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MS 544 : PART 1 : 2001

CODE OF PRACTICE FOR STRUCTURALUSE OF TIMBER :PART 1 : GENERAL(FIRST REVISION)

ICS : 91.080.20

Descriptors : materials, loading, accidental damage, service classes, moisture content, service

exposure, conditions, duration of loading, section size, load-sharing system, effectivecross sections, structural members, structural frameworks, floor and roof boarding

MALAYSIAN

STANDARD

© Copyright

DEPARTMENT OF STANDARDS MALAYSIA

L i c e n s e d t o U N I V E R S I T I T E K N O L O G I M A R A ( U I T M ) / D

o w n l o a d e d o n : 1 7 - M a y - 2 0 1 2 1 0 : 2 8 : 0 2 A M /

S i n g l e u s e r l i c e n s e o n l y , c o p y i n g a n d n

e t w o r k i n g p r o h i b i t e d

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DEVELOPMENT OF MALAYSIAN STANDARDS

The Department of Standards Malaysia (DSM) is the national standardisation and

accreditation body.

The main function of the Department is to foster and promote standards, standardisation and

accreditation as a means of advancing the national economy, promoting industrial efficiency

and development, benefiting the health and safety of the public, protecting the consumers,

facilitating domestic and international trade and furthering international cooperation in relation

to standards and standardisation.

Malaysian Standards are developed through consensus by committees which comprise of

balanced representation of producers, users, consumers and others with relevant interests,

as may be appropriate to the subject in hand. These standards where appropriate are

adoption of international standards. Approval of a standard as a Malaysian Standard is

governed by the Standards of Malaysia Act 1996 (Act 549). Malaysian Standards are

reviewed periodically. The use of Malaysian Standards is voluntary except in so far as they

are made mandatory by regulatory authorities by means of regulations, local by-laws or any

other similar ways.

The Department of Standards appoints SIRIM Berhad as the agent to develop Malaysian

Standards. The Department also appoints SIRIM Berhad as the agent for distribution andsale of Malaysian Standards.

For further information on Malaysian Standards, please contact:

Department of Standards Malaysia OR SIRIM Berhad

Tingkat 21, Wisma MPSA 1, Persiaran Dato' MenteriPersiaran Perbandaran P.O. Box 7035, Section 240675 Shah Alam 40911 Shah Alam

Selangor D.E. Selangor D.E.

Tel: 60 3 5519 8033 Tel: 60 3 5544 6000

Fax: 60 3 5519 2497 Fax: 60 3 5510 8095

http://www.dsm.gov.my http://www.sirim.my

Email:[email protected]





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CONTENTS

Page

Committee representation..........................................................................……..… ii

Foreword…….........................................................................................……….... iii

1 Scope……………………………………………………………………………………… 1

2 Referenced documents………………………………………………………………….. 1

3 Definit ions……………………………………………………………………………..…. 2

4 Symbols………………………………………………………………………………..… 5

5 Materials……………………………………………………………………………….… 7

6 Design considerations………………………………………………………………..… 8

Table 1 Moisture content of timber for various applications ………………………………... 12

Appendices

A List of modification factor K ….…………………..……………………………….….. 15

B Bibliography…………………………………………………………………………….... 17





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Committee representation

The Building and Civil Engineering Industry Standards Committee (ISC D) under whose supervision this MalaysianStandard was developed, comprises representatives from the following Government Ministries, Trade, Commerceand Manufacturing Associations, and Scientific and Professional Bodies:

Association of Consulting Engineers MalaysiaConstruction Industry Development Board MalaysiaDepartment of Standards Malaysia

Department of Occupational Safety and HealthJabatan Bomba dan PenyelamatPertubuhan Akitek MalaysiaMaster Builders Association Malaysia

Ministry of Housing and Local Government (Housing Department)Ministry of Works (Public Works Department)The Institution of Engineers, Malaysia

Universiti Teknologi Malaysia

The development of this Malaysian Standard is under the supervision of the following representatives of the CIDB

Standard Committee:

Ir. Mohamed bin Mohd Nuruddin General Manager, Technology Development DivisionMegat Kamil Azmi bin Megat Rus Kamarani Senior Manager, Standard and Quality Unit

Puan Zainora bt Zainal Manager, Standard and Quality UnitPuan Hanishahani Othman The Secretary of CIDB Standard Committee

The Technical Committee on Structural Use of Timber which developed this Malaysian Standard consists of thefollowing representatives :

Dr. Abdul Rashid bin Hj. Ab. Malik (Chairman) Forest Research Institute Malaysia

Puan Hanishahani Othman (Secretary) Construction Industry Development Board Malaysia

Tuan Hj. Mohd Shukari bin Midon Forest Research Institute Malaysia

Encik Hilmi bin Md. Tahir Jabatan Kerja Raya Malaysia

Encik Chow Wah/ Puan Dang Anom Md. Zin Jabatan Perumahan Negara

Prof. Madya Dr. Sabaruddin bin Mohd. Universiti Sains Malaysia

Prof. Dr. Zainai bin Mohamed/Dr. Abd. Latif bin Saleh Universiti Teknologi Malaysia

Prof. Madya Ir. Dr. Mohd Zamin bin Jumaat Universiti Malaya

Dr. Mohd Ariff bin Jamaludin Universiti Putra Malaysia

Encik Nor Zamri bin Mat Amin Malaysian Timber Industry Board

Ir. Yap Chin Tian Timber Trade Federation Malaysia

Tuan Hj. Wahab bin Abdul Razak General Lumber Fabricators and Builders Bhd.

Dr. Peter Kho C.Seng Sarawak Timber Association

Encik Lall Singh Gill Malaysian Wood Moulding and Joint Council

Encik Mohamad Omar bin Mohamad Khaidzir Forest Research Institute Malaysia





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FOREWORD

This Malaysian Standard was developed by the Technical Committee on Structural Use of Timber under the authority of the Building and Civil Engineering Industry StandardsCommittee.

Development of this standard was carried out by Construction Industry Development BoardMalaysia (CIDB), which is the Standards-Writing Organisation (SWO) appointed by SIRIM

Berhad to develop standards for the construction industry.

During the development of this standard, reference was made to BS 5268 : Part 2 : 1996,

‘Structural use of timber - Code of practice for permissible stress design, materials andworkmanship’.

MS 544 consists of the following parts and sections, under the general title, ‘Code of practice

for structural use of timber‘ :

Part 1 : General

Part 2 : Permissible stress design of solid timber

Part 3 : Permissible stress design of glued laminated timber

Part 4 : Timber panel productsSection 1 : Structural plywoodSection 2 : Marine plywoodSection 3 : Cement bonded particleboard

Section 4 : Oriented strand board

Part 5 : Timber joints

Part 6 : Workmanship, inspection and maintenance

Part 7 : Testing

Part 8 : Design, fabrication and installation of prefabricated timber for roof trusses

Part 9 : Fire resistance of timber structures Section 1 : Method of calculating fire resistance of timber members

Part 10 : Preservative treatment of structural timbers

Part 11 : Recommendation for the calculation basis for span tablesSection 1 : Domestic floor joistsSection 2 : Ceiling joists

Section 3 : Ceiling bindersSection 4 : Domestic rafters

Part 12 : Laminated veneer lumber for structural application.

This Malaysian Standard supersedes MS 544 : 1978, ‘Code of practice for the structural use

of timbers’.

Compliance with a Malaysian Standard does not of itself confer immunity from legal

obligations.





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MS 544 : PART 1 : 2001

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CODE OF PRACTICE FOR STRUCTURAL USE OF TIMBER :PART 1 : GENERAL

(FIRST REVISION)

1. Scope

This Part of Malaysian Standard MS 544 provides guidance on the structural use of timber,

glued laminated timber and timber-based products, in load bearing members. It includes

recommendations on quality, grade stresses and modification factors applicable to these

materials when use as simple members, or as parts of built-up components, or as parts of

structures in incorporating other materials. It also gives recommendations for the design of

nailed, screwed, bolted, connectored and glued joints. In addition, it provides

recommendations for a method of test to assess the adequacy of structural assemblies, and it

includes general advice on workmanship, various treatments which can be applied, inspection

and maintenance.

It does not, and it is not intended to, deal comprehensively with all aspects of timber

construction. In particular it does not cover well tried and traditional methods of timber

construction which have been employed successfully over a long period of time.

2. Referenced documents

The following referenced documents contain provisions which, through reference in this text,constitute provisions of this Malaysian Standard. For dated references, where there aresubsequent amendments to, or revisions of, any of these publications the Malaysian Standard

shall be amended or revised accordingly. However, parties to agreements based on thisMalaysian Standard are encouraged to investigate the possibility of applying the most recenteditions of the referenced documents. For undated references, the latest edition of the

publication referenced to apply.

MS 544 : Part 6 Code of practice for structural use of timber : Part 6 : Workmanship,

inspection and maintenance.

MS 544 : Part 7 Code of practice for structural use of timber : Part 7 : Testing.

CP3 : Chapter V : Part 2 : 1972 Wind loads.

BS 6100 Glossary of building and civil engineering terms.

ISO 3898 Cement-bonded particleboard - Boards of Portland or equivalent cementreinforced with fibrous wood particles.

BS 6399 : Part 1 Loading for buildings : Part 1 : 1984 Code of practice for dead and

imposed loads.

BS 6399 : Part 2 Loading for buildings : Part 2 : 1995 Code of practice for wind loads.

BS 6399 : Part 3 Loading for buildings : Part 3 : 1988 Code of practice for imposed roof

loads.





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3.6 End joint efficiency

Percentage ratio of the strength of the end joint to the strength of unjointed timber of the same

cross section and species containing no strength reducing characteristics.

3.7 Full sawn

Applied to timber that has been sawn oversize to allow for shrinkage and which should

therefore measure more than the specified dimensions until that timber has been fully

seasoned: also known as oversize.

3.8 Glued laminated member

Timber structural member obtained by gluing together a number of laminations having their grain essentially parallel.

3.9 Grade

An established use of quality classification of timber.

3.9.1 Select structural grade

Grade which is intended for special purposes, particularly when the strength/weight ratio of

the timber is to be a maximum.

3.9.2 Standard structural grade

Grade which is intended for normal purposes.

3.9.3 Common building grade

Grade which is intended for wooden members used in less important parts of building frames,

which are not usually designed by means of engineering calculations.

3.10 Grade stress

Stress which can safely be permanently sustained by material of a specific section size and of

a particular strength group or species and grade.

3.11 Horizontally glued laminated member

Glued laminated member whose laminations are parallel to the neutral plane.

3.12 Load-sharing system

Assembly of pieces or members which are constrained to act together to support a common

load.





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3.13 Machine stress grading

Machine stress grading is a grading method done by mechanical means that evaluates the

Modulus of Elasticity value of timber. The strength of the timber is predicted by using

correlation equation that is obtained empirically by previous testings of many pieces of timber.

Stress grade is assigned on each piece of timber after being evaluated by the stress grading

machine.

3.14 Member

Structural component which may be either a piece of solid timber or built up from pieces of

timber, plywood, etc. (e.g. floor joist, box beam, member in a truss, etc.)

3.15 Permissible stress

Stress that can safely be sustained by a structural material under a particular condition.

NOTE. For the purposes of this MS 544, it is the product of the grade stress and the appropriate modification factors

for section size, service, service class and loading.

A more precise demarcation of wet and dry service conditions has been deliberately avoided. For the purposes of Malaysian Standard the dry condition for solid timber approximates to a moisture content of 19 % or less inhardwood.

3.16 Principle member

Individual member on which the integrity of the structure depends (e.g. a trimmer beam).

3.17 Strength class

Classification of glued laminated timber based on particular values of grade stress, modulus

of elasticity and density.

3.18 Strength group

Grouping of solid timber based on particular values of grade stress.

3.19 Structural unit

Assembly of members forming the whole or part of a framework (e.g. truss, prefabricated floor

and wall, skeleton of a building or a complete structure).

3.20 Strength ratio

The ratio of the grade stress to basic stress.

3.21 Scant sawn

Applied to sawn timber that measures, at the time of inspection, less than the dimensions

specified also known as undersized.





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3.22 Surfaced timber / dressed timber

Timber that measures in dry condition, the same as the nominal dimension, planned or

otherwise machined on one or more surface. Also known as surfaced, planned or wrought

timber.

3.23 Vertically glued laminated member

Glued laminated member whose laminations are at right-angles to the neutral plane.

3.24 Visual stress grading

Visual stress grading is a grading method that involves the visual judgement of the quality of

timber. For solid timber, visual stress grading is done based upon guidelines specified in theMalaysian Grading Rule by trained timber grader. The amount of defects that exist on a piece

of timber will categorise it either as Select, Standard or Common grade.

3.25 Wet timber

Timber freshly felled, or still containing original free moisture in its cell cavities.

3.26 Wet stress/Green stress

Stress applicable to material exposed in conditions which would result in timber having a

moisture content exceeding 19 %. For glued laminated timber see MS 544 : Part 3.

NOTE. For the purposes of MS 544 : Part 2, wet timber has a moisture content greater than that produced byenvironmental conditions, which would result in solid timber having a moisture content greater than 19 %.

4. Symbols

The symbols used in this MS 544 are generally in accordance with ISO 3898 supplemented

by the recommendations of CIB-@J18-1 'Symbols for use in structural timber design',published by the International Council for Building Research Studies and Documentation,which takes particular account of timber properties.

The symbols used are:

a distance;

A area;

b breadth of beam, thickness of web, or lesser transverse dimension of a tension or

compression member;

d diameter;

E modulus of elasticity;





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F force or load;

h depth of beam, greater transverse dimension of a tension or compression member;

i radius of gyration;

K modification factor (always with a subscript);

L length; span;

m mass;

M bending moment;

n number;

r radius of curvature;

t thickness; thickness of laminations;

α angle between the direction of the load and the direction of the grain;

η eccentricity factor;

θ Angle between the longitudinal axis of a member and a connector axis;

λ Slenderness ratio;

σ Stress;

τ Shear stress;

Τ Moisture content;

I Second moment of area;

Z Section modulus; and

w Uniformly distributed load

The subscripts used are:

a) Type of force, stress etc:

c compression;

m bending; and

t tension.





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b) Significance:

a applied;

adm permissible;

e effective;

mean arithmetic mean;

cw clear wood; and

cg grade.

c) Geometry

apex apex;

r radial;

tang tangential;

|| parallel (to the grain);

⊥ perpendicular (to the grain); and

α angle.

It is recommended that where more than one subscript is used, the categories should be

separated by commas.

Subscripts may be omitted when the context in which the symbols are used is unambiguous

except in the case of modification factors K .

5. Materials

The materials used should comply with the appropriate Malaysian Standards or when such

are non available, with the appropriate Standards such as :

BS EN 386, BS EN 338, BS 449, BS 1202, BS 1203, BS 1204, BS 1210, BS 1579 and BS

5756 or other National Standards.

The timber shall be graded in accordance with the Malaysian Grading Rules for Sawn

Hardwood Timber or the appropriate British Standard for Glued Laminated timber members

by graders registered with the relevant Grading Authority in Malaysia or by authorised officers

of the Grading Authority.





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Timber graded will be stencilled with the following marks i.e. Grade Mark, Standard name of

the timber, the Registered Number of the Timber Grader, Name of Supplier and Parcel

Number. Details on how the timber shall be stencilled is explained in the MGR or relevant

British Standard. The grading shall be covered by grading summary.

In the case of timber being graded by a Quality Control Inspector it shall bear a mark

approved by MTIB.

6. Design considerations

6.1 General

6.1.1 All structural members, assemblies or frameworks in a building, in combinationwith the floors and walls and other parts of a building, should be capable of sustaining, with

due stability and stiffness and without exceeding the relevant limits of stress given in MS 544

the whole dead, imposed and wind loading and all other types of loading referred to in MS544.

The design requirements of this MS 544 may be satisfied either by calculation, using the laws

of structural mechanics, or by load testing in accordance with MS 544 : Part 7.

The design and details of parts and components should be compatible, particularly in view of

the increasing use of prefabricated components such as trussed rafters and floors. The

designer responsible for the overall stability of the structure should ensure this compatibility

even when some or all of the design and details are made by another designer.

To ensure a robust and stable design it is necessary to:

a) consider the geometry of the structure;

b) check any required interaction and connections between timber load-bearing

elements and between such elements and other parts of the structure; and

c) provide suitable bracing or diaphragm effect in planes parallel to the direction of the

lateral forces acting on the whole structure.

In addition, the designer should state whether special precautions or temporary propping arenecessary to ensure overall stability of the structure or its components during construction.

The strength properties of timber, plywood and joints are influenced by service and loading

conditions. The grade stresses for materials and basic loads for fasteners given in this MS544 apply to specific conditions and should be multiplied by the appropriate modification

factors given in MS 544 when the actual service and loading conditions are different.

6.1.2 With regard to the design process, design, including design for construction

durability and use in service should be considered as a whole. Unless clearly defined

standards for materials, production, workmanship and maintenance are provided and

complied with the design intentions may not be realised.





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6.1.3 With regard to basic assumptions covering durability, workmanship and materials, it

is assumed that the quality of the timber and other materials, and of the workmanship asverified by inspections, is adequate for safety, serviceability and durability.

6.2 Loading

For the purpose of design, loading should be in accordance with UBBL-1984 (Uniform

Building By-laws), BS 6399 : Part 1 and CP3 Chapter V : Part 2 or other relevant standards,

where applicable.

6.3 Accidental damage

In addition to designing a structure to support loads arising from normal use, there should be

a reasonable probability that the structure will not collapse catastrophically because of misuseor accident. No structure can be expected to be resistant to the excessive loads or forces

that could arise from an extreme cause, but it should not be damaged to an extent which is

disproportionate to the original cause.

Whilst, in general, the hazards and safeguards previously described should always be

considered by the designer, no specific robustness design requirements are normally

necessary for buildings up to four storeys.

Where timber is often used in conjunction with other structural materials which normally

perform the main load-bearing function, the effect on the structure of accidental loading

should be considered as required by the relevant standards for such materials.

Because of the particular occupancy of a structure, it may be necessary to consider the effect

of particular hazards and to ensure that, in the event of an accident, there is an acceptableprobability of the structure continuing to perform its main function after the event, even if in adamaged condition. Also, where there is a possibility of vehicles running into and damaging

vital load-bearing members of the structure in the ground floor, the provision of bollards, walls,retaining earth banks, etc., should be considered.

When considering the probable effects of misuse, accident or particular hazards, or when

computing the residual stability of the damaged structure, the designer normally shouldenhance the factor of safety by multiplying the values recommended by MS 544 for all longterm permissible stresses and permissible loads on fasteners by a factor of two.

6.4 Service classes for glued laminated timber and timber panel products

Because of the effect of moisture content on material mechanical properties, permissibleproperty values should be those corresponding to one of the following service classes.

a) Service class I is characterised by a condition whereby most timber will attain an

average moisture content of not exceeding 12 %. Typical example is an air-

conditioned environment with temperature of 24 °C and a relative humidity of not

more than 60 % most of the time.





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b) Service class II is characterised by a condition whereby most timber will attain an

average moisture higher than that of service class I, but not exceeding 20 %. This is

achieved, for instance, in a sheltered environment with temperature of 30 °C and a

relative humidity of not more than 90 % most of the time.

c) Service class III is characterised by a condition whereby most timber will attain an

average moisture content higher than of class II. Typical example is an external, fully

exposed condition such as the marine environment or higher humidity environment.

NOTE. Timber continuously exposed to wet and hot conditions, e.g. in cooling tower structures, is outside thescope of this MS 544 : Part 1 as regards exposure conditions.

6.5 Moisture content of timber

6.5.1 The timber should be seasoned as far as practicable to a moisture contentappropriate to the position in which it is to be used (see Table 1).

6.5.2 Timber with a higher moisture content at the time of erection than that indicated in

Table 1 may be used in particular forms of construction where experience has shown that

subsequent drying does not have an adverse effect.

6.5.3 The basis factors governing the moisture content of timber in buildings are as follows:

a) Wood is a hygroscopic material; its moisture content therefore depends on itsenvironment.

b) Unless wood is in contact with water or exposed to damp conditions, its moisturecontent stabilizes, in most cases, at between 15 % and 19 %, depending on the

relative humidity, which is very much lower than when the timber is freshly felled; the

drier the atmosphere and the higher the temperature, the lower the moisture content

which the wood attains.

c) At a moisture content below about 30 %, wood shrinks or swells as its moisture

content changes.

d) Wood is much less prone to decay if its moisture content is below 25 %, and may be

regarded as reasonably immune below 20 %.

e) Where wood of durability group 4 is to be used permanently in contact with the

ground or otherwise exposed to damp conditions or used in situations where suchconditions could occur, even if only temporarily, then it is recommended that pressure

treated timber and plywood be used (MS 322 : 1974).

6.5.4 All timber which is thoroughly air-dried in this country attains a moisture content

between 15 % and 19 % depending on weather conditions prevailing at the end of the drying

period.

6.5.5 Where it is intended to use the dry basic stresses, it is necessary to reduce the

moisture content of the timber to below 19 %. The cost of artificial drying increases sharply

for boards over thickness more 75 mm. Generally the basic stresses for wet timber should

always be used for solid timber members more than 100 mm thick.





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6.5.6 Care should be taken on site to ensure that the timber is adequately protected. This is

particularly important with material dried to below 19 % moisture content, since the full designload should not be applied if the moisture content rises above 19 %.

6.5.7 The moisture content of timber used in the manufacture of glued joints should comply

with MS 544 : Part 6.

6.5.8 Wood based panel products have a relatively low moisture content at the time of

manufacture. If expansion in use is likely to be a problem in a particular end-use situation,

they should be conditioned to a higher moisture content before installation.

Care should be taken on site to ensure that material supplied in a dry condition is adequately

protected from the weather (see MS 544 : Part 6 ).

6.5.9 The moisture content of timber in manufacture of glued laminated members should

conform to BS EN 385.

6.5.10 The moisture content of timber to be finger jointed should conform to BS EN 386.

6.5.11 The moisture content of materials used in components manufactured from separate

pieces of timber, timber panel products that are fastened together with glue (e.g. box beams,

single web beams, stressed skin panels, glued gussets) should conform to BS 6446.

6.5.12 Timber treated with a water-borne preservative should be dried before being used in

a structure whose design has been based on use in service classes 1 and 2.





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Table 1. Moisture content of timber for various applications

Applications Maximum m.c at time of installation for

non air-conditioned application

(non klin-dried timber)

Maximum m.c at time

installation for air-

conditioned application

Structural Components

Columns,

Beams,

Bearers,

Studs, joists ties and struts

30 % (thickness exceeding 100 mm)

25 % (thickness not exceeding 100 mm)

n.a

n.a

Roofing

Rafters, ties, struts, purlins and bracings

Battens

25 %

25 %

n.a.

n.a.

Staircase

Stringers, treads, trimmer beam and

handrill

Balustrades

19 %

19 %

12 %

12 %

Flooring

Floorboarding and parquetry

Skirtings

19 %

19 %

12 %

19 %

Walling

Wall, partition and framings

External wall hoardings

External wall boarding, slats and screens

Fascia board

19 %

19 %

19 %

19 %

12 %

n.a

12 %

n.aCeiling Frames

Cover battens to joints of ceiling sheets

Ceiling strips and soffit battens

25 %

19 %

n.a

12 %

Door and Window Frames

Door, window and vent frames including

their stops and grounds

Door leaves, window and vent sashes

19 %

19 %

12 %

12 %

Furniture

Built in fittings and furniture in general

Workshop furniture

Science laboratory tops

19 %

19 %

19 %

12 %

12 %

12 %

Beading fillets and edgings generally 19 % 12 %NOTE. n.a not applicable

6.6 Service exposure conditions for solid timber

Because of the effect of moisture content on strength properties, the permissible stresses

used in design should be those corresponding to the moisture content that the particular

member will attain in service. It is not possible to cover all service conditions and for the

purposes of MS 544 : Part 2 the following two exposure conditions only are defined.





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a) Dry exposure

All service conditions where the air temperature and humidity would result in solid

timber attaining an equilibrium moisture content not exceeding 19 % for any significant

period. This exposure includes most covered buildings, and internal uses. Stresses

are given in MS 544 : Part 2 for the dry exposure condition and are identified as dry

stresses.

b) Wet exposure

All service conditions, either in contact with water, or where the air temperature and

humidity would result in solid timber attaining an equilibrium moisture content

exceeding 19 % for any significant period. Permissible stresses should be obtained for

the wet exposure condition by multiplying the dry stresses by appropriate modificationfactors and such stresses are identified as wet stresses in MS 544 : Part 2.

NOTE. Timber continuously exposed to wet and hot conditions, e.g. in cooling tower structures, is outsidethe scope of MS 544 as regards to exposure conditions.

6.7 Duration of loading

The grade stresses and the joint strengths given in MS 544 are applied to long term loading.

Because timber and timber-based materials can sustain a much greater load for a period of few minutes than for a period of several years, the grade stresses and the joint loads may beincreased for other conditions of loading by the modification factors given in the appropriate

Parts of MS 544.

6.8 Section size

The bending, tension and compression stresses and the moduli of elasticity given in MS 544

are applicable to material of 300 mm deep or wide for tension.

Because these properties of timber are dependent on section size and size-related grade

effects, the grade stresses should be modified for section sizes other than the sizes given

above by the modification factors specified in the appropriate Parts of MS 544.

6.9 Load-sharing systems

The grade stresses given in MS 544 are applicable to individual pieces of structural timber.

Where two or more pieces of timber at a maximum spacing of 610 mm centre to centre act

together to support a common load, then some modification of these stresses may be

permitted in accordance with the appropriate Parts of MS 544.

6.10 Effective cross section

For the purpose of calculating the strength of a member at any section, the effective cross

section should be taken as the actual cross section appropriate to the exposure condition,

less due allowance for the reduction in area caused by sinking, notches, bolt or screw holes,

mortices etc., either at that section or within such a distance from it as would affect the

strength at that section.





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6.11 Structural members

Structural members should be so proportioned that the stresses or deformations induced by

all relevant conditions of loading do not exceed the permissible stresses or deformation limits

for the material or the service conditions, determined in accordance with MS 544.

6.12 Structural frameworks

6.12.1 Centroidal lines

The design should take due account of secondary moments induced by eccentricity if the

longitudinal axes of members do not intersect at joints.

NOTE. The recommendations for trussed rafters appear in BS 5268 : Part 3.

6.12.2 Secondary stresses

Many triangulated frameworks have continuous members and rigid or partially rigid joints.

Due account should be taken of the secondary stresses present in such frameworks.

6.12.3 Provision of camber

Where deflection of the framework would have an adverse effect on the function or

appearance of the structure, if possible the designer should specify any necessary camber to

ensure the intended configuration after application of the appropriate load.

6.13 Floor and roof boarding

6.13.1 Lateral distribution of load

Where the boards, other than roof boarding on pitched roofs, are not tongued and grooved,

each individual board should be designed to carry the full imposed load given in CP 3 :

Chapter V as the minimum load per 300 mm width of boarding.

If a wood strip, hardboard, wood chipboard or plywood wearing surface, is applied on top of

the boarding, or plywood sheathing on the underside, this may be considered as given

adequate lateral distribution of load and the above restriction is unnecessary.

6.13.2 Joints in boarding

Header joints should be staggered and should bear directly on a supporting member with

adequate bearing there on, unless end-matched and taken into account in design.





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Appendix A

List of modification factor K

Part 1 : General

Part 2 : Permissible stress design of solid timber

1. K1 - Modification factor K1 for duration of loading ……………………………………

2. K2 - Modification factor K2 for load sharing ……………………………………………

3. K3 - Modification factor K3 for bearing stress………………………………………….

4. K4 - Modification factor K4 for shear at notched ends…………………………………

5. K5 - Modification factor K5 for form factor……………………………………………….

6. K6 - Modification factor K6 for depth factor……………………………………………..

7. K7 - Modification factor K7 used to modify the minimum Modulus of elasticity for

trimmer joists and lintels……………………………………………………………..

8. K8 - Modification factor K8 for compression members…………………………………

9. K9 - Modification factor K9 for the effective length of spaced columns……………….

Part 3 : Permissible stress design of glued laminated timber

10. K10 - Modification factor K10 for width factor……………………………………………..

11. K11 K12 K13 K14, K15 K16 - Single grade glued laminated members and horizontally glued

laminated beams………………………………………………………………………

12. K17, K18 K19, - Vertically glued laminated members………………………………………..

13. K20 - Stresses and moduli for service class 1 and 2………………………………………

14. K21 K22, K23 - individually designed glued joints in horizontally glued laminated members

15. K24 - Bending tension and compression……………………………………………………

16. K25 - Bending stress………………………………………………………………………….





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Part 4 : Timber panel products

17. K26 - Modification factor K26 by which the grade stresses and moduli for long term

duration and service classes 1 and 2 for plywood should be multiplied to obtain

value for other duration and/ or service class 3.

Part 5 : Timber Joints

All K values refer to Parts 2 and 3

Part 6 : Workmanship, inspection and maintenance

Part 7 : Testing

18. K27 - Modification Factor K73 for acceptance of structure

19. K28 - Modification Factor K85 for strength test (Service classes 1 and 2 only)





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Appendix B

Bibliography

B1. AS 1720.1-1988 Timber structures code : Part 1 : Design methods.

B2. AS/NZS 2269 : 1994 Plywood structural.

B3. AS 1720-1975 Timber engineering code.

B4. BS 5268 : Part 2 : 1996 Code of practice for permissible stress design, materials

and workmanship.

B5. BS 5756 : 1997 Visual strength grading of hardwood.

B6. BS 6566 Plywood : Part 1-8 : 1985.

B7. BS 1088 Plywood for marine craft : 1966.

B8. BS EN 384 : 1995 Structural timber – Determination of characteristic values of

mechanical properties and density.

B9. MS 228 : 1991 Specification for plywood.

B10. MS 934 : 1986 Specification for wood cement board.

B11. NZS 3603 : 1981 Section 4 –Joints.

B12. Timber Design Handbook - Malaysian Forest Record No. 42.

B13. Structural Timber Joints by Malaysian Forest Record No : 32

B14. The Standard Product Manual for the Production of Malaysian Basic Structural Grade

(MBSG) Rated Plywood, Timber Technology Bulletin, No. l, August 1995, FRIM.

c e n s e d t o U N I V E R S I T I T E K N O L O G I M A R A ( U I T M ) / D




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