be kept during construction and be available for inspectionduring the progress of the work, and for at least 2 years after completion of the work.Such records should include, as appropriate

(a) the quantity, grade and type of reinforcing steel and prestressing steel;

(b) each date on which concrete was placed and the corresponding location of thatconcrete in the structure;

(c) the results of all tests on the concrete together with the locations in the structure ofthe batches sampled, and copies of the s uppliers identification certificates; and

(d) stressing details.

C1.6 DEFINITIONS

C1.6.3 Technical definitions

Cement The term cement is used throughout the Standard in the generic sense ofhydraulic cementitious materials since it is now defined as portland cement, orblended cement or either of these in combination with one or more of the permissiblesupplementary cementitious materials (fly ash, slag and silica fume). Refer toParagraph C4.5 for minimum cement content in normal class concrete.

Characteristic strength The concept of characteristic strength removes some of theconfusion regarding terms such as minimum strength, design strength, and targetstrength. The characteristic strength, as defined, is consistent with the 5% defectiveprobability adopted (although not stated as s uch) in CA21963 and thus identical with fcas defined in AS 14801974, the revised and metricated version of that Standard. (Seealso Section C20.)

Effective depth For a cross-section with multiple layers of reinforcement, or a mixture ofreinforcement and tendons, all the steel may not be at yield at the ultimate strengthconditions. In such cases the resultant tensile force will not be at the centroid of thetensile steel area. The new definition of effective depth accommodates this and istherefore equally applicable to reinforced, prestressed and partially prestressed members.

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Where all the tensile reinforcement is effectively at its yield stress under ultimate strengthconditions, the usual case for normal reinforced concrete beams, the resultant tensile forceacts at the centroid of the tensile steel area.

Lightweight concrete For the purpose of the Standard, the term lightweight concreteapplies only to structural concrete made with lightweight coarse aggregate andnormal-weight fine aggregate. Cellular concrete, no-fines concrete and concrete in w hichthe aggregates are entirely lightweight, are excluded from this definition.

C1.7 NOTATION

INTRODUCTION The change from the notation used in AS 1480 and AS 1481 to thepresent notation follows Standards Australia policy on limit-state Standards and a generalpolicy to adopt, whenever and as far as practicable, recommendations of theInternational Or ganization for Standardization (I SO).

The notation is based on ISO Standard 3898 (Ref. 3), which sets out rules for constructinga coherent and consistent set of symbols applicable to the design of structures. ThatStandard specifies only the general terms, so the particular terms relevant to concretestructures have been derived and included in this Standard.

The following text, tables and figures illustrate the notation and its derivation.

SYMBOLS FOR CONCRETE STRUCTURES

The symbol to represent a given quantity or term is chosen as follows:

(a) The leading or main character of the symbol is selected from Tables C2, C3, C4 orC5 in accordance with the criteria in Table C1.

(b) Descriptive subscripts are selected to suit. Where subscripts other than those in TablesC6, and C7 are used, they are defined.

(c) The first subscript indicates the material or part and the f ollowing subscripts qualifythis as to nature, type, location and the like. W here necessary to avoid confusion, afull stop is used between categories of subscripts (see Example 2).

(d) When there is no likelihood of confusion s ome or all subscripts are omitted.

(e) Numbers are sometimes used as subscripts, either alone or w ith letters.

To avoid confusion, some Roman and Greek letters are not used. These letters are marked(VOID) or otherwise noted in the tables.

Roman upper and lower-case O are not used as leading characters. However, the lower-case is used as a subscript, to mean zero.

Greek lower-case letters iota (), kappa (), omicron (), upsilon (), eta () and chi (),

are not used because of possible confusion with Roman letters.

The possible confusion of (numeral) 1 w ith (letter) l when typed is eliminated by adoptingupper case L for both leading characters and subscripts.

EXAMPLES

1. Symbol for Area of reinforcement The dimensions and usage columns of Table C1indicates a Roman capital letter. From Table C2 the letter A is selected as the leadingcharacter for Area.

As the material is steel, the subscript s is chosen from Table C6. Thus, As is thesymbol for the cross-sectional area of reinforcement.

If it is tensile reinforcement, the subscript t is added. Hence Ast is the symbol for thecross-sectional area of tensile reinforcement.

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2. Symbol for Concrete shrinkage strain As strain is dimensionless, Table C1 indicatesthe use of a Greek lower-case letter. From Table C4 the letter , is selected as theleading character for strain.

To symbolize concrete s hrinkage, subscripts are chosen from Table C6. T hus, cs isthe symbol for concrete shrinkage strain.

If further differentiation is required, the additional subscript is s eparated from the firstsubscripts by a full stop. Hence cs.b is the symbol for basic shrinkage strain.

3. Symbols for material strength

The dimension and usage columns of Table C1 indicate a Roman lower-case letter forthe leading character. Table C3 indicates the letter, f for strength. Superscripts andsubscripts are added as shown in the following diagram:

Thus fcc= the characteristic concrete strength in compression.

NOTE: The prime superscript () is not an ISO standard. It is used to indicate thecharacteristic value for concrete, in deference to long-standing practice in Australia and the

USA, and immediately follows the lead character.4. Symbols for loads, actions and action effects Loads and actions are represented by

the upper-case Roman letters F, G, P, Q, Sand W. Lower-case subscripts denote thetype of action, e.g. Fep is the force resulting from earth pressure and Fg+q would bethe force from dead plus live loads.

Action effects are denoted by the upper-case Roman letters N, Mand V representingaxial force, bending moment and shear force r espectively. If these ar e combinationsof loads factored for strength design, an asterisk is used as a superscript, e.g. M* isthe design bending moment for strength.

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TA BLE C 1

GUIDE TO THE USE OF LETTER TYPES IN THE CONSTRUCTION OF SYMBOLS

Type of letter Dimensions Usage

Roman capital Force, force times length, area to a power,temperature

Bending or torsional moment, shear,normal force, concentrated load, totalload

Area, first and second moments of area

Strain moduli ( exception todimensions)

Temperature

Roman lower-case Length, quotient of length and time to apower, force per unit length or area, exceptwhere used as subscripts, mass, time.

Unit moment, shear, normal force,load

Linear dimensions (length, width,thickness.)

Strength

Velocity, acceleration,

Descriptive letters (subscripts)

Greek capital

Reserved for mathematics and forphysical quantities excludinggeometric and mechanical quantities

Greek lower-case Di mensionless Coefficients and dimensionless ratios

Strain

Angles

Specific gravity (ratio of densities)

Stress (exception to dimensions)

NOTE: Letter types for usages not included above should correspond to the nearest appropriate category.

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TA BLE C 2

ROMAN CAPITAL LETTERS AS LEADING C HARACTERS

Letter Meaning

A

B

C

D

E

F

G

H

I

J

K

L

M

NO

P

Q

R

S

T

U

V

W

X

Y

Z

area; accidental action

(not assigned)

torsional second moment of area

depth (physical)

strain modulus; always used with a subscript

action (loads and imposed deformations), used as a leading letter w ith subscripts given in

Table 7; force in general

dead loadheight

second moment of area

torsional modulus

stiffness; any quantity but with a specific dimension in the absence of a specific symbol

span, length of m ember (physical); left

bending moment

normal force(VOID)prestressing force

live load

resultant force; reaction; right; relaxation; resistance

first moment of an area; action effect used as a leading letter with subscripts given in

Table 7 (internal M, N, V, T); snow load

torsional moment; temperature; period of time

(not assigned)

shear force; vertical component of force

wind load

reactions or forces in general, parallel to axisx

reactions or forces in general, parallel to axisy

reactions or forces in general, parallel to axisz ; section modulus

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TA BLE C 3

ROMAN LOWER-CASE LETTERS AS LEADING CHARACTERS

Letter Meaning

a

b

c

d

e

f

g

h

i

j

k

l

m

n

op

q

r

s

t

u

v

w

x

y

z

acceleration; distance

width

concrete cover

effective depth; diameter

eccentricity

strength

distributed dead load; acceleration due to gravity

(not assigned)(not assigned)

number of days

any coefficient with proper dimensions

replaced byL to avoid ambiguity

bending moment per unit length or width; mass; average value of a sample

normal force per unit length or width

(VOID)geometrical ratio of reinforcement; pressure; probability

distributed live load

radius; radius of gyrationdistributed snow load; Standard deviation of a sample; spacing

time; torsional moment per unit length o r width; thickness of thin members

perimeter

shear force per unit length or width; velocity

distributed wind load

coordinate; depth of neutral axis

coordinate; depth of rectangular stress block

coordinate; lever arm

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TA BLE C 4

GREEK LOWER-CASE LETTER AS LEADING CHARACTERS

Letter Symbol Meaning

Alpha

Beta

Gamma

Delta

Epsilon

Zeta

Eta

ThetaIota

Kappa

Lambda

Mu

Nu

Xi

OmicronPiRho

Sigma

Tau

Upsilon

Phi

Chi

Psi

Omega

angle; ratio e.g. = E/E

c; coefficient

angle; ratio; coefficientspecific gravity; shear strain (angular deformation)

coefficient of variation; coefficient

strain

(VOID)

(VOID)

rotation; angle

(VOID)

(VOID)slenderness ratio; coefficient

coefficient of friction; relative bending moment; average of a population; corrective factor

Poissons ratio; relative normal force

(not assigned)

(VOID)(see Table 5)

mass density

normal stress; standard deviation of a populationshear stress

(VOID)

creep coefficient; strength reduction factor; angle

(VOID)

ratio; relative humidity; reduction coefficient

angular velocity

TA BLE C 5

MATHEMATICAL AND SPECIAL SYMBOLS

Symbol Meaning

()c

or //

*

sum

difference; increment; deflection

characteristic strengthbase of Napierian logarithms

the ratio of the circumference to the diameter of a circle ( 3.1416)

number of

parallel to

perpendicular to; normal to

design value

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TA BLE C 6

ROMAN LOWER-CASE LETTERS AS SUBSCRIPTS

Symbol Meaning (see Note 1)

a

b

c

d

e

f

g

hi

j

k

l

m

n

opq

r

s

t

u

v

w

xy

z

0, 1, 2

axial; accidental action

bond; bar; beam; basic

concrete; compression ; column; creep

design value; duct

elastic limit

forces and other actions; flange; flexure; friction fitment

dead load

horizontal; hypotheticalinitial in time; value of a variable in a series

number of days; joint

characteristic (see Note 2)

longitudinal; long term

average value; materials; moment

net; normal

numeral zero (see also below); at the originprestress

live load

resistance

steel; snow;slab; short term; shrinkage

tension

ultimate (limit state)

shear ; vertical

wind: wire; web; wall

linear coordinate

linear coordinate; yield

linear coordinate

particular values of quantities

NOTES:

1 Meanings in bold type correspond to international agreements and arepreferred.

2 Characteristic values are defined in terms of probability of exceedance.

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TA BLE C 7

SUBSCRIPTS FORMED FROM ABBREVIATIONS

Letters Meaning

abs

admcal

crit (or cr)

dyn

ef

el

ep

eq

estexc

ext

fat

im

inf

int

lat

limmax

min

nom

obs

par

per

pl

redrel

rep

serst

sup

tem

tor

tottra

var

absolute

admissible (permissible)calculated (as opposed of observed)

critical

dynamic

effective

elastic in general

earth pressure

earthquake

estimatedexceptional

external

fatigue

impact

inferior

internal

lateral

limitmaximum

minimum

nominal

observed

parallel

perpendicular

plastic

reducedrelative

representative

serviceabilitystatic

superior

temperature

torsion

totaltransversal

variable

NOTE: Abbreviations which are not contained in this Table shouldbe derived from words having Latin roots. If there is no risk ofconfusion, these subscripts may be reduced t o one or two letters.

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REFERENCES

1 CHOY R.S., High-strength concrete, Technical Report TR/F112, Cement andConcrete Association of Australia, Sydney, 1988.

2 RUSSELL H.G., High-strength concrete in North America, International Symposium

on utilization of high-strength concrete, Stavanger, Norway, 1987.3 ISO 3898:1987, Bases for design of structures Notations General symbols,

International Or ganization f or Standardization.

4 FE RGU SON B.J ., Reinforcement Detailing Handbook, Concrete Institute ofAustralia, Sydney, 1988.

5 AS 1100, Par t 501, Structural engineering drawing, SAA, Sydney, 1985.

6 HA NNA NT D .J ., Fibre cements and fibre concretes, John Wiley and Sons Ltd,London, 1978.

7 AITCIN P-C., LAPLANTE P. AND LA PALME P., The use of fibre reinforcedconcrete for highway rehabilitation, Etude #231, IGM 85-305-231, University of

Sherbrooke and the Industrial Materials Research Institute, Quebec, 1985. (InEnglish.)

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S E C T I O N C 2 D E S I G N R E Q U I R E M E N T S A N DP R O C E D U R E S

C2.1 DESIGN REQUIREMENTS This is a new Clause drawing attention to theprobabilistic basis of design.

The design requirements apply to the complete structure and its component members.During construction there may be critical periods for the partially built structure whenunusual load paths are called into play. The designer should consider such conditions.

C2.3 DESIGN FOR STRENGTH The design procedure is the same in all essentialaspects as the ultimate strength design method of AS 1480.

The design strength of a member is the ultimate strength, calculated in accordance withthe relevant Clauses, multiplied by a strength reduction factor () which is always lessthan one. The rules for calculating the ultimate strength of a member are based on chosen

limiting states of stress, strain, cracking or crushing as appropriate, and conform toresearch data for each type of structural action.

The strength reduction factor () takes the following into account:

(a) Variation in material strength, material properties, position of reinforcing orprestressing steel, size of members and homogeneity.

(b) Differences between the ultimate strength obtained from tests and the ultimatestrength of the member in the structure.

(c) Inaccuracies in the design equations related to member design and an incompleteunderstanding of internal a ctions.

(d) Degree of ductility and required reliability of the member under the action effects

being considered.

(e) Importance of the member in the structure.

For example, the factor used for columns is lower than that for beams because a columnhas less ductility, is more sensitive to variations in concrete strength and the consequencesof failure are likely to be more serious.

Values given in Table 2.3 for the strength reduction factor, (), are lower than thosepreviously used in AS 1480. However these changes have to be considered together withcorresponding changes in the load factors given in AS 1170.1. For example, in thecombination of dead and live loads, the load factors have been reduced from 1.5 to 1.25and from 1.8 to 1.5 respectively, while the factor for bending has decreased from 0.9 to0.8.

In this case the overall factor of safety has been lowered by 6%. This brings it into linewith the overall safety factors used in the American Code (Ref. 23), the Canadian Code,and very close to those used in the British Code (Ref. 22), although in the latter case aclear-cut comparison is difficult to make. The adjusted load factors and factors representmore realistically the sources and magnitudes of variability in the processes of design andconstruction.

The reduction in the overall safety f actors is justified by refinements to calculations fordesign action effects and member strengths incorporated elsewhere in the Standard.

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Table 2.3 In most instances in the Table, is assigned a single value in the range 0.6 0.8. For certain cases of bending without axial force and for all cases of bendingcombined with axial f orce, the value of varies with the ductility of the section underconsideration. Fully ductile behaviour is assigned a value of 0.8, and non-ductilebehaviour a value of 0.6. The neutral axis parameter ku is used as a measure of ductility.

In rows (a) and (b) members subjected to axial tension are deemed to be ductile, as aremembers subjected to bending without axial force when ku 0.4, and in both cases = 0.8. Members in axial compression are non-ductile with = 0.6 and, for members inbending without axial f orce, reduces from 0.8 to 0.6 as ku increases above 0.4 andductility decreases ( as indicated in row (b)(ii)).

For members in axial tension and for ductile flexural members (i.e. ku 0.4 in purebending), = 0.8. For non-ductile flexural members (i.e. ku > 0.4 in pure bending),0.6 0.8 as indicated in row (c).

For m embers in combined bending and axial compression, is specified in row (d) of theTable and depends on the magnitude of Nu with respect to Nub. When Nu Nub, a primarycompressive failure occurs, and deformation at failure is small. Accordingly, = 0.6.When Nu < Nub, a primary tensile failure occurs, deformation at failure is relatively largeand increases linearly from 0.6 (when Nu = Nub) to its value in pure bending (given inrow (c) of the Table).

Where strength depends primarily on the behaviour of both concrete and steel, and theductility varies for the different load carrying elements, is taken as 0.7. This includesthe shear strength and the torsional strength of beams, and for members in which strengthis determined by strut and tie modelling.

Concrete in bearing and in plain concrete elements is considered non-ductile and therefore = 0.6.

C2.4 DESIGN FOR SERVICEABILITY

C2.4.1 General The important serviceability criteria are usually excessive deflectionand cracking. Other criteria should be examined where required.

C2.4.2 Deflection limits for beams and slabs The deflection limits in Table 2.4.2 aredifferent from those in AS 1480 and reflect experience gained from examining theperformance of structures designed to that Code.

The limit of Span/250 for total deflection is intended to control the final deflected shapeof the member after allowing for the long-term effects due to sustained dead and liveloads plus the short-term effect due to the transitory component of the live load additionalto the sustained live load. The component values for short-term and long-term effects arespecified in A S 1170.1.

Designers s hould note that the limit of Span/250 may not be sufficient to meet particularaesthetic or functional requirements such as visual sagging and ponding of water.

The Standard implies that the total deflection is measured from the as-cast position butdoes not provide specific guidance on the treatment of camber which could be used toeliminate the effect of part or all of the total deflection and possibly permit slendermembers, particularly for longer spans. If camber is used to significantly reduce thestiffness of the floor otherwise required to meet this limit, then care should be taken tocheck the incremental deflection, support rotations, and the possibility of excessivevibration.

A limit on incremental deflection is required for all members supporting masonrypartitions or other sensitive attachments. The incremental deflection comprises that part of

the long-term effects due to the sustained dead and live loads which occur after the

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addition of partitions and the short-term effect due to the transitory component of the liveload under service conditions.

Usually this criterion will be more severe than the limit on total deflection, unlessprovision is made to minimize the effect of the movement by detailing joints and delayingthe erection of the masonry walls until a substantial part of the long-term deflection hasoccurred. This latter precaution may not be practicable if speed and flexibility ofconstruction are desired.

Details of the methods of calculating deflections are s et out in Clause 8.5, Deflection ofbeams, and Clause 9.3, Deflection of slabs.

C2.4.3 Lateral drift Unbraced frames are more sensitive to the effects of lateralloading than braced f rames or shear wall structures. The limit on interstorey lateral driftof storey height/500 is intended to provide a reasonably stiff and serviceable structure.

C2.4.4 Cracking The control of cracking under service conditions is required fordurability and long-term performance. The detailed design requirements are set out inClause 8.6 for beams and Clause 9.4 for slabs.

C2.4.5 Vibration The design of structures subject to dynamic loads, such that thevibrations generated do not exceed acceptable levels, is a complex subject. References 1to 18 provide an introduction to the specialist literature in this field. Essential to thesolution is a detailed understanding of the magnitude and nature of the dynamic loadsapplied (harmonic, transient, or random force), the acceptability criteria relevant to thetype of structure under consideration and the nature of the loads.

Among the dynamic loads that may require consideration for the serviceability limit stateare:

(a) Pedestrian traffic on suspended floors and footbridges (References 1 to 5).

(b) Wind loads on structure (References 6 to 9).

(c) Service loads due to plant and manufacturing processes, e.g. forging hammers,generators, presses, etc. (References 10 to 14).

(d) Adjacent road or rail traffic (References 15, 16).

(e) Blasting (assuming a nearby quarry) (References 15 to 18).

The designer should be careful to use appropriate acceptability criteria in judging theadequacy of the design. For example the reduced comfort boundary levels nominated inAS 2670, Vibration and shockG uide to the evaluation of human exposure to wholebody vibration, are unlikely to be acceptable in an apartment or office whereas they maybe acceptable in a machine shop.

The difficulties of obtaining precise information on the dynamic loads and of finding

relevant acceptability criteria, means that the designer is unlikely to obtain solutions withthe confidence levels that apply to static problems.

Although AS 2670 provides data on the evaluation of human exposure to whole bodyvibrations, the NOTES to Clause 3.1.4 of that Standard indicate that there are limits to itsusefulness for the evaluation of disturbance due to building vibration.

C2.6 DESIGN FOR DURABILITY Durability may be a critical design considerationfor many structures and hence needs to be investigated at the s ame time as the other listedrequirements.

C2.7 DESIGN FOR FIRE RESISTANCE Fire resistance has now been made a design

requirement, the provisions of Section 5 replacing the recommendations of AS 1480Appendix B.

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C2.8 OTHER DESIGN REQUIREMENTS Fatigue is not a significant designconsideration in normal building structures. For structures subject to repeated or dynamicloads, reference should be made to specialist literature such as References 19 and 20.

Progressive collapse means a continuous sequence of f ailures initiated by the local failureof one part of the structure.

Progressive collapse may be prevented by providing either

(a) adequate s tructural strength and continuity of the structure and its parts; or

(b) alternative load paths, whereby applied forces can be transmitted safely through thestructure.

Structural continuity may rely upon, among other things, moment, shear, or tensileconnections, depending on the kind of s tructural system employed. The designer shouldnote the importance of this consideration in precast or combinations of precast and in-situconstruction (Ref. 21). See for example, the provisions of BS 8110.1 (Ref. 22).

REFERENCES

1 WHEELER J.E., Prediction and Control of Pedestrian Induced Vibrations inFootbridges, Journal of the Structural Division, ASCE, Vol. 108, No. ST9,September 1982.

2 McCORMICK M.M. AND MASON D., Office Floor Vibrations Design Criteriaand Tests, Noise Shock and V ibration Conference, Monash University, 1974.

3 CARO J.C., LARKINS G.K. AND CAIRNES T.H., Vibration in Prestressed Slabswith P articular Reference to Hospital Structures, Institution of Engineers Aust.Conference, Melbourne, 1975.

4 ELLINGWOOD B. AND TALLIN A., Structural ServiceabilityFloor Vibrations,Journal of the Structur al Div ision, ASCE, Vol. 110, No. ST2, February 1984.

5 ALLEN D.E., RAINER J.H. AND PERNICA G., Vibration Criteria for Long SpanConcrete Floors, ACI Special Publication No. 60, Vibrations of Concrete StructuresNo. SP-60, American Concrete Institute, Detroit.

6 IRWIN A.W., Human Reactions to Oscillations of Buildings, Build International,8, 1975, pp. 89102.

7 IRWIN A.W., Human Response to Dynamic Motion of Structures, StructuralEngineer, Vol. 56A, No. 9, September 1978.

8 HANSEN R.J., REED J.W. AND VANMARCKE E.H., Human Response to WindInduced Motion of Buildings, Journal of the Structural Division, ASCE, Vol. 99,ST7, July 1973.

9 ASCE, Monograph on Planning and Design of Tall Buildings, Volume PC,Chapter 13, Motion Perception and Tolerance.

10 BAKER J.K., Vibration Isolation, Engineering Design Guides No. 13, OUP, 1975.

11 Building Research Station Digests, Vibrations in Buildings1, D igest 117, May1970, Vibrations in Buildings2, Digest 118, June 1970.

12 STEFFENS R.J., Structural Vibration and Damage, Building Research Establish-ment Report, 1974.

13 MA JOR A. , Dynamics in Civil Engineering, Vols 1 to 4, Akademiai KiadoBudapest, 1980.

14 MACINANTE J.A., Seismic Mountings for Vibration Isolation, John Wiley andSons, 1984.

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15 TYNAN A.E., Ground Vibrations, Australian Road Research Board, Melbourne,Special Report No. 11, 1974.

16 HOLMBERG R., Vibrations Generated by Traffic and Building ConstructionActivities, Swedish Council for Building Research, Stockholm, 1984.

17 MAINSTONE R.J., The Hazard of Internal Blast in Buildings, Building ResearchEstablishm ent, UK, Current Paper CP 11/73, 1973.

18 GOLDBERG J.L. AND DREW P., The Response of High Rise Buildings to GroundVibration from Blasting, 10th International Congress on A coustics, Sydney, 1980.

19 ACI 215-74, Considerations for the Design of Concrete Structures Subjected to

Fatigue Loadings, Journal of the Am erican Concrete Institute, Proc. Vol. 71, No. 3,March 1974.

20 AC I SP- 75, Fatigue of Concrete Structures, Am erican Concrete Institute, Detroit,1982.

21 VERGE G.C. AND GAMBLE S.N., Progressive collapse provisions for large panel

buildings, ACSE 50th Anniversary Conference, June 1983.22 BRITISH STANDARDS INSTITUTE, BS 8110.1, Structural Use of Concrete,

Part 1: Code of practice for design and construction , 1985.

23 AC I C OMMI TT EE 318, Building Code requirements for reinforced concrete(ACI 318M-83), American Concrete Institute, De troit, 1984.

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S E C T I O N C 3 L O A D S A N D L O A DC O M B I N A T I O N S F O R S T A B I L I T Y ,

S T R E N G T H A N D S E R V I C E A B I L I T Y

C3.1 LOADS AND OTHER ACTIONS

C3.1.1 Loads Accidental loading includes collisions, explosions, subsidence ofsubgrades, extreme erosion and tornadic storms in regions not normally exposed to them.

The deemed-to-comply wind loads in AS 4055 (Ref.1) may be used for housing where thelimitations of that Standard apply. H owever, there may be advantages in using the morerigorous wind load procedures from AS 1170.2 (Ref 2) especially for larger housingestates.

Loads specified in the ANZRC Railway Bridge Design Manual are generally applicable toall rail bridges. Loads specified in the AUSTROADS Bridge Design Code are applicableto all road and pedestrian bridges under the jurisdiction of the Austroads member

authorities and are generally applicable for road and pedestrian bridges of otherauthorities and organizations. However, other authorities and organizations may specifyreduced design live loads for bridges where the owner of the bridge has full control of thetraffic.

C3.1.2 Construction loads Some guidance on construction loads is provided inAppendix D of AS 1170.11989 (Ref. 1), although the Standard itself gives no specificvalues for them. AS 3610 (Ref. 3) gives construction live loads with a minimum of1.0 kPa to be used for workmen and equipment and 4.0 kPa for stacked materials. Both ofthese documents emphasize the need for careful assessment of the loads induced byfloor-to-floor propping in multi-storey c onstruction (see also C19.6.2).

C3.1.3 Other actions No guidance is given in the Standard on the level of the listed

actions because of uncertainties in their implications. The designer should be aware thatthe actions given in (a), (b), (c), (e) and (f) do not affect the strength of the member if itis sufficiently ductile. However, these actions may need to be considered forserviceability.

C3.2 LOAD COMBINATION FOR STABILITY DESIGN Unlike similar provisionsin AS 1480, these requirements are stated in limit state terms and give a safety indexconsistent with other design aspects. For each situation, the designer is required to decidewhich are the loads or load effects producing instability and which are those resistinginstability.

The reduction factor of 0.8 applies to the resistance offered by the foundations, ground

anchor, anchor piles and the like as well as to the counter-balancing effects of portions ofthe structure itself. Variable loads are generally not included in the loads resistinginstability unless they have a permanent component which can be evaluated, in which caseonly that component may be included.

C3.3 LOAD COMBINATIONS FOR STRENGTH DESIGN Load combinations forstructures other than bridges are included in AS 1170.1 (Ref. 4), except that an alternativefor the combination of multiple loads is given here and specific requirements forprestressing f orces are given.

The designer should not assume that the combinations of loadings given arecomprehensive, as other loads and combinations may need to be considered.

Various combinations of loading will need to be considered to determine the most cr iticaldesign condition, particularly where strength is dependent on more than one load ef fect,

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such as strength for combined flexure and axial load, or shear strength in members withaxial load.

In determining the most critical combination of loadings, the designer should alsoconsider the direction of the load, as one type of load may produce effects of oppositesense to that produced by another type. The load combinations with 0.8 G are specificallyincluded for the case where dead load reduces the effects of other loads.

For structures such as parking buildings, loading docks, warehouse floors and elevatorshafts, impact effects should be considered and impact forces, if any, included with liveloads in the various equations for required strength. In all equations substitute (Q +impact) for Q where required.

Load factors and combinations must be consistent with the loads to which they apply.Thus if loads are based on the Austroads Bridge Design Code or the ANZRC RailwayBridge Design Manual, the load factors, strength reduction factors and load combinationsneed to be taken from the same code or be independently specified by the relevantauthority or organization.

REFERENCES

1 AS 4055, Wind loads for housing , Standards Australia, Sydney, 1992.

2 AS 1170, SAA Loading Code, Part 2: Wind loads, Standards Australia, Sydney,1989.

3 AS 3610, Formwork for concrete, Standards Australia, Sydney, 1990.

4 AS 1170, Minimum design loads on structures (known as the SAA Loading Code),Part 1: Dead and live loads and load combinations , Standards Australia, Sydney,1989.

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S E C T I O N C 4 D E S I G N F O R D U R A B I L I T Y

INTRODUCTION

Since AS 1480 was published in 1974, durability has been recognized as a major designconsideration. This is reflected in the Standard by the inclusion of this Section. I n it, therequirements for durability design have been collected together and placed at thebeginning of the design Section, instead of being scattered as detailing requirements,throughout the Standard.

The importance of designing for durability is highlighted by an es timated annual cost in1979 of $50 million (Ref. 1) to repair damage due to inadequate durability.

In Clause 2.1.1 durability is indirectly defined as the ability of a member to withstand theexpected wear and deterioration throughout its intended life without the need f or unduemaintenance. The expected wear and deterioration may include the influences ofweathering, chemical attack and abrasion. It is a complex matter involving a large number

of interrelated factors (Ref. 2), such as

(a) attention to design details, including reinforcement layout, appropriate cover andprovision for shedding of water from exposed surfaces;

(b) good mix design; and

(c) correct construction practices, including adequate fixing of reinforcement and theplacing, compacting and curing of the concrete,

all of which are important.

This Standard specifies requirements for only some of these areas. Reference should alsobe made to the Institution of Engineers Code of Practice: Quality Assurance for DurableConcrete Structures (Ref. 3) and the CIA Recommended Practice: Durable Concrete

(Ref. 4).

C4.1 APPLICATION OF SECTION The fact that these requirements are minimumrequirements is emphasized in the concluding note. Provisions are formulated for only alimited range of environments, considering a limited number of types of attack, e.g.corrosion of reinforcement and abrasion.

Reactions between the alkalis in cement and reactive silica or other alkali-reactiveconstituents in aggregates are also possible causes of deterioration. They are collectivelyknown as alkali-aggregate reaction (AAR). Generally, the reaction and its products aresensitive to the presence of moisture. I n the presence of m oisture the products swell andoccupy a greater volume than the initial constituents. This may lead to cracking and

deterioration of the concrete. Usually, the reaction is slow but the consequences mayinvolve the demolition of the structure. Three conditions must be fulfilled for A AR tooccur; the presence of reactive aggregates; a sufficient supply of alkalis; the presence ofadequate moisture. The problem can be avoided by not using reactive aggregates, limitingthe available alkalis or keeping the member dry. While the occurrence of AAR inAustralia is rare and has been largely confined to North Queensland and WesternAustralia, designers should be aware of the potential problem. It was however believedthat nothing particular in this regard need be specified in the Standard. For furtherinformation see Reference 18.

The current state of knowledge of durability design is not sufficiently advanced for designlife to be used as an input parameter within the Standard. Therefore, the requirementshave been formulated for buildings with a normal design life of 40 to 60 years in mind.For monumental structures more stringent requirements should be adopted: fortemporary structures less rigorous requirements may be acceptable.

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C4.2 DESIGN FOR DURABILITY This Clause sets out the procedure for design fordurability, i.e. determination of the exposure classification followed by consideration ofconcrete quality, chemical content and cover.

The S tandard recognizes corrosion of reinforcement to be the most common and obviousform of durability failure. This can manifest itself as any one of, or a combination ofsurface staining, cracking along r einforcement close to a surface and spalling of a surface.

The following simplified explanation of the corrosion process will assist users inunderstanding the basis of measures provided in the Standard to prevent this type ofdurability failure.

For simplicity, the process of corrosion can be divided into two phases initiation andpropagation. Generally the reinforcement is protected against corrosion by the alkalinityof the concrete surrounding it. The initiation phase is considered to be the period overwhich this alkalinity is reduced to the level where active corrosion can commence. Thepropagation phase is considered to be the period from commencement of corrosion to thestage where corrosion products cause a failure in the surrounding concrete.

In the initiation phase, the protection afforded by the alkalinity of the concrete can bereduced by two processes carbonation (neutralization of the high pH by infiltration ofatmospheric carbon dioxide, a slow, continuous process) and ionization (an increase in theconcentration of reactive ions such as chlorides, a relatively rapid, random process).

In the propagation stage, the reinforcement will corrode at a rate which depends on theavailability of oxygen and moisture, the temperature of the concrete, the presence ofreactive ions and residual alkalinity.

It follows from the above that the time to initiation and the subsequent rate of corrosionwill depend to a large extent on the environment to which a concrete surface is exposed.For a given quality and thickness of cover, hot, humid seaside environments lead to morerapid corrosion rates than cooler, dry inland environments. Thus for a given durability

level, exposure to the former environment will require thicker covers and better qualityconcrete than exposure to the latter environment.

Chloride ions can be introduced into the concrete by way of admixtures, contaminatedaggregates, salt depositions on reinforcement and formwork, or they can permeate into thehardened concrete during acid etching or from salt spray deposited on the membersurface. Limitations, therefore, are placed on the quantity of chlorides which can beintroduced into the fresh concrete from any source (see Clause 4.9).

The procedure given in the Standard for durability design is firstly to classify the severityof the environment to which the concrete surfaces are exposed. For that exposureclassification, a minimum concrete quality is specified by strength and, wherereinforcement is to be protected, a minimum cover is then required. The basic principle is

that where corrosion of the reinforcement, once initiated, is likely to be fast, then higherlevels of protection are required. More severe environments require increasingly betterprotection and this is reflected by the r equirement for better quality concrete and largercovers.

Because strength can be easily specified and measured, fc has been adopted as the qualitycriterion. However it should be remembered that fc is at best only an indirect measure ofconcrete quality from a durability viewpoint (Ref. 13), in reality reflecting the quality ofconcrete after 28-day curing in a fog room. This amount of curing is seldom achieved onthe site. Research by the CSIRO (Ref. 5) has shown the importance of early, continuouscuring and this is the basis for the curing requirements for concrete in the variousexposure classifications (Clauses 4.4 and 4.5). The findings also stressed that, after initialcuring, further improvement in concrete properties due to exposure to the weather is

doubtful, being highly dependent on the orientation of the member and local climaticconditions.

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Appropriate covers for the given exposure classification, depending on the chosenconcrete quality, are specified in Clause 4.10.

Requirements for abrasion resistance and exposure to freezing and thawing are additionalto the general requirements of Clause 4.2.1. For example, a concrete pavement wouldhave to satisfy the requirements for abrasion resistance (Clause 4.7) and may, dependingon its location, also need to satisfy the requirements f or freezing and thawing (Clause 4.8)in addition to the requirements given in Clauses 4.3 to 4.6.

C4.3 EXPOSURE CLASSIFICATION An important part of the new provisions is thesystem of exposure classification. This classification focuses on conditions leading tocorrosion of reinforcement. However, guidance is also given regarding the severity ofattack on the concrete itself.

Definitions of environmental conditions have been derived from the general conceptsgiven in AS 2312 (Ref. 6). The classifications may be summarized as follows:

(a) Exposure classifications A1 and A2 relatively benign environments, such as in theinterior of most buildings, or in inland country towns remote f rom the coast, w herethe provision of adequate cover will give satisfactory performance.

(b) Exposure classifications B1 and B2 moderately aggressive environments, such aslocations close to the coast, for which protection can be satisfactorily provided by acombination of appropriate concrete quality and associated cover.

(c) Exposure classification C the most aggressive environments for which guidance isgiven on concrete quality and cover.

(d) Exposure classification Uthese are environments for which the Standard gives noguidance. They may be more severe than exposure classification C, or as benign asexposure classification A1. For them the designer has to quantify the severity of theexposure along the above lines and choose methods of protection relevant to that

exposure.A conflict exists between the effect of climate on the r ate of carbonation (and therefore,the time to initiation of corrosion) and its effect on the rate of corrosion once initiated.For the purpose of the Standard, the rate of corrosion of the steel (i.e. the propagationphase) has been taken as the dominant factor for the following reasons:

(i) In severe climates of high humidity or tropical conditions, although subsequentcuring by weather may be better and carbonation might be slower, the presence ofmoisture and probable chlorides means that corrosion, once initiated, could proceedat a rapid rate.

(ii) For a dry climate, although the rate of carbonation might be high, the propagationof the corrosion, once initiated, proceeds at a negligible rate.

In practical terms, the climatic conditions are less significant than proximity to the coast.The closer to the sea, the more severe the exposure tends to be, with wind-driven sprayimposing a heavy load of chlorides on exposed concrete. In some circumstances, the limitof 1 km for B2 exposure classification should be increased and this is discussed in Note 5to Table 4.3. For example, many locations in N.S.W. are known to be influenced bystrong NE winds which carry chlorides well inland. On the other hand, high coastal cliffsmay offer some protection. The protected conditions inside the reef in northernQueensland do not seem to lead to such severe conditions as are experienced in areasadjacent to exposed seas but the 1 km limit would still be prudent in such cases.

Structures actually built in the water are covered in Table 4.3. Structures occasionallysubject to direct contact by the sea should be assessed by the designer as to the

appropriate classification of B2 or C.

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The emission of certain pollutants by industry is known to increase the risk of degradationof the concrete or corrosion of r einforcement. Industrial plants burning sulfide-containingfuels, or emitting acidic gases, may be considered a severe risk and subject to theindustrial classification. The limit of 3 km given in the Standard r epresents a r easonableestimate, but engineering judgement should be used, depending on the nature and scale of

the industrial pollutants and the prevailing wind directions.Contact with liquids is a difficult area in which to provide firm classifications. Freshwater can cause significant leaching of the partly soluble concrete components, as canrepeated exposure to condensation. Running water and frequent wet-and-dry cycles inwater-retaining structures can also cause physical and chemical degradation. Theseproblems become additive to those associated with reinforcement corrosion. The Standardproposes a range of classifications, based primarily on experience, which depend on thetype of structure. Exposure to tidal and splashing salt water is classified as C. Themore-moderate exposure of being permanently submerged in seawater is classified as B2.Despite the high content of sulfates and chlorides in seawater, an extra level of protectionis provided by the formation of an impermeable surface layer of carbonates, and the lackof dissolved oxygen, particularly at depth.

The S tandard focuses on groundwater containing sulfates, or sulfides that may oxidize tosulfates, which can attack concrete in a rapid and destructive manner. Groundwatercontaining high levels of chlorides or organic matter can also be destructive. Higherquality concrete can provide some protection, but for groundwater containing more than1 gram/litre of sulfates, special cements and other protective methods are needed. Sulfateattack is unlikely to be a problem in clay soils because of their low permeability.

The protection offered by an impermeable membrane under a slab on the surface of theground should provide an environment equivalent to classification A 1.

For practical reasons only one grade of concrete will be used in any member, therefore thequality is determined by the most severe exposure classification for any of the surfaces

(see Figure C4.3.1).

FIGURE C4.3.1 SELECTION OF CONCRETE GRADE

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Care should be exercised when assessing the ability of a surface coating to protect thesurface and to continue to do so during the life of the building. Originally, it was hopedthat a definition of impermeability could be produced to aid in this. However, it provedtoo difficult to firstly define an appropriate test method and secondly to determinesuitable limiting values.

The choice of a suitable coating is outside the scope of the Standard, but the designershould be w arned that an inadequate, poorly maintained coating m ay lead to more rapiddegradation than no coating (Ref. 7).

C4.3.2 Concession for exterior exposure of a single surface An illustration of theinterpretation of this Clause is shown in Figure C4.3.2.

FIGURE C4.3.2 ILLUSTRATIONS OF CONCESSION FOR EXTERIOR EXPOSURE OFAN EDGE OR SINGLE SURFACE

C4.4 REQUIREMENTS FOR CONCRETE FOR EXPOSURE CLASSIFICATIONSA1 AND A2 The r equirements for concrete are a minimum fc and an initial curingperiod of not less than three days. Where accelerated curing methods are used, e.g. steamcuring in a precast factory, a minimum average compressive strength is required,determined in accordance with the principles of Clause 19.6.2.8.

C4.5 REQUIREMENTS FOR CONCRETE FOR EXPOSURE CLASSIFICATIONSB1, B2 AND C The strength and curing r equirements are similar to, but more stringentthan, those of the previous Clause. Where accelerated curing methods are used, e.g. steamcuring in a precast factory, a minimum average compressive strength is required,determined in accordance with the principles of Clause 19.6.2.8.

The addition of fly ash, slag or silica fume to portland (GP) cement may improve theimpermeability and the long-term durability of concrete made with such blends, providedthat appropriate adjustments have been made to the mix design by the supplier and propercompaction and curing have been carried out on site. However, these supplementarymaterials (particularly fly ash and slag) may also reduce the rate of strength gain of theconcrete at early ages. For normal-class concrete w here early-age strength is a design orconstruction consideration (e.g. f or durability, early stripping or prestressing), it thereforerecommended that specification of the early-age option given in AS 1379 (i.e. the additionof the suffix E3 or E7 to the grade designation) is exercised. This should ensure that both

the strength and durability requirements of this S tandard can be satisfied by normal-classconcrete made from a wide range of blended mixes.

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Where special-class concrete is required, additional parameters are also to be specified,namely cement type and content, taking due account of the nature and severity of theenvironmental exposure. As a guide to the specifier, Table C4.5 sets out suggestedminimum cement content for special-class concretes, although the amount actually neededwill depend on the type of cement and type of aggregates being used.

Water-to-cement r atios have not been given in the Standard or this Table because firstlythey cannot be readily measured once the concrete has been mixed, and secondly theyhave not been conclusively shown to be any better measure of durability thancharacteristic compressive strength.

TABLE C4.5

SUGGESTED MINIMUM CEMENT

CONTENTS FOR SPECIAL-CLASS

CONCRETE

Exposure

classification

Required

minimum fc

(MPa)

Suggested minimum

cement content

(kg/m 3)

B1

B2

C

3240

50

285330

400

C4.6 REQUIREMENTS FOR CONCRETE FOR EXPOSURE CLASSIFICATION UExposure classification U will include a range of exposures from more severe than C,down to those as benign as A1. In many cases classifications ranging f rom A1 to C maybe selected, based on the principles of Clause 4.3. Guidance on appropriate measures forsome severe exposures is given in the following references.

Durability in general: Reference 14

Liquid-retaining structures: Reference 15

Salt water (marine exposure): Reference 16

Sulfates: Reference 12

Acids, sulfuric acid, carbonic acid and soft water: Reference 17

For guidance on coatings: Reference 18

Reference(5) should also be consulted for further information.

C4.7 ADDITIONAL REQUIREMENTS FOR ABRASION Abrasion of industrialfloors is a common cause of serviceability failure. Compressive strength was selected asthe most important, readily specified parameter but consideration should also be given to

methods of construction (Ref. 8), since abrasion resistance is strongly influenced bycuring and surface finish as well as compressive strength.

The Clause specifies additional requirements for abrasion exposure, i.e. the concrete mustalso satisfy the requirements for other exposure criteria. For example, concrete for areinforced concrete external pavement subject only to light, pneumatic-tyred traffic, butlocated in the coastal zone, would have to comply with the requirements for B2 and thoserequirements would take precedence. On the other hand, for an internal factory floorsubject to m edium to heavy pneumatic-tyred traffic, the requirements for abrasion underthis Clause would take precedence.

C4.8 ADDITIONAL REQUIREMENTS FOR FREEZING AND THAWING Th erole of air entrainment in providing resistance to freeze-thaw degradation is wellestablished and this Clause presents the usually accepted values. Those given represent anenvelope of accepted practice. In general the larger the nominal aggregate size, the lowerthe required amount of entrained air to give the desired protection.

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Severity of exposure is also dependent on the presence of moisture on the s urface prior tofreezing (Refs 9 and 10).

If the surface is also subject to abrasion, the upper values of air entrainment given may betoo high to permit the desired abrasion r esistance to be achieved; if so, an intermediatevalue will have to be chosen.

C4.9 RESTRICTION ON CHEMICAL CONTENT IN CONCRETE

C4.9.1 Restriction on chloride-ion content for corrosion protection The protectionof reinforcement by the provision of an adequate cover of dense concrete relies primarilyon the protection afforded by the alkalinity of the concrete. This protection will preventthe initiation of corrosion until carbonation has advanced close to the steel surface,which usually takes decades. However, if chloride-ions are present, corrosion can beinitiated even in an alkaline environment. Moreover, chloride-ions accelerate the corrosionprocess so their presence should be minimized.

When considering the effect of chlorides on corrosion it is necessary to distinguishbetween free chloride present in the pore water and chloride bound by the cement in thematrix. The bound chlorides do not take part directly in corrosion, whereas the free

chlorides may rupture the passive protective film on the surface of the bars. Freechloride-ions increase the electrical conductivity of the pore water and the rate ofdissolution of m etallic-ions. Nevertheless, as the proportion of free to bound chloridesis subject to change, and bound chlorides may go into solution, it is considered desirableto place limits on the total chloride content rather than just the free chloride content. Forthis reason limits were placed on the acid-soluble chlorides, as determined by standardtest, which are closely related to total chlorides.

Limits on chloride-ion content are quoted as mass per cubic metre of concrete which isconsistent with the test method. To simplify the application of normal-class concrete theone level of 0.8 kg/m 3 is given for reinforced,