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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