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    PROTECTION BY DESIGN

    Ir. Muhammad Azman Bin Jamrus

    Senior Chief Assistant DirectorCivil, Structural & Bridge Engineering Branch

    Public Works Department (PWD)

    Headquaters Malaysia

    Kuala Lumpur

    Technical Seminar On Timber In Construction

    The Legend Hotel, Kuala Lumpur17 November 2011

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    The general believe in Malaysia is that timber is not a durable

    or worthy structural materials

    Timber structure presents a higher fire hazard when

    compared to concrete and bricks. Shortage of good quality timber

    Poor workmanship

    Quality assurance of timber e.g. species, treatment, grading

    Enforcement of these procedure and accreditation, need to be

    enhanced

    Hence to address some of these issues, protection of timber

    by design will help to overcome these perceptions

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    GENERAL HAZARDS FOR TIMBER STRUCTURES

    Sun

    Drying of timber

    Shrinkage and cracking

    Weathering

    Timber surface fibersloose & erode

    Surface checks

    Splits

    Moisture

    Fungal growth & insect attack Affects mechanical & strength properties

    Corrosion of fixings

    Swelling & cracking

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    Fire

    Combustible

    Flame spreads over the surface

    Chemical

    Degradation of chemical structure of timber

    Coating on timber can cause resin exudation from

    timber

    Time

    Structural timber subject to different hazard during its

    life cycle.

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    PROTECTION BY DESIGN :

    Natural durability of timber is defined as its resistance to decay and

    insect attack.

    Durability of timber is the capacity of the timber component, system,structure to perform its function for a specified period of time.

    To minimise durability risks, irrespective of the natural durability levels

    and preservative treatment that are used, protection by design can be

    adopted to utilise the full durability of the timber .

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    BASIC PRINCIPLES OF TIMBER PROTECTION BY DESIGN

    a) Protect timber from insects such as bores, termites

    b) Protect timber from water

    c) Protect timber from sun/heat

    * In Malaysia the exposure condition category is severe

    i.e surfaces exposed to severe rain, alternate wetting & drying or

    severe condensation

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    CATEGORIES OF SERVICE LIFE FOR TIMBER BUILDINGS.

    Design life category Period

    (Years)

    Example of generic

    timber forms

    Temporary Up to 10 Exhibition & temporarybuildings

    Short life Minimum 10 Specific commercial &

    temporary housing

    schemes.

    Medium life Minimum 30 Commercialdevelopment and

    refurbishment projects

    Normal life Minimum 60 General new build

    housing.

    Long life Minimum 120 Special buildings whereclient demands this level

    of service life, major

    bridges.

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    Code of Practice for Structural Use of Timber :

    MS 544 Part 1 : Generalclause 6.4 : service class characterised by average moisture

    content that timber can attained

    - service class 1, 2 or 3

    clause 6.5 : moisture content

    clause 6.8 : service exposure conditions for solid timber- wet/dry

    MS 544 Part 10 : Preservative Treatment For Structural Timber clause 4.3 : good design

    - design can reduce risk of degradation

    - high standard of workmanship & maintenance

    - design detailing that can eliminate source of moisture,

    water ponding, weathering

    - treatment of timber by preservatives is a supplementary

    and cannot be regarded as a substitute for appropriate

    design

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    Eurocode 5 (EN 1995)

    materials with sufficient natural durability

    moisture content < 20% for load bearing timber elements

    constructional protective measures to prevent / reduce direct weathering of

    timbers by rain or solar radiation

    limitation measures of standing water/openings/direct absorptions on timbercomponents by inclinations of timber components/ using barriers

    (if partial or complete covering of structural elements is not practicable)

    prevention of fissures & delaminations in all positions especially where end grainis exposed by sealing or cover plates

    Natural ventilation by geometry

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    Reduction of hazards by design detailing is a key component for

    durability, whether preservative treatments or naturally durable

    timbers are used.

    Design features to consider such as moisture/ vapour barriers,

    vertilation, provision of damp-proof cources, sealing of end grain &avoidance of water traps.

    Good design together with workmanship.

    BS 5589 : Code of Practice for Preservation of

    Timber

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    PROTECTIVE DESIGN REQUIREMENTS:

    Correct selection of timber species, grades & size to suit specific applications

    Correct selection of adhesives, seals, fasteners & surface coatings. For examples

    specify suitable exterior glues

    Use value added/engineered timber

    Specify inside specification:

    Strength grade

    Appropriate moisture content

    Service class

    Visual grading

    Quality control system

    Handling, transportation

    & installation

    Good engineering practice

    Maintenance schedule

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    Corrosion resistance fasteners

    Minimising construction joints

    Geometry of building

    Provide physical barrier which there is no direct path from

    ground to timber

    Design & connection detailing that minimise exposure to hazard

    Analysis and design of timber structure which take intoconsideration bending resistance and charring rate of timber

    Maintenace schedule to ensure protection remains functional

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    PROJEK PUSAT PROMOSI PERKAYUAN MALAYSIA,

    MUKIM TEBRAU, JOHOR

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    Protection against weathering by: Geometry of the

    Structure

    Timber frame with

    inclination prevent

    accumulation of water

    on the structure

    components

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    Glulam timber frames rest

    on reinforced concrete

    beam and stump at 3.5m

    above the ground floor level

    for fire resistance &

    durability requirement

    (no direct contact with

    ground and no direct path

    from ground to glulamframe)

    Protection against fire by : Combined with other Structural

    Systems

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    Protection against weathering & moisture by : Covering/Shed

    Roof covering

    protects the glulamframes from direct

    exposure to

    weathering by rains

    and solar

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    Protection against weathering & moisture by : Shed

    Purlins overhang can shed

    water satisfactorily

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    Protection against weathering & moisture by :

    Corrossion Resistance of Fasteners

    Purlins overhang can shed

    water satisfactorily

    Corrosion ResistanceFasteners

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    The glulam bridge

    structures was protected

    from direct exposure to

    weathering by steel plate

    covering

    Protection against moisture by : Covering

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    Protection against fire by : Mechanical System

    Fire Fighting

    System:

    Sprinkler System

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    Protection against weathering & moisture by : Mechanical System

    Proper drainage of

    surface runoff water

    from glulam frame

    by Fast Flow System

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    Protection by Coatings

    Moisture Resistant

    Coating for Timber

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    Protection against weathering & moisture by : Sequence of

    Construction

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    A monitoring plan by UITM was established forTebrau project to ensure the durability andexpected service life of the construction. The

    plan was set up with the aim of detecting in duetime any manufacturing problems and alsoproblems in glued in rods due to exposureambient conditions (air temperature and

    relative humidity),

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    The objective was to measure the surface temperature of

    timber, cured adhesive, at the surface of the internal 32 mm

    diameter steel shear bars and at the surface of the shear bar

    integral connection plate. This last plate has a greater heatsink than the bars and also its exterior surface is closer to the

    outer surface of the timber.

    FROM ZAKIAH ET AL

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    Surface MoistureContent between10% to 15%

    FROM ZAKIAH ET AL