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MALAYSIAN STANDARD
MS 544 : PART 1 : 2001
CODE OF PRACTICE FOR STRUCTURAL USE 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, effective cross sections, structural members, structural frameworks, floor and roof boarding
© Copyright DEPARTMENT OF STANDARDS MALAYSIA
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. Licensed to GAN CHIN PHANG / Downloaded on : 15-Sep-2016 06:24:01 PM / Single user license only, copying and networking prohibited
adoption of international standards.
These standards where appropriate are
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governed by the Standards of Malaysia Act 1996 (Act 549).
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MS 544 : PART 1 : 2001
CONTENTS
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Page
Committee representation..........................................................................……..…
ii
Foreword…….........................................................................................………....
iii
1
Scope………………………………………………………………………………………
1
2
Referenced documents…………………………………………………………………..
1
3
Definitions……………………………………………………………………………..….
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
i
MS 544 : PART 1 : 2001
Committee representation The Building and Civil Engineering Industry Standards Committee (ISC D) under whose supervision this Malaysian Standard was developed, comprises representatives from the following Government Ministries, Trade, Commerce and Manufacturing Associations, and Scientific and Professional Bodies:
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Association of Consulting Engineers Malaysia Construction Industry Development Board Malaysia Department of Standards Malaysia Department of Occupational Safety and Health Jabatan Bomba dan Penyelamat Pertubuhan Akitek Malaysia Master 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 Megat Kamil Azmi bin Megat Rus Kamarani Puan Zainora bt Zainal Puan Hanishahani Othman
General Manager, Technology Development Division Senior Manager, Standard and Quality Unit Manager, Standard and Quality Unit The Secretary of CIDB Standard Committee
The Technical Committee on Structural Use of Timber which developed this Malaysian Standard consists of the following 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
ii
MS 544 : PART 1 : 2001 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 Standards Committee. Development of this standard was carried out by Construction Industry Development Board Malaysia (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 and workmanship’. MS 544 consists of the following parts and sections, under the general title, ‘Code of practice for structural use of timber‘ :
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Part 1 : General Part 2 : Permissible stress design of solid timber Part 3 : Permissible stress design of glued laminated timber Part 4 : Timber panel products Section 1 : Structural plywood Section 2 : Marine plywood Section 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 tables Section 1 : Domestic floor joists Section 2 : Ceiling joists Section 3 : Ceiling binders Section 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. iii
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MS 544 : PART 1 : 2001 CODE OF PRACTICE FOR STRUCTURAL USE OF TIMBER : PART 1 : GENERAL (FIRST REVISION) 1.
Scope
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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 are subsequent amendments to, or revisions of, any of these publications the Malaysian Standard shall be amended or revised accordingly. However, parties to agreements based on this Malaysian Standard are encouraged to investigate the possibility of applying the most recent editions 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 BS 6100
Wind loads.
Glossary of building and civil engineering terms.
ISO 3898 Cement-bonded particleboard - Boards of Portland or equivalent cement reinforced with fibrous wood particles. BS 6399 : Part 1 Loading for buildings : Part 1 : 1984 imposed loads.
Code of practice for dead and
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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MS 544 : PART 1 : 2001
BS 6446 : 1984 Specification or manufacture of glued structural components of timber and wood based panel products. BS 5268 : Part 3 : 1985 Code of practice for trussed rafter roofs. BS 5756 : 1997
Visual strength grading of hardwood.
BS EN 338 : 1995
Structural timber – Strength classes.
BS EN 385 : 1995 Finger jointed structural timber - Performance requirements and minimum production requirements. BS EN 386 : 1995 Glued laminated timber - Performance requirements and minimum production requirements.
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The Uniform Building By-Laws 1984. MGR – Malaysian Grading Rule 1984.
3.
Definitions
For the purposes of this Malaysian Standard the definitions given in BS following apply. 3.1
6100 and the
Bare sawn
Applied to sawn timber that measures, at the time of inspection, the same as the dimensions specified. 3.2
Basic stress (Clear wood stress)
Stress that can safely be permanently sustained by solid timber containing no visible strength reducing characteristics. 3.3
Connector
Device generally consisting of a plate, disc or ring which, when partly embedded in each or in one of the contact faces of two members held together by a connecting bolt, is capable of transmitting a load from one member to another. 3.4
Connector axis
Line joining the centres of a pair of adjacent connectors located on the same surface. 3.5
Dry stress
Stress applicable to material exposed in conditions which would result in solid timber having moisture content not exceeding 19 % in service. NOTE. For the purpose of MS 544 : Part 2, the moisture content for dry stress should not exceed 19 % in service.
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MS 544 : PART 1 : 2001
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
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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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MS 544 : PART 1 : 2001
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.)
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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 in hardwood.
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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MS 544 : PART 1 : 2001
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
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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 the Malaysian 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 by environmental 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;
5
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MS 544 : PART 1 : 2001 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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MS 544 : PART 1 : 2001 b)
Significance: a
applied;
adm permissible; e
effective;
mean arithmetic mean;
c)
cw
clear wood; and
cg
grade.
Geometry apex
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r
apex; 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.
7
MS 544 : PART 1 : 2001 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
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6.1.1 All structural members, assemblies or frameworks in a building, in combination with 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 MS 544. 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 are necessary 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 MS 544 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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MS 544 : PART 1 : 2001
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 as verified 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.
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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 misuse or 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 acceptable probability of the structure continuing to perform its main function after the event, even if in a damaged 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 should enhance the factor of safety by multiplying the values recommended by MS 544 for all long term 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, permissible property 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 airconditioned environment with temperature of 24 °C and a relative humidity of not more than 60 % most of the time.
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MS 544 : PART 1 : 2001
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 the scope of this MS 544 : Part 1 as regards exposure conditions.
6.5
Moisture content of timber
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6.5.1 The timber should be seasoned as far as practicable to a moisture content appropriate 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 its environment.
b)
Unless wood is in contact with water or exposed to damp conditions, its moisture content 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 such conditions 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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MS 544 : PART 1 : 2001
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 design load 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 ).
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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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MS 544 : PART 1 : 2001
Table 1. Moisture content of timber for various applications Applications
Structural Components Columns, Beams, Bearers, Studs, joists ties and struts
Maximum m.c at time of installation for non air-conditioned application (non klin-dried timber)
30 % (thickness exceeding 100 mm)
n.a
25 % (thickness not exceeding 100 mm)
n.a
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Roofing Rafters, ties, struts, purlins and bracings Battens Staircase Stringers, treads, trimmer beam and handrill Balustrades Flooring Floorboarding and parquetry Skirtings Walling Wall, partition and framings External wall hoardings External wall boarding, slats and screens Fascia board Ceiling Frames Cover battens to joints of ceiling sheets Ceiling strips and soffit battens Door and Window Frames Door, window and vent frames including their stops and grounds Door leaves, window and vent sashes Furniture Built in fittings and furniture in general Workshop furniture Science laboratory tops Beading fillets and edgings generally NOTE. n.a not applicable
6.6
Maximum m.c at time installation for airconditioned application
25 % 25 %
n.a. n.a.
19 %
12 %
19 %
12 %
19 % 19 %
12 % 19 %
19 % 19 % 19 % 19 %
12 % n.a 12 % n.a
25 % 19 %
n.a 12 %
19 %
12 %
19 %
12 %
19 % 19 % 19 %
12 % 12 % 12 %
19 %
12 %
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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MS 544 : PART 1 : 2001
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
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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 modification factors 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 outside the 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 be increased 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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MS 544 : PART 1 : 2001
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.
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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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MS 544 : PART 1 : 2001
Appendix A List of modification factor K
Part 1 : General Part 2 : Permissible stress design of solid timber
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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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MS 544 : PART 1 : 2001
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
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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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MS 544 : PART 1 : 2001
Appendix B
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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.
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