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CHAPTER 5
T IMBER
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5.1 Timber Classification.
5.2 Timber Structure.
5.3 Moisture, Shrinkage and Strength.
5.4 Timber Defect
5.5 Treatment and Curing
5.6 Timber Products.
5.7 Wood in constructions
5.8 Timber Standard Testing
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Definition of wood, timber and lumber:
Wood vs Timber vs Lumber
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Wood : May be defined as
the material that forms the
trunks and branches of
trees
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Timber : Wood cut from
the trunk which can be
used for constructing
houses, furniture, bridges
and etc.
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I. HEAVY HARD WOOD (HHW) - over 880 kg/m3
- constructional timbers -some of them contain toxic material within their tissue such as alkaloids and other substances - can be used in most exposed conditions without undergoing preservative treatment - however, sapwood requires preservative treatment because less durable compare to heartwood - About 14 species under “Malaysian Grading Rules 1984 Edition 1”
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HARDWOOD classification
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II. MEDIUM HARDWOOD (MHW)
- 720 – 880 kg/m3 at 15% moisture content – MSS 544: 2001 (Consider Dry condition < 19%)
- Moderately heavy to heavy construction - Come of the timbers (kempas and tualang) are heavy
and strong, but insuffient for used in exposed condition and in ground contact.
- About 36 species under “Malaysian Grading Rules 1984 Edition 1”
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HARDWOOD classification
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II. LIGHT HARDWOOD (LHW)
- less than 720 kg/m3
- general utility timbers – joinery work, cabinet marking, furniture, decorative paneling and etc.
- require preservative treatment as a precaution against wood destroying agents such as fungi an insects.
- About 47 species under “Malaysian Grading Rules 1984 Edition 1”
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HARDWOOD classification
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SOFTWOOD (KAYU LAMPUNG)
No specific classification for softwood.
About 3 species under “Malaysian Grading Rules 1984
Edition 1”
Damar minyak is of commercial importance at the
moment.
Density range about 385 – 735 kg/m3
Timber mainly used as decorative plywood and paneling
Characteristics-not all soft, some softwoods are very hard.
-Eg; yew-strong and durable.
-derive from coniferous trees which are mainly evergreens.
-the leaves with needle shape and no dry outer covering of seeds.
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SOFTWOOD classification
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HARDWOODS (KAYU KERAS)
from broad-leaved trees
deciduous and majority of tropical trees are
evergreens.
densest, strongest and most durable timbers.
some hardwoods contain resins and/or oils which
interfere with the hardening of paints.
Eg; silica – make working difficult.
greater moisture movement than any softwoods.
examples of hardwoods;
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HARDWOOD characteristics
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Examples of hardwoods;
HEAVY MEDIUM LIGHT
Balau, balau merah, bitis,
cengalKapur, kasai, kempas
Durian, pulai,
bintangor,nyatoh
Giam, merbau, keranji, Keledang, keruing, kulimJelutong, macang,
merawan, ramin
Resak, tembusu, kekatongSimpoh, punah, mengkulang,
merpauh
Meranti, terap,
kedondong, gerutu
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HARDWOOD characteristics
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Wood Formation • Wood formed as a result of continuous secondary growth in cell.
When seed of a tree germinates, it forms a shoot consisting of thin medulla of spongy tissue commonly known as the pith. The pith is completely enclosed within thin meristematic tissue known as cambium, which is turn is protected on the outside tissue call bark.
• Growth of tree is a result of division of cambium cells, provides new cells to be added to the existing system. The accumulation of woody cells resulting from the cyclic activity of the cambium from year to year, accounts for the growth in height and diameter of a stem of a tree. The cambium produces bark tissue (phloem) on the outside and woody tissue (xylem) on the inside of the stem.
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TIMBER structure
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The wood functions are: a) Conduction of water and dissolved
mineral salt solution from the roots to leaves for manufacture of plant food materials
b) Storage and distribution of manufactured and reserved food materials
c) Provision of mechanical strength of the tree as a shole
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TIMBER structure
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SAPWOOD
food conduction and storage
less resistant to fungi and insect
can often be recognized, as it is usually lighter in colour
proportion decrease continuously with the age of tress
young tress being almost almost all sapwood
may be less than 20 % in mature three
HEARTWOOD
structural support
no longer store food
structural features is similar with sapwood except, the cell walls of the
latter are often permeated with resinous or gummy substances
more resistant to fungi and insect
it is usually darker in colour
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TIMBER structure
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BARK
the outer surface of the tree is protected by bark.
then followed by bast(basta)-the layer which transmits the nourishment from
leaves to the roots and to other parts.
then followed by cambium-thin layer. At certain age, the cambium will
change to sapwood and continue to heartwood with the growth of tree.
GRAIN
the comparative width of annual rings, the direction and the arrangement of
the cells and fibres are the causes of the wood grains.
the wood is said to be straight-grained when the cells are straight. And
cross-grained when the cells don’t run parallel to the axis.
cross-grain has a pronounced weakening effect on the strength of beams
when the slope of the grains is 1:15 or greater.
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TIMBER structure
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By late autumn (after the fall of the leaves), growth for the year
end.
When the growth resumes in early spring, the cambium starts
putting on large and porous cells which contrast significantly in
texture with the cells of the immediate preceding layer of late
autumn wood. This contrast produces growth rings.
Tropical Species
Clear growth rings are exceptional because there are indistinct
seasonal changes in climate.
No notable differences between the textures of wood produced.
Therefore, in tropical woods, these rings even if distinct, are not
criterion of the age of the tree which calculated one year per
ring like temperate species.
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TIMBER structure
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Temperate Species
The rings of wood formed during each growing season may be
clear differentiated because the vigor of growth during a single
growing season is not uniform throughout.
Early spring, the tissue produced consists of large and porous cells.
This is followed by a gradual decline vigor (energy of growth)
which made the tissue become smaller and denser cells.
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Definition of rings
Usually one ring-gelang is added each year. The rings are widest at the
centre and narrower nearer the bark. The rings are widest at the bottom
in young, thrifty trees and near the top in old ones.
The rings consist of minute tabular or fibrous cells tightly cemented
together by lignin which gives the strength to wood and each ring has
two parts; the earlywood/springwood-kayu awal and the
latewood/summerwood-kayu akhir.
The types of ring:
Growth ring- gelang tumbesaran = one set of circumference added to
tree.
Annual ring- gelang tahunan = also known as growth ring.
These annual rings give valuable information about the age, the
rapidity and uniformity of its growth
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TIMBER rings
Shrinkage
All structures made from timber have the possible effect of shrinkage.
Strength
The factors affecting strength of timber are:
i) Density Normally, young trees often give low density and reduced stresses.
ii) Moisture content Mechanical properties if wood influenced by moisture content.
But the modulus of elasticity is less affected by changes in moisture.
iii) Temperature An increasing of temperature, the timber strength will decrease.
iv) Grains structure It determines the permissible stress and modulus of elasticity.
v) Condition of growth Environmental factors affecting tree growth such as temperature,
type of soil, spacing between trees.
vi) Defects
It can effects the strength of the wood and can
be classified natural defect, decay and insects
and parasites attacked. Common defect types
are shown in figure below:
• Buku (knots)
Occurs on the trunks and branches of a tree.
• Saku Kulit (bark pocket)
Occurs on the defect of cambium cell
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TIMBER defects
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TIMBER defects
Teras rapuh (brittle heart)
Due to decaying fungi attack in the
middle of the stem
Pepusar/ bonggol (burl)
due to abnormal plant growth
Kegagalan Mampatan (Compression
Failure)
-due to a series of woven fibers are
damaged
-by compression stress during plant
growth
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TIMBER defects
Dry root
Wet rot / Decay
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TIMBER diseases
Drywood termites
Beetle
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TIMBER diseases
Powderpost beetleOld house borer
1) Oil type preservatives
the moisture content in timber should not be more than 14%.
applied over outside of exposed timber.
unpleasant smell.
not suitable when timber is to be painted.
examples; creosote, carbolinium, solignum, with or without admixture with petroleum or suitable oils.
2) Water soluble preservatives
moisture content of 20 to 30% is permissible.
Odor less organic or inorganic salts and adopted for inside location only.
examples of leachable type of preservatives; zinc chloride, boric acid(borax), etc.
the types of zinc chloride, sodium fluoride and sodium-pentachloro-phenate are toxic to fungi. These types are expensive and odourless.
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TIMBER treatment and curing
benzene-hexa-chloride is used as spray against
borers.
Boric acid is used against Lyctus borers and to
protect plywood in tea chests.
another type;
i) copper-chromate-arsenic composition.
ii) acid-cupric-chromate composition.
iii) chromate-zinc chloride composition.
iv) solvent treatment.
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TIMBER treatment and curing
3) Various treatment processes.
i) Surface application
by spraying, dipping or brushing the preservatives for a short period.
at least two coats should be applied.
the subsequent coats should not be applied until the first one has
dried or soaked into the wood.
used mostly for treating timber at site and re-treatment of cut
surfaces.
ii) Soaking treatment
submerging debarked timber in the preservatives solution for
sufficiently long period until the required absorption of the
preservative is obtained.
chapter 5
TIMBER treatment and curing
iii) Hot and cold process ensures sterilisation against fungi and insects.
the timber is submerged in the preservation solution which is heated to
about 90°C to 95°C and maintained at this temperature. Then allowed
to cool until the required absorption is obtained. During the heating
period, air in the timber expands and is partially expelled.
while cooling, the residual air in the timber creates a partial vacuum
which causes the preservative to be sucked into the timber.
generally, two baths are used. First-containing the water to prepare the
hot treatment. Second-cold bath-containing the preservatives into which
the timber is transferred immediately after heating.
this to solve the danger of precipitation of chemicals at high
temperature. Also helps to make the process continuous in case the
quantity of timber is large.
Timber Products
Veneers (lapisan)
thin sheet of wood
manufacture in various grades.
it popular to make a furniture, concrete
mould.
Plywood
it used in beam making
easily can make curve shape for
designing
Boards
two types namely particleboard and
fiberboards.
Wood in constructions
Timber can be used for structural and non-structural member in construction. For the structural purposes, the properties have to be in compliance with the MS 544 standard requirements.
For Furnitures
Leban, Gading, Jati and Arang trees are used.
always this wood small sizes and expensive.
For Bridge
i.e. Cengal, Resak, Merbau
normally this wood is used to build high structure and exposed to weather.
this wood is strong and soft even easy to work but expensive.
For houses
piling foundation : Bakau, Kempas and Keruing.
Mast(tiang kapal) : Balau Merah, Cengal, Keruing, Meranti Merah Tua.
door and window frame : Meranti Merah Muda, Meranti Kuning.
stair : Keruing, Kapor, Mengkulang.
floor : Bintangor, Sepetir, Cengal.
For columns Balau, Balau Merah, Cengal.
Timber Standard Testing
1) Specific gravity
2) Volumetric shrinkage and swelling
3) Static bending strength
4) Impact bending strength
5) Compressive strength
6) Tensile strength
7) Brittleness test
8) Moisture content
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For example, if the initial weight of the piece was 30.51g and its dry weight
22.60g, then the difference of 7.91g is the weight of moisture initially in the
piece and its initial moisture content would be:
(30.51 - 22.60)/22.60 x 100 = 7.91/22.60 x 100 = 35.0%
Alternatively the formula can be written:
Moisture content (%) = [(Initial weight/Dry weight) - 1 ] x 100
So that only the division sum needs to be carried out:
[(30.51/22.60) - 1] x 100 = 0.35 x 100 = 35.0 %
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