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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

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Protection by design for timber is viable option that must be adopted to

make sure that timber can perform prolong durability under its service

life without harmful effects to human.

Where design is not practical to protect the timber, the use of naturally

durable timber or timber treated with chemical preservatives is

undertaken. The chemical preservatives treatments are

complementary to good design and workmanship but not substitute for

it.

CONCLUSION

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Thank You