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REVISED MALAYSIAN CODE OF PRACTICE FOR STRUCTURALUSE OF TIMBER

Abdul Rashid A.M.1, Mohd Shukari Midon2, Mohd Zamin Jumaat3 & Wan MahmoodWan Ab. Majid4

1. Senior Director/Chairman Technical Committee on Timber Structures, ForestResearch Institute Malaysia (FRIM), Kepong, 52109 Kuala Lumpur,MALAYSIA.

2. Senior Research Officer, Forest Research Institute Malaysia (FRIM), Kepong,52109 Kuala Lumpur, MALAYSIA.

3. Assoc. Professor, Department of Civil Engineering, Faculty of Engineering,Universiti Malaya, 50603 Kuala Lumpur, MALAYSIA.

4. Professor, Department of Civil Engineering, Universiti Teknologi Mara (UiTM),40450 Shah Alam, Selangor D.E., MALAYSIA

SUMMARYThe Malaysian Standard (M.S.) 544:1978, The Code of Practice for Structural Use ofTimber is being revised. The revision is being coordinated by the Technical Committeeon Timber Structures (TC 4), a committee formed by the Construction IndustrialDevelopment Board Malaysia (CIDB). The new M.S. 544 will have 12 Parts and 11Sections. So far TC 4 has completed 10 Parts and 8 Sections including Parts on fireresistance and design for glued-laminated timber members. The revision of the Standardis in its final stages. The task involves ten Working Groups formed by TC 4 andcomprised sixty members. Once completed the Standard contains basic working stresses,design methods and general guidance on structural use of Malaysian timbers includingwood-based panel products and glued-laminated timber members. This paper highlightssome of the features of the newly published Parts.Keywords: Code, Standard, Timber, Strength grouping, Joints, Glued laminatedmembers, Panel products, Fire resistance

1. INTRODUCTION

In the past, design and detailing of timber structures in Malaysia was done according tothe Malaysian Standard (M.S.) 544: 1978, Code of Practice for Structural Use of Timber[1]. The Code was purely a carbon copy of the British Codes of Practice for design oftimber structures, CP 112: 1967, except for the species used [2]. The code has never beenrevised since its first circulation. Only in late 1997 was revision for the Standard initiatedby the Technical Committee on Timber Structures (TC 4). TC 4 was formed by theConstruction Industrial Development Board Malaysia (CIDB), a Standard WritingOrganisation on building material appointed by the Standards Industrial ResearchInstitute of Malaysia (SIRIM) Bhd.The revision of the Standard is currently in its final stages. The prodigious task has beenundertaken by 10 Working Groups (WG), commissioned by TC 4. The WG comprises 60members from various government agencies, research institutions and professional

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bodies. Unlike the previous Code of Practice, the new Code will ultimately be publishedinto 12 Parts under the title ‘Code of Practice for Structural Use of Timber’ [3].Part 1: General (revised)Part 2: Permissible stress design of solid timber (revised)Part 3: Permissible stress design of glued-laminated timber (new)Part 4: Timber panel products (new)

Section 1: Structural plywood Section 2: Marine plywood Section 3: Cement-bonded particleboard Section 4: Oriented-strand board (OSB)

Part 5: Timber joints (revised)Part 6: Workmanship, inspection and maintenance (revised)Part 7: Testing (revised)Part 8: Design, fabrication and installation of prefabricated timber for roof trusses (new)Part 9: Fire resistance of timber structures (new)

Section 1: Methods of calculating fire resistance of timber membersPart 10: Preservative treatment of structural timbers (new)Part 11: Recommendations for the calculation basis for span tables and their calculations (new)

Section 1: Domestic floor joists Section 2: Ceiling joists Section 3: Ceiling binders Section 4: Domestic rafters

Part 12: Laminated veneer lumbers for structural application (new)Out of the twelve Parts, seven Parts are considered new and five are revised documents.The first document was published in 2001, after about four years since the inception ofTC 4.For promotion, CIDB and TC 4 have organised several workshops to introduce the newlypublished Parts of the Standard to professional engineers, architects, contractors andgovernment bodies.This paper highlights some of the features of the newly published Parts. Emphasis will begiven to some of the new Parts, namely, designs of glued-laminated timber (Part 3),timber panel products (Part 4), timber joints (Part 5) and fire resistance of timberstructures (Part 9).

2. DESIGN OF SOLID MEMBERS

Part 2 of the Code outlines design procedures to be followed depending on the type ofelement being designed. It is based on permissible stress design (elastic design) ratherthan limit state design. The designs of curved and tapered members are not within thescope of the Standard.

2.1 Timber Classification

Based on densities, Malaysian timbers are generally classified into four categories,namely, heavy hardwoods (800–1120 kg/m3), medium hardwoods (720-880 kg/m3), light

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hardwoods (400–720 kg/m3) and softwoods [4]. So far, about 100 timber species withdensities ranging from 350 kg/m3 to 1100 kg/m3 (measured at 19% moisture content)have been included in the new MS 544: Part 2: 2001: Code of Practice for Structural Useof Timber - Permissible Stress Design of Solid Timber compared with 56 species in theprevious Code.

2.2 Strength Grouping

For design purposes the species are divided into seven strength groups, SG 1 to SG 7, inthe order of decreasing strength (Table1). SG 7 is considered weak and is generallyunsuitable for many structural applications. The wet and dry grade stresses for strengthgroups are given Table 2. The strength data are based on small clear test specimens.

Table 1. Strength groups of Malaysian timber S.G.1 S.G.2 S.G.3 S.G.4 S.G.5 S.G.6 S.G.7A) Naturally DurableBalau Belian Bekak Giam TeakBitis Mata ulat Delek Malabera TembusuChengal Kekatong Keranji MerbauPenaga ResakB) Requiring Treatment

Dedaru Agoho Berangan Alan bunga Bayur AraKempas Balau, red Dedali Babai Damar minyak BataiMerbau Kelat Derum Balek angin bopeng Durian GeronggangMertas Kembang semangkok Kapur Bintangor Jelutong Laran

Kulim Kasai Brazil nut Jenitri PelajauPauh Kijang Keruntum Gerutu Jongkong PulaiPenyau Mempening Kayu kundur Kasah SesendokPerah Meransi Kedondong Machang TerentangPetaling Meranti bakau Keledang MedangRanggu Merawan Keruing Melantai/KawangDurian batu Merpauh Ketapang Meranti, light redTualang Nyalin Kungkur Meranti, yellow

Perupok Melunak MersawaPunah Mempisang TerapRengas MengkulangSimpoh Meranti, dark red

Meranti, whiteNyatohPenarahanPetaiRaminRubberwoodSengkuangSepetir

Notes:1. For naturally durable timbers, sapwood should be excluded. If sapwood is included, preservative treatment is necessary. (Source: MS360, 1986)2. For timber requiring treatment, they should be amenable to preservative treatment

Table 2. Wet and dry grade stresses for various strength groups of Malaysian timber (stresses and moduli expressed in N/mm2)

Strength groups

Condition1)

Bendingparallel to grain

Tension parallel to grain

Compressionparallel to grain

Compressionperpendicular to grain 2)

Shear parallel to grain

Modulus ofelasticity for all grades

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Sel Std Com3) Sel Std Com Sel Std Com Basic Sel Std Com Sel Std Com Mean Minimum

SG1

SG2

SG3

SG4

SG5

SG6

SG7

WetDry

WetDry

WetDry

WetDry

WetDry

WetDry

WetDry

29.2 23.0 18.233.6 26.5 21.0

20.7 16.3 13.023.3 18.3 14.6

18.1 14.2 11.320.2 15.9 12.6

14.2 11.2 8.816.8 13.2 10.5

11.0 8.6 6.812.1 9.5 7.5

9.4 7.4 5.911.3 8.9 7.1

6.6 5.2 4.2 8.2 6.5 5.1

17.5 13.8 10.920.2 15.9 12.6

12.4 9.8 7.814.0 11.0 8.8

10.9 8.5 6.812.1 9.5 7.6

8.5 6.7 5.310.1 7.9 6.3

6.6 5.2 4.1 7.3 5.7 4.5

5.6 4.4 3.5 6.8 5.3 4.3

4.0 3.1 2.5 4.9 3.9 3.1

26.8 21.1 16.828.5 22.5 17.8

18.8 14.8 11.723.4 18.5 14.7

15.3 12.0 9.517.8 14.1 11.1

12.1 9.5 7.614.1 11.1 8.8

9.1 7.2 5.710.8 8.5 6.7

7.9 6.2 5.0 8.8 6.9 5.5

5.3 4.2 3.3 6.9 5.4 4.3

4.59 3.90 3.67 3.444.67 3.97 3.74 3.50

3.50 2.97 2.80 2.623.82 3.25 3.05 2.86

2.38 2.02 1.90 1.782.61 2.22 2.09 1.96

1.83 1.55 1.46 1.372.06 1.75 1.65 1.54

1.12 0.95 0.90 0.841.42 1.21 1.14 1.06

1.02 0.87 0.82 0.761.28 1.09 1.02 0.96

0.62 0.53 0.50 0.460.77 0.65 0.62 0.58

2.54 1.98 1.592.94 2.28 1.84

2.24 1.74 1.402.51 1.95 1.57

1.84 1.43 1.152.07 1.61 1.30

1.53 1.19 0.961.58 1.23 0.99

1.21 0.95 0.761.37 1.07 0.86

1.05 0.82 0.661.11 0.86 0.69

0.91 0.71 0.570.98 0.76 0.61

1700018800

1570016800

1330014300

1070011000

8800 9100

6700 7300

5700 6600

13300 14000

11700 12600

9800 10300

7400 7600

6100 6300

4900 5200

3000 3400

1) Moisture content for Wet > 19%, for Dry 19%2) When there is no wane at the bearing area, the basic stress figures may be used for all grades3) Sel, Std and Com stand for select structural, standard structural and common building grades respectively as defined in the Malaysian Grading Rules (MGR)

3. DESIGN OF TIMBER JOINTS

Part 5 of the Code outlines recommendations for the design of joints in solid timberintended for use with various types of mechanical fasteners. Numerous changes andaddition have been made in the revised edition of the Code.

3.1 Additional Species to the Joint Groups

Timber species are classified into five joint groups, J1, J2, J3, J4 and J5, in decreasingorder of strength as in the previous Code. However, a total of 90 species are listedcompared with 53 species in the previous Code.

3.2 Plywood to Timber Joint

Part 5 also provides the basic working loads for plywood to timber joints that was notcovered in the previous Code. Structural or marine plywood are recommended for theapplication. The determination of basic load is based on the standard nail penetration.

3.3 Eccentric Joints

The Code also gives guidelines for the eccentric joints which state that the combinedeffects of primary and secondary stresses due to the resulting bending and shear stressshall be checked.

3.4 Coach Screws

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The uses and designs of coach screws are also highlighted in the new Code. The basiccalculation is similar to the designs of bolted joints. However, some conditions have to bemet when coach screws are used laterally in dry timber.

4. DESIGN OF GLUED-LAMINATED TIMBER

Currently, glued-laminated structure is not a common construction material used inMalaysia. However, concerted efforts have been made by FRIM and other relevantgovernment agencies and universities to promote the use of this product for futureapplications.

Part 3, a new component of the Code, deals with the guidelines on the designs ofstructural components made of glued laminated members. Glued-laminated membersshould be manufactured in accordance with BS EN 386. Glued-laminated strengthclassifications for structural tropical hardwoods are based on strength classes graded inaccordance with BS 5756. There are seven strength classes, namely, C22, C24, D35,D40, D50, D60 and D70 in increasing order of strength. By and large, Part 3 of the Codefollows closely Part 2 of BS 5268, except with the inclusion of two additional localspecies [5]. Table 3 shows the tropical hardwoods strength classes and the correspondingcharacteristic bending strengths for glued-laminated timber design.

Table 3. The tropical hardwoods strength classes and their correspondingcharacteristic bending strengths for glued laminated timber design

Standard Name Strength Class Characteristic bending strength ( N/mm2)

Meranti, Light Red C22 22.0Meranti, Yellow C24 24.0Meranti, Dark Red D35 35.0Mengkulang D40 40.0MerbauKeruing

D50 50.0

KapurKempas

D60 60.0

Balau D70 70.0NOTE: Additional species/grades could be incorporated in accordance with BS EN 338

5.0 DESIGN OF STRUCTURAL USE OF TIMBER PANELS

Unlike the previous Code, the new Code includes a new part, Part 4, on the design ofstructural use of timber-panel products. This Part provides guidance on structural use oftimber-based panels, namely, structural plywood, marine plywood, cement-bondedparticleboard and oriented-strand board in load bearing members. Recommendations onquality, grade stresses and modification factors are included for these materials whenused as simple members, or as parts of built-up components, or as parts of structures in

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incorporating other materials. The Standard applies only to Malaysian basic structuralgrade (MBSG) plywood, MBSG- rated marine plywood, compressed cement-bondedplywood (CBP) as well as medium and heavy duty oriented-strand board (OSB).

6. FIRE RESISTANCE OF TIMBER STRUCTURES

Part 9, a new scope of the Standard, outlines a method for evaluating the duration of fireresistance of an exposed load bearing of solid or a glued-laminated timber. The methodof calculation is based on the notional charring rates of 0.5 mm/min and 0.7 mm/min forstrength groups SG 1 to SG 3 and SG 4 to SG 5 respectively. The rates were based on BS5268: Part ? and confirmed by a study done on the charring rates of twelve Malaysianstructural timber species [6]. The same charring rates are applied to members laminatedwith approved heat resistant adhesive. Part 9 also includes a section on the fire protectionof metal fasteners and components.

7. CONCLUSION

The Technical Committee on Timber Structures (TC 4) formed by the ConstructionIndustrial Development Board Malaysia (CIDB) has almost completed a prodigious taskon the revision of the old MS 544. So far ten Parts have been published as the new Codeof Practice for structural use of Malaysian timber.

8. ACKNOWLEDGEMENTS

The authors would like to express their deepest appreciation to the ConstructionIndustrial Development Board Malaysia (CIDB) for the continued support rendered to theTechnical Committee on Timber Structures (TC 4). The authors are also grateful tomembers of the TC 4 and the Working Groups for their valuable contributions.

9. REFERENCES

[1] Anon, Code of Practice for the Structural Use of Timbers, M.S. 544: 1978,Standard Industrial Research Institute Malaysia (SIRIM), 1978.

[2] Anon, The Structural Use of Timber. British Code of Practice, CP 112: 1967,British Standard Institution, London, 1967.

[3] Anon, Code of Practice for the Structural Use of Timbers, MS 544:Parts 1 – 12:2001, Department of Standards Malaysia, 2001.

[4] Wong, T. M, A Dictionary of Malaysian Timbers. Malayan Forest Records No.30. Forest Research Institute Malaysia, 2002, 210 pp.

[5] Anon, Code of Practice for Permissible Stress Design, Materials andWorkmanship. BS 5268: Part 2: 1996. British Standard Institution, London, 1996.

[6] Chu, Y. P., Ho, K. S., Mohd Shukari Midon and Abdul Rashid, A.M., TimberDesign Handbook. Malayan Forest Record No. 42. Forest Research InstituteMalaysia, 1997, 288 pp.