as 1720-1988 part 1 - timber structures

AS 1720.1—1988

Australian Standard

SAA TIMBER STRUCTURES CODEPart 1—DESIGN METHODS

This Australian Standard was prepared by Committee TM/102, timber Engineering. Itwas approved on behalf of the Council of the Standards Association of Australia on21 April 1988 and published on 15 July 1988.

The following interests are represented on Committee TM/102:

Australian British Chamber of Commerce

Australian Federation of Timber Merchants Associations

Australian Institute of Building

Australian Timber Importers’ Federation

CSIRO, Division of Construction and Engineering

Department of Forestry, Qld

Electricity Supply Association of Australia

Forest Products Association, W.A.

Forestry Commission of N.S.W.

Master Builders Federation of Australia

National Association of Australian State Road Authorities

New South Wales Timber Advisory Council

Public Works Department, New South Wales

Radiata Pine Research Institute Inc.

Rail Track and Sleeper Association

Railways of Australia Committee

Royal Australian Institute of Architects

Tasmanian Timber Promotion Board

The Association of Consulting Engineers Australia

Timber Merchants Association of South Australia

Timber Merchants Association of Victoria

Timber Preservers Association of Australia

Timber Promotion Council

Timber Research and Development Advisory Council

Timber and Building Material Merchants Association, N.S.W

Universities and colleges

Victorian Sawmillers Association

Woods and Forests Department, S.A

Additional interests participating in preparation of Standard:

Australian Timber Research institute Inc.

Australian Uniform Building Regulations Co-ordinating Council

Review of Australian Standards.To keep abreast of progress in industry, Australian Standards are subjectto periodic review and are kept up to date by the issue of amendments or new editions as necessary. It isimportant therefore that Standards users ensure that they are in possession of the latest edition, and anyamendments thereto.

Full details of all Australian Standards and related publications will be found in the 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which subscribing members receive, and which gives details of new publications, new editionsand amendments, and of withdrawn Standards.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 to 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 madewithout delay in order that the matter may be investigated and appropriate action taken.

This Standard was issued in draft form for comment as DR 83171.

AS 1720.1—1988

Australian Standard

SAA TIMBER STRUCTURES CODEPart 1—DESIGN METHODS

First published as AS CA65—1972.Revised and redesignated AS 1720—1975.Revised and redesignated AS 1720.1—1988.Incorporating:Amdt 1—1993

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

ISBN 0 7262 5090 2

AS 1720.1—1988 2

PREFACE

This Standard was prepared by the Association’s Committee on Timber Engineeringto supersede AS 1720—1975,SAA Timber Engineering Code.

In considering the revision of AS 1720—1975 the committee decided that it would beappropriate if its subject matter and other material to be included in the revision wasdivided into four parts as follows:

Part 1: Design methods(this Standard)

Part 2: Timber properties(in course of preparation)

Part 3: Non-standard connectors(in course of preparation

Part 4: Fire resistance of timer structures(in course of preparation)

While this Standard is primarily concerned with design methods, it also containsstructural design properties for a modest range of timber species and metal connectors.Section 1 deals with general matters such as definitions and conditions for theapplication of this Standard. Design rules are given in Sections 2 to 7, with Section 2containing the basic structural design properties of timber essential to the use of theStandard.

Normal procedure for users is to note the general requirements of Section 1, obtain thebasic structural design properties from Section 2 and then to proceed to one ofSections 3 to 7 depending on th type of element being designed.

In general, the simpler design situations are covered in the main body of the text, andacceptable procedures for detailed design situations are given in the related appendices.For ease of use the appendices correlate sequentially with the sections of the text, i.e.Appendices A, B, C etc are related to the Sections 1, 2, 3, etc, in the main body of thistext. It should be noted that Appendix A gives rules for the acceptance of timberstructures based on proof and prototype testing.

The appendices, which form an integral part of this Standard, have been drafted inmandatory terms to facilitate cross reference by Regulatory Authorities.

Design information for timber piles which was included in the previous edition of thisStandard is now provided in AS 2159,SAA Piling Code.

Copyright STANDARDS AUSTRALIA

Users of Standards are reminded that copyright subsists in all Standards Australia publications and software. Except where theCopyright Act allows and except where provided for below no publications or software produced by Standards Australia may bereproduced, stored in a retrieval system in any form or transmitted by any means without prior permission in writing fromStandards Australia. Permission may be conditional on an appropriate royalty payment. Requests for permission and information oncommercial software royalties should be directed to the head office of Standards Australia.

Standards Australia will permit up to 10 percent of the technical content pages of a Standard to be copied for useexclusively in-house by purchasers of the Standard without payment of a royalty or advice to Standards Australia.

Standards Australia will also permit the inclusion of its copyright material in computer software programs for no royaltypayment provided such programs are used exclusively in-house by the creators of the programs.

Care should be taken to ensure that material used is from the current edition of the Standard and that it isupdated whenever theStandard is amended or revised. The number and date of the Standard should therefore be clearly identified.

The use of material in print form or in computer software programs to be used commercially, with or without payment, or incommercial contracts is subject to the payment of a royalty. This policy may be varied by Standards Australia at any time.

3 AS 1720.1—1988

CONTENTS

Page

SECTION 1. SCOPE AND GENERAL

1.1 SCOPE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51.2 REFERENCED DOCUMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . 51.3 NEW MATERIALS AND METHODS . . . . . . . . . . . . . . . . . . . . . 51.4 TIMBER QUALITY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51.5 GENERAL DESIGN CONSIDERATIONS . . . . . . . . . . . . . . . . . . 51.6 DESIGN AND SUPERVISION . . . . . . . . . . . . . . . . . . . . . . . . . . 61.7 WORKMANSHIP AND MAINTENANCE . . . . . . . . . . . . . . . . . . 71.8 DEFINITIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71.9 NOTATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71.10 UNITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

SECTION 2. BASIC PROPERTIES OF STRUCTURAL TIMBER

2.1 GENERAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82.2 STRUCTURAL CLASSIFICATIONS . . . . . . . . . . . . . . . . . . . . . . 82.3 BASIC WORKING STRESSES AND MODULUS OF ELASTICITY 82.4 DESIGN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82.5 MODIFICATION FACTORS . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

SECTION 3. DESIGN OF BASIC STRUCTURAL MEMBERS

3.1 GENERAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183.2 BEAM DESIGN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183.3 COLUMN DESIGN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213.4 TENSION MEMBER DESIGN . . . . . . . . . . . . . . . . . . . . . . . . . 223.5 COMBINED BENDING AND AXIAL STRESSES . . . . . . . . . . . 22

SECTION 4. CONNECTIONS

4.1 GENERAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234.2 NAILED JOINTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234.3 SCREWED JOINTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264.4 BOLTED JOINTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274.5 COACH SCREWS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 364.6 SPLIT-RING CONNECTORS . . . . . . . . . . . . . . . . . . . . . . . . . . 374.7 SHEAR PLATE CONNECTORS . .. . . . . . . . . . . . . . . . . . . . . . 37

SECTION 5. PLYWOOD

5.1 GENERAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 405.2 BASIC WORKING STRESSES AND STIFFNESS . . . . . . . . . . . 405.3 DESIGN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 405.4 MODIFICATION FACTORS . . . . . . . . . . . . . . . . . . . . . . . . . . 405.5 JOINTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

SECTION 6. ROUND TIMBERS

6.1 GENERAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 436.2 BASIC WORKING STRESSES AND STIFFNESS . . . . . . . . . . . 436.3 DESIGN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 436.4 ADDITIONAL MODIFICATION FACTORS . . . . . . . . . . . . . . . 436.5 DESIGN DETAILS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

SECTION 7. GLUED-LAMINATED CONSTRUCTION

7.1 GENERAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 457.2 DESIGN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 457.3 MODIFICATION FACTORS . . . . . . . . . . . . . . . . . . . . . . . . . . 457.4 OTHER REQUIREMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

AS 1720.1—1988 4

Page

APPENDICES

A ACCEPTANCE TESTING OF TIMBER STRUCTURES ANDELEMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

B BASIC DESIGN PROPERTIES OF STRUCTURAL TIMBER . . . 52C DESIGN OF BASIC STRUCTURAL MEMBERS . . . . . . . . . . . . 53D JOINTS IN TIMBER STRUCTURES . . . . . . . . . . . . . . . . . . . . . 67E BUCKLING STRENGTH OF PLYWOOD DIAPHRAGMS . . . . . 71F CONNECTIONS FOR ROUND TIMBERS . . . . . . . . . . . . . . . . . 76G GLUED-LAMINATED CONSTRUCTION—SPECIAL CONDITIONS 77H REFERENCED AND RELATED DOCUMENTS . . . . . . . . . . . . . 79I NOTATION AND FACTORS . . . . . . . . . . . . . . . . . . . . . . . . . . 80

INDEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85

5 AS 1720.1—1988

STANDARDS ASSOCIATION OF AUSTRALIA

Australian Standard

TIMBER STRUCTURES

PART 1: DESIGN METHODS

SECTION 1. SCOPE AND GENERAL

1.1 SCOPE.This Standard sets out the design methodsfor the structural use of timber which are based on theprinciples of structural mechanics and on data establishedby research. The Standard is intended for use in thedesign or appraisal of structural elements comprised oftimber or wood products and of structures comprisedsubstantially of timber. To this end, the Standardprovides design data for sawn timber, laminated timber,timber in pole form, plywood and various types offastenings. In addition, it provides methods of test forcomponents or assemblies of unconventional designwhich may not be readily amenable to detailed analysis.

For ease of use, the simpler design situations are coveredin the main body of the text. Related appendices, whichform an integral part of the Standard, give acceptableprocedures for detailed design situations.

1.2 REFERENCED DOCUMENTS. A list with titlesof the documents referred to in this Standard is given inAppendix H.

1.3 NEW MATERIALS AND METHODS. ThisStandard shall not be interpreted to prevent the use ofmaterial or of methods of design or construction notspecifically referred to herein. Nor is the classification oftimbers into strength groups (Clause 1.4) or theirgrouping for joint design (Clause 4.1) to be interpretedas precluding the use of design stresses or other designdata derived for a particular timber or grade of timber onthe basis of authoritative research information.

NOTE: It usually will be necessary to seek approval from theBuilding Authority or other appropriate Regulatory Authority for theuse of new materials or methods.

1.4 TIMBER QUALITY. All timber used in accordancewith this Standard shall comply with the requirements ofappropriate Australian Standards. The following pointsshall be noted:

(a) General. Tables 2.1 and 2.2 herein and AS 1720.2,list common species used for structural purposestogether with their strength classifications and designdensity.

(b) Timber classification. Timber species are classifiedinto seven strength groups S1 to S7 in theunseasoned condition and eight strength groups SD1to SD8 in the seasoned condition. The timber speciesare also classified into six joint groups J1 to J6 ifused unseasoned, and JD1 to JD6 if used seasoned.Sawn structural timber, pole timbers and plywoodare classified into 12 stress grades F2 to F34 whenthese have been graded according to the appropriategrading Standard or other approved specification.

(c) Stress grade and species identification.Structuraltimber used in conjunction with this Standard shallhave its stress grade identified.

For many purposes it may also be necessary tospecify a particular species. When a particularspecies is specified the specification shall requirethat all pieces of timber be suitably identified as tospecies.NOTES:1. The design properties recommended in this Standard have

been chosen on the assumption that structures of unseasonedtimber that are allowed to dry will not receive their full designload until a period of air drying for at least 2 weeks has takenplace. Freshly sawn timber which is unseasoned, or hasrecently been treated with waterborne chemicals, tends to havea reduced resistance and stiffness to sustained loads during theinitial drying period.

2. Usually, only a limited number of the timber species andstress grades listed in this Standard will be readily available atany particular place and time.

(d) Change of grade or durability.Care shall be takento account for any change in original grading orpreservative treatment as a result of sawing ordressing. Regrading will be necessary if membersare longitudinally resawn. Machining may removepreservative envelopes rendering the treatmentineffective.

(e) Special provisions.Design loads for timber jointsand design rules for notched beams given herein arebased on the assumption that there are no looseknots, severe sloping grain, gum veins, gum or rotpockets, lyctus-susceptible sapwood, holes or splitsin the near vicinity of any connectors or notch roots.

(f) Treated timber.Timber, treated by impregnationwith waterborne chemicals such as preservatives, isclassified as unseasoned timber unless seasoning isspecified.NOTE: Where the material is reseasoned, regrading wouldnormally be required.

1.5 GENERAL DESIGN CONSIDERATIONS.

1.5.1 Loads.

1.5.1.1 General. A structure, and any part of astructure, shall be designed for the loads specified inAS 1170 or such other loading Standard as is appropriateto the end-use of a specific structure or part of astructure.

1.5.1.2Load duration.The significance of duration ofloading in the design of timber structures shall be notedand particular attention paid to the term ‘duration ofloading’. (For the definition of this term see Clause 1.8.2and for further information Clause 2.5.1.)

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AS 1720.1—1988 6

1.5.2 Design methods.

1.5.2.1 General.A structure, or part of a structure, oran individual structural element shall be capable ofsustaining the most adverse likely combination of loads.Every part of the structure shall be proportioned so thatthe permissible stresses determined in accordance withthis Standard are not exceeded.

NOTE: Some of the clauses of this Standard have been simplified asfar as practicable to permit rapid calculation and may as aconsequence involve some degree of conservatism. Whereappropriate, more refined design methods are given in theappendices which form an integral part of this Standard.

1.5.2.2 Stress analysis.All stresses shall be calculatedon the basis of elastic theory in order that therequirements of this code in regard to permissiblestresses may be satisfied with regard to the load effectsat any particular location. For example the appliedbending momentM and shear forceV on a beam ofrectangular cross-section shall be checked by—

M ≤ (bd2/6)Fb . . . . . . . . . . . . . . . . . . . . . (1.1)V ≤ (2bd/3)Fs . . . . . . . . . . . . . . . . . . . . . (1.2)

whereb andd = the breadth and depth of the memberFb andFs = the permissible design stresses in

bending and shear.

When several materials are glued together to form astructural element, stresses may be calculated from anequivalent transformed section, where the transformationis made with respect to the moduli of elasticity.

1.5.2.3Experimentally based design.Where a structureor a structural element is of an unconventional orcomplex nature, and it is demonstrated by the full-scaletests specified in Appendix A that requirements forstrength, deformation, stability and serviceability aresatisfied, the corresponding design requirements of thisStandard shall be deemed also to have been satisfied.

1.5.3 Other design considerations.

1.5.3.1Stability.The stability of the structure as a wholeshall be investigated, and mass and anchorage shall beprovided so that the structure is in overall equilibrium.

NOTE: Suitable recommendations for this purpose will be given inAS 1170.1.

1.5.3.2Buckling restraints.Where there may be somedoubt as to the effectiveness of buckling restraints,appropriate computations, such as those indicated inParagraph C7, Appendix C, shall be made to check thestiffness and strength of the restraints.

1.5.3.3Erection and other extraneous forces.Adequateprovision shall be made to resist the lateral and otherforces that can occur during the transport of structuralelements, and during and after the erection of a structure.

1.5.3.4Secondary stresses.Careful consideration shall begiven to possible secondary stresses. Where these cannotbe reduced to negligible proportions, suitable provisionsin the design or some reduction in permissible primarystresses shall be made.

1.5.3.5 Shrinkage. When using unseasoned timber,consideration shall be given to the effects of shrinkage.Detailing of the joints shall not restrain shrinkage wheresplitting could render the joint ineffective. Considerationshall also be given to architectural detailing to avoid

damage or unsightly appearances resulting fromdifferential movement on structural members caused bytimber shrinkage. These comments also apply to timberwhich has been impregnated with waterborne chemicalsand which has not been reseasoned after treatment.

NOTE: For most timbers the magnitude of shrinkage is in the rangeof 0.1% to 0.3% in the direction of the wood grain and 2% to 10%transverse to this direction. Information on shrinkage for specificspecies can be obtained from:(a) KINGSTON, R.S.T. and RISDON C.J.E. ‘Shrinkage and

Density of Australian and Other South-west Pacific Woods’.Division of Forest Products Technological Paper No 13,CSIRO, 1961.

(b) BUDGEN, B. ‘Shrinkage and Density of some Australian andSouth-east Asian Timbers’. Division of Building ResearchTechnological Paper (Second Series) No 38, CSIRO, 1981.

1.5.3.6Deformations.Timber structures shall be designedso that deformations incurred in-service do not impair thestrength and serviceability of the structures or any partthereof, nor cause damage to other building components.Timber members shall have sufficient stiffness so thatundesirable deflections and vibrations are avoided.

NOTES:1. The responsibility for deflection and stiffness limits should rest

with the design engineer.2. In computing design deflections, it should be appreciated that

timber is variable with respect to its structural properties. Itshould also be noted that the moduli given in Table 2.3 refer todesign values for groups of timber. If for some reason (e.g. tospecify camber) accurate predictions of deflection are required,detailed information relevant to the specific species of timberunder consideration should be used.

1.5.3.7Timber dimensions for engineering calculations.All engineering calculations shall be based on theminimum net cross-section. Such calculations shall notbe based on the nominal cross-section.

1.5.3.8Timber in natural pole form.For logs or polescomplying with the quality requirements of AS 2209, thecorrespondence between strength groups and stressgrades is as shown in Table 6.1.

1.5.3.9Biological deterioration.Generally, timber undercover and in well ventilated conditions and not in contactwith the ground or free water, is not subject to fungalattack. However, such timber may be subject to termiteattack and to attack by other insects in parts of Australia.If conditions favourable for biological attack exist, thensteps shall be taken to eliminate the hazards. This isparticularly important in structures where there is no loadsharing capacity, e.g. large trusses.

1.6 DESIGN AND SUPERVISION.1.6.1 Design.The design of timber structures to whichthis Standard applies, including the specification ofmaterials and any protective treatment, shall be carriedout in accordance with the requirements of this Standardand the relevant documents in Appendix H.

NOTE: The design of a structure complying with this Standardshould be the responsibility of a design engineer experienced in thedesign of such structures.

1.6.2 Supervision.The fabrication and erection of thetimber structures or the parts of structures to which thisStandard applies shall be supervised to ensure that all ofthe requirements of the design are satisfied in thecompleted structure.

NOTE: The supervision of fabrication and erection of timberstructures should be the responsibility of a supervision engineerexperienced in the fabrication and erection of such structures.

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7 AS 1720.1—1988

1.7 WORKMANSHIP AND MAINTENANCE.1.7.1 General.The following requirements are intendedto help ensure that a structure or element whenfabricated performs, and will continue to perform,structurally in the manner intended by the designer of thestructure.1.7.2 Moisture content.When structures or elements areto be fabricated with seasoned timber in situations wheredimensional stability is critical, the designer of thestructure shall ascertain the average equilibrium moisturecontent for the environment in which the structures orelements are to be erected, and shall specify that eachpiece of timber used shall have an average moisturecontent at the time of fabrication that is within 3 percentof the equilibrium value.

NOTES:1. Definitions used in this Standard for the moisture content of

seasoned and unseasoned timber are given in Clause 1.8.2. Forintermediate values of moisture content, the term ‘partiallyseasoned timber’ will be used.

2. Information on equilibrium moisture content values in timberslocated in Australia can be obtained from the followingreferences:(a) FINIGHAN, R. ‘Moisture Content Predictions for Eight

Seasoned Timbers under Sheltered Outdoor Conditions inAustralia and New Guinea’. Division of Forest ProductsTechnological Paper No 44, CSIRO, 1966.

(b) BRAGG, C. ‘An Equilibrium Moisture Content Survey ofTimber in Queensland’. Queensland Department ofForestry Technical Paper No 40, QFD, 1986.

1.7.3 Corrosion.The designer of the structure shall takedue account of any possible corrosive effects on metalconnectors.

NOTE: Information on the protection of steel can be obtained fromAS 2312.

1.7.4 Maintenance.Where in the opinion of the designerof a structure special maintenance is required for astructure to fulfil its intended function, then suchmaintenance shall be specified in relevant documents.

1.8 DEFINITIONS. For the purpose of this Standard,the definitions given in AS 01 and those below apply.

1.8.1 Administrative definitions.

Building Authority or other Regulatory Authority— bodyhaving statutory powers to control the design anderection of buildings or structures, including scaffolding,in the area in which the building or structure concernedis to be erected.

Engineer—person qualified for Corporate Membership ofThe Institution of Engineers, Australia.

NOTE: The definition of engineer does not require that the personbe a Corporate Member of The Institution of Engineers.

1.8.2 Technical definitions.

Basic working stress—stress appropriate to an arbitrarilychosen, but constant, basic reference set of conditions. Itis derived from the known strength properties of atimber, due allowance having been made for such factorsas material variability, long-duration loading, grade oftimber, and a safety factor.

Basic working load for connectors—load appropriate toan arbitrarily chosen, but constant, basic reference set ofconditions. It is derived from the known strengthproperties of the timber-connector system, due allowancehaving been made for such factors as material variability,

long-duration loading, grade of timber, and a safetyfactor.

Collapse-susceptible timber—timber for which theshrinkage values before and after reconditioning differ bymore than 2 percent.

NOTE: Information on shrinkage values can be obtained from:(a) KINGSTON, R.S.T. and RISDON C.J.E. ‘Shrinkage and

Density of Australian and Other South-west PacificWoods’. Division of Forest Products Technological PaperNo 13, CSIRO, 1961.

(b) BUDGEN, B. ‘Shrinkage and Density of some Australianand South-east Asian Timbers’. Division of BuildingResearch Technological Paper (Second Series) No 38,CSIRO, 1981.

Corewood—timber adjacent to or including the pith, thatis of density less than 80 percent that of the density ofmature trees.

NOTE: For plantation grown softwoods, corewood may be avoidedby excluding all timber within a radius of 50 mm from the pith, thathas a ring width greater than 6 mm.

Duration of loading—period during which a member, astructural element or a complete structure is stressed asa consequence of the loads applied.

NOTES:1. For the purposes of interpretation in the use of load-duration

factors in this Standard, see Clause 2.5.1.2. The strength properties of timber under load are time dependent.

In-grade verification — verification of the designproperties assigned to stress graded timber. Whereapplicable, these properties shall be evaluated inaccordance with AS 4063.

NOTE: Where AS 4063 is employed to assign design properties tostress graded timber, the stress grading procedures should besubjected to a continuing quality-control program.

Permissible stress—maximum stress to be used in thedesign of an element of a structure. It is obtained fromthe basic working stress appropriately modified for thetype of structure and service conditions.

Seasoned timber—wood in which the maximum moisturecontent anywhere within a piece does not exceed15 percent.

NOTE: Seasoned timber is sometimes referred to as ‘dry’ or ‘air-dried’ timber. It includes kiln-dried timber.

Stress grade—classification of timber for structuralpurposes by means of either visual or machine gradingto indicate the basic working stresses and stiffnesses tobe used for structural design purposes.

NOTE: The stress grade is designated in a form such as ‘F7’ whichindicates that, for such a grade of material, the basic working stressin bending is approximately 7 MPa.

Unseasoned timber—wood in which the averagemoisture content of each piece exceeds 25 percent.

NOTE: Unseasoned timber is sometimes referred to as ‘green’timber.

1.9 NOTATION. Except where specifically defined ina particular clause, the quantity symbols and factors usedin this Standard are listed in Appendix I.

1.10 UNITS. Unless otherwise stated, the units ofmeasurement used in this Standard are in accordancewith the International System of Units (SI).

NOTE: In general N (newton), mm (millimetre) and MPa(megapascal) are appropriate units to be used.

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AS 1720.1—1988 8

SECTION 2. BASIC PROPERTIES OF STRUCTURAL TIMBER2.1 GENERAL. Permissible stresses for structuraltimber shall be obtained through modifying basicworking values by factors appropriate to the serviceconditions. This general procedure applies to all types ofstructural timber, including sawn timber, laminatedtimber, natural round timber and plywood.2.2 STRUCTURAL CLASSIFICATIONS. Tables 2.1and 2.2 list the structural classifications and designdensities (for computing dead loads) of timber speciesand species groups that are commonly used in Australia.The data given in Tables 2.1 and 2.2 are taken fromother Standards, in particular AS 2082, AS 2209,AS 2269, AS 2858 and AS 2878; any changes to theseStandards shall be taken to supersede the data citedherein. In addition, any stress grades evaluated throughin-grade testing of full size structural material shall betaken to supersede all the above information.

NOTES:1. The density of unseasoned timber depends on its moisture

content which reduces as the timber dries. The values given inTables 2.1 and 2.2 have been computed on the basis that thepercentage saturation of the timber is 45 and 80 percent forsoftwoods and hardwoods respectively.

2. The values of density given in Tables 2.1 and 2.2 do notrepresent average values for the species indicated; they areintended for use in computing the dead loading imposed bytimber.

3. The moduli of elasticity given in Table 2.3 are intended torepresent average values except where species mixtures orspecies with high variability are concerned; in the latter case, thecited moduli of elasticity are less than the average values.

4. A more extensive list of timber species and species groups willbe given in AS 1720.2.

2.3 BASIC WORKING STRESSES AND MODULUSOF ELASTICITY.2.3.1 Basic working stresses parallel to grain, andshear stresses in beams.These basic working stressesare given in Table 2.3 for the various stress grades.2.3.2 Basic working stress in compressionperpendicular to the grain and shear stress at jointdetails. These basic working stresses are given inTable 2.4 for each strength group and are applicable toall stress grades within the strength group.2.3.3 Basic working stress in compression at an angleto the grain. The basic working stress in compression atangles to the grain other than 0° and 90° shall be

denoted by and shall be calculated from theHankinson formula

. . . (2.1)where

= the angle between the direction of the loadand the direction of the grain.

2.3.4 Modulus of elasticity and rigidity. Design valuesof the modulus of elasticity and rigidity are given inTable 2.3.

NOTE: It should be noted that the modulus of elasticity, for thevarious stress grades given in Table 2.3, refers to the averagemodulus of elasticity for the stress-graded timbers that are groupedtogether within a stress grade. Therefore, when a better estimate fordeflection is required, the modulus of elasticity values derived solelyfrom Table 2.3. for a given stress grade should either beconservatively modified or accurate values should be obtained fromin-grade verification.

2.3.5 Basic working stresses in tension (softwoodsonly). The basic working stresses in tension, for the

various F-grades given in Table 2.3 for softwoodtimbers, shall be multiplied by the factor 0.85.2.4 DESIGN.2.4.1 Permissible stresses.Permissible stresses forstructural timber, whether sawn or laminatedconstruction, or in pole form, shall be obtained bymultiplying the basic working stresses given inClause 2.3 by modification factors such as those given inClause 2.5 as are appropriate to the service conditions.For example,Fb the permissible stress in bending isgiven by —

Fb = . . . . . . . . . . . . . . . . . . . . . (2.2)where

k = the product of the relevant modificationsfactors, such as those in Clause 2.5, as areappropriate to the particular serviceconditions for which the structural memberis being designed.

NOTES:1. As an example, the factork for the design bending stress of a

solid timber beam is typically given byk = k1k2k8k11k12.2. For convenience, the modification factors are collated and

referenced in Appendix I.

2.4.2 Deflections.Deflection calculations shall take intoaccount the modification factors in Clause 2.5.1.2.2.5 MODIFICATION FACTORS.2.5.1 Duration of load.2.5.1.1Effect on strength.In order to derive permissibledesign stresses, the basic working stress shall bemultiplied by the appropriate duration of load factork1

from Table 2.5. This factor is shown graphically inFigure 2.1.In checking the strength of a structural element, all loadcombinations must be considered.For any given combination of loads of differing duration,the factork1 to be used is that appropriate to the loadwhich is of the shortest duration. In Table 2.5, theeffective duration of a peak load refers to the cumulativeduration for which the peak load occurs.For the purposes of interpretation in the selection ofload-duration factors in this Standard, the following shallapply:(a) Dead loads, and live loads which are removed or

replaced at regular intervals such that the structureremains fully loaded for a substantial proportion ofits life, are to be considered ‘permanent loads’.

(b) Live loads (such as those due to vehicles or people)that act on floors, and are applied at frequent butirregular intervals such that the structure is unloaded,or loaded well below the allowable maximum, formost of each day, are to be considered ‘loads of fivemonths duration’.

(c) Live loads, such as those arising during erection andmaintenance, and at infrequent crowd loading,applied for periods of a few days and at infrequentintervals, are to be considered ‘loads of five daysduration’.

(d) Gust wind loads with a long return period, suchasthose referred to in AS 1170.2, and impact loadssuch as those caused by falling weights or snatchlifts, are to be considered ‘loads of five secondduration’.

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9 AS 1720.1—1988

TABLE 2.1STRENGTH CLASSIFICATIONS AND DESIGN DENSITY FOR SOME COMMON GROUPS OF TIMBER

Species group Moisturecondition

Strengthgroup(1) Joint group(2)

Stress gradeDesign

density (6)

kg/m3

Structural timber (3) Structuralplywood(4)

Pole timber(5)

StructuralNo 1

StructuralNo 2

StructuralNo 3

StructuralNo 4

StructuralNo 5

Mixed Australian hardwoods(excluding rainforest species)from S.A. and southern N.S.W.

Unseasoned S4 J3 F14 F11 F8 F7 — — F11 1050

Seasoned SD4 JD3 F22 F17 F14 F11 — F17 — 650

Ash-type Eucalypts from NSWHighlands— Victoria andTasmania



Non-ash-type Eucalypts from Qldand N.S.W



Rainforest species Unseasoned S7 J4 F7 F5 F4 — — — F8 800


Mixed pinusspecies (Australiangrown)

Unseasoned — — — — — — — — — 850


Mixed softwood species (excl.pinusspecies)

Unseasoned — — — — — — — — — 850

Seasoned SD8 JD4 F8 F7 F5 — — F7 — 500

Imported softwoods(unidentified)

Unseasoned S7 J6 F7 F5 F4 — — — — 850


NOTES:1. For classification into strength groups—see AS 2878.2. For joint strength—see AS 1649.3. For mechanical stress grades—see AS 1748.4. For structural plywood—see AS 2269.5. For timber poles—see AS 2209.6. For use only in computing dead load due to mass in timber.

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AS 1720.1—1988 10

TABLE 2.2STRENGTH CLASSIFICATIONS AND DESIGN DENSITY FOR SOME COMMON SPECIES OF TIMBER

Species Moisturecondition


Stress grade Designdensity(6)

kg/m3

Structural timber (3)

Structuralplywood(4) Pole timber(5)

StructuralNo 1

StructuralNo 2

StructuralNo 3

StructuralNo 4

StructuralNo 5

ash, alpine Unseasoned S4 J3 F14 F11 F8 F7 — — F17 1 050


ash, mountain Unseasoned S4 J3 F14 F11 F8 F7 — — F17 1 050


ash, silvertop Unseasoned S3 J2 F17 F14 F11 F8 — — F22 1 100


balau Unseasoned S2 J2 F22 F17 F14 F11 — — F27 1 150


blackbutt Unseasoned S2 J2 F22 F17 F14 F11 — — F27 1 150


box, brush Unseasoned S3 J2 F17 F14 F11 F8 — — F22 1 150


box, grey, coast Unseasoned S1 J1 F27 F22 F17 F14 — — F34 1 200

Seasoned SD1 JD1 F34 F34 F27 F22 — F34 — 1 100

brown barrel Unseasoned S4 J3 F14 F11 F8 F7 — — F17 1 100


chengal Unseasoned S1 J2 F27 F22 F17 F14 — — F34 1 150


fir, Douglas, North America Unseasoned S5 J4 F11 F8 F7 F5 F4 — F14 710

Seasoned SD5 JD4 F14 F11 F8 F7 F5 F14 — 550

fir, Douglas, elsewhere Unseasoned S6 J5 F8 F7 F5 F4 — — F11 710


gum, blue, southern Unseasoned S3 J2 F17 F14 F11 F8 — — F22 1 150


gum, blue, Sydney Unseasoned S3 J2 F22 F17 F14 F11 — — F27 1 100


gum, red, river Unseasoned S5 J2 F11 F8 F7 F5 — — F14 1 150


gum, rose Unseasoned S3 J2 F17 F14 F11 F8 — — F22 1 100


(continued)

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11 AS 1720.1—1988

TABLE 2.2 (continued)



Stress grade Designdensity(6)

kg/m3


Structuralplywood(4) Pole timber(5)

StructuralNo 1

StructuralNo 2

StructuralNo 3

StructuralNo 4

StructuralNo 5

gum, spotted Unseasoned S2 J1 F22 F17 F14 F11 — — F27 1 200


hardwood, Johnstone River Unseasoned S2 J1 F22 F17 F14 F11 — — F27 1 150


Hemlock, western Unseasoned S6 J4 F8 F7 F5 F4 — — F11 750


Hem-fir(7) Unseasoned S7 J5 F7 F5 F4 — — — F8 750


ironbark, grey Unseasoned S1 J1 F27 F22 F17 F14 — — F34 1 250

Seasoned SD1 JD1 — F34 F27 F22 — F34 — 1 100

ironbark, red, narrow-leaved Unseasoned S2 J1 F22 F17 F14 F11 — — F27 1 250


jarrah Unseasoned S4 J2 F14 F11 F8 F7 — — F17 1 100


kapur Unseasoned S3 J2 F17 F14 F11 F8 — — F22 1 100


karri Unseasoned S3 J2 F17 F14 F11 F8 — — F22 1 150


kempas Unseasoned S2 J1 F22 F17 F14 F11 — — F27 1 100


kwila (Merbau) Unseasoned S2 J2 F22 F17 F14 F11 — — F27 1 150


lumbayu, Chengkulang Unseasoned S5 J3 F11 F8 F7 F5 — — F14 1 100


mahogany, red Unseasoned S2 J1 F22 F17 F14 F11 — — F27 1 200


marri Unseasoned S3 J2 F17 F14 F11 F8 — — F22 1 100


meranti, dark red(7) Unseasoned S5 J4 F11 F8 F7 F5 — — F14 1 100

Seasoned SD6 JD4 F14 F11 F8 F7 — F11 — 600-750

(continued)

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AS 1720.1—1988 12



Strengthgroup(1)

Joint group(2)Stress grade

Designdensity(6)

kg/m3


Structuralplywood(4)

Pole timber(5)

StructuralNo 1

StructuralNo 2

StructuralNo 3

StructuralNo 4

StructuralNo 5

mersawa Unseasoned S6 J3 F8 F7 F5 F4 — — F11 1050


messmate Unseasoned S3 J3 F17 F14 F11 F8 — — F22 1100


oak, tulip brown Unseasoned S2 J2 F22 F17 F14 F11 — — F27 1150


pine, cypress, white Unseasoned S5 J3 — — F7 F5 F4 — F14 850

Seasoned SD6 JD3 — — — — — F11 — 700

pine, hoop Unseasoned S6 J4 F8 F7 F5 F4 — — F11 800


pine, radiata (Australia andNew Zealand)

Unseasoned S6 J4 — — — — — — F11 800


pine, slash Unseasoned S5 J3 F11 F8 F7 F5 F4 — F14 850


spruce-pine-fir(7) Unseasoned — — — — — — — — — 700


stringybark brown Unseasoned S3 J2 F17 F14 F11 F8 — — F22 1100


stringybark yellow Unseasoned S3 J2 F17 F14 F11 F8 — — F22 1150


tallowwood Unseasoned S2 J1 F22 F17 F14 F11 — — F27 1200


turpentine Unseasoned S3 J2 F17 F14 F11 F8 — — F22 1050


wandoo Unseasoned S2 J1 F22 F17 F14 F11 — — F27 1250


NOTES:1. For classification into strength groups—see AS 2878.2. For joint strength—see AS 1649.3. For mechanical stress grades—see AS 1748.4. For structural plywood—see AS 2269.5. For timber poles—see AS 2209.6. For use only in computing dead load due to mass in timber.7. Species mixture.

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13 AS 1720.1—1988

TABLE 2.3BASIC WORKING STRESSES AND STIFFNESS FOR STRUCTURAL TIMBER

Stress grade

Basic working stress, MPaShort duration

modulus ofelasticity*

Short durationmodulus of rigidityBending Tension parallel to

grain Shear in beams Compressionparallel to grain

(E) (G)

F34F27F22

34.527.522.0

20.716.513.2

2.452.051.70

26.020.516.5

21 50018 50016 000

1 4301 2301 070

F17F14F11

17.014.011.0

10.28.46.6

1.451.251.05

13.010.28.4

14 00012 00010 500

930800700

F8F7F5

8.66.95.5

5.24.13.3

0.850.700.60

6.65.24.1

9 1007 9006 900

610530460

F4F3F2

4.33.42.7

2.62.01.6

0.500.450.35

3.32.62.1

6 1005 2004 500

410350300

* The modulus of elasticity includes an allowance of about 5 percent for shear deformation.NOTE: For the basic working stresses in tension for softwoodsonly, refer to Clause 2.3.5.

TABLE 2.4BASIC WORKING STRESSES FOR COMPRESSION

PERPENDICULAR TO GRAIN AND SHEAR AT JOINTS

StrengthBasic working stress, MPa

Compressionperpendicular to grain Shear at joints details

Unseasoned Seasoned

———

S1S2S3

S4S5S6

S7

SD1SD2SD3

SD4SD5SD6

SD7SD8—

—

10.49.07.8

6.65.24.1

3.32.62.1

1.7

4.153.452.95

2.452.051.70

1.451.251.05

0.85

TABLE 2.5DURATION OF LOAD FACTOR FOR STRENGTH

Type of load Effective duration ofpeak load

Multiplying factor ( k1)

Basic stresses for solidtimber

Basic working loads forlaterally loaded

connectors*

InstantaneousStandard testShort term

Medium termLong termPermanent

5 seconds5 minutes5 hours

5 days5 months50+ years

1.751.751.70

1.651.401.00

2.001.751.50

1.351.201.00

* For connectors loaded in withdrawal and for the strength of steel in connectors,k1 = 1.00.

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AS 1720.1—1988 14

2.5.1.2Effect on stiffness.For members in bending andcompression or for members in tension, the calculatedshort-term deformation shall be multiplied by theappropriate creep factorj2 or j3, as given in Table 2.6and illustrated graphically in Figures 2.2 and 2.3.

Values intermediate between those given in Table 2.6may be obtained through an interpolation involving thelogarithm of time, and a linear function of initialmoisture content as shown in Figures 2.2 and 2.3.

When several types of load act on a timber member, themaximum deformation shall be taken to be equal to thesum of the deformations computed for each type of loadacting alone.

The modification factorsj2 andj3 given in Table 2.6 arenot applicable to collapse susceptible hardwoods (seeClause 1.8.2) when their initial moisture content is above25%. For these timbers the creep factors may beconsiderably greater than the values shown.

NOTES:1. The loads to be considered in computing deflections are not only

the peak loads used for strength checks, but all loads that actduring the life of the structure. In general, peak values of liveload are not of a permanent nature; accordingly if a designerwishes to compute the long term deformations of a structure hemust first estimate the portion of the load that is permanently orsemi-permanently applied, and then use an appropriate creepfactor.

2. Where there is a recovery period of more than ten times that ofthe applied load, the creep component of deformation may beassumed to be totally recovered.

TABLE 2.6

DURATION OF LOAD FACTOR FOR DEFLECTION

Initial moisturecontent*

%

For bending, compression andshear members (j2)

For tension members(j3)

Load duration≤ 1 day

Load duration≥ 1 year

Load duration≤ 1 day

Load duration≥ 1 year

≤ 15≥ 25

11

23

11

11.5

* Moisture content at the time of load application.

FIGURE 2.1. DURATION OF LOAD FACTOR k1

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15 AS 1720.1—1988

2.5.2 Moisture condition. Depending on the initialmoisture content of the timber and the moisture contentat time of loading and throughout its life, the basicworking stresses shall be modified as follows:

(a) Unseasoned timber. Where unseasoned timber isused, the basic working stresses shall be those inTables 2.3 and 2.4 appropriate to the stress gradeand strength group of the unseasoned timber asindicated in Tables 2.1 and 2.2.

(b) Unseasoned timber partly dry before use. Whereunseasoned timber is used under normal conditionsof temperature and humidity and will not be subjectto its full design load until it has partly seasoned, i.e.to below 25% moisture content, the basic workingstresses for unseasoned timber may be increased bymultiplying by the factork4 given in Table 2.7.

TABLE 2.7PARTIAL SEASONING FACTOR

Least dimension ofmember

38 mm orless 50 mm 75 mm 100 mm

or more

Value of k4 1.15 1.10 1.05 1.00

(c) Seasoned timber.

(i) Where seasoned timber is used, the basicworking stresses shall be those in Tables 2.3and 2.4 appropriate to the stress grade andstrength group of the timber in the seasonedcondition as indicated in Tables 2.1 and 2.2.

(ii) Where seasoned timber is subjected toconditions in which its average moisturecontent for a 12-month period is expected toexceed 15%, the basic working stresses shall

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AS 1720.1—1988 16

be decreased by multiplying by the factork5

determined as the greater of:

k5 = (2.3(a))

and

k5 = . . . . . . . . . . . . . . . . . . (2.3(b))

whereEMC = the highest value of the annual

average moisture content (percent)that the timber will attain inservice.

F′ (seasoned) = the basic working stress for theseasoned material

F′ (unseasoned) = the basic working stress formaterial of the same grade in theunseasoned condition.

2.5.3 Temperature.For covered timber structures underambient conditions, no modification to the basic workingstresses need be made for the effect of temperatureexcept that where seasoned timber is used in structureserected in the coastal regions of Queensland north oflatitude 25°S and all other regions of Australia north oflatitude 16°S, the basic working stresses shall bemultiplied by a factork6 of 0.9.

NOTE: Information on the effects of high temperatures can beobtained from:MEYER, R.W. and KELLOG, R.M.Structural Use of Wood inAdverse Environments. Van Nostrand, 1982

2.5.4 Length and position of bearing.For rectangularbearing areas for bearings of length less than 150 mmand with the bearing surface 75 mm or more from theend of a piece of timber, the basic working stress inbearing perpendicular to the grain given in Table 2.4may be multiplied by the appropriate factork7 inTable 2.8, the length of bearing being measured parallelto the grain of the loaded member.

For circular bearing areas the effective bearing lengthshall be taken as being equal to the diameter of thebearing area.

TABLE 2.8LENGTH OF BEARING FACTOR

Length of bearingof member 12 25 50 75 125 150 or

more

Value of k7 1.85 1.60 1.30 1.15 1.05 1.00

2.5.5 Load sharing.

2.5.5.1General. When a structural system consists ofparallel acting elements that interact to assist each other,then the basic working stresses may be increased by theappropriate load sharing factor.

2.5.5.2Parallel structural systems. For structural systemscomprised of two or more elements effectively connectedso that all of the elements are constrained to the samedeformation, the load sharing factork8 may be obtainedfrom Table 2.9, and applied to the basic working stressesfor bending and compression. If the effective number ofelements is not an exact integer, then a suitable value ofk8 may be derived by linear interpolation.

TABLE 2.9PARALLEL SUPPORT FACTOR

Effective number of elements carryingcommon load (neff)

Factor k8

123

1.001.141.20

456

1.241.261.28

789

1.301.311.32

10 or more 1.33Except for laminated timber members, the effectivenumber of elements (neff) may be taken to be the totalnumber of members acting together.

For laminated timber members, the effective number ofelements (neff) to be used in Table 2.9 shall be takenas—

neff = nm × nL . . . . . . . . . . . . . . . . . . (2.4)where

nm = total number of membersnL = effective number of lamination elements

per member as defined in Clause 7.3.2.Where the factork8 is applied to laminated membersacting in parallel, the factork23 discussed in Clause 7.3.2shall be taken to be equal to unity.

2.5.5.3Grid systems. Where constructions are such thatthree or more members act together to support either anoverlying set of members usually laid at right angles tothe supporting members or a structural sheathingmaterial, a load sharing factork9 may be applied to thebasic working stress for bending, in beams. This factoris given by the equation:

k9 = k0 + (k8 - k0) [1.0 - 2(s/L)] . . . . . . . . . (2.5)but not less thank0, where

s = the centre-to-centre spacing of thesupporting members

L = span of the supporting memberk8 = load sharing factor for parallel structural

systems (see Clause 2.5.5.2)k0 = 1.0 for solid timber

= k23 for glued- laminated timber(Clause 7.3.2).

The load sharing factork9 is illustrated graphically inFigure 2.4.

NOTE: In addition to load sharing characteristics, grid systems alsoprovide a method for laterally distributing concentrated loads asdescribed in Paragraph C8, Appendix C.

2.5.6 Size factor for flexural and tension members.The basic working stress in bending and tension shall bemultiplied by the size factork11 as given in Table 2.10.Linear interpolation may be used for intermediate sizes.

For beams of depthd greater than 1500 mm, the valueof k11 shall be taken to be given by —

k11 = (300/d)0.167 . . . . . . . . . . . . . . . . . . (2.6)NOTE: The size factor for beams refers to beams of solid timber orglulam. For built up beams the size factor shall be applied to theindividual components; an example of this would be the tensionflange of a box beam.

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17 AS 1720.1—1988

2.5.7 Stability factor. In the design of slender structuralmembers, a factork12 is used to allow for the effects ofslenderness on strength. It is defined by —

F = k12F0 . . . . . . . . . . . . . . . . . . . . (2.7)where

F = t h e n o m i n a l d e s i g n s t r e s sF0 = the value ofF if the structural member

were completely stable.

The factorkl2 depends on both material factors and theslenderness coefficientS. These factors and theslenderness coefficient are defined for each type ofslender structural member in the section of this Standardappropriate to that element.

2.5.8 Material and application factor. For all timbermembers, the basic working stresses given in Tables 2.3and 2.4 shall be multiplied by the material andapplication factK2, shown in table 2.11

TABLE 2.10SIZE FACTORS FOR BEAMS AND TENSION MEMBERS

Maximum depth of beam or twicewidth of tension member

mm300 375 500 625 750 1 000 1 250 1 500

Value of k11 1 0.96 0.92 0.89 0.86 0.82 0.79 0.77

RELATIVE SPACING (s/L)

FIGURE 2.4. LOAD SHARING FACTOR k9 FOR GRID SYSTEMS

TABLE 2.11MATERIAL AND APPLICATION FACTOR

Consequence of failureclassification*

Material and application factor (k2)

Basis for assignment of structural properties

From in-grade verification All other methods

Normal 1.0 1.0

High 0.9 0.7

* Normal consequence of failure can be interpreted as that associated with housingconstruction, secondary framing in commercial or industrial scale structures andprimary elements in farm buildings. High consequence of failure can beinterpreted as that associated with primary structural elements in commercial orindustrial scale structures, bridges and similar.

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AS 1720.1—1988 18

SECTION 3. DESIGN OF BASIC STRUCTURAL MEMBERS

3.1 GENERAL. This Section shall be applied inconjunction with the clauses of Section 2. This Sectionapplies to the design of basic structural members such ascolumns, beams and ties. In particular many of thedesign parameters given refer to members of rectangularcross-section, for which the notation used is shown inFigure 3.1 . The corresponding parameters for membersof less usual shape are given in Appendix C. Specialdesign requirements related to the use of pole timbers,glued-laminated construction and plywood are given inlater sections. Clauses for the design of more complexstructural elements are given in Appendix C. Theseinclude clauses related to —

(a) the design of spaced columns (Paragraph C6);(b) buckling restraint systems (Paragraph C7);(C) grid systems (Paragraph C8);(d) notched beams (Paragraph C9);(e) notched columns (Paragraph C10); and(f) notched tension members (Paragraph C11).

NOTE: In beam design deflection considerations will usually governmember sizes (See Clauses 1.5.3.6, 2.3, 2.4 and 2.5).

FIGURE 3.1. NOTATION FOR ARECTANGULAR CROSS-SECTION

3.2 BEAM DESIGN.

3.2.1 Maximum stresses.Calculated values for thestresses in a beam shall not exceed the permissiblestresses in bendingFb, in shearFs, and in compressionperpendicular to the grainFp, determined in accordancewith Clause 2.4 for sawn and laminated timber and forpoles. Due regard shall be paid to the beam’s effectivespan and lateral stability, and to an acceptable deflection.(See also Clause 3.5 and Paragraph C5 for combinedbending and axial loading, and Paragraph C7, AppendixC for the design of lateral and torsional restraints.)

When calculating a shear force in a beam, loads lyingwithin a distance of the support of 1.5 times the depth ofthe beam from the inside face of the support may bedisregarded, except in the design of notched beams(Paragraph C9, Appendix C).

For unnotched beams, the permissible stress shall becalculated by the following equations:(a) In bending—

Fb = . . . . . . . . . . (3.1)

(b) In shear-

Fs = . . . . . . . . . . . . . . . (3.2)

(c) In compression perpendicular to the grain —

Fp = . . . . . . . . . . . . . (3.3)

where the factorsk1 to k11 are given in Section 2 andk12

is the stability factor defined in Equation 3.8 (see Clause3.2.4). For beams in grid systems the load sharing factork8 is replaced byk9.

3.2.2 Effective span.The effective span of flexuralmembers shall be taken as the distance between thecentres of areas of bearing.

For members that extend over bearings longer than isnecessary, the span may be taken as the distance betweencentres of imaginary bearings which are chosen in sucha way that their lengths are adequate to comply with therequirements of this Standard.

3.2.3 Slenderness coefficient for lateral buckling.

3.2.3.1General. For the general case, and for severaluseful specific cases, equations for evaluating the

FIGURE 3.2. NOTATION FOR BEAM RESTRAINTS

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19 AS 1720.1—1988

slenderness coefficient are given in Paragraph C3,Appendix C. For the special cases of solid beams ofrectangular cross-section, the simple approximationsgiven in Clause 3.2.3.2 may be used.

3.2.3.2Beams of rectangular cross-section. For beams ofrectangular cross-section, the slenderness coefficientsmay be taken as follows:(a) Beams that bend only about their major axis. For

discrete restraint systems that effectively restrain thecompression flange of the beam at pointsLay apart,the slenderness coefficient, denoted by S1, may betaken to be—

S1 = 1.25(Layd/b2)1/2 . . . . . . . . . . . . . (3.4)For restraint systems that are continuous along thecompression flange of the beam, the slendernesscoefficient may be taken to be—

S1 = 0.0 . . . . . . . . . . . . . . . . . . . . . (3.5)For restraint systems that are continuous along thetension flange of the beam, and in addition the loadis applied to the tension flange, the slendernesscoefficient may be taken to be—

S1 = 2.5d/b . . . . . . . . . . . . . . . . . . . (3.6)(b) Beams that bend only about their minor axis. For all

cases, the slenderness coefficient, denoted byS2,may be taken to be—

S2 = 0.0 . . . . . . . . . . . . . . . . . . . . . (3.7)(c) Beams that bend about both axes. The design of

such beams described in Clause 3.2.5, is based on aninteraction of the two special cases for bendingabout single axes only, and hence no specialdefinition of slenderness is required for this case.

3.2.4 Stability factor. The stability factor k12 formodification of the basic working stress in bending shallbe given by—(a) For S ≤ 10—

k12 = 1.0 . . . . . . . . . . . . . . . . . . . (3.8(a))(b) For 10≤ S ≤ 20—

k12 = 1.5 - 0.05 S . . . . . . . . . . . . (3.8(b))(c) For S ≥ 20—

k12 = 200/( S)2 . . . . . . . . . . . . . . (3.8(c))where a conservative value of the material constant

is given in Table 3.1; more accurate values ofare given by Equations C1 and C2 and tabulated inTables C1 and C2 of Appendix C. The shape of thestability factor curve is illustrated in Figure 3.3.

For large beams, where a size factork11 < 1.0 is usedeither for solid beams or the tension flanges of built upbeams, the material constant inserted in Equations 3.8above may be replaced by * where—

* = . . . . . . . . . . . . . . . . . . . . (3.9)

3.2.5 Allowable nominal bending stress.The followingare the design criteria for the allowable bending stress ina beam:(a) Beam that is bent only about its major axis (the

x-axis) —fbx/Fbx ≤ 1 . . . . . . . . . . . . . . . . . . . . . (3.10)

(b) Beam that is bent only about its minor axis (they-axis)

fby/Fby ≤ 1 . . . . . . . . . . . . . . . . . . . . . (3.11)

TABLE 3.1

MATERIAL CONSTANT FOR BEAMS

Stress gradeMaterial constant

Seasoned timber Unseasoned timber

F34F27F22

1.231.181.13

1.321.271.22

F17F14F11

1.081.041.00

1.171.141.09

F8F7F5

0.950.910.88

1.051.010.97

F4F3F2

0.840.800.78

0.930.900.87

FIGURE 3.3. EFFECT OF SLENDERNESSCOEFFICIENT ON THE STABILITY FACTOR

FOR BEAMS AND COLUMNS

(c) Beam that is bent about both major and minoraxes—

(fbx/Fbx) + (fby/Fby) ≤ 1 . . . . . . . . . . (3.12)where

fbx, fby = Mx/Zx, My/Zy = calculated bendingstresses about the major andminor axes respectively

Fbx, Fby = permissible design values offbx,fby if the beam were bent aboutonly one axis.

For a less conservative criterion, see Equation C14 ofAppendix C.

3.2.6 Strength of notched beams.Clauses for thedesign strength of notched beams are given inParagraph C9, Appendix C.

3.2.7 Concentrated loads and partial area loads ongrid systems.Clauses to assist in the design of floor gridsystems to resist concentrated and partial area loads aregiven in Paragraph C8, Appendix C.

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AS 1720.1—1988 20

(a) For buckling about major axis (b) For buckling about minor axis

FIGURE 3.4. NOTATION FOR COLUMN RESTRAINTS

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21 AS 1720.1—1988

3.3 COLUMN DESIGN.3.3.1 Maximum stresses.The average compressivestress (fc), calculated on the effective cross-sectionalareaA of a member concentrically loaded by an axialforceP, shall not exceed the maximum permissible stress(Fc) in compression parallel to the grain as determined inaccordance with Clause 2.4 for sawn and laminatedtimber and for poles. (See also Clause 3.5.1 forcombined bending and compression, and Paragraph C7,Appendix C, for the design of lateral and torsionalrestraints.)For unnotched columns, the permissible stress incompression shall be given by —

Fc = . . . . . . . . . . . . . . (3.13)

where the factorsk1 - k8 are given in Section 2 andk12 isthe stability factor defined by Equations 3.18(a), 3.18(b)and 3.18(c).

TABLE 3.2

EFFECTIVE LENGTH FACTOR g13,FOR COLUMNS WITHOUT INTERMEDIATE

LATERAL RESTRAINT

Condition of end restraintEffective

length factor(g13)

Flat ends 0.7

Restrained at both ends in position and direction 0.7

Each end held by two bolts (substantiallyrestrained)

0.75

One end fixed in position and direction, the otherrestrained in position only

0.85

Restrained at both ends in position only 1.0

Restrained at one end in position and directionand at the other end partially restrained indirection but not in position

1.5

Restrained at one end in position and directionbut not restrained in either position or directionat the other end

2.0

3.3.2 Slenderness coefficients for lateral buckling.3.3.2.1General. For the general case, and for severaluseful specific cases, equations for evaluating theslenderness coefficient are given in Paragraph C4,Appendix C. For the case of solid columns of rectangularcross-section as shown in Figure 3.1, the simpleapproximations given below may be used.3.3.2.2 Columns of rectangular cross-section. Forcolumns of rectangular cross-section, the slendernesscoefficients may be taken as follows:(a) Columns that can bend only about their major axis.

For the case of discrete restraint systems, theslenderness coefficient, denoted byS3, shall be takento be the lesser of the following:

S3 = Lax/d . . . . . . . . . . . . . . . . . (3.14(a))and

S3 = g13L/d . . . . . . . . . . . . . . . . (3.14(b))where

Lax = the distance between points ofeffectively rigid restraints against lateralmovement in the direction of the y-axisas shown in Figure 3.4(a)

g13 = the coefficient given in Table 3.2.For restraint systems that restrain movement in thedirection of they-axis, and are continuous along the

length of the column, the slenderness coefficient may betaken to be—

S3 = 0.0 . . . . . . . . . . . . . . . . . . . (3.15)(b) Columns that can bend only about their minor axis.

For discrete restraint systems, the slendernesscoefficient, denoted byS4, may be taken to be thelesser of the following:

S4 = Lay/b . . . . . . . . . . . . . . . (3.16(a))and

S4 = g13L/b . . . . . . . . . . . . . . (3.16(b))where

Lay = the distance between points ofeffectively rigid restraints againstlateral movement in the direction of thex-axis as shown in Figure 3.4(b)

g13 = the coefficient given in Table 3.2.For restraint systems that act continuously along oneedge only and which restrain movement in thedirection of thex-axis, the slenderness coefficientmay be taken to be—

S4 = 3.5 d/b . . . . . . . . . . . . . . . (3.17)(c) Columns that can bend about both axes. The design

of such columns, described in Clause 3.5.1, is basedon an interaction of the two special cases forbending about single axes only, and hence no specialdefinition of slenderness is required for this case.

3.3.3 Stability factor. The stability factor k12 formodification of the basic working stress in compressionshall be given by:(a) For S ≤ 10—

k12 = 1.0 . . . . . . . . . . . . . . . . . . (3.18(a))(b) For 10≤ S ≤ 20—

k12 = 1.5 - 0.05 S . . . . . . . . . . (3.18(b))(c) For S ≥ 20—

k12 = 200/( S)2 . . . . . . . . . . . . . (3.18(c))where a conservative value of the material constant isgiven in Table 3.3; more accurate values of are givenby Equations C3 and C4 and tabulated in Tables C3 andC4, Appendix C. The shape of the stability factor curveis illustrated in Figure 3.3.

TABLE 3.3MATERIAL CONSTANT FOR COLUMNS


Seasoned timber Unseasoned timber

F34F27F22

1.261.221.18

1.441.391.35

F17F14F11

1.131.101.06

1.301.271.22

F8F7F5

1.010.980.95

1.181.151.11

F4F3F2

0.910.880.85

1.071.041.01

3.3.4 Allowable nominal axial stress. Allowablecompression stress in a column is given by —

fc ≤ Fcx . . . . . . . . . . . . . . . . . . . . . . . . (3.19)fc ≤ Fcy . . . . . . . . . . . . . . . . . . . . . . . (3.20)

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AS 1720.1—1988 22

where

fc = nominal compression stress in column= P/A

Fcx, Fcy = permissible compression stress formember as a column able to buckle onlyabout its major or minor axis respectively,(see Equation 3.13).

3.3.5 Strength of notched columns.The appropriatedesign procedure for notched columns is given inParagraph C10, Appendix C.

3.3.6 Spaced columns.The slenderness coefficientsrequired for computing the design axial strength ofspaced columns are given in Paragraph C6, Appendix C.

3.4 TENSION MEMBER DESIGN.

3.4.1 Axial stress in tension members.In an axiallyloaded tension member, the average tensile stress(f t),calculated on the net area, shall not exceed thepermissible stress in tension (Ft), determined inaccordance with Clause 2.4 for sawn and laminatedtimber and for poles. (See also Clause 3.5.2 forcombined bending and tension and Paragraph C11,Appendix C for notched tension members.)

For unnotched tension members, the permissible stress intension shall be given by—

F t = . . . . . . . . . . . . . . . . . (3.21)

where the factorsk1, to k11, are given in Section 2.

3.4.2 Slenderness coefficient. The slendernesscoefficient for a tension member shall be defined as forcolumns in accordance with Clause 3.3.2.

3.4.3 Notched tension members.The appropriate designprocedure for the design of notched tension members isgiven in Paragraph C11 of Appendix C.

3.5 COMBINED BENDING AND AXIALSTRESSES.

3.5.1 Combined bending and compression.Arectangular member with cross-section as shown inFigure 3.1 subject to combined axial compression andbending about thex-axis only shall be proportioned sothat—

(fbx/Fbx)2 + (fc/Fcy) ≤ 1 . . . . . . . . . . . . . . . . (3.22)

(fbx/Fbx) + (fc/Fcx) ≤ 1 . . . . . . . . . . . . . . . (3.23)

where

fbx = Mx/Zx = nominal bending stress aboutthe major axis

Fbx = permissible design values offbx

(Equation 3.1)

fc = P/A = nominal compression stressacting on column

Fcx, Fcy = permissible design value of thecompression stress (fc) if the memberwere used as a column that couldbuckle only about its major or minoraxis respectively (see Equation 3.13)

NOTE: Equations 3.22 and 3.23 contain an allowance for the effectof bending moment amplification due to the axial load. Fornon-rectangular members, Equations 3.22 and 3.23 may be used inthe absence of other information.

For the unusual case of a beam-column subjected tobending simultaneously about both thex and y axes, aconservative criterion of strength is given by EquationC14, Appendix C.

3.5.2 Combined bending and tension.The nominalbending stressfbx and axial stressft of a member subjectto combined bending and axial tension shall be givenby—

. . . . . . . . . . . . . . . . . (3.24)

fbx - f t ≤ Fbx . . . . . . . . . . . . . . . . . . . . . (3.25)

whereFt andFb are the permissible tension and bendingstresses for the member used as a tie or beamrespectively (see Equations 3.1 and 3.21)

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23 AS 1720.1—1988

SECTION 4. CONNECTIONS4.1 GENERAL.4.1.1 Scope of section. This Section applies to joints insolid timber fabricated with mechanical fastenersdescribed by Australian Standards and characterized bya long history of use in timber structures. These includejoints fabricated with the following mechanical fasteners:(a) Nails.(b) Wood screws.(c) Bolts.(d) Coach screws.(e) Split-ring connectors.(f) Shear-plate connectors.

NOTES:1. Design rules for specialized and patented mechanical fasteners

and for variants of conventional fasteners which will have beensubjected to tests specified in AS 1649, will be given inAS 1720.3.

2. This Standard does not specifically cover glued timber-to-timberor timber-to-plywood connections as occur in fabricatedcomponents such as stressed skin panels or plywood webbedbeams. In such cases, joint design can be based on the timbercomponents in the connection, provided that the joint isfabricated using a rigid, durable adhesive. Phenolic typeadhesives meet these requirements. The design of fabricatedcomponents comprising glued connections is therefore based onthe fact that with correct bonding practice and quality control, ajoint is developed in which the adhesive bond strength anddurability will be superior to the timber components comprisingthe joint.

3. Joints with plywood are covered in Paragraph D1. Informationon methods for assessing the deformation of joints is given inParagraph D2.

4.1.2 Joint groups. For the purpose of joint design,timber species have been classified into six joint groups:J1, J2, J3, J4, J5 and J6 for unseasoned timber and JD1,JD2, JD3, JD4, JD5 and JD6 for seasoned timber. Thejoint group classifications for specific timbers are shownin Tables 2.1 and 2.2.Where joints comprise more than one species of timber,the design load to be used in the absence of otherinformation is that appropriate to the weakest species inthe joint.4.1.3 Timber grade.No allowance for grade of timberhas been made in design data for fasteners. Design loadsfor joints have been based on the assumption that thereare no loose knots, severe sloping grain, gum veins, gumor rot pockets, lyctus-susceptible sapwood, corewood,holes or splits near any fastener. Accordingly, all ofthese defects except for corewoodshall be avoided at fastener locations. Corewood shallonly be permitted at fastener locations if the design jointstrength is taken to be that of a timber that is in a jointgroup that is one lower than the normal value for thespecies used.4.1.4 Tendency to split.Special precautions shall bespecified in the use of timber that has a tendency to splitto an extent that may be detrimental to connectorstrength. In the absence of other guidance, the criterionfor tendency to split shall be based on the parameter∝defined by—

α = ε2/γwhere

ε = tangential shrinkage, in percentγ = tangential cleavage strength of unseasoned

timber, in newtons per millimetre (N/mm), asmeasured by BS 373 or ASTM D143.

Species for whichα > 0.8 often have a high tendency tosplit, particularly in exposed locations; species for whichα < 0.55 may be considered to have a negligibletendency to split.

NOTES:1. Information on shrinkage and cleavage strength for specific

species can be obtained from the following:(a) KINGSTON, R.S.T. and RISDON, C.J.E. ‘Shrinkage and

Density of Australian and other South-West PacificWoods’. Division of Forest Products Technological PaperNo 13, CSIRO, 1961.

(b) BUDGEON, B. ‘Shrinkage and Density of some Australianand South-East Asian Timbers’. Division of BuildingResearch Technological Paper (Second Series) No 38,CSIRO, 1981.

(c) BOLZA, E. and KLOOT, N.H. ‘The Mechanical Propertiesof 174 Australian Timbers’. Division of Forest ProductsTechnological Paper No 25, CSIRO, 1963.

2. It will be found that most Eucalypts and most hardwoods of drysclerophyll forests that have a basic density of less than 700kg/m3 will have a splitting parameterα > 0.8; most softwoodsand most rainforest hardwoods have a splitting parameterα < 0.8.

4.1.5 Eccentric joints. When it is impracticable toensure that all the members meeting at a joint arearranged symmetrically, with their centrelinesintersecting on a common axis which is also the axis ofresistance of the fastener or group of fasteners, thecombined effects of primary stresses and secondarystresses due to the resulting bending and shear stressshall be checked.

4.2 NAILED JOINTS.4.2.1 Lateral loads.4.2.1.1Basic working loads. The basic working loads forplain shank, low carbon steel nails specified in AS 2334,whether driven by hand or by gun, in single shear intimber fabricated in the unseasoned condition are givenin Table 4.1(A) and in timber fabricated in the seasonedcondition in Table 4.1(B).

TABLE 4.1LATERAL LOADS FOR ONE NAIL IN

SINGLE SHEAR IN SIDE GRAIN(comprising Tables 4.1(A) and 4.1(B))

4.1(A) UNSEASONED TIMBER

Speciesgroup

Basic working load per nail, N

Nail diameter, mm

2.5 2.8 3.15 3.75 4.5 5.0 5.6

J1J2J3J4J5J6

33026018513010075

40031522516012090

490385275195150110

665525375265200150

915720515365275210

1 100870620440330250

1 3401 060

755540400300

4.1(B) SEASONED TIMBER

Speciesgroup

Basic working load per nail, N

Nail diameter, mm

2.5 2.8 3.15 3.75 4.5 5.0 5.6

JD1JD2JD3JD4JD5JD6

435330260185150115

530400315225185140

650490385275230170

885665525375310235

1 210915720515425320

1 4601 100

870620510385

1 7801 3401 060

755620470

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AS 1720.1—1988 24

4.2.1.2Permissible loads.The permissible loadQ of alaterally loaded nail shall be taken to be given by —

Q = k1,k13k14k16k17 . . . . . . . . . . . . . . . (4.1)where

k1 = the factor for duration of load given inTable 2.5

k13 = 1.0 for nails in side grain= 0.6 for nails in end grain

k14 = 1.0 for nails in single shear= 2.0 for nails in double shear

k16 = 1.2 for nails driven through close fitting holesinto metal side plates

= 1.1 for nails driven through plywood gussets= 1.0 otherwise

k17 = factor for multiple nailed joints given in Table4.2(A) for longitudinal tension joints andTable 4.2(B) for rotational joints

Q′ = basic working load given in Tables 4.1(A)and 4.1(B)

For longitudinal joints containingn nails,Pn, the designload capacity of the joint, shall be taken to be givenby—

Pn = nQ . . . . . . . . . . . . . . . . . . . . . . . . (4.2)

For rotational joints containingn nails, Mn, the designin-plane moment capacity of the joint shall be taken tobe given by—

Mn = . . . . . . . . . . . . (4.3)

where

ri = the distance from theith nail to thecentroid of the nail group,

rmax = the maximum value ofr i.

Longitudinal and rotational joints are illustrated inFigure 4.1.

TABLE 4.2VALUES OF FACTOR k17 FOR USE IN

THE DESIGN OF MULTIPLE NAIL ANDSCREW JOINTS

(Comprising Tables 4.2(A) and 4.2(B))

4.2(A) TO CARRY DIRECT LOADS

Conditionof

timber

Values of k17

Fasteners

na ≤ 4 na = 5 na = 10 na ≥ 20

UnseasonedSeasoned

1.001.00

0.900.94

0.800.90

0.750.85

na = total number of rows of fasteners per interface (seeFigure 4.1(a))

4.2(B) TO CARRY IN-PLANE MOMENTSna k17

2510

1.001.051.10

20100 or greater

1.151.20

na = number of nails per interface for whichri/rmax ≥ 0.7r i = distance fromi th nail to centroid of nail grouprmax = maximum value ofri. (See Figure 4.1(b))

FIGURE 4.1. ILLUSTRATION OF A LONGITUDINAL AND ROTATIONAL JOINT

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25 AS 1720.1—1988

4.2.1.3 Spacing, edge and end distances.Table 4.3provides recommended minimum spacings, edge and enddistances for nails in terms of nail diameterD. Forspacings at an angle to the grain, interpolation by meansof Hankinson’s formula may be used.

NOTE: For timber that has a tendency to split (see Clause 4.1.4)some mitigation measure such as preboring or increased spacing isrecommended. The fabrication of prototype joints is a useful methodof checking the efficacy of mitigation measures.

TABLE 4.3MINIMUM SPACING, EDGE AND END

DISTANCES FOR NAILS

Spacing type

Minimum distance

Holes not preboredHoles prebored to80 percent of nail

diameter

End distanceEdge distance

20D5D

10D5D

Between nails— along grain— across grain

20D10D

10D3D

4.2.1.4Nail length and timber thickness.For the basicloads given in Tables 4.1(A) and 4.1(B) to be applicable,timber thicknesses and nail length as shown in Figure 4.2shall be as follows:

(a) Two-member joints (nails in single shear).Thicknessof first member,t1 > 10D, depth of penetration ofnail into second member,tp > 10D.

For lesser values oft1 andtp, the basic load shall bereduced in proportion to the decrease int1 or tp

(whichever gives the greater decrease), and the nailsshall be considered as non-loadbearing ift1 or tp isless than 5D.

(b) Three-member joints (nails in double shear).Thickness of central member,tm > 10D, thickness ofouter member,to > 7.5D, depth of penetration of nailinto outer member,tp > 7.5D.

For lesser values oftm, to and tp, the basic load shallbe reduced in proportion to the decrease intm, to andtp (whichever gives the greatest decrease), and thenails shall be regarded as being in single shear iftp

is less than 5D.

4.2.1.5Avoidance of splitting.The basic loads for nailshave been derived on the assumption that splitting of thetimber does not occur to any significant extent. Inunseasoned timber which shows a marked tendency tosplit (see Clause 4.1.4), the use of prebored holes ofdiameter 80 percent of the nail diameter isrecommended.

4.2.2 Withdrawal loads.

4.2.2.1Basic working loads. The basic working loads inwithdrawal for plain shank, low carbon steel nails asspecified in AS 2334 driven by hand, into side grain ofunseasoned timber are given in Table 4.4(A) and fromside grain of seasoned timber are given in Table 4.4(B).

NOTE: Withdrawal loads for gun-driven plain shank nails may beconsiderably less than withdrawal loads for the same nails driven byhand.

TABLE 4.4WITHDRAWAL LOADS FOR PLAIN SHANK

STEEL NAILS IN SIDE GRAIN(Comprising Tables 4.4(A) and 4.4(B))

4.4 (A) UNSEASONED TIMBER

Speciesgroup

Basic working load, N per mm penetration of nail

Nail diameter, mm

2.5 2.8 3.15 3.75 4.5 5.0 5.6

J1J2J3

J4J5J6

118.97.6

6.75.44.0

12108.5

7.56.04.5

14119.6

8.46.85.1

161311

1086

191614

12107

211815

13118

242017

15129


Speciesgroup

Basic working load, N per mm penetration of nail

Nail diameter, mm

2.5 2.8 3.15 3.75 4.5 5.0 5.6

JD1JD2JD3

JD4JD5JD6

17127.6

4.93.12.2

19138.5

5.53.52.5

21159.6

6.23.92.8

251711

7.44.73.3

302114

8.85.64.

342315

9.86.34.5

382617

1175

FIGURE 4.2. TIMBER THICKNESSES AND FASTENER LENGTHS FORNAILS, WOOD SCREWS AND COACH SCREWS

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AS 1720.1—1988 26

4.2.2.2Permissible loads. The permissible loadQ of asingle nail in withdrawal from side grain shall be takento be given by —

Q = . . . . . . . . . . . . . . . . . . . . . . (4.4)where

= the basic working load in withdrawal givenin Tables 4.4(A) and 4.4(B).

4.3 SCREWED JOINTS.4.3.1 Lateral loads.4.3.1.1Basic working loads. The basic working loads forplain steel wood screws as specified in AS 1476,whether driven by hand or by machine, in single shear inunseasoned timber are given in Table 4.5(A) and inseasoned timber are given in Table 4.5(B).

NOTE: In the absence of specific data, these loads may also beused for other forms of steel screws intended for the fabrication oftimber joints. Loads for other diameters may be derived by linearinterpolation in direct proportion to diameters raised to the powerof 1.75.

TABLE 4.5LATERAL LOAD FOR ONE STEEL WOOD

SCREW IN SINGLE SHEAR IN SIDE GRAIN(Comprising Tables 4.5(A) and 4.5(B))


Speciesgroup

Basic working load per screw, N

Screw size number

4 6 8 10 12 14 18

Shank diameter, mm

2.74 3.45 4.17 4.88 5.59 6.30 7.72

J1J2J3J4J5J6

38030021015011070

580450320230170110

800630450320230150

1 060830600420300200

1 3401 060

750530390250

1 6501 300

930660480310

2 3601 8601 330

940680440


Speciesgroup

Basic working load per screw, N

Screw size number

4 6 8 10 12 14 18

Shank diameter, mm

2.74 3.45 4.17 4.88 5.59 6.30 7.72

JD1JD2JD3JD4JD5JD6

510380300210150110

760580450320230170

1 060800630450320230

1 4001 060

830600420300

1 7801 3401 060

750530390

2 1901 6501 300

930660480

3 1302 3601 8601 330

940680

4.3.1.2Permissible loads. The permissible loadQ for alaterally loaded screw shall be taken to be given by —

Q = k1k13k16k17 . . . . . . . . . . . . . . (4.5)

where

k1 = the factor for duration of load given inTable 2.5

k13 = 1.0 for screws in side grain= 0.6 for screws in end grain

k16 = 1.2 where the load is applied throughmetal sideplates of adequate strength totransfer the load and the screws are a closefit to the holes in these plates

= 1.0 otherwisek17 = factor for multiple screw joints given in

Tables 4.2(A) and 4.2(B)= basic working load given in Tables 4.5(A)

and 4.5(B)4.3.1.3 Spacing, edge and end distances. Table 4.6provides recommended minimum spacings, edge and enddistances for screws stated in terms of the shankdiameter D.

TABLE 4.6MINIMUM SPACING, EDGE AND END

DISTANCES FOR SCREWS

Spacing Type Minimumdistance

End distanceEdge distance

10D5D

Between screws— along grain— across grain

10D3D

D = shank diameter of screws.

For spacings at an angle to the grain, interpolationaccording to Hankinson’s formula may be used.

4.3.1.4Screw length and timber thickness. For the basicworking loads given in Tables 4.5(A) and 4.5(B) to beapplicable, timber thicknesses and screw length as shownfor nails in Figure 4.2(a) shall be such that —(a) thickness of first member,t1 > 10D; and(b) depth of penetration into second member,tp > 7D.For lesser values oft1 and tp, the basic load shall bereduced in proportion to the decrease int1, or tp and thescrew shall be considered as non-load-bearing ift1 or tp

is less than 4D.4.3.1.5Preboring. The values given in Tables 4.5(A) and4.5(B) apply when the correct size lead holes have beenbored. The diameter of the hole for the shank must beequal to the diameter of the shank, and the lead hole forthe threaded portion of the screw must not be greaterthan the root diameter of the screw.4.3.2 Withdrawal loads.4.3.2.1Basic working loads. The basic working loads forplain wood screws as specified in AS 1476 (driven byhand or by machine), from the side grain of unseasonedtimber are given in Table 4.7(A) and of seasoned timberin Table 4.7(B). As for lateral loads, in the absence ofspecific data these loads may also be used for otherforms of screws.The maximum working load that may be applied to anyone screw shall not exceed the value appropriate to thediameter and metal from which the screw ismanufactured as given in Table 4.8. Loads for otherdiameters may be obtained by linear interpolation in alltables.The basic working loads for wood screws driven into endgrain shall not exceed 60 percent of the values given inTables 4.7(A) and 4.7(B).

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27 AS 1720.1—1988

TABLE 4.7WITHDRAWAL LOADS FOR PLAIN

WOOD SCREWS IN SIDE GRAIN(Comprising Tables 4.7(A) and 4.7(B))


Speciesgroup

Basic working load, N per mm penetration of thread

Screw size number

4 6 8 10 12 14 18

Shank diameter, mm

2.74 3.45 4.17 4.88 5.59 6.30 7.72

J1J2J3

J4J5J6

292217

12108

372821

161310

443426

191512

524030

221814

604634

252116

675239

282318

826347

352822


Speciesgroup

Basic working load, N per mm penetration of thread

Screw size number

4 6 8 10 12 14 18

Shank diameter, mm

2.74 3.45 4.17 4.88 559 6.30 7.72

JD1JD2JD3

JD4JD5JD6

423225

191512

534132

241915

655038

292318

765845

342721

876652

393124

987558

443527

1209271

544333

TABLE 4.8

MAXIMUM PERMISSIBLE WITHDRAWALLOAD PER SCREW

Metal

Maximum permissible withdrawal load, N

Screw size number

4 6 8 10 12 14 18

Steel and 18/8stainless steel

730 1 110 1 650 2 270 2 960 3 780 5 600

Brass andsilicon bronze

560 850 1 270 1 750 2 280 2 910 4 310

Aluminium alloy 430 650 970 1 340 1 740 2 230 3 300

4.3.2.2 Permissible loads. The permissible loadQ for ascrew in withdrawal shall be taken to be given by the lesserof the value given in Table 4.8 and the value —

Q = k13 . . . . . . . . . . . . . . . . . . . . . . . (4.6)where

k13 = 1.0 for screws in side grain= 0.6 for screws in end grain

= basic working load for wood screws in sidegrain, given in Tables 4.7(A) and 4.7(B).

4.4 BOLTED JOINTS.

4.4.1 General.The basic working loads given in Clauses4.4.2.1 and 4.4.2.2 are applicable to steel bolts as specifiedin AS 1111, when fitted into prebored holes of diameterapproximately 10 percent greater than the bolt diameter andwhen fitted with washers as given in Clause 4.4.2.6.

Reference shall be made to Paragraph D3, Appendix D forequations for computing basic working loads for values ofbolt diameters and effective timber thicknesses that are notincluded in Tables 4.9 and 4.10.

4.4.2 Lateral loads.

4.4.2.1Basic working load parallel to the grain. The basicworking load for a single bolt bearing parallel to thegrain and acting in single shear is given for a selection ofbolt diameters and effective timber thicknesses inTables 4.9(B) and 4.9(C).

4.4.2.2Basic working load perpendicular to the grain. Thebasic working load for a single bolt bearingperpendicular to the grain and acting in single shear is givenfor a selection of bolt diameters and effective timberthicknesses in Tables 4.10(B) and 4.10(C).

4.4.2.3Basic working load for a bolted joint system.Thebasic working load for a bolted joint system, denoted byis derived as follows:

(a) For systems loaded parallel to the grain ,

where is the system capacity given in Table 4.9(A).(b) For systems loaded perpendicular to the grain,

, where is the system capacity given inTable 4. 10(A).

(c) For systems loaded at an angle to the grain, the systemcapacity is given by use of Hankinson’s formula asfollows—

= . . . . . . (4.7)

Hankinson’s formula is conveniently evaluated bymeans of the nomograms given in Figures 4.3 to 4.6.

4.4.2.4 Permissible loads. The permissible loadQs of alaterally loaded bolt system shall be taken to be givenby—

Qs = . . . . . . . . . . . . . . . . . . . . . (4.8)

wherek1 = factor for duration of load given in Table 2.5k16 = 1.2 for bolts that transfer load through metal

sideplates of adequate strength, and the bolts area close fit to the holes in these plates providedthatb/D > 5 for loads acting parallel to the grainand b/D > 10 for loads acting perpendicular tothe grain (whereb denotes the effective timberthickness andD is the bolt diameter)

= 1.0 otherwisek17 = factor for multiple bolted joint given in Table

4.11= basic working load as derived in Clause 4.4.2.3.

4.4.2.5Spacings, edge and end distances. Spacings, edgeand end distances shall comply with the followingrequirements:(a) Loads parallel to grain. The basic working loads given

in Tables 4.10(A), 4.10(B) and 4.10(C) apply to jointsin which the edge, end and between-fastener spacingsare not less than those shown in Figure 4.7(a). Thedistancea indicated in the figure shall be at least(n - 2)D with a minimum of 2.5D, wheren is the total

COPYRIGHT

AS 1720.1—1988 28

number of bolts in the joint andD is the diameter of thebolt.Similarly, the required end distancelpar shall be at least8D in tension joints in unseasoned timber, 7D in tensionjoints in seasoned timber, and 5D in compression jointsand in joints subject to bending moment for bothmoisture conditions. However, lesser end distances maybe used in tension joints provided that the basic load isreduced in proportion to the reduction in end distance.Nevertheless, in no case shall the end distance fortension joints be less than 6D for unseasoned timber and5D for seasoned timber.

(b) Loads perpendicular to grain. The minimum edge, endand between-fastener spacings shall not be less thanthose shown in Figure 4.7(b). The distancea shall be atleast 2.5D for a b/D ratio of 2, and it shall be increasedproportionately so that it is at least 5D for a b/D ratioof 6 or more, whereb is the thickness of the memberloaded perpendicular to the grain.

(c) Loads acting at an angle to the grain. For loads actingat an angle 0° to 30° to the grain, the spacings, edgeand end distances may be taken as for loads parallel tothe grain. For loads acting at an angle of 30° to 90° tothe grain, the spacings, edge and end distances may betaken as for loads acting perpendicular to the grain.

TABLE 4.9

BASIC WORKING LOADS FOR SINGLE BOLTS PARALLEL TO GRAIN(comprising Tables 4.9(A), 4.9(B) and 4.9(C))

4.9(A) SYSTEM CAPACITY

Type of joint Effective timber thicknessSystem capacity

1. Two member Smaller oft1 and t2

2. Three member Smaller oft2 and 2t12

3. Multiple member (i) Between A and B—smaller oft1 and t2

(ii) Between B and C—smaller oft2 and t3

(iii) etc

(i)

(ii)

(iii) etc

= sum ofbasic loads(i), (ii), etc

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29 AS 1720.1—1988

TABLE 4.9(B)IN UNSEASONED TIMBER: PARALLEL TO GRAIN

Jointgroup

Effectivetimber

thicknessmm

Basic working load , N

Bolt diameter

M6 M8 M10 M12 M16 M20 M24 M30 M36J1 25

385075

100150200

980980980980980980980

1650174017401740174017401740

2100270027002700270027002700

2500380039003900390039003900

3300500066007000700070007000

410063008300

10900109001090010900

500075009900

14900157001570015700

62009400

1240018600250002500025000

7400113001490022000300003500035000

J2 25385075

100150200

820820820820820820820

1300146014601460146014601460

1630230023002300230023002300

1950300033003300330033003300

2600400052005800580058005800

3300490065009100910091009100

390059007800

11700131001310013100

490074009800

14600195002000020000

59008900

1170017600230002900029000

J3 25385075

100150200

760760760760760760760

1050134013401340134013401340

1310200021002100210021002100

1580240030003000300030003000

2100320042005400540054005400

2600400053007900840084008400

3200480063009500

121001210012100

390060007900

11800158001890018900

470072009500

14200189002700027000

J4 25385075

100150200

600600600600600600600

830106010601060106010601060

1040158016601660166016601660

1250189024002400240024002400

1660250033004200420042004200

2100320042006200660066006600

2500380050007500960096009600

3100470062009300

125001490014900

370057007500

11200149002200022000

J5 25385075

100150200

500520520520520520520

660930930930930930930

830125014501450145014501450

990150019802100210021002100

1320200026003700370037003700

1650250033005000580058005800

1980300040005900790084008400

25003800500074009900

1310013100

3000450059008900

119001780018800

J6 25385075

100150200

400460460460460460460

530810810810810810810

660101012701270127012701270

800121015901830183018301830

1060161021003200330033003300

1330200027004000510051005100

1590240032004800640073007300

19903000400060008000

1140011400

24003600480072009500

1430016500

TABLE 4.9(C)IN SEASONED TlMBER: PARALLEL TO GRAIN

Jointgroup

Effectivetimber

thicknessmm


Bolt diameter

M6 M8 M10 M12 M16 M20 M24 M30 M36JD1 20

3040507085

100

1200120012001200120012001200

1640220022002200220022002200

2100310034003400340034003400

2500370049004900490049004900

3300490066008200870087008700

410062008200

10300135001350013500

490074009800

12300172001950019500

62009200

1230015400220002600030000

7400111001480018500260003140037000

JD2 203040507085

100

990104010401040104010401040

1320185018501850185018501850

1650250029002900290029002900

1980300040004200420042004200

2600400053006600740074007400

3300500066008300

116001160011600

4000590079009900

139001660016600

500074009900

12400173002100025000

59008900

1190014900210002500030000

JD3 203040507085

100

780940940940940940940

1040156016601660166016601660

1300195026002600260026002600

1560230031003700370037003700

2100310042005200670067006700

26003900520065009100

1040010400

3100470062007800

109001330015000

3900590078009800

137001660019500

470070009400

11700164001990023000

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AS 1720.1—1988 30

TABLE 4.9(C) (continued)

Jointgroup

Effectivetimber

thicknessmm


Bolt diameter

M6 M8 M10 M12 M16 M20 M24 M30 M36

JD4 203040507085

100

630760760760760760760

840126013401340134013401340

1050158021002100210021002100

1260189025003000300030003000

1680250034004200540054005400

2100320042005300740084008400

25003800500063008800

1070012100

3200470063007900

110001340015800

3800570076009500

132001610018900

JD5 203040507085

100

500660660660660660660

660100011701170117011701170

830125016601830183018301830

1000149019902500260026002600

1330199027003300460047004700

1660250033004200580071007300

199030004000500070008500

10000

25003700500062008700

1060012500

3000450060007500

105001270014900

JD6 203040507085

100

400570570570570570570

530790

10101010101010101010

660990

13201580158015801580

790119015801980230023002300

1060158021002600370041004100

1320198026003300460056006300

1580240032004000550067007900

1980300040005000690084009900

24003600480059008300

1010011900

TABLE 4.10

BASIC WORKING LOADS FOR SINGLE BOLTSPERPENDICULAR TO THE GRAIN

(Comprising Tables 4.10(A), 4.10(B), and 4.10(C))

4.10(A) SYSTEM CAPACITY

Type of joint Effective timber thicknessSystem capacity

1. Two member 2t1

2. Three member, Type A t2 2

3. Three member, Type B 2t1 2

4. Multiple member (i) Between A and B—t2(ii) Between B and C—t2(iii) Between C and D—t4(iv) Etc

(i)

(ii)

(iii)(iv) Etc.

= sum of basic loads(i), (ii), (iii), etc

NOTE: At each interface, the strength of the bolted joint with respect to the member aligned parallel to thedirection of the stress must be checked according to Table 4.9.

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31 AS 1720.1—1988

TABLE 4.10(B)IN UNSEASONED TIMBER: PERPENDICULAR TO GRAIN

Jointgroup

Effectivetimber

thicknessmm


Bolt diameter

M6 M8 M10 M12 M16 M20 M24 M30 M36

J1 25385075

100150200

500750970970970970970

660100013201490149014901490

830125016502100210021002100

990150019802700270027002700

1320200026004000420042004200

1650250033005000590059005900

1980300040005900780078007800

25003800500074009900

1080010800

3000450059008900

119001430014300

J2 25385075

100150200

390590780920920920920

520790

10401410141014101410

650990

13001950197019701970

780119015602300260026002600

1040158021003100400040004000

1330198026003900520056005600

1560240031004700620073007300

19503000390059007800

1030010300

23003600470070009400

1350013500

J3 25385075

100150200

250380500730730730730

330500660990

112011201120

410630830

1240157015701570

500750990

1490198021002100

660100013201980260032003200

830125016502500330044004400

990150019803000400058005800

1240188025003700500074008100

149023003000450059008900

10700

J4 25385075

100150200

157240310470520520520

210320420630810810810

260400520790

105011301130

310480630950

126014801480

420640840

1260168023002300

520800

10501580210032003200

630960

12601890250038004200

790120015702400310047005900

940144018902800380057007600

J5 25385075

100150200

105159210320390390390

140210280420560600600

175270350530700840840

210320420630840

11101110

280430560840

112016801700

350530700

1050140021002400

420640840

1260168025003100

530800

10501580210032004200

630960

12601890250038005000

J6 25385075

100150200

5279

105157195195195

70106140210280300300

87133175260350420420

105159210320420550550

140210280420560840850

175270350530700

10501190

210320420630840

12601560

260400530790

105015802100

320480630950

126018902500

TABLE 4.10(C)IN SEASONED TIMBER: PERPENDICULAR TO GRAIN

Jointgroup

Effectivetimber

thicknessmm


Bolt diameter

M6 M8 M10 M12 M16 M20 M24 M30 M36

JD1 203040507085

100

520780

10401280128012801280

700104013901740197019701970

870131017402200280028002800

1040157021002600360036003600

1390210028003500490056005600

1740260035004400610074007800

210031004200520073008900

10200

26003900520065009100

1110013100

3100470063007800

110001330015700

JD2 203040507085

100

400600800

1010118011801180

540800

10701340182018201820

670101013401680230025002500

800121016102000280033003300

1070161021003700380046005100

1340200027003400470057006700

1610240032004000560068008000

200030004000500070008500

10100

24003600480060008400

1030012100

JD3 203040507085

100

300450600750

105011001100

400600800

1000140017001700

500750

10001250175021002400

600900

12001500210026003000

800120016002000280034004000

1000150020002800350043005000

1200180024003000420051006000

1500230030003800530064007500

1800270036004500630077009000

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AS 1720.1—1988 32

TABLE 4.10(C) (continued)

Jointgroup

Effectivetimber

thicknessmm


Bolt diameter

M6 M8 M10 M12 M16 M20 M24 M30 M36

JD4 203040507085

100

220330440560780920920

300440590740

104012601420

370560740930

130015701850

440670890

1110155018902200

590890

11801480210025003000

740111014801850260031003700

890133017802200310038004400

1110167022002800390047005600

1330200027003300470057006700

JD5 203040507085

100

156230310390550660780

210310420520730880

1040

260390520650910

11001300

310470620780

109013301560

420620830

1040146017702100

520780

10401300182022002600

620940

13001560220027003100

780117015601950270033003900

940140018702300330040004700

JD6 203040507085

100

108162220270380460540

144220290360500610720

180270360450630770900

220320430540760920

1080

290430580720

101012201440

360540720900

126015301800

430650860

1080151018402200

540810

10801350189023002700

650970

13001620230028003200

FIGURE 4.3. MOGRAM FOR HANKINSON’S FORMULA, RANGE I

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33 AS 1720.1—1988

FIGURE 4.4. NOMOGRAM FOR HANKINSON’S FORMULA, RANGE II

FIGURE 4.5. NOMOGRAM FOR HANKINSON’S FORMULA, RANGE III

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AS 1720.1—1988 34

TABLE 4.11VALUE OF k17, FOR USE IN THE DESIGN OF MULTIPLE CONNECTOR

JOINTS OF BOLTS, COACH SCREWS, SPLIT RINGS AND SHEAR PLATES

Type of jointValues of k17

na ≤ 4 na = 5 na = 10 na = 15 na ≥ 16

Seasoned timber 1.0 1.0 1.0 1.0 1.0

Unseasoned timber (no transverserestraint*)

1.0 0.95 0.80 0.55 0.50

Unseasoned timber (transverserestraint*)

0.5 0.5 0.5 0.5 0.5

na = total number of rows of fasteners per interface.* The term ‘transverse restraint’ refers to the possibility of restraint to timber shrinkage due to the joint

detail.

FIGURE 4.6. NOMOGRAM FOR HANKINSON’S FORMULA, RANGE IV

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35 AS 1720.1—1988

FIGURE 4.7. SPACINGS, EDGE AND END DISTANCES FORBOLTED JOINTS

COPYRIGHT

AS 1720.1—1988 36

4.4.2.6 Washers. In all timber-to-timber bolted structuraljoints, every bolt shall be provided with a washer at eachend, of a size not less than in Table 4.12.If smaller washers are used then the basic working loadgiven in Clause 4.4.2 shall be reduced in proportion to thedimension of the washer diameter or side length.

4.4.3 Axial loads. Where bolts are loaded axially, the

TABLE 4.12MINIMUM REQUIRED SIZE OF WASHERS

FOR STRUCTURAL BOLTED JOINTS

Bolt

Washer size, mm

ThicknessMinimum

diameter forround washers

Minimum sidelength for

square washers

M6M8M10

1.62.02.5

303645

253240

M12M16M20

3.04.05.0

556572

505765

>M20 6.0 85 75

basic working load of the bolt shall be taken as the lesserof the axial strength of the bolt and the bearing strengthof the timber under the washer when loaded perpendicularto the grain. The design axial strength of bolts and theeffective diameter for use in computing the bearingpressure on the timber are given in Table 4.13.

TABLE 4.13DESIGN PARAMETERS FOR BOLTS UNDER

AXIAL LOAD

Bolt sizeAxial strength

of bolt*kN

Effective diameter of astandard washer† in bearing

mm

M6M8M10

4.07.5

11.5

162127

M12M16M20

1732.050.0

313150

M24M30M36

72115165

606978

* Bolts to be of grade 4.6, AS 1111.† Standard washers are washers having the minimum

dimensions shown in Table 4.12. The effective diameter isless than the actual diameter because it includes an allowancefor bending of the washer.

4.5 COACH SCREWS.4.5.1 General. The basic working loads given in thefollowing clauses are applicable to steel coach screws asspecified in AS 1393.4.5.2 Lateral loads.For coach screws bearing laterally inunseasoned timber, the provisions of Clause 4.4 for boltsshall apply, subject to the following conditions:(a) For the purpose of Clause 4.4, a coach screw shall be

considered to be a bolt of diameter equal to the shankdiameter of the screw.

(b) The screws shall be fitted with washers as specifiedin Clause 4.4.2.6.

(c) In a two-member joint, the thinner member shall havea minimum thickness of three times the shankdiameter of the coach screw.

(d) The diameter of the hole for the shank shall be notless than the shank diameter of the screw nor exceedit by more than 1 mm or 10 percent of the shank

diameter, whichever is the lesser. The diameter of thehole for the threaded portion of the screw shall notexceed the root diameter of the screw.The depth of the hole shall not be less than theintended depth to which the screw is to be driven.The screw shall not be hammered into place butturned with a hand operated or machine operatedwrench.

(e) Timber thicknesses and screw lengths as shown inFigure 4.2(a) shall be such that—(i) thickness of first member,t1 > 3D;(ii) depth of penetration into second member, for

species groups —J1, JD1, J2, JD2, JD3 -tp > 7D,J3, JD4 -tp > 8D,J4, JD5 -tp > 10D,J5, J6, JD6 -tp > 12D.

For lesser values oftp, the basic load shall bereduced in proportion to the decrease intp and thecoach screw shall be considered as non-loadbearingif tp is less than 4D.

4.5.3 Withdrawal loads.4.5.3.1Basic working loads. The basic working loads forcoach screws in withdrawal from the side grain are givenin Table 4.14. Basic working loads for coach screws fixedinto end grain shall not exceed 60 percent of the valuesgiven in Table 4.14.4.5.3.2 Permissible loads. The permissible withdrawalload Q for a coach screw in withdrawal shall be taken tobe given by—

Q = k13 . . . . . . . . . . . . . . . . . . . . . . (4.9)but not greater than the value given in Table 4.1 4(C)

wherek13 = 1.0 for coach screws in side grain,

= 0.6 for coach screws in end grain

= basic working load for coach screws in sidegrain, given in Tables 4.14(A) and 4.14(B).

TABLE 4.14WITHDRAWAL LOADS FOR

COACH SCREWS IN SIDE GRAIN(Comprising Tables 4.14(A), 4.14(B) and 4.14(C))


Speciesgroup

Basic working load, N per mm penetration ofthread

Shank diameter, mm6 8 10 12 16 20

J1J2J3

776143

876951

987958

1088764

12510074

14011384

J4J5J6

342620

362720

403022

433525

514030

584333


Speciesgroup

Basic working load, N per mm penetration ofthread

Shank diameter, mm6 8 10 12 16 20

JD1JD2JD3

967654

1098663

1209973

13510980

15612593

175141106

JD4JD5JD6

433225

453425

503828

544431

645038

725441

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37 AS 1720.1—1988

TABLE 4.14(C)MAXIMUM PERMISSIBLE WITHDRAWAL

LOAD PER COACH SCREWNominal diameter of coach

screwmm

Maximum permissiblewithdrawal load

N

6810

2 0004 0006 000

121620

9 00020 00031 500

4.6 SPLIT-RING CONNECTORS.

4.6.1 General. The following requirements relate tosplit-ring connectors of nominal size 64 mm and102 mm.

An M12 bolt is used in conjunction with the 64 mmconnector and an M20 bolt is used with the 102 mmconnector. The bolts are fitted with washers as given inClause 4.4.2.6.

NOTE: In computations for the design of the timber members, theprojected area of the groove to receive the connector in one membermay be taken as 710 mm2 for the 64 mm connector and 1450 mm2

for the 102 mm connector.

4.6.2 Basic loads.The basic working loads for joints inunseasoned timber are given in Table 4.15. These loadsapply to a connector unit comprising one split-ring in thecontact faces of a timber-to-timber joint with its bolt insingle shear.

4.6.3 Permissible loads.The permissible loadQ for asplit-ring connector shall be taken to be given by —

Q = k1k15k17k18 . . . . . . . . . . . . . . (4.10)where

k1 = factor for duration of load given inTable 2.5

k15 = 1.0 for unseasoned timber= factor for seasoned timber given in

Table 4.16k17 = factor for multiple connector joints given in

Table 4.11k18 = 1.0 for loads applied in compression along

the grain, and for loads appliedperpendicular to the grain

= factor for tension loads applied along thegrain, given in Table 4.17(Values of k18 for intermediate directionsmay be obtained by the use of Hankinson’sformula, see Clause 4.4.2.3.)

= basic load given in Table 4.15.

4.6.4 Spacings, edge and end distances.Table 4.18provides recommended minimum values of spacings,edge and end distances which are defined and illustratedin Figure 4.8.

4.7 SHEAR PLATE CONNECTORS.

4.7.1 General. The following requirements relate toshear plate connectors of nominal 67 mm and 102 mmsize.

An M20 bolt is used in conjunction with a 67 mmconnector and an M24 bolt with a 102 mm connector.Where required, bolts are fitted with washers as specifiedin Clause 4.4.2.6.

NOTE: In computations for the design of the timber members, theprojected area of the groove in the timber to receive the connectormay be taken as 632 mm2 for the 67 mm connector and 1600 mm2

for the 102 mm connector.

4.7.2 Basic loads. The basic working loads forshear-plate connectors in unseasoned timber are given inTable 4.19. These basic loads apply to a connector unitcomprising one shear-plate in the contact face of atimber-to-steel joint with its bolt in single shear.

4.7.3 Permissible loads.The permissible loadQ for ashear-plate connector shall be the lesser of —

Q = 24 000 Nor

Q = k1k15k17k18 . . . . . . . . . . . . . (4.11)wherek1, k15, k17, andk18 are as defined in Clause 4.6.3

and is the basic load given in Table 4.19.NOTE: Loads marked with an asterisk in Table 4.19 exceed24 000 N but are included for interpolation purposes.

4.7.4 Spacings, edge and end distances.Table 4.18provides recommended minimum values of spacings,edge and end distances which are defined and illustratedin Figure 4.8.

LEGEND:a1 = spacing parallel to grain a3 = end distancea2 = spacing perpendicular to grain a4 = edge distance

FIGURE 4.8. SPACING, EDGE AND END DISTANCES FOR SPLIT-RING AND SHEAR-PLATE CONNECTORS

COPYRIGHT

AS 1720.1—1988 38

TABLE 4.15BASIC WORKING LOADS FOR A SINGLE SPLIT-RING CONNECTOR IN UNSEASONED TIMBER

Joint groupInternal

diameter ofring mm

Minimum nominal thicknessof timber, mm Basic working load per connector in single shear, N

Connectors inone side only

Connectorsopposite intwo sides

Angle of load to grain

0° 15° 30° 45° 60° 75° 90°

J1 64

102

—25—38

38505075

11900178902290031200

11300169002220030300

9880148002060028000

8440126001870025400

7370110001710023200

6740110001610021800

65409790

1580021400

J2 64

102

—25—38

38505075

9520142001970026700

9000134001880025500

7780116001690022900

65809870

1470020000

57008560

1310017800

51907800

1210016500

50307560

1180016600

J3 64

102

—25—38

38505075

8900134001800023000

8260124001690021670

6910104001430018710

56508500

1190015770

47807190

1020013630

429064509210

12400

414062308900

12000

J4 64

102

25—38—3850

38506450—75

636087209520

139001490018400

618085009260

132101440017570

576079209630

116301340015650

5260723079209990

1220013610

4850666063008760

1120012040

4580630069008040

1050011110

4500618067607800

1030010800

J5 64

102

25—38—3850

38506450—75

510074007620

110001190013600

481070206420

104801156013120

4170616069109270

1071011940

35305280632080109740

10690

306046105820705089309650

279042305510649084109010

270041005400630082408800

J6 64

102

25—38—3850

38506450—75

41006000610092009500

11000

38805710593087309230

10610

337050405520766085609670

286043405040656077908630

249038104640574071507790

227035004390526067407270

220034004300510066007100

TABLE 4.16FACTOR k15 FOR SPLIT-RING CONNECTORS IN SEASONED TIMBER

Species group JD1, JD2, JD3JD4,JD5,JD6

Angle of load to grain 0° 15° 30° 45° 60° 75° 90° any

Factork15 1.25 1.29 1.33 1.38 1.42 1.46 1.50 1.25

TABLE 4.17FACTOR k18 FOR TENSION LOADS ON SPLIT RINGS AND SHEAR PLATES

Size of split ring or shearplate mm

Factor k18

Connector remote fromends of members*

Connector at ends of members

Seasoned timber Unseasoned timber†

64, 67102

1.00.8

1.00.6

0.50.3

* A connector may be taken to occur in the middle of a member if the distance from the connector to theend of the timber is greater than 10D, whereD is the connector diameter.

† Factors for seasoned timber may be used if the timber has negligible tendency to split (see Clause 4.1.4).

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39 AS 1720.1—1988

TABLE 4.18MINIMUM SPACINGS, EDGE AND END DISTANCES FOR SPLIT RINGS

AND SHEAR PLATE CONNECTORS

Spacing typeMinimum distance

mm

D = 64 mm and 67 mm D = 102 mm

End distance:tension memberscompression members

150100

180140

Edge distance:0° to 30° angle of load to grain

30° to 90° angle of load to grain:compression sideopposite compression side

45

7045

70

9570

Between fasteners:0° to 30° angle of load to grain:Spacing parallel to grainspacing perpendicular to grain30° to 90° angle of load to grain:spacing parallel to grainspacing perpendicular to grain

18090

90115

230140

140165

TABLE 4.19BASIC WORKING LOADS FOR A SINGLE SHEAR PLATE CONNECTOR IN

UNSEASONED TIMBER

Joint group

Externaldiameter ofshear plate

mm

Boltdiameter

Minimum nominalthickness of timber, mm Basic working load per connector unit and bolt in single shear, N

Connectorsin one side

only

Connectorsopposite intwo sides

Angle of load to grain

0° 15° 30° 45° 60° 75° 90°

J1 67102

M20M24

38—50

505075

142002290031100*

134002220030300*

117002050027900*

101001870025400*

88101710023100

80501600021800

78301580021400

J2 67102

M20M24

38—50

505075

114001970026700*

109001880025500*

93401690022900

79201470020000

68501310017800

63201210016500

60501180016000

J3 67102

M20M24

38—50

505075

107001800024500*

99301690023000

83201430019500

67601190016100

57201010013700

51609210

12400

49808900

12000

J4 67102

M20M24

38—50

505075

87001070014200

80701040013800

67209660

12800

54808810

11700

46208100

10700

41507610

10100

400074709920

J5 67102

M20M24

38—50

505075

60009600

13000

56709270

12540

49208490

11430

41707610

10210

362068909210

330064508600

320063008400

J6 67102

M20M24

38—50

505075

49007800

10500

46307530

10120

401068909200

340061708180

295055807370

268052206870

260051006700

* See Clause 4.7.3.

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AS 1720.1—1988 40

SECTION 5. PLYWOOD5.1 GENERAL. Permissible stresses for structuralplywood shall be obtained by modifying the basicworking stresses by factors appropriate to the serviceconditions. Provision is made in this Standard only forplywood which has been stress graded by visual ormechanical means to AS 2269.Where plywood isexposed to water or to damp conditions such that itsmoisture content may exceed 20 percent for prolongedperiods, only plywood with a Type A bond as defined inAS 2754.1 shall be used.5.2 BASIC WORKING STRESSES ANDSTIFFNESS.The basic working stresses and moduli ofelasticity and rigidity for structural plywood are given inTable 5.1 for the various stress grades.5.3 DESIGN.5.3.1 Permissible stresses.Permissible stresses forstructural plywood shall be obtained by multiplying thebasic working stresses given in Clause 5.2 by themodification factors given in Clause 5.4, as appropriateto the service conditions and the assembly of theplywood.5.3.2 Deflections.Deflection calculations shall take intoaccount the modification factors in Clause 2.5.1.2.5.4 MODIFICATION FACTORS.5.4.1 Duration of load. The multiplying factorsk1, j2

and j3 given in Clause 2.5.1 should be used whereappropriate.5.4.2 Moisture condition. For plywood at a moisturecontent of 15 percent or less, the basic working stressesshall be taken in accordance with Table 5.1. Whereplywood is liable to be subjected to conditions such thatthe average moisture content for a 12 month period will

exceed 15 percent, then the basic working stresses shallbe modified by linear interpolation between those for 15percent moisture content and those for 25 percentmoisture content, obtained by multiplying the basicworking stresses in Table 5.1 by the moisture contentfactor k19 given in Table 5.2(A). Similarly the stiffnessshould be modified by use of the moisture content factorj6 given in Table 5.2(B).5.4.3 Temperature.The provisions of Clause 2.5.3 forseasoned timber shall apply in a similar manner tostructural plywood.5.4.4 Plywood assembly factor.The values shown inTable 5.1 refer to basic properties of plywood veneer inthe direction of the grain. In order to use these values toderive the properties of plywood formed from severallayers of veneer, the basic working stress and stiffnessappropriate to a particular property shall be modified inaccordance with the assembly factor given in Tables5.3(A) and 5.3(B) applicable to the relative direction ofstress in the plywood and the direction of grain in itsface plies.

NOTE: The simplified methods of calculations shown in Tables5.3(A) and 5.3(B) must be modified as shown in Appendix E forstructures so proportioned that the strength of plywood is reduceddue to buckling distortions.

5.4.5 Stability factors. Stability factors for plywooddiaphragms are given in Appendix E.

5.5 JOINTS.5.5.1 Nailed and screwed joints.Recommendations for the design strength and stiffness ofnailed and screwed joints between plywood and solidtimber are given in Appendix D.

5.5.2 Glued joints.For information on glued joints seeTable 5.3(B) and Clause 4.1.1.

TABLE 5.1BASIC WORKING STRESSES AND STIFFNESS FOR STRUCTURAL PLYWOOD

(Moisture content 15% or less)

Stress grade

Basic working stress, MPa

Bending Tension ShearCompression inthe plane of the

sheet

Compressionnormal to theplane of sheet

Short durationmodulus of

elasticity MPa(E)

Short durationmodulus or

rigidity MPa(G)

F34F27F22F17F14F11F8F7

34.527.522.017.014.011.08.66.9

20.716.513.210.28.46.65.24.1

2.302.302.302.302.051.801.601.40

25.920.616.512.810.58.36.55.2

10.49.07.86.65.24.13.32.6

21 50018 50016 00014 00012 00010 5009 1007 900

1 075925800700625525455395

TABLE 5.2FACTORS FOR SOAKED PLYWOOD WITH MOISTURE CONTENT 25% OR GREATER

(comprising Tables 5.2(A) and 5.2(B))

5.2(A) STRENGTH FACTOR k19

Type of stress Factork19

BendingTension in plane of sheetShearCompression in plane of sheetCompression normal to plane of sheet

0.60.70.60.4

0.45

5.2(B) STIFFNESS FACTOR j 6

Type of stiffness Factorj6

Modulus of elasticityModulus of rigidity

0.80.6

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41 AS 1720.1—1988

TABLE 5.3ASSEMBLY FACTORS FOR PLYWOOD

(Comprising Tables 5.3(A) and 5.3(B))

5.3(A) GENERAL

PropertyStress direction with

respect to graindirection in face plies

Assembly factor

Portion of cross-section to be considered incomputing area or second moment of area

(moment of inertia)Modification of basic values in Table 5.1

Tension Parallel orperpendicular

Parallel plies* only Basic stress for tension parallel to grain

±45° Full cross-sectional area 0.17× basic working stress for tension parallelto grain

Compression† Parallel orperpendicular

Parallel plies* only Basic stress in compression parallel to grain

±45° Full cross-sectional area 0.34× basic working stress in compressionparallel to grain

Deformation incompression or tension

Parallel orperpendicular

Parallel plies*only Basic value for modulus of elasticity

± 45° Full cross-sectional area 0.17× basic value for modulus of elasticity

Shear throughthickness


Full cross-sectional area Basic working shear stress

±45° Full cross-sectional area 1.5× basic working shear stress

Compressionperpendicular to faceof plywood

— Full loaded area Basic working stress in compressionperpendicular to grain

Strength in bending‡(perpendicular to planeof plies)


The basic working bending moment capacity

shall be computed from:

whereg19 = 1.20 for three-ply plywood having thegrain of the outer plies perpendicular to the spanandg19 = 1.00 for all other plywood

= basic working stress for extreme fibre inbendingI = second moment of area (moment of inertia)computed on basis of parallel plies onlyYmax = distance from neutral axis to outer fibreof outermost ply having its grain in the directionof the span

Basic working stress for extreme fibre inbending

Deflection in bending Parallel orperpendicular

Deflection may be calculated by the usualformula, taking as the second moment of area(moment of inertia) that of the parallel plies +0.03 times that of the perpendicular plies

Basic value for modulus of elasticity

Shear deformation inplane of sheet


Full cross-sectional area Basic value for modulus of rigidity

Shear deformationthrough the thickness


Full cross-sectional area Basic value for modulus of rigidity

* By ‘parallel plies’ is meant those plies whose grain direction is parallel to the direction of principal stress.† The effect of buckling on compression strength is given in appendix E.‡ For bending in the plane of the plies, check the in-plane compression and tension stresses. The effect of buckling on the compression

strength is given in appendix E.

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AS 1720.1—1988 42


5.3(B) SHEAR IN PLANES OF PLIES

Type of construction Position of shearStress direction with

respect to grain direction inface plies

Assembly factor

Area to be considered Modification of basic values in Table5.1

Plywood beams Longitudinal shear between plies Parallel or perpendicular Full shear area 0.4× basic shear stress

Box beams and I-beams with plywoodwebs

Shear between plies of web or between weband flange

Parallel or perpendicular Full area of contact betweenplywood and flange

0.2 × basic shear stress

±45° Full area of contact betweenplywood and flange

0.2 × basic shear stress

Panels with plywood covers stressed incompression or tension or both

Shear between plies or between cover andframing members when: (a) depth ofmember exceeds twice its width and endnogging is used, or (b) depth of member isnot more than twice its width and no endnogging is used

Parallel or perpendicular Full area of contact betweenplywood and members

0.4 × basic shear stress for interiorframing

0.2 × basic shear stress for edge framingmembers

±45° Full area of contact betweenplywood and framing member

0.4 × basic shear stress for interiorframing member

0.2 × basic shear stress for edge framingmembers

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43 AS 1720.1—1988

SECTION 6. ROUND TIMBERS6.1 GENERAL. Whether naturally round timbers areused as simple structural members, i.e. as poles or pilesor as elements of a composite structure, the designprocedures shall be similar to those given in Section 3,subject to the provisions of Clauses 6.2, 6.3 and 6.4.

6.2 BASIC WORKING STRESSES ANDSTIFFNESS. The basic working stresses and stiffnessfor untrimmed logs, poles or piles conforming in qualityto the requirements of AS 2209 shall be those given inTables 2.3 and 2.4. For any particular species, theappropriate stress grade is derived from its strengthgroups as given in Table 6.1.

TABLE 6.1

CORRESPONDENCE BETWEEN STRENGTHGROUP AND STRESS GRADE FOR ROUND

TIMBERS GRADED TO AS 2209Strength group Stress grade

S1S2S3

F34F27F22

S4S5S6

F17F14F11

S7 F8

NOTE: The equivalence expressed in Table 6.1 is based on theassumption that all poles or logs are cut from mature trees.Factors for immaturity are given in Clause 6.4.1.

6.3 DESIGN.

6.3.1 Permissible stresses.To obtain permissible stressesfor naturally round timbers, the basic working stressesshall be modified by such of the factors given inClause 2.5 as are applicable to the service conditions. Inaddition, the modification factors specified in Clause 6.4shall also be applied where appropriate.

6.3.2 Deflections.Deflection calculations shall take intoaccount the modification factors in Clause 2.5.1.2.

6.4 ADDITIONAL MODIFICATION FACTORS.

6.4.1 Factor for immaturity. For poles having mid-length diameters less than 250 mm, due allowance mustbe made for the properties of immature timber. Foreucalyptusspecies and radiata pine, this may be donethrough multiplication of basic stresses and modulus ofelasticity by the factorsk20 and j9 respectively given inTable 6.2.

NOTE: For species other than eucalyptus or radiata pine,conservative assumptions should be used in design unless specialinvestigations have been undertaken to derive accurate values.

6.4.2 Shaving factor.For timber members in naturalpole form, the basic working stresses shall be reduced ifthe poles have been shaved. For poles of eucalyptusspecies and radiata pine that have been shaved to asmooth cylindrical form, the shaving factork21 shall betaken as specified in Table 6.3. In addition, it shall beassumed that the effect of shaving will be to reduce themodulus of elasticity by 5 percent.

6.5 DESIGN DETAILS.

6.5.1 Effective pole cross-section.The effectivediameter of a cross-section between two points of lateralrestraint shall be taken as the mean of the diameters atthe points of lateral restraint.

6.5.2 Effective cross-section of untreated timber.Unless subjected to adequate preservative treatment inaccordance with an approved Standard, the sapwood ofall timbers shall be disregarded in assessing the effectivestructural cross-section of poles at or above theground-line where exposed to the weather or when usedas piles above permanent water level.

6.5.3 Moisture content of timbers in ground contact.Irrespective of whether poles are used in the unseasoned,partially seasoned or fully seasoned condition, it shall beassumed that all parts of poles within 1 m of aground-line contact are, for design purposes, in theunseasoned condition.

6.5.4 Connectors.For information on connectors seeAppendix F.

TABLE 6.2IMMATURITY FACTORS

6.2(A) IMMATURITY FACTOR k20 FOR STRESSES

SpeciesFactor k20 for stresses

D = 75 D = 100 D = 125 D = 150 D = 175 D = 200 D = 225 D = 250

Eucalyptus species 0.80 0.90 1.00 1.00 1.00 1.00 1.00 1.00

Radiata pine 0.70 0.75 0.80 0.85 0.90 0.95 1.00 1.00

D = pole diameter at mid-length, mm.

6.2(B) IMMATURITY FACTOR j 9 FOR STIFFNESS

SpeciesFactor k20 for stresses

D = 75 D = 100 D = 125 D = 150 D = 175 D = 200 D = 225 D = 250

Eucalyptus species 0.80 0.90 1.00 1.00 1.00 1.00 1.00 1.00

Radiata pine 0.70 0.75 0.80 0.85 0.90 0.95 1.00 1.00

D = pole diameter at mid-length, mm.

AS 1720.1—1988 44

TABLE 6.3

SHAVING FACTOR k21

StressFactor k21

EucalyptusSpecies Radiata pine

Bending 0.85 0.75

Compression parallel to grain 0.95 0.90

Compression perpendicular to grain and shear 1.00 1.00

Tension 0.85 0.75

45 AS 1720.1—1988

SECTION 7. GLUED-LAMINATED CONSTRUCTION

7.1 GENERAL. This Section shall be applied inconjunction with Sections 2 and 3. The provisions of thisSection apply specifically to glued-laminated timbermembers manufactured in accordance with AS 1328.

NOTE: The structural characteristics of laminated timber are verysimilar to those of solid timber. The laminating process does notaffect the stiffness of the timber, but does provide a slight increasein strength. Design procedures to account for the effects ofbutt-joints in the laminations are given in Paragraph G2, AppendixG. Butt joints are a source of considerable weaknesses inglued-laminated timber and in general it is not economical to designmembers so that they contain butt joints in locations subjected tohigh tension stresses.

Where any glued-laminated member is likely to beexposed to water or to damp conditions, only a phenolicglue shall be used in its manufacture.

7.2 DESIGN.

7.2.1 Basic and permissible stresses.The basic stressesfor structural timber set out in Section 2, and thepermissible stresses given in Section 3 shall apply toglued-laminated timber subject to the additionalrequirements of Clauses 7.3 and 7.4.

7.2.2 Deflections.Deflection calculations shall take intoaccount the modification factors in Clause 2.5.1.2.

7.3 MODIFICATION FACTORS.

7.3.1 Moisture condition.For glued-laminated members,Clause 2.5.2(c) shall be applied in deriving permissiblestresses.

7.3.2 Lamination effects.

7.3.2.1 Vertically laminated timber.For a member ofrectangular cross-section comprised of two or morelaminations securely fastened together by gluing andloaded in a direction parallel to the plane of theglue-lines, the basic working stresses in bending, shearand compression parallel to the grain may be increasedby the appropriate factork23 given in Table 7.1. In theuse of this Table,nL (the effective number of laminationscarrying a common load) shall be taken as the totalnumber of laminations in the member for bending andshear. For compression parallel to the grain, the value ofnL shall be taken to be equal to the total number oflaminations for the case of buckling in the plane of thelaminations, and half of the total number of laminationsfor the case of buckling normal to the plane of thelaminations.

If several laminated members act together to form aparallel support system, then the effect of load sharingon bending and compression stresses may be obtained bytaking the factork23 to be unity and making use of thefactor k8 as given in Clause 2.5.5.2.

For some timbers, such as radiata pine, hoop pine andDouglas fir, a special lamination factork30 may be usedas an alternative to the factork23 in Table 7.1. Thisfactor, together with the special conditions required forits use, is given in Appendix G.

7.3.2.2Horizontally laminated timber. For a member ofrectangular cross-section comprising two or morelaminations securely fastened together by gluing andloaded in a direction perpendicular to the plane of thegluelines, the basic stresses parallel to the grain may be

increased by the appropriate factork23 given in Table 7.1.The value ofnL, the effective number of laminations tobe used in Table 7.1, may be taken to be 1.0, 0.5 and0.25 times the number of member laminations inevaluatingk23 for application to the basic tension stressof tension members, the compression stress of columnsand the bending stress of beams respectively. Inevaluatingk23 for modifying the basic shear stress ofbeams, the effective number of elements for shear shallbe taken as four or the number of laminations, whicheveris the lesser.

If several laminated members act together to form aparallel support system, then the effect of load sharingon bending and compression stresses may be obtained bytaking the factork23 to be unity and making use of thefactor k8 as indicated in Clause 2.5.5.2.

For some timbers, such as radiata pine and Douglas fir,a special lamination factork30 may be used as analternative to the factork23 in Table 7.1. This factor,together with the special conditions required for its useis given in Appendix G.

NOTE: The factorsk23 and k30 are applied to the basic workingstresses for solid timber and are intended to account for the effectsof glue laminating. Hence they are not used when the basic workingstresses of glulam elements have been derived directly through thetesting of such glulam elements.

7.4 OTHER REQUIREMENTS.

TABLE 7.1PARALLEL SUPPORT FACTOR k23

Effective number of laminationscarrying common load (nL)

Factork23

123

1.001.141.20

456

1.241.261.28

789

1.301.311.32

10 or more 1.33

7.4.1 General. The requirements of Clauses 7.4.2 to7.4.7 apply specifically to glued-laminated timbermembers. Most of the provisions given below are set outin AS 1328 but are repeated here for the convenience ofthe designer.

7.4.2 End joints in laminations.

7.4.2.1Butt joints. Clauses for the design strength of buttjoints are given in Appendix G.

7.4.2.2Glued end joints. Glued end joints shall complywith the requirements of AS 1328 with regard tostrength, otherwise they shall be treated as butt jointswith respect to spacing and design.

AS 1720.1—1988 46

7.4.2.3Spacing of end joints.

(a) See Appendix G for spacing of butt joints.

(b) For limitations on the spacing of finger joints andscarf joints, see AS 1328.

7.4.3 Edge joints in laminations.A lamination maycomprise two or more pieces of timber placed edge toedge, i.e. side by side. The gluing and spacing of edgejoints shall be in accordance with the requirements ofAS 1328.

7.4.4 Lamination thickness.For straight members thethickness of seasoned boards shall be 50 mm or less. Forcurved members, the thickness of laminations shall belimited to 1/150 of the radius of curvature of themembers, unless it can be demonstrated that a tightercurve can be fabricated without adverse effects to thetimber. In all cases, the moisture content of the laminateshall be uniform and the seasoning defects shall benegligible as specified in AS 1328.

7.4.5 Combination of grades of timbers.Combinationof grades of timber within any member is practicablewhere the material of higher grade is placed in the mosthighly stressed zones, lower grade material being placedin the more lightly stressed zones. Even if all laminationsare nominally of the same grade, those portions oflaminations in tension zones subjected to maximumstress shall be carefully selected to be of the highestquality available within that grade.

The stiffness properties of a glued-laminated beam madefrom material of different grades may be obtained by themethod of transformed area. In this method, the effectivewidth of each lamination is given by —

bi(eff) = bi × Ei /Eo . . . . . . . . . . . . . . . . . . . (7.1)

where

Ei = modulus of elasticity of thei th lamination

bi = actual width of thei th lamination

Eo = modulus of elasticity of outermostlamination in tension.

The position of the neutral axis, the second moment ofarea (moment of inertia) and the section modulus arethen calculated in the usual way using the effectivewidths instead of the actual widths. In calculating thedeflection and bending strength of a beam, the modulusof elasticity and allowable bending stress for theoutermost lamination are used.

In calculating the allowable shear stress, or the deflectiondue to shear, a transformation procedure based on therelative moduli of rigidity of the various grades ofmaterial may be used where these values are known.However, it is simpler and safe to use the actualcross-sectional dimensions and assume that all materialhas the shear properties of the laminations of the lowestgrade used.

7.4.6 Combination of species.Laminations of differenttimber species may be combined within the same beam.Calculations for estimating the strength and stiffness ofmembers with combined species shall be made using thetransformed area method as described in Clause 7.4.5.

7.4.7 Curved and tapered members.Due account shallbe taken of secondary stresses and instabilities arisingfrom any curvature and taper in glued-laminated timbermembers.

NOTE: The secondary effects due to the camber of nominallystraight beams may be ignored.

47 AS 1720.1—1988

APPENDIX A

ACCEPTANCE TESTING OF TIMBER STRUCTURES ANDELEMENTS

(This Appendix forms an integral part of this Standard)

A1 GENERAL.

A1.1 Limitations of acceptance testing.The methods of test given in this Appendix areapplicable to structures or structural elements and are not appropriate for the testing ofstructural models or the establishment of general design data for timber or connections.

Two types of load test are considered. One is a ‘proof’ load test which shall be applied toevery structure of a population of structures for them to be accepted. The other is a‘prototype’ load test which need be applied only to a portion of a population of structuresfor all structures of that population to be accepted. It should be noted that to carry a givenload, a different structure will be necessary depending on whether the design is based onproof testing, prototype testing or computation. Partly, this arises from the necessity to usea load factor to provide for the effect of variability in structural strength. Design by prooftesting implies that every structure of a population is tested and design by computation isusually based on the results of laboratory tests on large samples of structural elements,typically 100. Hence in general, acceptance based on proof testing will lead to the smallestoverall load factor and that based on prototype testing of a few structural elements will leadto the largest load factors.

It will be noted that where a structure comprises several types of components, the specifiedratio between test loads and working loads can vary considerably from one component toanother. Since the test load to be used is the largest one required, it may be mosteconomical to subdivide a structure into various groups of components and to test each suchgroup individually. This may be effected by temporarily strengthening those parts of thestructures that are not under test. However, if such temporary strengthening is carried out,care shall be taken to ensure that the components under test receive their correct loading,and do not receive artificial restraints or other forms of strengthening that would not existin the real structure.

A1.2 Circumstances requiring tests. Structures or parts of structures designed inaccordance with this Standard are not required to be tested unless by agreement between theparties concerned. Tests may be accepted as an alternative to calculation or may becomenecessary in circumstances which include —

(a) where a structure or part of a structure is not amenable to sufficiently accuratecalculation;

(b) where materials or design methods are used other than those for which there is arelevant specification or code of practice;

(c) where there is doubt or disagreement as to whether the structure or some part of itcomplies with design rules, or as to whether the quality of the materials used is to therequired Standard.

A1.3 Testing authority. The testing of a structure or element shall be designed, supervisedand certified by an engineer or other competent authority to ensure that tests are inaccordance with this Standard.

NOTE: An example of a competent authority would be a laboratory registered with the National Associationof Testing Authorities, Australia.

A1.4 Information required. A copy of the detailed drawings and the specification, togetherwith any other data or information that might be required for the purpose of the test, shallbe deposited with the testing authority before the tests are commenced.

A2 DEFINITIONS. For the purpose of this Appendix, the following definitions apply:

A2.1 Prototype testing-application of test loads to a structure or element to ascertain thestructural characteristics of structures or elements which are nominally identical to the unitor units tested.

A2.2 Proof testing-application of test loads to a structure or element to ascertain thestructural characteristics of only that one unit under test.

AS 1720.1—1988 48

A3 METHOD OF TESTING.

A3.1 General.The method by which the loading should be applied to the unit to be tested,and the positions at which deflections should be measured can only be decided with specialreference to the particular structure or element and to the particular loading conditions tobe investigated.

A3.2 Test load.The test load should be applied and resisted in a manner that reasonablyapproximates the actual service conditions. Although in general both proof and prototypetesting are most likely to involve symmetrical loading in a vertical plane, the engineerand/or the relevant approving authority (see Clause 1.8.1 ) may require, either additionallyor alternatively, asymmetric loading of a structure or element to simulate, for example, theeffect of wind loading. Lateral support to the unit as a whole or to individual members ofthe unit shall also represent as closely as possible actual service conditions.

A3.3 Eccentricities.Any eccentricities not inherent in the design of the structure or element,or not resulting from typical loading in service, shall be avoided at points of loading andreaction, and care shall also be taken to ensure that no inadvertent restraints are present.Where it is clear that the method of test involves a significant or appreciable divergencefrom service conditions, either in loading or restraint, due allowance shall be made tocompensate for this. All likely combinations of permanent loads and imposed loads ofshorter duration, including those due to wind and, where applicable, those due to impact,shall be taken into account when determining the worst loading conditions. The latter shallbe converted in accordance with Paragraph A.4 or Paragraph A.5, as appropriate, into anequivalent test load.

A3.4 Load-deflection curve.A load-deflection curve shall be plotted during each test oneach unit. Such a curve will serve not only as a check against observational errors, but alsoto indicate any irregularities in the behaviour under load of the structure or element and soenable a particular weakness to be investigated as the test progresses. It is desirable that aminimum of six points, not including the zero load point, be obtained to define the shapeof the load-deflection curve if the latter is predominantly linear, and a minimum of tenpoints if the curve is significantly non-linear.

A4 PROOF TESTING.

A4.1 Equivalent test load.For the purpose of establishing an equivalence between theservice loading for which the structure or element has been designed and the loading to beapplied for test purposes, the following procedure shall be adopted:

(a) For each element of a structure, ascertain the critical combination of design loads fromeither the engineer responsible for the design or from the information supplied inaccordance with Paragraph A1.4.

(b) For each element of a structure, calculate the equivalent total test load (ETL) whichincludes any loading already on the structure before the test commences as follows:

ETL = (2.1k26k27/k1)[PD + 1.4(PL + Pw)] . . . . . . . . . . . . . . . . . . . . . . . . . . (A1)

where

PD = known permanent load on the structure, such as its self-weight

PL, PW = all other imposed loads (for working stress codes)

k1 = the factor from Table 2.5 appropriate to the design load of shortestduration included in the critical combination

k26 = 1.00 for structural elements in which the effect of duration of load onstrength is similar to that of simple beams. (Values ofK26 for some other special cases aregiven in Table A1.)

k27 = factor obtained from Table A2 to compensate for the fact that test loadis not of 15 min duration.

(c) Select the largestETL thus obtained.

A4.2 Loading. The equivalent test load shall be applied to the unit at a rate as uniform asis practicable. TheETL shall not remain on the unit for longer than 15 min before it isremoved. Should circumstances not permit the removal of the whole of the test load withina reasonably short period, at least 25 percent of theETL shall be removed within 15 minsubsequent to completion of the test, and 50 percent within the following hour.

49 AS 1720.1—1988

TABLE A1COMPENSATION FACTOR k26

Structural component Factor k26

Beams with slenderness coefficients greater than 10,and all columns —

timber initially drytimber initially green

1.11.4

Metal connectors —failure in timber that is initially greenfailure in timber that is initially dryfor failure of steel

1.21.0

0.6 (k1/k27)

TABLE A2COMPENSATION FACTOR k27

Time to reach ETL 15 min 1 h 6 h

Factork27 for bending and tension strength1.00 1.00 0.95

Factork27 for compression strength, and forstrength of metal connectors 1.00 0.95 0.90

A4.3 Acceptance for strength.At no stage shall the unit show any sign of distress, orexcessive distortion of any part or member. Furthermore, should the load-deflection curveshow any discontinuities or a considerable departure from linearity, the engineer and/or thetesting authority may require a repeat of the test to establish that no fault has developed inthe unit not detected in the first test.

A4.4 Acceptance of deflection.A check as to whether the deflection characteristics of astructure are acceptable shall be made from the deflections measured for loads up to thetotal design load. It should be noted that for long duration components of the load, the effectof creep is to produce long-term deflections that are two and three times the short-termdeflections measured for structures made from timbers initially seasoned and unseasonedrespectively. (See Clause 2.5.1.2.)

Should the residual deflection on unloading the structure exceed 30 percent of the deflectionat ETL, the structure shall not be accepted unless the engineer supervising the test issatisfied that no serious permanent damage has been done to the structure. This may bechecked by reloading the structure again to theETL.

A5 PROTOTYPE TESTING.

A5.1 General.For prototype testing, provisions of Paragraphs A5.2 to A5.8 shall apply inaddition to those specified in Paragraphs A1 and A3.

A5.2 Materials. The timber used in the prototype shall contain material only of the stressgrade which is being, or will be, used in manufacture. No material of a higher stress gradeshall be incorporated in the unit to be tested.

A5.3 Manufacture. The manufacture and assembly of the prototype shall comply with thedesign specifications, and the method of fabrication used shall simulate, as closely aspossible, that which would be used in production.

A5.4 Equivalent test load.For the purpose of establishing an equivalence between theservice loading for which the structure or element has been designed and the loading to beapplied for test purposes, the following procedure shall be adopted:(a) For each element of a structure, ascertain the critical combination of design loads from

either the engineer responsible for the design or from the information supplied inaccordance with Paragraph A1.4

(b) For each element of a structure, calculate the equivalent test load (ETL) as follows:ETL = (2.2k26k27k28/k1)(PD + PL + Pw) . . . . . . . . . . . . . . . . . . . . . . . . . . . (A2)

wherePD + PL + Pw = the critical combination of dead, live and wind loads (for working

stress codes)k1 is the factor from Table 2.5 appropriate to the design load of shortest durationincluded in the critical combination.k26, k27 andk28 are factors obtained from Tables A1, A2 and A3.It should be noted that the factork28 depends on the number of units to be tested andon the estimated coefficient of variation of strength for the total population fromwhich the test units are selected. For guidance to the engineer in making anassessment of the coefficient of variation, a likely range of values is provided inTable A4.

AS 1720.1—1988 50

(c) Select the largestETL thus obtained.

TABLE A3SAMPLING FACTOR k28

Number of similar units to be testedValue of sampling factor k28 for estimated coefficient ofvariation (percent) of strength of individual units of—

15 25 35

123

45

10

100

1.81.61.5

1.51.51.3

1.0

2.82.42.2

2.01.91.7

1.0

4.33.53.0

2.82.62.1

1.0

NOTE: For intermediate coefficients of variation, use linear interpolation on a log-log plot of coefficient ofvariation againstk28.

TABLE A4LIKELY VALUES OF COEFFICIENTS OF VARIATION

Structural element Likely range of coefficients of variation ofstrength of individual unit, percent

Scantlingsbendign strengthtensile strengthcompression strength (as short column)

Finger-jointed elementsbending strength

Connectionsnailed jointstoothed plate and other mechanical fasteners

25 to 4030 to 5015 to 25

15 to 20

1510 to 15

A5.5 Test procedure.

A5.5.1 Preloads. A load equal to the design load shall be applied to the unit, maintainedfor 5 min and then removed. Deflections need not be measured during this preloading unlessspecifically requested by the engineer. This load sequence is then repeated and during thisthe maximum deflection, residual deflection and any other deflections requested by theengineer shall be recorded.

A5.5.2 Test loading.Each prototype shall be loaded at a rate as uniform as practicable tofailure or theETL, whichever occurs first.

A5.6 Acceptance of prototype.

A5.6.1 For strength.At no stage in its testing shall a unit have shown any failure of anypart or member up to a load equal to theETL.

A5.6.2 For deflection. Each unit shall meet the requirements of Paragraph A4.4 and, inaddition, the residual deflection or deformation resulting from second preloading of any partor member of the unit shall not exceed 5 percent of the acceptable deflection or deformationunder short-duration loading or such other limit as may be specified by the engineer or theapproving authority.

A5.6.3 Acceptance of production units. Production-run units similar in all respects to theunit or units tested shall be deemed to be structurally acceptable if the results of the testedunit or units comply fully with the requirements of Paragraph A5.6.2.

A6 REPORT OF TESTS. The report of the test on each unit, whether a proof test orprototype test, shall contain in addition to the test results a clear statement of the conditionsof testing including the method of loading and of measuring deflection, together with anyother relevant data. The nature and size of defects in the timber, especially at the points offailure, if any, and its moisture content should be recorded. The report should also containa statement as to whether or not the structure or part tested satisfies the acceptanceconditions.

51 AS 1720.1—1988

A7 USE OF TESTED STRUCTURES.Any unit tested in accordance with Paragraphs A4or A5 and found to satisfy the standards of acceptability specified therein may only beconsidered satisfactory for practical use as a structural unit subject to agreement betweenthe engineer, client and supplier.

NOTE: It should be realized the conformity with the acceptance requirements of Paragraphs A4 and A5 is anecessary condition but may not be sufficient for total acceptability of a structure or element. The engineerand/or approving authority may require that other criteria apart from strength and stiffness be satisfied havingregard to the particular service conditions of the structure or element. In deciding on the acceptability of astructure or element fabricated of unseasoned timber, the engineer and/or approving authority should byinspection or otherwise assess the likelihood of any potential loss of strength or serviceability as a result ofmembers shrinking on drying, particular attention being paid to the effects of differential shrinkage and checkingor splitting of members at joints.

AS 1720.1—1988 52

APPENDIX B

BASIC DESIGN PROPERTIES OF STRUCTURAL TIMBER(This Appendix forms an integral part of this Standard)

Basic design properties and additional design information on roughly 40 species commonlyused in Australia will be given in Part 2 of this Standard.

NOTE: Design information, including strength grouping, on hundreds of other species from Australia andoverseas can be found in AS 2878 and the following publications:

BERNI, C., BOLZA, E. and CHRISTENSEN, F.J.South American timbers-the characteristics, properties anduses of 190 species. CSIRO Division of Building Research, Melbourne, 1979.

BOLZA, E. and KEATING,W. African timbers-the properties, uses and characteristics of 700 species.

CSIRO Division of Building Research, Melbourne, 1972.

BOLZA, E. and KLOOT, N.H.The mechanical properties of 174 Australian Timbers.Technological PaperNo 25, CSIRO Division of Forest Products, 1963.

KEATING, W.G. and BOLZA, E.Timbers of commerce, Vol. 1. South East Asia, Northern Australia andPacific. Incata Press, Melbourne, 1982.

53 AS 1720.1—1988

APPENDIX C

DESIGN OF BASIC STRUCTURAL MEMBERS(This Appendix forms an integral part of this Standard)

C1 SCOPE. This Appendix extends the design recommendations given in Section 3. It givesaccurate values of the material constant referred to in Clauses 3.2 and 3.3, and providesinformation for the design of complex structural elements not adequately covered by Section 3.

C2 THE MATERIAL CONSTANT . The -factor may be obtained from the followingequations:For beams of seasoned timber

= . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(C1)

For beams of unseasoned timber

= . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(C2)

For columns of seasoned timber

= . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(C3)

For columns of unseasoned timber

= . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(C4)

where denotes the basic working stress in bending andr = temporary load/total load. Themaximum value of used need not exceed the value computed for the caser = 0.25. In the caseof beams where a temporary load causes a stress reversal, the value of to be used is thatcorresponding tor = 1.0.Values of the material constant computed from Equations C1-C4 are given in Tables C1-C4.

TABLE C1MATERIAL CONSTANT FOR BEAMS OF SEASONED TIMBER


r = 0 r = 0.25 r = 0.50 r = 0.75 r = 1.0F34F27F22

F17F14F11

F8F7F5

F4F3F2

1.231.181.13

1.081.041.00

0.950.910.88

0.840.800.78

1.231.181.13

1.081.041.00

0.950.910.88

0.840.800.78

1.181.131.08

1.031.000.95

0.910.880.84

0.800.770.74

1.151.101.06

1.010.970.93

0.890.860.82

0.780.750.72

1.131.081.04

0.990.960.92

0.870.840.81

0.770.740.71

r = (temporary load)/(total load), where the term ‘temporary load’ in this context refers to loads that act for aduration of less than 12 months; when the temporary load causes a stress reversal, then the value ofr tobe used is 1.0.

TABLE C2MATERIAL CONSTANT FOR BEAMS OF UNSEASONED TIMBER


r = 0 r = 0.25 r = 0.50 r = 0.75 r = 1.0F34F27F22

F17F14F11

F8F7F5

F4F3F2

1.321.271.22

1.171.141.09

1.05

1.010.97

0.930.900.87

1.321.271.22

1.171.141.09

1.051.010.97

0.930.900.87

1.221.181.13

1.091.051.01

0.970.940.90

0.860.830.81

1.171.131.08

1.041.010.97

0.930.890.86

0.830.800.77

1.131.091.05

1.010.970.94

0.900.870.83

0.800.770.75

r = (temporary load)/(total load), where the term ‘temporary load’ in this context refers to loads that act for aduration of less than 12 months; when the temporary load causes a stress reversal, then the value ofr tobe used is 1.0.

TABLE C3

AS 1720.1—1988 54

MATERIAL CONSTANT FOR COLUMNS OF SEASONED TIMBER


r = 0 r = 0.25 r = 0.50 r = 0.75 r = 1.0

F34F27F22

F17F14F11

F8F7F5

F4F3F2

1.261.221.18

1.131.101.06

1.010.980.95

0.910.880.85

1.261.221.18

1.131.101.06

1.010.980.95

0.910.880.85

1.201.161.12

1.071.041.00

0.960.930.90

0.860.830.81

1.171.121.09

1.041.010.97

0.940.900.87

0.840.810.78

1.141.101.06

1.020.990.95

0.920.880.85

0.820.790.77

r = (temporary load)/(total load), where the term ‘temporary load’ in this context refers to loads that actfor a duration of less than 12 months. When a member is normally subjected to axial tension stress,but may act in compression due to temporary loads such as winds, the material constant may betaken from Table C1 for the case ofr = 1.0.

TABLE C4MATERIAL CONSTANT FOR COLUMNS OF UNSEASONED TIMBER


r = 0 r = 0.25 r = 0.50 r = 0.75 r = 1.0

F34F27F22

F17F14F11

F8F7F5

F4F3F2

1.441.391.35

1.301.271.22

1.181.151.11

1.071.041.01

1.441.391.35

1.301.271.22

1.181.151.11

1.071.041.01

1.301.261.22

1.181.141.11

1.071.031.00

0.970.940.91

1.231.191.15

1.111.081.04

1.010.980.94

0.910.880.86

1.181.141.10

1.061.031.00

0.970.940.91

0.870.850.82

r = (temporary load)/(total load), where the term ‘temporary load’ in this context refers to loads that actfor a duration of less than 12 months. When a member is normally subjected to axial tension stress,but may act in compression due to temporary loads such as winds, the material constant may betaken from Table C2 for the case ofr = 1.0.

C3 SLENDERNESS COEFFICIENTS FOR BEAMS.

C3.1 General. To evaluate the stability factork12 referred to in Clause 2.5.7, the slendernesscoefficientS1 of a beam shall be defined by —

S1 = . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(C5)where

(EI)x = the rigidity in bending about thex-x axisymax = distance from the neutral axis to the extreme fibreMcr = critical elastic buckling moment of the beam, applies about the major axis.NOTE: In some odd cases, the evaluation of the above equation for a solid beam of rectangular section, can lead toa value ofS1 greater than given by the equations in Clause 3.2.3. In such a case, the value as given by Clause 3.2.3may be used for obtainingk12 (Equation 3.8(a), 3.8(b) and 3.8(c)).

The evaluation of the slenderness coefficient requires a knowledge ofMcr, the critical elasticbuckling moment. Values of the critical elastic moment for particular structural situations can beobtained from standard texts on structural analysis. However, as an aid to design, some values ofthe critical elastic moment are presented in the following paragraphs.

C3.2 End-supported beams.

C3.2.1 General. The following recommendations are applicable to end-supported beams ofbisymmetrical cross-section for which the contribution of warping stiffness to the buckling strengthmay be neglected.

55 AS 1720.1—1988

The ends at supports are assumed to be effectively restrained against twisting. This condition willbe satisfied if the supports possess a torsional stiffness in excess of 20(GJ)/L, whereGJ is thetorsional rigidity of the beam andL is its length.

For information on more general sections, including the effects of warping stiffness, a usefulreference is the following:

NETHERCOT, D.A. and ROCKEY, K.C., ‘Unified Approach to the Elastic Lateral Buckling ofBeams’,The Structural Engineer, vol. 49, No 7, July 1971, pp 321-330. (For erratum see vol. 51,No 4, April 1973, pp 138-139.)

C3.2.2 Beams with intermediate buckling restraints.The critical elastic value of the maximummoment between two buckling restraints may be taken as —

Mcr = . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (C6)

whereg25 = constant obtained from Table C5Lay = distance between effectively rigid buckling restraints(EI)x, = effective rigidity for bending about the major and minor axes respectively(EI)y

(GJ) = effective torsional rigidity.NOTE: In computing the effective torsional rigidity of beams of solid rectangular cross-section, the value ofG canbe obtained from Table 2.3 and the value ofJ is given by—

J =

TABLE C5

COEFFICIENTS FOR SLENDERNESS FACTOR OF BISYMMETRICALBEAMS WITH INTERMEDIATE BUCKLING RESTRAINTS

Slenderness factorg25

Moment parameter β(see Figure C1(c))

Free restraint condition* Fixed restraint condition*

1.00.50.0

3.14.15.5

6.38.2

11.1

-0.5-1.0

7.38.0

14.014.0

* The buckling restraints must prevent rotation of the beam about thez-axis. The terms ‘free’ and ‘fixed’restraint condition refer to the possibility for rotation of the beam about they-y axis at the restraintlocations, as shown in Figure C1.

FIGURE C1. NOTATION FOR BEAMS WITH INTERMEDIATE BUCKLINGRESTRAINTS

AS 1720.1—1988 56

For rectangular sections of solid wood, a conservative approximation to the value of slendernesscoefficient obtained from Equations C5 and C6 is —

S1 = . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(C7)

C3.3 Beams with no intermediate buckling restraints.For this case the critical elastic value ofmaximum moment may be taken as:

Mcr = . . . . . . . . . . . . . . . . . . . . . . . . . . . . (C8)

where(EI)x, (EI)y, (GJ) have the meanings defined in Paragraph C3.2.2yh = height above centroid of the point of load applicationg26, g27 = constants obtained from Table C6Lay = L = span of beam.

For beams loaded only by end moments, Equation C8 may be used withg27 = yh = 0 and the coefficientg26 taken from Table C5.For rectangular sections of solid wood, a conservative approximation of the value of slendernesscoefficient obtained from Equation C8 and C5 is —

S1 = . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(C9)

Equation C7 and C9 are good approximations for B≤ 0.5D.NOTE: In Table C6, the values of the coefficient isg26 andg27 apply to beams with lateral restraints only at their end points.However, these coefficients may be used for any other beam load system that has a similar shape of bending moment diagrambetween points of lateral restraint.

C3.4 Continuously restrained beams.For beams of bisymmetrical cross-section, continuously restrainedagainst lateral displacement at a distanceyo below the neutral axis (see Figure C2), the critical elasticmomentMcr may be taken as—

Mcr = . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(C10)

whereyh = the location above the neutral axis of the loading point (see Figure C2)Laφ = distance between points of effectively rigid rotational restraints.NOTE: The parameteryh may take on negative values. If Equation C10 leads to a negative value ofMcr, then a value ofMcr = ∞may be used to compute the slenderness coefficientS, i.e.S= 0.0. A rotational restraint may be obtained by the use of diagonalflybraces.

C4 SLENDERNESS COEFFICIENTS FOR COLUMNS.C4.1 End supported columns. Evaluation of the stability factor k12 referred to inClauses 2.5.7 and 3.3.2.1, requires an evaluation first of the slenderness coefficient of a column, denotedby S3 for bending only about the major axis andS4 for bending only about the minor axis. The value ofthe slenderness coefficient shall be obtained from —

S = [0.823 (EA)/Pcr]1/2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(C11)

where(EA) = the effective axial rigidityPcr = the critical elastic axial buckling load of the column.

Both (EA) andPcr are referenced to the appropriate axis.C4.2 Continuously restrained columns.For a bisymmetrical column, continuously restrained againstlateral displacement at a distanceyo from the neutral axis (see Figure C3), the slenderness coefficient withrespect to lateral buckling may be obtained from the following equations:

S = . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(C12)

Pcr = . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (C13)

57 AS 1720.1—1988

where(EA) = effective axial rigidity(EI)x, = effective bending rigidity about major and minor axes respectively(EI)y

(GJ) = effective torsional rigidityye = distance from centroid to the point of load application, Figure C3Laφ = distance between points of effectively rigid rotational restraints.NOTE: The parameterYe may take on negative values. If Equation C13 leads to a negative value ofPcr, then a value ofPcr = ∞may be used in computing the slenderness coefficientS, i.e.S = 0.0.

TABLE C6COEFFICIENTS FOR SLENDERNESS FACTORS OF BISYMMETRICAL BEAMS WITH

NO INTERMEDIATE BUCKLING RESTRAINTS

LoadingBending moment

MCondition of end restraint against

rotation about y-y axis*Slenderness factors

g26 g27

FreeFixed

3.66.1

1.41.8

FreeFixed

4.15.4

4.95.2

FreeFixed

4.26.7

1.72.6

FreeFixed

5.36.5

4.55.3

FreeFixed

3.3—

1.3—

Fixed 4.0 2.0

Fixed 6.4 2.0

* For direction ofy-y axis, see diagram in figure C1 (free ends of cantilevers excepted).

AS 1720.1—1988 58

59 AS 1720.1—1988

C5 BEAM-COLUMN BENT ABOUT BOTH AXES. For the case of a beam-column ofrectangular cross section, subjected to an axial compression load and bent about both axes,the following conservative criteria for strength may be used in the absence of more accurateinformation.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (C14(a))

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (C14(b))

NOTE: Equations C14(a) and C14(b) contains an allowance for the effect of bending moment amplificationdue to the axial load. For non-rectangular members, Equations C14(a) and C14(b) may be used in the absenceof other information.

C6 SPACED COLUMNS.

C6.1 Definitions. Spaced columns have the individual shafts spaced apart by end andintermediate packing pieces or batten plates. These packing pieces and batten plates may befastened by glue, nails, screws, bolts or split-ring connectors. The notation used for spacedcolumns is shown in Figure C4.

NOTE: The following paragraphs provide a design procedure for a particular set of spaced columns. For spacedcolumns with other parameters and geometrics, design information may be obtained from overseas Standards.

C6.2 Special requirements for spaced columns.

C6.2.1 Size of connecting pieces. Packing pieces and batten plates shall be large enoughto accommodate the required number of fasteners.

End packing pieces shall not be shorter in length measured along the column axis than 6times the thickness of the thinnest shaft.

Intermediate packing pieces shall be not less than 230 mm long in the direction of thecolumn axis.

C6.2.2 Bolted connections. Bolts shall not be used with unseasoned timber unless it ispracticable to ensure that they are tightened periodically as the timber dries out and shrinks.

C6.2.3Glued connections. Batten plates may be glued to the shafts but sufficient nails orother mechanical fasteners shall also be employed to transmit the shearing force. Thisprovision does not apply to glued packing pieces, but if nails, screws or bolts are used toobtain clamping pressure then they shall be used in sufficient number and at suitable spacingto obtain adequate pressure over the full area of each piece.

C6.2.4 Spacing of intermediate packing pieces and batten plates.The centre-to-centredistance between packing pieces or batten plates shall not exceed the least of the following:

(a) one-third of the distance between centres of the end packing pieces or end batten plates;(b) 30 times the thickness of the thinnest shaft;(c) the value such that the slenderness coefficient of the portion of an individual shaft

between any pair of packing pieces or batten plates is not greater than 0.7 times themaximum slenderness coefficient of the whole column, where the effective length ofthe individual shaft is taken as equal to the distanceLs (see Figure C4) betweencentroids of the fasteners or glued areas in the adjacent packing pieces or batten plates.

C6.2.5Distance between shafts. The clear space between individual shafts shall not exceed3 times the thickness of the thinnest shaft measured in the same plane.

C6.2.6Battened columns. Batten plates shall not be made from unseasoned timber.

C6.3 Shear between components.

C6.3.1The design shear force. The connections between the packing pieces or batten platesof spaced columns shall be designed to transmit the stresses resulting from a lateral shearforce—

V = V1 + V2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(C15)where

V1 = shear force due to applied loadsV2 = shear force due to curvature of the column

= 0.75P for end packing piece or batten plates= 0.001 (Lay/d)P for intermediate packing pieces or batten plates

AS 1720.1—1988 60

P = axial column loadLay = distance between points of lateral restraint on the spaced columns. (An end

packing piece or batten plate shall be required at each point of lateralrestraint.)

d = a + 2ts.C6.3.2 Force effects on packing pieces. The interface of each packing piece and itsconnections shall be designed to transmit a shear forceVpack equal to—

Vpack = VLs/a . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(C16)where

V = resulting lateral force as defined in Paragraph C6.3.1Ls = the centre-to-centre distance of packing pieces, see Figure C4a = distance between shafts (see Figure C4).

(a) Column fabricated with packing pieces (b) Column fabricated with batten plates

FIGURE C4. SPACED COLUMNS

61 AS 1720.1—1988

C6.3.3 Force effects on batten plates.Each batten plate and its connections shall bedesigned to transmit simultaneously a longitudinal shear forceVbat and momentMbat, givenby —

Vbat = 0.5VLs/(a + ts) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(C17)and

Mbat = 0.25VLs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(C18)where

V = resulting lateral force as defined in Paragraph C6.3.1Ls = the centre-to-centre distance between batten plates as defined in

Paragraph C6.2.4a = distance between shafts (see Figure C4)ts = shaft thickness (see Figure C4).

C6.4 Permissible loads.C6.4.1Slenderness coefficients.C6.4.1.1Slenderness coefficients of individual shafts. The effective lengthLs of individualshafts of spaced columns shall be taken as the distance measured along the column axisbetween centroids of the fastener groups or glued areas in adjacent packing pieces or battenplates. From this effective length, the slenderness coefficients of the individual shafts maybe obtained in accordance with Clause 3.3.2.C6.4.1.2 Slenderness coefficient of composite cross-sections. For spaced columns withpacking pieces, composed of two shafts of timber, the slenderness coefficient for bendingabout they-axis will be denoted byS5 and is given by —

S5 = 0.3g13g28L(A/I)1/2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(C19)where

g13, g28 = modification factors as given in Table 3.2 and Table C7 respectively.L = length of composite columnI = second moment of area (moment of inertia) of the net composite

cross-section about they-axisA = net cross-sectional area of the shafts.

The slenderness coefficient for bending about thex-axis may be taken to be that of a solidtimber column having the cross-sections shown in Figure C4.

TABLE C7MODIFICATION FACTOR g28 FOR THE EFFECTIVE LENGTH OF

SPACED COLUMNSSpace Value ofg28

Shaft spacing

(see Figure C4)

Glued packing pieces andbatten plates

Packing pieces and batten platesfastened by metal connectors

0123

1.01.11.31.4

1.62.22.73.0

C6.4.2Design procedure. The permissible load shall be taken as the least of —(a) that for a solid column whose area is that of the sum of the cross-sectional areas of the

shafts, bending about thex-axis;(b) that for a column bending about they-axis, whose geometrical properties of

cross-section are those of the composite column but whose slenderness coefficient isas given in Equation C19, however, in the use of this slenderness coefficient, the loadsharing factork8 = 2.00 shall be used for computing the permissible stress on the spacedcolumn; and

(c) the sum of the permissible loads for the individual shafts where the permissible load foreach shaft is equal to that for a solid column, the effective length of which is equal tothe values ofLs defined in Paragraph C6.4.1.1.

C7 BUCKLING RESTRAINTS.

C7.1 Definitions. For most design situations, no check need be made on the effectivenessof buckling restraints. However in the case of an unusually light restraint system being usedfor a critical (i.e. non-load-sharing) engineered structure it may be advisable to assess theeffect and the capacity of the restraints.

AS 1720.1—1988 62

The following method may be used for a design of slender beams and columns havingequally spaced buckling restraints. The restraint systems considered are either lateral ortorsional ones as shown in Figure C5, where the restraint stiffnessesKA andKB are definedas follows:

PR = KA ∆A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(C20)TR = KB φB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(C21)

wherePR andTR are the restraint force and torque respectively that occur when the pointof attachment of the restraint to the beam undergoes a displacement∆A and rotationφB. Itis assumed that the ends of beams are effectively restrained against torsional rotation (seeParagraph C3.2.1).

C7.2 Notation. Notation to be used in this Paragraph is as follows:

h26 = 1.0 when loads are live loads only= 1.5 when loads are dead loads only and timber is initially seasoned= 2.0 when loads are dead loads only and timber is initially unseasoned (Values

of h26 for other conditions may be obtained by linear interpolation)h27 = 1.0 for sawn members

= 0.4 for laminated and other carefully fabricated timber membersg38 = lesser of (m + 1)/2 and 5m = number of members supported by each restraint systemn = number of equally spaced intermediate restraintsSmax = slenderness coefficient if there are no restraintsSmin = slenderness coefficient if the restraints are effectively rigid.

(a) Column lateral (b) Beam lateral (c) Beam torsionalrestraint restraint restraint

FIGURE C5. INTERMEDIATE RESTRAINTS

C7.3 Columns.

C7.3.1 Load capacity. In computing the load capacity of a column of length L with nintermediate lateral restraints as shown in Figure C5(a), the slenderness coefficient S4 forbuckling about the minor axis may be taken as —

S4 = . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(C22)

but not less thanSmin and not more thanSmax and where —

α1 = . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (C23)

A similar method may be used to compute the effect of restraints against buckling about themajor axis.

C7.3.2 Force on lateral restraints. The design forcePR on each lateral restraint may betaken to be given by—

PR = . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (C24)

wherePa is the applied axial load on the column.

63 AS 1720.1—1988

C7.4 Beam with lateral restraints.C7.4.1Load capacity. In computing the load capacity of a beam of lengthL with n intermediate lateralrestraints as shown in Figure C5(b), the slenderness coefficientS1 may be taken as —

S1 = . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(C25)


α2 = . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(C26)

C7.4.2Force on lateral restraints. The design forcePR on the lateral restraints may be taken to be givenby —

PR = for members of rectangular section and . . . . . . . . . . . . . . (C27(a))for box beams

PR = for I-beams . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . (C27(b))

whereMa is the applied bending moment on the beam.

C7.5 Beam with torsional restraints.C7.5.1Load capacity. In computing the load capacity of a beam of length L with n intermediate lateralrestraints as shown in Figure C5(c), the slenderness coefficientS1 may be taken as —

S1 = . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(C28)


α3 = . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(C29)

C7.5.2Torque on torsional restraints. The design torqueTR on each restraint may be taken to be givenby —

TR = for members of rectangular section and . . . . . . . . . . . . . . (C30(a))for box beams

TR = for I-beams . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . (C30(b))

whereMa is the applied bending moment on the beam.

C8 CONCENTRATED LOADS AND PARTIAL AREA LOADS ON GRID SYSTEMS.C8.1 General.In the absence of further information, the following provides a method for assessing thelateral distribution effects of a beam grid system with respect to concentrated and partial area loads. Theload sharing factork9 specified in Clause 2.5.5.3 may be taken as additional to the following lateraldistribution effects.C8.2 Concentrated load.For a beam located within a grid system and subjected to a point load P asshown in Figure C6(a), the maximum bending and shear stresses, and also the maximum deflection, maybe taken to be equal to that of an isolated beam loaded by a point loadPeff defined by —

Peff = g42P . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(C31)whereg42 is bounded by the range 0.2≤ g42 ≤ 1.0, and in this range it is given by —

g42 = 0.20 log10(hB/nChC) + 0.95 . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . .(C32)where

hB = EBIB/L3

hC = EcIc/s3

EBIB, ECIC = flexural rigidity of a single beam and a single crossing member respectivelynC = number of crossing membersL, s = span and spacing of beams (see Figure C6).

For Equation C32 to hold, the centroid of the loads must lie within the middle half of the beam, and theloaded beam must be at least two beams in from the edge. For loads outside these limits,g42 may beobtained by interpolating between the above value ofg42 and 1.0.Values ofg42 derived according to Equation C32 are shown in Figure C7.

NOTE: If the point loadP shown in Figure C6(a) is located somewhere between two main beams, then a conservative loaddistribution factor may be obtained by using the valueg43 given in Paragraph C8.3 for the case of a partial area load of widthequal tos.

AS 1720.1—1988 64

FIGURE C6. NOTATION FOR BEAM-GRID SYSTEM SHOWINGCONCENTRATED AND PARTIAL AREA LOADS

FIGURE C7. GRID FACTORS g42 AND g43

65 AS 1720.1—1988

C8.3 Partial area load.For a beam located within a grid system and subjected to a load of intensity wdistributed uniformly over an area of width a as shown in Figure C6(b), the maximum bending and shearstresses, and also the maximum deflection may be taken to be equal to that of an isolated beam loadedby a load of intensityweff defined by —

weff = g43w . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(C33)

For the case of a =s, the value ofg43 is given by —

g43 = 0.15 log10(hB/nchc) + 0.75 . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . .(C34)

The value ofg43 is bounded by 0.2≤ g43 ≤ 1.0.

For the case ofa = 0, the value ofg43 is given byg42 as in Equation C32.

For the case of 0 <a < s, the value ofg43 may be obtained by linear interpolation between the two abovecases.

For Equation C34 to hold, the centroid of the loads must lie within the middle half of the beam, and theloaded beam must be at least two beams in from the edge. For loads outside these limits,g43 may beobtained by interpolating between the above value and 1.0.

Values ofg43 derived according to Equation C34 are shown in Figure C7.

C9 NOTCHED BEAMS. For a rectangular beam of depth d, notched as shown in Figure C8, the nominalmaximum bending stressfb = and nominal maximum shear stressfs = 3V/2bdn calculated for thenet section shall comply with the following interaction equation:

fb + 4fs ≤ g40Fsj . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(C35)

where g40 is computed as shown in Table C8 andFsj is the permissible shear stress for joint detailsfrom —

Fsj = . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(C36)

where the factorsk1 to k12 are given in Section 2.

The stability factork12 need not be considered in checking the fracture strength of notched beams,provided that the notch is not located within the middle third of the beam.

Defects shall not be permitted within 150 mm of the notch roots of critical beams, i.e. non-load-sharingbeams.

If, according to the sign convention shown in Figure C8,ƒb is negative, it may be taken as zero in theapplication of Equation C35. Similarly, ifƒs is negative, it may also be taken as zero in the applicationof Equation C35.

NOTE: In addition to the check on fracture strength according to Equation C35, the net section of depthdn must also be checkedfor its unnotched strength according to Clause 3.2.1, i.e.fb ≤ Fb and fs ≤ Fs. Moreover, it should be noted that in calculating theshear stressfs for use in Equation C35, all loads on the beam shall be taken into consideration, including those loads lying withina distance of 1.5 times the height of the beam from the inside face of the support.It should be noted that notching creates a significant reduction in the strength of a beam unless the notching is limited to thevicinity of support points. The adverse effects of notching may be minimized by increasing the opening angle of the notch.A typical example of a beam notched on the compression edge would be that of a continuous member notched over a supportacross which it rests. In this casefb may be neglected, but an effective value offs still occurs for use in Equation C35.

FIGURE C8. NOTATION FOR NOTCH

AS 1720.1—1988 66

TABLE C8COEFFICIENT g40 FOR SAWN NOTCH ON BEAM EDGE

Notch angle slope(see Figure C8)

g40

dnotch > 0.1 d dnotch < 0.1 d

lnotch/dnotch = 0 9.0/d0.45

3.2/


4.2/


5.2/

NOTE: lnotch, dnotchandd are to be stated in millimetres.

C10 NOTCHED COLUMNS. For a column, notched in the middle third, and with a stability factork12 < 0.5, a check shall be made that the fracture strength is adequate.

The fracture strength may be considered to be adequate if the member, considered as a beam, is capableof sustaining a nominal bending stressfb = k1Fc(1 - 2k12) at the notch root when a check is made inaccordance with Paragraph C9.

C11 NOTCHED TENSION MEMBERS. In the absence of other information the permissible nominaltension stress in the net section of a notched member shall be taken to be equal to that of the permissiblebending stress of a similar notched member. This permissible bending stress shall be computed accordingto Equation C36 except that the factorsk12 may be omitted.

In computing the nominal tension stress, due account shall be taken of any stresses induced by bendingdue to notching and any other geometric asymmetries.

67 AS 1720.1—1988

APPENDIX D

JOINTS IN TIMBER STRUCTURES(This Appendix forms an integral part of this Standard)

D1 CONNECTORS FOR PLYWOOD.

D1.1 General.The following paragraphs refer to the use of nail and screw connectors to joinplywood to solid timber.

D1.2 Strength of joints with plywood.

D1.2.1Joint strength grouping.The grouping of common timber species for joint design is givenin Tables 2.1 and 2.2.

(a) Fastener in single shear (b) Fastener in double shearFIGURE D1. PLYWOOD THICKNESS AND NAIL LENGTH

D1.2.2 Permissible lateral loads for nails and screws in plywood. The permissible load for a laterallyloaded plywood-to-timber joint fastened with nails or screws may be taken as 10 percent greater than thevalues given for timber-to-timber joints in Section 4 except that fastener diameter and length and plywoodthickness (see figure D1) shall be such that —

to/D > 1.5

tp/D > 10

tw/D > 10

where

D = nail diameter, in millimetres

to = thickness of plywood as indicated in Figure D1, in millimetres

tp = penetration of nail as indicated in Figure D1, in millimetres

tw = thickness of solid timber as indicated in Figure D1, in millimetres

For values of (to/D) < 1.5, the basic load shall be reduced linearly with respect to (to/D) so as to reach zerowhen (to/D) = 0. For values oftp/D andtw/D less than 10, the basic load shall also be reduced linearly withrespect totp/D andtw/D but in addition the fastener shall be considered as non-load-bearing if eithertp/Dor tw/D is less than 5. These requirements shall apply whether the fastener is in single or double shear.

AS 1720.1—1988 68

In the case of shear joints, such as occurs in the nailing of plywood webs to the solid timber flanges ofbox beams, the multiple nail factork17 = 1.0 shall be used in Equation 4.1

D2 DEFORMATION OF JOINTS.

D2.1 General.The load-displacement characteristics of a joint are highly nonlinear. However, where alinear joint stiffness is required for design purposes, a secant stiffness may be used. A suitable definitionof the secant stiffness (Ksec) is given by —

Ksec = Po/∆o . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(D1)

where∆o is the deformation of the joint (including long duration effects) when the design loadPo isapplied.

In the following paragraphs, the equations of deformation are good estimates for the deformation due tothe first application of a load; for repeated loads, due allowance must be made for incremental slip andchanges in joint stiffness.

Where both a long duration loadPD and a short duration loadPL act on a connector, then non-linear load-deformation characteristics must be considered in evaluating the maximum deformation. In the absenceof further information, the maximum deformation may be taken to be equal to the long durationdeformation due to loadPD minus the short duration deformation due to loadPD plus the short durationdeformation due to loadPD + PL.

D2.2 Displacement of nailed and screwed joints in solid timber.The displacement of nailed or screwedjoints in single shear for solid-wood to solid-wood joints may be estimated as follows:

(a) For displacements∆ < 0.5 mm

∆ = . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(D2(a))

where

∆ = joint displacement, in millimetres

D = diameter of nail or screw, in millimetres

j12 = duration factor given in Table D2

P = load per nail or screw, in newtons

h32 = stiffness factor given in Table D1.

(b) For a displacement of∆ = 2.5 mm —

P = 0.165D1.75j13h32 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(D2(b))

where the duration factorj13 is given in Table D2.

(c) For a displacement 0.5 mm <∆ < 2.5 mm the corresponding applied load P shall be obtained bylinear interpolation between the values to give∆ = 0.5 mm and∆ = 2.5 mm.

NOTES:1. The displacement∆ = 2.5 mm usually occurs for applied loads above the allowable design load; however this value is included

for interpolation purposes for 0.5 mm <∆ < 2.5 mm.2. For the case of metal and plywood side plates, Equations D2(a) and D2(b) lead to conservative over-estimates of nail slip.

D2.3 Displacement of solid timber joints fabricated with bolts, split-ring connectors and shear platesconnectors.

D2.3.1General. Where relevant specific test information is not available, the following paragraphs maybe used to estimate the displacement of joints fabricated with bolts, split-ring connectors and shear-plateconnectors.

D2.3.2For loads acting parallel to the grain. For this case, the displacement∆ may be taken to be givenby —

∆ = ∆i + (j14/h33)(P/ ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(D3)

where

∆ = total displacement, millimetres

∆i = initial displacement due to oversize holes, millimetres

= 0, for a load superimposed on an existing load, otherwise

= 1/√ncon for bolted joints

= 1/2√ncon for split ring connectors or shear-plate connectors

69 AS 1720.1—1988

ncon = number of connector sets in the jointj14 = duration factor given in Table D3h33 = stiffness factor given in Table D4P = applied load per fastener, in newtons

= basic load per fastener as defined in Section 4, in newtons.

Equation D3 is a good approximation for applied loads up to the allowable design load.

D2.3.3For loadings acting perpendicular to the grain. For this case the displacement∆ may be taken tobe given by —

∆ = ∆i + (j14/h33h35)(P/ ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(D4)

whereh35 = 1.5 for bolted joints of Types 1, 2 and 3 as defined in Table 4.10

= 2.5 for bolted joints of Type 4 as defined in Table 4.10= 1.0 for split-ring connectors and shear-plate connectors

P = applied load per fastener, in newtons

= basic load per fastener as defined in Section 4, in newtons

∆i, j14 andh33 are taken as defined in Paragraph D2.3.2.Equation D4 is a good approximation for applied loads up to the allowable design load.

TABLE D1STIFFNESS FACTOR h32 FOR CONNECTIONS OF SOLID TIMBER

Initial moisture condition Species joint group Factor h32

Unseasoned J1J2J3

1 4501 050

750

J4J5J6

550410300

Seasoned JD1JD2JD3

1 6001 250

990

JD4JD5JD6

750590470

TABLE D2DURATION FACTORS j 12 AND j13

Initial moisture condition Duration of load Factor j12 Factor j13

Unseasoned More than 3 years5 monthsLess than 2 weeks

941

0.50.7

1

Seasoned More than 3 yearsLess than 2 weeks

41

0.51

NOTE: If required, intermediate values ofj12 and j13 may be obtained by linear nterpolation with log-time.

TABLE D3DURATION FACTOR j 14

Initial moisture condition Duration of load Factor j14

Unseasoned More than 3 years5 months2 weeksLess than 5 minutes

42

1.51

Seasoned More than 3 years5 months2 weeksLess than 5 minutes

32

1.51

NOTE: Intermediate values ofj14 may be obtained by linear interpolation with log-time.

AS 1720.1—1988 70

D3 EQUATIONS AND TABLES FOR BASIC WORKING LOADS FOR BOLTS.

D3.1 Load . The basic working load for a single bolt bearing parallel to the grain and acting insingle shear shall be the least of —

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(D5)

in timber of groups J1 and JD1 . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . .(D6)

in timber of groups J2 and JD2 . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . .(D7)

in timber of groups J3, J4, JD3 and JD4 . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . (D8)

in timber in groups J5 and JD5 . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . .(D9)

in timber of groups J6 and JD6 . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . .(D10)whereD = bolt diametert = effective timber thickness as defined in Table 4.9(A)

= appropriate stress value for the species group and seasoning condition as given in Table D5.Basic working loads computed in accordance with Equation D5 to D10 are given inTables 4.9(B) and 4.9(C).

D3.2 Load . The basic working load for a single bolt bearing perpendicular to the grain and actingin single shear shall not exceed the lesser of —

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(D11)

√D3 in timber of groups J1 and JD1 . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . .(D12)




√D3 in timber of groups J5 and J6 . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . .(D16)

√D3 in timber of groups JD5 and JD6 . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . .(D17)whereD = bolt diametert = effective timber thickness as defined in Table 4.10(A)

= appropriate stress value for the species group and seasoning as given in Table D6.Basic working loads computed in accordance with these equations are given in Tables 4.10(B) and4.10(C).

TABLE D4STIFFNESS FACTOR h33

Initial moisturecondition

FactorBolted joints Split rings and shear

plate connectorsWithout metal sideplates

With metal side plates

UnseasonedSeasoned

2.02.5

3.03.8

1.21.5

TABLE D5

VALUES OF FOR BOLTED JOINTSJoint group J1 J2 J3 J4 J5 J6

, MPa16.5 13.0 10.5 8.3 6.6 5.3

Joint group JD1 JD2 JD3 JD4 JD5 JD6

, MPa20.5 16.5 13.0 10.5 8.3 6.6

TABLE D6

VALUES OF FOR BOLTED JOINTSJoint group J1 J2 J3 J4 J5 J6

, MPa6.6 5.2 3.3 2.1 1.4 0.7

Joint group JD1 JD2 JD3 JD4 JD5 JD6

, MPa8.7 6.7 5.0 3.7 2.6 1.8

APPENDIX E

71 AS 1720.1—1988

BUCKLING STRENGTH OF PLYWOOD DIAPHRAGMS(This Appendix forms an integral part of this Standard)

E1 SCOPE.If large sheets of thin plywood are used in composite construction, it is possible for bucklingdistortions to cause a reduction in the load capacity of the plywood membrane. In the following paragraph,strength reductions of this type are stated in terms of a stability factork12 for some typical membranes andplywood lay-ups.

E2 BUCKLING STRENGTH FOR DIAPHRAGMS LOADED IN-PLANE.

E2.1 General.The following paragraphs apply to the design of members constructed from continuoussheets of plywood attached to continuous solid timber edge members. Where either of these isdiscontinuous, these requirements shall apply only if they are spliced so as to develop the strength andstiffness equivalent to that of continuous elements.

E2.2 Diaphragms with lateral edges supported and subjected to uniformly loaded edge forces.

E2.2.1 Slenderness coefficient. Figure E1 illustrates the notation to be used for a typical plywooddiaphragm. The diaphragm is of lengthL, depthdw, and thicknesstw. The face grain of the plywood is atan angle to the longitudinal edge as shown. The diaphragm is loaded along its edge by a combinationof stresses comprising a shear stressfs, a direct compression stressfc, and a compression stress due toedgewise bending that has a maximum value offcb.

Where all edges are simply supported, the slenderness coefficient S for computation of the stability factork12 for resistance to the stressesfs, fc and fcb may be taken to be —

S = g60 (dw/tw) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(E1)

where the factorg60 is given in Table E1.

For short panels in which the lengthL is less than the characteristic lengthLch given in Table E2, theslenderness coefficient may be taken to be —

S = g60 (L/Lch)1/2 (dw/tw) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(E2)

If the lateral edges AB and CD shown in Figure E1 are effectively fixed, and AD and BC are simplysupported, then the slenderness coefficients may be taken as 80 percent of those computed according toEquations E1 and E2.

FIGURE E1. PLYWOOD DIAPHRAGM WITH SUPPORTED LATERAL EDGESAB AND DC

AS 1720.1—1988 72

TABLE E1

FACTOR g60 FOR SLENDERNESS COEFFICIENTS OF PLYWOODDIAPHRAGMS WITH LATERAL EDGES SUPPORTED

Plywood lay-up*

Factor g60

Stressfc Stressfcb Stressfs

= 0° = 90° = 0° = 90° = 0° = 90°tpo/tpi = 0.53 ply5 or more plies

0.710.63

0.710.63

0.280.24

0.280.24

0.460.34

0.300.31

tpo/tpi = 1.03 ply5 or more plies

0.930.73

0.660.60

0.370.28

0.260.23

0.600.40

0.310.30


1.050.83

0.610.58

0.410.32

0.240.23

0.670.46

0.310.30

* All plies assumed to be of the same species; all inner plies assumed to be of equal thickness.tpo/tpi = ratio of thickness of outer to inner plies.

NOTE: For direction of , see Figure E1.

TABLE E2CHARACTERISTIC LENGTH OF PANELS

Plywood lay-up*

Characteristic side ratio Lch/dw

(see Figure E1)

Stressfc Stressfcb Stressfs

= 0° = 90° = 0° = 90° = 0° = 90°tpo/tpi = 0.53 ply5 or more plies

1.541.09

0.650.92

1.090.77

0.460.65

1.651.15

0.690.96


1.931.36

0.520.74

1.370.96

0.370.52

2.131.44

0.570.78


2.121.56

0.470.64

1.501.10

0.330.45

2.381.67

0.530.69



E2.2.2Stability factor for edge shear stresses. The stability factork12 for the modification of the basicworking stress in shear shall be taken as the lesser of the following:k12 = 1.0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(E3(a))

k12 = . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(E3(b))whereE = modulus of elasticity specified in Table 5.1, in megapascalsk1 = duration factor as specified in Table 2.5

= basic design stress in shear as specified in Table 5.1, in megapascalsS = slenderness coefficient derived according to Paragraph E2.2.1NOTE: From the data in Tables 5.1 and E1, it follows thatk12 = 1.0 for all plywood of stress grade equal to or greater than F7,and web thickness ratiodw/tw ≤ 19.

E2.2.3 Stability factor for edge compression and edge bending stresses. The stability factor for themodification of the basic working stress in compression, shall be taken to be the lesser of the following:k12 = 1.0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(E4(a))

k12 = . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(E4(b))whereE = modulus of elasticity specified in Table 5.1, in megapascalsk1 = duration factor as specified in Table 2.5

= basic design stress in compression as specified in Table 5.1, in megapascalsS = slenderness coefficient derived according to Paragraph E2.2.1NOTE: From the data in Tables 5.1 and E1, it follows that k12 = 1.0 for all plywoods of stress grade equal to or less than F34,and web thickness ratiodw/tw ≤ 10.

73 AS 1720.1—1988

E2.2.4 Permissible stresses. The permissible values of the stressesFs Fb and Fcb shall be obtained by

modifying the basic stresses and given in Table 5.1 by the factorsk1 andk12, together with otherappropriate factors as specified in Sections 2 and 5.E2.2.5Stress combinations. When more than one type of stress acts simultaneously on the diaphragm, thefollowing interaction equation may be used to check the design:(fc/Fc) + (fcb/Fcb)

2 + (fs/Fs)2 ≤ 1.0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(E5)

whereFc, Fcb andFs would be the permissible design values offc, fcb and fs respectively if each type ofstress were acting on its own.

FIGURE E2. NOTATION FOR AXIALLY LOADED DIAPHRAGM WITHFREE LATERAL EDGES AC AND BD

E2.3 Diaphragms with lateral edges free and subjected to uniformly loaded edge forces.For adiaphragm, as shown in Figure E2, with lateral edges AC and BD free and end edges AB and CD simplysupported, the slenderness coefficient S for the stressfc may be taken to be given by —

S = g61(dw/tw) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(E6)

where the factorg61 is given in Table E3. If the edges AB and CD are fixed, then the slendernesscoefficient may be taken to be 70 percent of that calculated by Equation E6.

The appropriate stability factorkl2 to be used for modification of the basic working stress is that given inEquations 3.18(a), 3.18(b) and 3.18(c) of Clause 3.3.3 for solid timber members.

E2.4 Diaphragms subjected to concentrated edge forces.

E2.4.1Effective width. In assessing the resistance of a plywood web to the concentrated load and supportreaction as shown in Figure E3, the effective bearing width of the load, denoted byl eff shall be taken asfollows:

(a) For the midspan concentrated load —

leff = lb + 2tf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(E7)

(b) For the end support reaction —

leff = lb + tf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(E8)

E2.4.2Slenderness coefficients. In assessing the resistance of a plywood web to the concentrated load andthe support reaction as shown in Figure E3, the slenderness coefficient of the web shall be defined by thefollowing:

S = . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (E9)

and for the end support reaction —

S = . . . . . . . . . . . . . . . . . . . . . . . . . . . . (E10)

AS 1720.1—1988 74

whereg61, andg62 = the geometry factors given in Tables E3 and E4dw, tw, tf and lb = the dimensions (in millimetres) indicated in Figure E3.

FIGURE E3. NOTATION FOR BEAM WITH UNSTIFFENED PLYWOOD WEB

E2.4.3Stability factor. The stability factork12 to be used for the modification of the basic working stressis —

k12 = 1.0 - 0.5S(k1 /E)1/2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(E11)

where

S = slenderness coefficient

k1 = duration factor specified in Table 2.5

= basic design stress in compression as specified in Table 5.1, in megapascals

E = modulus of elasticity as specified in Table 5.1, in megapascals.

E2.5 Stiffeners for beam webs.At supports or load points, where the buckling strength of the webs isinadequate, the webs should be reinforced by vertical stiffeners. The size of the stiffeners will be adequateif they extend the full width of the flanges and have a cross-section equal in area to that of one flange.

For webs in which the slenderness coefficient for the shear stress (ƒs), as shown in Figure E1, is greaterthan 15, it is desirable that vertical stiffeners be placed at intervals along the web in order to reduce sheardistortions normal to the web. It is recommended that each of these stiffeners have a cross sectional areanot less than 0.25 times the area of a flange and that they be spaced not further than 1.5g62dw apart, wherethe factorg62 is given in Table E4.

All vertical stiffeners should extend from flange to flange.

TABLE E3FACTOR g61 FOR SLENDERNESS COEFFICIENTS OF DIAPHRAGMS

WITH FREE EDGES

Plywood layup*Factorg61

= 0° = 90°tpo/tpi = 0.53 ply5 or more plies

1.81.1

0.750.91


2.21.3

0.830.87


2.31.5

0.870.87



75 AS 1720.1—1988

TABLE E4

FACTOR g62 FOR EFFECTIVE BUCKLING WIDTHOF CONCENTRATED LOADS

Plywood layup*Factorg61

= 0° = 90°tpo/tpi = 0.53 ply5 or more plies

1.541.09

0.650.92


1.931.36

0.520.74


2.121.56

0.470.64



AS 1720.1—1988 76

APPENDIX F

CONNECTIONS FOR ROUND TIMBERS

For the case of standard connectors the recommendations given in Section 4 of this Standard areapplicable.

NOTE: Information on non-standard connectors will be given in AS 1720.3.

77 AS 1720.1—1988

APPENDIX G

GLUED-LAMINATED CONSTRUCTION—SPECIAL CONDITIONS

(This Appendix forms an integral part of this Standard)

G1 SPECIAL LAMINATION FACTOR. Laboratory tests have indicated that a special lamination factorrelated to local reinforcement effects may be applicable to some species of timber. This lamination factor,denoted byk30, applies where the stress grade of a lamination is limited solely by local defects such asknots, holes, gum pockets and localized grain distortion, and the local slope of grain does not exceed 1in 10. Test data show that carefully selected radiata pine, Douglas fir and hoop pine laminations fulfilthese necessary conditions.

Values of the special lamination factork30 are given in Table G1. Subject to the grade limitationsspecified, this alternative lamination factork30 may be used instead of the factork23 given in Clause 7.3.2for modifying the basic stress in bending and tension.

TABLE G1

SPECIAL LAMINATION FACTORLaminationthickness

mm

Factor k30 for special grades*

L1 L2 L3 L4

504030

1.001.001.00

1.101.101.10

1.151.201.20

1.201.251.30

252015

1.001.001.00

1.151.151.15

1.251.251.30

1.351.401.45

105

1.001.00

1.201.25

1.351.45

1.551.70

* Special lamination grades correspond to the following grades with the special limitation that the slope ofgrain does not exceed 1 in 10:L1 special grade = Structural Grade No 1 (75 percent grade)L2 special grade = Structural Grade No 2 (60 percent grade)L3 special grade = Structural Grade No 3 (48 percent grade)L4 special grade = Structural Grade No 4 (38 percent grade).NOTES:1. Typical examples of species that usually satisfy the requirements for application of the special

lamination factork30 are radiata pine, Douglas fir and hoop pine.2. The factork30 is applied to the basic working stresses for solid timber and is intended to account for

the effects of glue laminating. Hence it is apparent that it is not used when the basic working stressesof glulam elements have been derived directly through the testing of such glulam elements.

G2 DESIGN STRENGTH OF BUTT JOINTS.

G2.1 General.The nominal tension stress (ft) and shear stress (fs) at a butt joint (computed on the grosscross-section) shall comply with the requirements in Paragraphs G2.2 and G2.3.

G2.2 Tension members and horizontally laminated beams.

(a) For outermost laminations —[(ft√t)/(7Fsj)] ≤ 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(Gl)

(b) For inner laminations —[(ft√t)/(10Fsj)] + [( fs√t)/(1.7Fsj)] ≤ 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(G2)

Fsj = k1k2k5k6k12k33 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(G3)where

t = lamination thickness, in millimetresk33 = 1.00 when there are four or fewer butt joints located in zones of maximum stress,

= 1.3/(n0.2) when the number (n) of butt joints in zones of maximum stress exceeds four.and the factorsk1 to k12 are defined in Sections 2 and 3.

The factork12 need not be applied in the case of tension members, nor in the case of beams when the buttjoint under consideration is outside the middle third of the beam.

AS 1720.1—1988 78

G2.3 Vertically laminated beams.(a) For outermost laminations d —

[(ft√t)/(15Fsj)] ≤ 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(G4)(b) For inner laminations —

[(ft√t)/(20Fsj)] ≤ 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(G5)whereFsj is derived according to Equation G3.

G2.4 Columns.For columns which have a stability factork12 < 0.5, a check shall be made that the buttjoint strength is adequate to resist a stress distribution that varies linearly from a compression stress ofk1Fc at one face to a tension stressk1Fc(1 - 2k12) at the other. It is assumed that any face may receive thetension stress. The parametersFc, k1 andk12 refer to the normal design compression stress, duration factorand stability factor for the design of a glulam column.G2.5 Conditions of use.Condition for the use of butt joints shall be as follows:(a) In members designed as straight beams and the straight portions of structural members containing

curves.(b) The design working stresses given above may be used only if butt joints within any set of four

adjacent laminations are spaced at least six lamination thicknesses (6t) apart. However, if theallowable design working stresses are taken to be 50 percent of those given above, then butt jointsin adjacent laminations may be placed as close as two lamination thicknesses apart.

NOTE: Many straight glued-laminated beams have a built-up camber. For the purpose of this code a glued-laminated beam maybe considered to be straight if the camber does not exceed 0.01 of the span.

79 AS 1720.1—1988

APPENDIX H

REFERENCED AND RELATED DOCUMENTS(This Appendix forms an integral part of this Standard)

AS1111 ISO metric hexagon commercial bolts and screws

1143 High temperature creosote for the preservation of timber

1144 Arsenical creosote for the preservation of timber

1148 Nomenclature of commercial timbers imported into Australia

1170 SAA Loading CodePart 1: Dead and live loads (AS 1170.1)Part 2: Wind forces (AS 1170.2)

1328 Glued-laminated structural timber

1393 Coach screws (metric series) (with ISO hexagon heads)

1397 Hot-dipped zinc-coated or aluminimum/zinc-coated steel sheet in coil and cut lengths

1442 Carbon steels and carbon-manganese steels — Hot-rolled bars and semi-finished products

1491 Laminated and/or finger-jointed radiata pine scantlings

1476 Metric wood screws

1604 Preservative treatment for sawn timber, veneer and plywood

1605 Methods for the sampling and analysis of wood preservatives and preservative-treated wood

1649 Methods for the determination of basic working loads for metal fasteners for timber

1684 SAA Timber Framing Code

1694 Code of practice for physical barriers used in the protection of buildings against subterraneantermites

1748 Mechanically stress-graded timber

1749 Rules for mechanical stress grading of timber

2057 Soil treatment for buildings under construction for protection against subterranean termites

2082 Visually stress-graded hardwood for structural purposes

2209 Timber poles for overhead lines

2269 Structural plywood

2271 Plywood and blockboard for exterior use

2272 Marine plywood

2312 Guide to the protection of iron and steel against exterior atmospheric corrosion

2334 Steel nails —Metric series

2543 Nomenclature of Australian timbers

2754 Adhesives for timber and timber products

Part 1: Adhesives for plywood manufacture (AS 2754.1)

2858 Timber—Softwood —Visually stress-graded for structural purposes

2878 Timbers—Classification into strength groups

K55 Creosote oil for the preservation of timber

O1 Glossary of terms used in timber Standards

O80 Decking timbers from Eastern and South-eastern Australian hardwoods

O98 Seasoned size-matched framing timber (including finger-jointed pieces) from South-easternAustralian hardwoods

ASTMD143 Standard methods of testing small clear specimens of timber

BS373 Methods of testing small clear specimens of timber

1579 Connectors for timber

AS 1720.1—1988 80

APPENDIX I

NOTATION AND FACTORS(This Appendix forms an integral part of this Standard)

This Appendix sets out the notation used in this Standard (see Table I1), lists the modification factors forstiffness (j) (see Table I2) and for strength (k) (see Table 13). Figure I1 below illustrates examples ofdimensional symbols used.

NOTE: sub = subscript indicating details of quantity.

FIGURE I1. ILLUSTRATIVE EXAMPLES OF DIMENSIONAL SYMBOLS USED

81 AS 1720.1—1988

TABLE I1QUANTITY SYMBOLS

A = area of net cross-sectiona = general dimensionb = breadth or width of memberbi = width of ith laminationbi(eff) = effective width ofith lamination, Clause 7.4.5c = general dimension, Figure 4.2D = diameter of a metal fastener or poled = depth of member (see Figure I1)dn = net depth of notched beam, Figure C8dnotch = notch depth, Figure C8dW = depth of web of I-beam or box beamE = modulus of elasticity(EA) = effective axial rigidity(EI)x = rigidity in bending about x-axisEBIB = flexural rigidity of a single beamEcIc = flexural rigidity of a single crossing member(EI)y = rigidity in bending about y-axisEi = modulus of elasticity of ith laminationEo = modulus of elasticity of outermost lamination, Clause 7.4.5EMC = equilibrium moisture contentETL = equivalent test load, Paragraphs A4.1 and A5.1F = permissible design stressF′ = basic working stress

= permissible stress for timber at moisture content less than 15%, Clause 2.5.2

= permissible stress for timber at moisture content greater than 15%, Clause 2.5.2

Fb = permissible design stress in bending

= basic working stress in bending

Fbx = permissible design stress in bending about x-axisFby = permissible design stress in bending about y-axisFc = permissible design stress in compression parallel to grain

= basic working stress in compression parallel to grain

Fcb = permissible design value offcb if no other stresses are present, Paragraph E2.2.5

= basic bolt bearing stress along grain, Paragraph D3.2

Fco = permissible design compressive stress for stable columnsFcx = permissible compression stress for member as a column able to buckle about the x-axis onlyFcy = permissible compression stress for member as a column able to buckle about the y-axis only

= basic working stress in compression at an angleθ to the grain

Fo = permissible design stress for stable membersFp = permissible design stress for bearing perpendicular to grain

= basic working stress for bearing perpendicular to grain

= basic bolt bearing stress perpendicular to the grain, Paragraph D3.2

Fs = permissible design stress for shear in beams

= basic working stress for shear in beams

Fsj = permissible design stress for shear in joint details

= basic working stress for shear at joint details

Ft = permissible design stress in tension

= basic working stress for tension parallel to grain

f = nominal applied stressfb = applied nominal stress in bendingfbx = applied nominal stress in bending about x-axisfby = applied nominal stress in bending about y-axisfc = applied nominal stress in compression parallel to grainfcb = applied compression stress due to edgewise bending on a plywood diaphragm,

Paragraph E2.2.1fp = applied nominal stress for bearing perpendicular to grainfs = applied nominal stress for shear in beamsfsj = applied nominal stress for shear in joint detailsft = applied nominal stress for tension parallel to grain

(continued)

AS 1720.1—1988 82

TABLE I1 (continued)G = modulus of rigidityGJ = torsional rigidityg = modification factor for geometry effectsh = modification factor for material and load characteristicshB, hc = EBIB/L3, EcIc/s

3

I = second movement of area (moment of inertia)J = St Venant torsion constantj = modification factor applied to stiffnessKA, KB = stiffness, Paragraph C7.1Ksec = secant modulus of a joint, Paragraph D2.1k = modification factor applied to strengthL = length of column or span of beamLaφ = distance between points of effectively rigid rotational restraintsLax = distance between points of effectively rigid restraints against lateral movement in y-directionLay = distance between points of effectively rigid restraints against lateral movement in x-directionLch = characteristic length in buckling of plywood webs, Paragraph E2.2.1lb = bearing length of range of I-beam or box beam, Figure E3leff = effective compression width, Figure E3lnotch = notch length, Figure C8lpar = end distance, Clause 4.4.2.5M, Ma = applied bending momentMcr = critical elastic buckling momentMn = in-plane moment capacity of multiple connector joint, Clause 4.2.1.2Mx = applied bending moment, about x-axisMy = applied bending moment, about y-axism = number of members supported by each restraint system, Paragraph C7.2n = number of itemsnL = effective number of laminationsna = number of fasteners or rows of fasteners, Table 4.2(A) and 4.2(B), Table 4.11nc = number of crossing members in a grid systemncon = number of connectorsneff = effective number of elements in a load-sharing systemnm = total number of members in a load-sharing systemP = applied load or forcePD = dead loadPL = live loadPR = force acting on lateral restraintPW = wind loadPcr = elastic buckling loadPeff = effective point load, Paragraph C8.2Pn = direct load capacity of a multiple connector joint, Clause 4.2.1.2Q = permissible load capacity of a single fastenerQs = permissible load for a laterally loaded bolt system, Clause 4.4.2.4

= basic load capacity

= basic load for a single bolt in bearing along the grain

= basic load for a single bolt in bearing perpendicular to the grain

= basic working load of a laterally loaded bolt system, Clause 4.4.2.3

= basic load capacity of a bolted joint system loaded parallel to the grain direction

= basic load capacity of a bolted joint system loaded perpendicular to the grain direction

r = temporary load/total load, Tables 3.1, 3.2, 3.5, 3.6r i = distance toith nail, Clause 4.2.1.2rmax = distance to the farthest nail, Clause 4.2.1.2S = slenderness coefficientSmax = slenderness coefficient if there are no restraintsSmin = slenderness coefficient if the restraints are effectively rigids = centre-to-centre spacing of supporting members in a grid systemT = torque loadTR = torque acting in lateral restraintt = thickness of timber (see Figure I1)t1, t2, t3, t4 = thickness of timber in bolted joint, Table 4.9(A) and Table 4.10(A)tf = flange thickness of I-beam or box beam Figure E3

(continued)

83 AS 1720.1—1988

TABLE I1 (continued)

ti = thickness of first member of a two-member jointtm = thickness of member of a nailed joint, Figure 4.2to = thickness of member of a nailed joint, Figure 4.2 and Figure D1tp = depth of nail penetration into second member of a two member joint or a third member of a

three member joint, Figure 4.2 and Figure D1tpi = thickness of an inner ply of plywoodtpo = thickness of outermost ply of plywoodts = thickness of spaced column member, Figure C4tw = thickness of web of I-beam or box beamtw = thickness of timber member, Figure D1V = applied shear forcew = applied uniformly distributed loadweff = effective uniformly distributed load, Clause 6.6.3x = cartesian coordinatey = cartesian coordinateye = distance from column centroid to point of load application, Figure C3yh = height above beam centroid of the point of load application, Figure C2yo = distance of lateral restraint below the neutral axis, Figure C2 and C3Zx = section modulus about x-axisZy = section modulus about y-axisz = cartesian coordinateα = parameter related to tendency to split, Clause 4.1.4α1 = parameter defined C7.3.1α2 = parameter defined C7.4.1γ = tangential cleavage, N/mm∆ = deflection∆i = initial displacement of connector

= rotationε = tangential shrinkage, percent

= material constant Tables 3.3, C1, C2, C3, C4* = material constant, when k11 < 1.0, Clause 3.2.4

= angle between the direction of the load and the direction of the grain

TABLE I2

MODIFICATION FACTORS FOR STIFFNESS ( j)Factor Definition Text reference

j2j3

Factor for duration of load for bending, compression and shearFactor for duration of load for tension

Section 22.5.1.22.5.1.2

j6 Factor for moisture content of plywoodSection 55.4.2

j9 Factor for immaturity of round timbersSection 66.4.1

j12

j13

j14

Factor for duration of load on nailed and screwed jointsFactor for duration of load on nailed and screwed jointsFactor for duration of load on split ring connectors and shear-plateconnectors

Appendix DD2.2D2.2

D2.3

AS 1720.1—1988 84

TABLE I3MODIFICATION FACTORS FOR STRENGTH ( k)

Factor Definition Text reference

k0

k1

k4

k5

k6

k7

k8

k11

k12

Factor for load sharing in grid systemsFactor for load durationFactor for partial seasoning of nominally unseasoned timberFactor for high moisture content of seasoned timberFactor for temperature/humidity effectFactor for bearing lengthFactor for load sharing in parallel structural systemsFactor for load sharing in grid systemsFactor for member sizeFactor for instability

Section 22.5.5.32.5.1.12.5.22.5.22.5.32.5.42.5.5.22.5.5.32.5.62.5.7

k13

k14

k15

k16

k17

k18

Factor for end grain effects

Factor for effect of double shearFactor for effect of seasoning of timberFactor for plywood or metal side platesFactor for multiple connector effect

Factor for effect of tension loads

Section 44.2.1.2, 1.3.1.2,4.3.2.2, 4.5.3.24.2.1.24.6.34.2.1.24.2.1.2, 4.3.1.2,4.4.2.4, 4.6.34.6.3, 4.7.3

k19 Moisture content of plywoodSection 55.4.2

k20

k21

Factor for timber immaturityFactor for effect of shaving

Section 66.4.16.4.2

k23 Factor for load sharing effect of laminatingSection 77.3.2.1

k26

k27

k28

Factor related to design load durationFactor for duration of testFactor for effect of sample size

Appendix AA.4.1A.4.1A.5.4

k30

k33

Special lamination factorFactor for multiple butt joints

Appendix GG1.1G2.2

NOTES:1. In the design of solid timber beams, the following are the modification factors usually considered:

For bending strength: k1 k8 k11 k12

For shear strength: k1

For end bearing: k1 k7

For deflection: j2

2. In the design of solid timber columns, the following are the strength modification factors usuallyconsidered:

k1 k12

3. In the design of glued-laminated members, the modification factors to be considered are usually those forsolid timber beams and columns together with the following:

k23 or k30

85 AS 1720.1—1988

INDEX

ITEM REFERENCE

Acceptance testing App. A

Basic working stressBasic working load, connectorsBeams—general—glued-laminated—notched—solid rectangularBearing stressesBending stresses—glued-laminated timber—plywood—poles—solid timberBuckling restraintsbutt joints

1.8.2, 2.31.8.2

3.2, C3Sect. 7, app. GC93.22.3, 2.5

7.2, App. G5.26.22.3, 2.5, 3.2C3.2G2

Collapse susceptible timberColumns—general—glued-laminated timber—notched—solid rectangularCombined stresses—bending and axial compression—bending and axial tensionCompression stresses parallel to the grain—glued-laminated timber—plywood—poles—solid timberCompression stresses perpendicular to thegrain—glued-laminated timber—plywood—solid timberCorewoodCreep factors—connectors—wood

1.8.2

3.3, C3Sect. 7, app. GC103.3

3.5.13.5.2

7.2, app. G5.26.22.3, 3.5, 3.3

7.2, App. G5.22.3, 2.51.8.2

App. D2.5.1.2

DefinitionsDeflectionsDuration of load factor

1.81.5.3.6, 2.4.22.5.1.1

Hankinson’s formula 2.3.3, 4.4.2.3

Joints—bolted joints—butt-jointscoach screws—joint deformations—nailed joints—screwed joints—shear-plate connectors—split-ring connectors

4.4, D2, D3G24.5D24.2, D1, D24.3, D24.7, D2.34.6, D2.3

Load sharingLoad tests

2.5.5App. A

Modification factors—stiffness—strengthModulus of elasticity—glued-laminated timber—plywood—poles—solid timber

Table I2, App. ITable I3, App. I2.3.47.1, 7.4.55.26.22.3

ITEM REFERENCE

NotationNotched members—beams—columns—tension members

App. I, Table II

C9C10C11

Permissible stressPlywood—basic design properties—buckling strength—connectorsPole timbersProof testingPrototype testing

1.8.2

Sect. 5App. ED1Sect. 6A4A5

Referenced documents

Scope of codeShear stresses—glued-laminated timber—plywood—poles—solid timberSpaced columnsStability factorStiffness factorsStrength factorsStress—basic working—bearing—bending

—glued-laminated timber—plywood—poles—solid timber

—combined—bending and axial compression—bending and axial tension

—compression, parallel to the grain—glued-laminated timber—plywood—poles—solid timber

—compression, perpendicular to the grain—glued-laminated timber—plywood—solid timber—permissible (definition)

—shear—glued-laminated timber—plywood—poles—solid timber

—tension—glued-laminated timber—plywood—poles—solid timber

1.1

7.2, App. G5.26.22.3, 2.5C62.5.7Table I2, app. ITable I3, app. I

1.8.2, 2.32.3, 2.5

7.2, App. G5.26.22.3, 2.5, 3.2

3.5.13.5.2

7.2, app. G5.26.22.3, 2.5, 3.2

7.2, app. G5.22.3, 2.51.8.2

7.2, app. G5.26.22.3, 2.5

7.2, app. G5.26.22.3, 2.5, 3.4

Temperature factorTendency to splitTension members—general—glued-laminated timber—notchedTension stresses—glued-laminated timber—plywood—poles—solid timber

2.5.34.1.4

3.4Sect. 7, App. GC11

7.2, App. G5.26.22.3, 2.5, 3.4

Washer sizes 4.4.2.6

as 1720-1988 part 1 - timber structures

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