TIMBER

Any wood which is used in engineering construction is termed as timber. Timber has been one of
the primary engineering construction materials since the earliest times.

Timber has several advantages over other construction materials. They are as follows:
i. Timber can be easily worked with tools of any size and can take good polish.
ii. It is comparatively stronger than other materials commonly used when considered in
proportion to weight.
iii. It can be used as both a load-bearing and non-load-bearing member in structures and
structural connections can be made very easily.
iv. Timber construction is very economical because even a small piece can be utilized in one
way or another, minimizing waste.
v. Its use for making furniture, sports goods and other decorative and attractive articles of
artistic design is quite important and is accepted universally without doubt.
vi. Timber has low thermal conductivity high electrical resistance and good soundproofing
property. All these have always contributed to its importance as a very useful building
material.
vii. Timber structures are unquestionably durable if properly treated and carefully from direct
exposure to weather, and alternate wet and dry conditions by applying preservatives.
viii. Various types of timber products, like Plywood, veneers, laminated boards and other
reconstructed woods are mostly used nowadays for their lightness and beauty.
ix. Another important feature of timber which is worth mentioning is that it has a great resale
value. The discarded timber can be utilized as fuel. Even sawdust can be utilized to make
reconstructed woods like hard boards, light-weight planks, partex boards, etc.

Moisture Content in Timber

Logs contain large amounts of water in the form of moisture. As the strength, durability and other
properties of timber depend upon the moisture content in it, it is necessary to know how much
moisture is present in the timber. The moisture content of a wood sample is determined from thin

Dr. Md Abdur Rashid Sarker, Associate Professor, Dept. of ACEE, SAU

pieces, whose broad surfaces are perpendicular to the grain of the wood, or from wood chips After
careful weighing, these are heated in an oven at approximately l00 oC (212 oF) until there is no
further loss of weight. The sample is taken out, cooled at room temperature and weighed again.
The loss of weight (moisture content) divided by the oven-dry weight expressed as percentage, is
known as the moisture content.

Loss of wt of the sample

Moisture Content (percent) = × 100
wt of oven dry sample

Measurement of Timber
The timber usually is measured in volume. The following are the various methods of measurement
of timber:
If d1 and d2 are the two end diameters of the log in inches and L is the length of the same in ft, the
volume of the log is given by the following expression:

(𝑑 +𝑑 + 𝑑 𝑑 )
Volume in cu. ft. = 0.2618 ×𝐿
144

Defects in Timber
A defect is any irregularity or imperfection in or on wood which may lower its strength, durability,
and utility. Defects are usually two types:
i. Natural defects due to abnormal growth and rupture of tissues and
ii. Artificial defects arising due to conversion and uses.

Natural Defects: Natural defects are (a) knots; (b) twisted fibers; (c) shakes; (d) upsets; (e) rind
galls (also known as burls or excrescences); (f) foxiness; (g) compression wood; and (h) pitch
pockets.
Artificial Defects: Artificial defects are (a) Warping; (b) Splitting and cracking; (c) defects due
to fungal action and (d) defects due to insects.

Dr. Md Abdur Rashid Sarker, Associate Professor, Dept. of ACEE, SAU

Seasoning of Timber
The seasoning or drying of timber frequently precedes its application for structural purposes. The
main purpose of seasoning is to dry sap and to reduce the moisture content of timber.
The following are the main objectives of seasoning timber:
i. Expelling water
ii. Reducing weight for transportation
iii. Create resistance to decay and deformation due to weather action.
iv. Suitable for cutting and using in work
v. Impart suitability for painting and polishing
Or:
i. To bring timber to a state of equilibrium moisture content this is essential for all subsequent
conversion and use.
ii. To reduce the weight of timber to facilitate transportation and handling.
iii. To make timber durable and more resistant to decay due to fungal action.
iv. To make timber strong, hard and stiff as unseasoned timber is weak and soft and more
vulnerable to decay.
v. To dry the sap and to reduce the moisture content to a certain degree to apply preservatives
on timber.
vi. To make timber more suited for polishing and painting.

Methods of Seasoning of Timber

The following are the principal methods of seasoning of timber:
i. Natural or Air Seasoning
ii. Artificial Seasoning (kiln seasoning, Chemical seasoning, Electrical seasoning,
Steaming, Boiling, Smoke seasoning)
iii. Water seasoning.

Natural or Air Seasoning

 This process of seasoning is also known as air drying. The natural seasoning is done by
long outdoor exposure of timber to the action of the air.

Dr. Md Abdur Rashid Sarker, Associate Professor, Dept. of ACEE, SAU

  The timbers are stacked in a dry elevated platform which is covered by a temporary shed
to protect timbers from the action of rain. Sometimes permanent shed is also erected for
the same.
 Timber is generally turned frequently to ensure equal drying all rounds, because irregular
drying causes splits and cracks.
 This is a very slow process and the time required varies from 2 to 3 years to remove the
moisture by evaporation to the desired extent. This method is commonly employed all over
Bangladesh

Artificial Seasoning
The drying of timber by exposure for a limited period to high temperatures in a closed chamber or
by applying chemicals, steam and smoke is termed artificial seasoning. The following are the
various methods of artificial seasoning.

(a) Kiln Seasoning

Two types of kilns are available for artificial seasoning:
(i) Compartment kiln in which the conditions of temperature and humidity are changed as
the drying progresses, the timber being stacked in the compartment, and
(ii) Progressive kiln in which a low temperature with high humidity condition is maintained
at the entering end of the kiln and a high temperature with low humidity condition at
the exit end, timber being moved periodically through the kiln.
 In kiln seasoning temperatures 70 to 82oC are usually employed. Softwoods generally
require 4 to 6 days and for hard wood it requires 6 to 12 days. This method is used in
Bangladesh.

(b) Chemical Seasoning

This is also known as salt seasoning. In this method, timber is first soaked in an aqueous solution
of a suitable chemical salt (usually, solution or urea) before it is passed through the process of kiln
seasoning. The vapour pressure of the salt solution is less and therefore, the interior moisture of
the timber is drawn out. The drying of timber from the center to the surface is at a uniform rate.
The drying process is also accelerated. The most commonly used chemical is urea. It is a very

Dr. Md Abdur Rashid Sarker, Associate Professor, Dept. of ACEE, SAU

good dehydrating agent and does not cause any harm to the seasoned timber. This method is not
generally used in our country.

(c) Electrical Seasoning

In this process, high-frequency alternating currents are passed through timber in a closed chamber
and the resistance caused by the passage of the currents produces heat which dries the timber. This
is a very quick process of seasoning but is not used in this country.

(d) Steaming
In this process, steam is passed through the stacked timber in a closed chamber and after that timber
is dried gradually in natural air. The steam is usually passed for 4 to 6 hours. This is a quick method
but it reduces the elasticity and strength of timber. This method is used in certain parts of this
country.

(e) Boiling
In this process, the timber is immersed in boiling water for a certain period. Thereafter, the timber
is dried slowly by natural air. This is also a quick process but it also reduces the elasticity and
strength of timber. This method is very rarely used in Bangladesh.

(f) Smoke Seasoning

This is a very old practice of drying timber in smoke heat over a fire of straw, sawdust and wood
savings. This method is claimed to be efficient in making timber more durable and resistant to
decaying agents. Heat is gradually applied to prevent splitting and warping. This method is very
frequently used in Bangladesh in boat-making industries.

3. Water Seasoning: In this process, timbers and logs are immersed and allowed to remain in the
water for a couple of days, thereafter they are dried in natural air. In this process, the sap is diluted
and is partly removed. This reduces the possibility of decay and increases the durability of timber.
Water seasoning timber also dries more quickly. This process of seasoning is good for timber
containing a lot of sap, but it reduces the strength of timber to some extent. This method is
commonly used all over Bangladesh.

Dr. Md Abdur Rashid Sarker, Associate Professor, Dept. of ACEE, SAU

Characteristics of Good Timber
The following are the characteristics of good timber:
i. It should be strong, stiff, tough and durable.
ii. It should be free from both natural and artificial defects.
iii. It should be radially sawn.
iv. The annual growth rings should be regular, uniform and closely spaced.
v. The colour should be uniform and lustrous. There should not be any sudden change in
colour as this would indicate a disease (defect) in timber. The dark uniform colour
usually indicates the strength and durability of timber.
vi. When struck with a hammer, timber should give a clear sound. A dull sound usually
indicates defects in timber.
vii. It should be obtained from the heart of a fully grown tree with straight and regular girth.
viii. The density of the timber should be high, because heavier timbers are always stronger
and more durable.
ix. It should have good workability.
x. It should be elastic because this property is necessary in timber used for carriage shafts,
bows, sports goods, etc.
xi. It should be resistant to compression because this property is needed when timber is
used as struts, piles, wheel spokes, posts, props, etc.
xii. It should be fire resistant, i.e., it should have low combustibility. Dense timber offers
greater resistance to fire than light and porous ones.
xiii. Timber should retain its shape during the period of use.

Uses of Timber
The following are the various uses of timber:
 Permanent structural works: Timbers used in permanent structural works are mainly of
two types:
i) Light structural members and
ii) Heavy structural members.

i) Light structural members

Dr. Md Abdur Rashid Sarker, Associate Professor, Dept. of ACEE, SAU

 Beams, posts, roof trusses, floor boards, door and window frames, and battens, railway
sleepers, bridge floorings, electric poles, fencing poles, gates, railings etc.

ii) Heavy structural members

 Piles, bridge piers, trestles foundation and superstructure, wood staves, stairs, etc.
 Furniture works: cots, beds, etc.
 Transportation works: For making country boats, launches, speed boats, ships, and body
frames of railway coaches and buses. For making jetties and landing platforms. Also used
for making cart-wheels.
 Temporary works during construction: Centering works (formworks) of all types in R.C.C.
construction works. For providing shoring and strutting to support the sides of soft soil
excavation. Timber is used for making packing boxes and pattern-making in foundry
castings.
 Commercial uses: Timber is used for manufacturing sport-goods, toys, and for making
veneers which are used in manufacturing plywood batten boards, laminated boards, etc.
and reconstructed wooden boards like insulating boards, hardboard, fiberboards, particle
boards, linoleum, etc.
 Industrial uses: Wood is used for the manufacture of matches, paper, newsprint, cardboard,
wallpaper, artificial synthetic fibers, roofing felt, preservatives, etc.
 Ornamental and Decorative Works: Timber is used for ornamental and decorative purposes
like table lamp holders, flower vases, ashtrays, cabinet partitions, interior decorative works,
etc.
 Miscellaneous Uses: For making utensils, bows, wheel spokes, shafts mallets, tool handles,
rollers, spindles, ploughs, tent pegs, weel-curbs, ladders, household fittings picture frames,
combs, brush backs, etc.

Dr. Md Abdur Rashid Sarker, Associate Professor, Dept. of ACEE, SAU