Chittagong University

Department of Water
of Engineering &
Resources Engineering
Technology

CE-281
Engineering Materials

Sumaya Sadia Toha

Lecturer
Department of Civil Engineering
Timber
1. Denotes structural wood obtained
from tree
2. A standing tree is called standing
timber
3. When a tree has been cut and its
stems and branches are roughly
converted into pieces of suitable
lengths, it is known as rough
timber
4. When a roughly converted timber
is further sawn and converted into
commercial size, such as: plank,
logs, batten, post, beam, etc., it is
called converted timber
Difference Between Wood &
Timber
➢Wood includes all types of wood
which may be burning wood,
structural wood, furniture wood,
etc.
➢However, wood used as a
structural material is called timber
 Advantages of Using Timber
1. Easily available everywhere
2. High salvage value
3. Can be transported easily by converting into small
commercial sizes
4. Working with timber (i.e., repairing, alteration,
addition, etc.) is easy
5. Can be easily jointed
6. Not corroded (so, it can be used in marine works)
7. Light weight
8. Withstands shocks better than iron and concrete
9. Good insulator of heat and electricity
10. Good sound absorbing material
Classification of Trees
Classification of Trees

Evergreen
Trees/Conifers
Exogenous Trees

Deciduous Trees

Endogenous Trees
Exogenous Trees
➢These trees increase in bulk by the formation
of successive annual rings radially on the
outside under the bark
➢Every year a new ring is added to the tree
section
➢Age of tree can be determined from the
number of annual rings
➢Used for engineering purposes
 Evergreen Trees
/Conifers

Having pointed needle-like leaves bearing

cone-shaped fruits
Exogenous
Trees
Yield softwood

Examples: Pines, Fur, Kail, Ceder, Chir,

Deodar and Cypress Trees
Pine Tress
Ceder Trees
 Deciduous Trees

Having flat broad leaves, which fall in

autumn and new leaves appear in spring Exogenous
Trees
Yield hardwood

Examples: Oak, Mehogany, Teak, Sal,

Gorjon, Chambal, Telsu, Nageshwar, etc.
Mehogany
Trees
Endogenous Trees
➢These trees grow inward by depositing each
fresh layer internally.
➢Thus, the older formations/layers of wood
material are on the outside
➢They grow vertically in a fashion that the
links (approx. annual growth) placed end-to-
end with knot connecting two adjacent links
➢Example: Bamboo, Palm, etc
Endogenous Trees
Endogenous Trees
 Hardwood & Softwood

Hardwood Softwood

Conifers (needle-leafed trees) yield

Broad-leaved trees yield softwood
hardwood
Softwoods are comparatively less
dense, lighter in color
Hardwoods are dense with They are not very strong but are soft
having narrow and well- with straight grains
defined annual rings
Softwoods have more uniformity of
structure than hardwoods
 Elements of Timber Section
Pith
➢Central part
➢Dark colored
➢Consists of cellular tissues and nourishes the
plant in its young age
➢In old age, the pith dries up and decays
➢Sap is transmitted by fibers deposited round
the pith
 Elements of Timber Section

Cambium Layer
A thin layer of sap lying between sapwood and the
inner bark
It is full of sap which is yet to convert into
sapwood
This is very sensitive layer
If it is exposed by removing the bark, cell stopped
transmitting sap into the inner part and the tree dies
Elements of
Timber Section
Medullar Ray
➢These are thin radial fibers, extending from
cambium layer right up to pith
➢ These rays help in holding together annual
rings of both heartwood and sapwood
➢They may be continuous but mostly they are
broken
Elements of
Timber Section
Heartwood
➢Dark colored portion of the tree surrounding
the pith
➢Almost dead portion of tree and does not
take active part in its growth
➢It provides strongest and durable timber for
various engineering purposes
 Elements of Timber Section
Sapwood
➢Light colored wood lying between heartwood
and cambium layer
➢Light in weight and is of recent growth
containing a lot of sap
➢This is the active part of the wood and thus
helps in growth in the tree
Felling of Trees
Cutting of trees in order to get timber from them
is called felling of timber

The facts Age of Trees

considered while
felling trees
Season of Felling
Felling of Trees
Season of Felling
➢Trees should be cut only when sap is not
active, i.e., in mid-summer and mid-winter
➢In autumn and spring sap is in vigorous
motion, hence felling should be avoided
➢For hilly region, mid-summer and for plain
areas, mid-winter are proper seasons for
felling trees
Felling of Trees
➢Trees should be felled only when it has just
attained maturity
➢Under-aged trees would yield more of
sapwood, while over-aged trees develop
certain defects in heartwood
 ➢Felling should be entrusted to an experienced
person
➢Before felling, slope of the tree is assessed
and cut is given to the stem on the side of the
slope of the tree, as near to the ground as
Method of possible. Then cut is made on the opposite
side of the slope to fell the tree
Felling Trees
➢If tree is to be felled against the direction of
the slope, ropes are tied to the tree and pulled
to the direction of felling by giving suitable
cut to the stem
Conversion of
Timbers
1. The process by which timber is cut and
sawn into suitable marketable sizes is
known as conversion of timber
2. After felling, stems and branches of trees
are cut into logs of suitable lengths
3. The logs are then transported to the saw-
mill and converted into marketable
sections (i.e., planks, battens, beams, etc.)
 Conversion of
Felled Timber trees
1. Log
2. Lumber
3. Squared Timber
4. Plank
5. Deal
6. Batten
7. Board
8. Scantlings
9. Poles
 Sawing of Timbers

Ordinary Sawing or Cross Sawing

Radial or Rift Sawing

Tangential or Slash Sawing

Quarter Sawing

Combination Sawing
 Wastage of Timber for Sawing

➢Bark – 05%
➢Side Trimming – 18%
➢Saw Dust – 12%
➢Loss of Moisture – 5%
 Defects In Timber
NATURAL DEFECTS ARTIFICIAL DEFECTS
1. Knots 1. Warping
2. Twisted Fiber 2. Splitting & Cracking
3. Shakes 3. Defects Due to Fungal action
4. Upsets 4. Defects Due to Insects
5. Rind Galls
6. Foxiness
7. Compression Wood
 Seasoning of Timbers

The process of removing surplus

moisture (in excess of
equilibrium moisture content)
from freshly converted timber is
seasoning
 Advantages of Seasoning
➢Seasoned timber is light
➢Improves strength properties
➢Easy to transport and handle
➢Timber less liable to be attacked by fungus and insects
➢Reduces the tendency to shrink and warp
➢Can easily be worked with
➢A seasoned timber maintains the shape of timber article
unchanged
Methods of Seasoning

Natural Seasoning

Artificial Seasoning

Water Seasoning
 Natural Seasoning

❖After felling, timbers are sawn into commercial sizes

❖They are stacked under covered shed
❖Sufficient space is left around each sawn piece for free air-
circulation
❖Also known as air seasoning; natural air remains
circulating around each piece of the stack and in due course
of time, seasoning is brought about
 Natural Seasoning

Advantages

No skilled supervision is
required

Simple and cheap method of

seasoning

Thick section can be

successfully seasoned
 Natural Seasoning

Disadvantages
1. Since depends on natural air, no control can be exercised
over it
2. Slow method; depends on climatic conditions, size and
shape of the timber
3. Seasoning non uniform and uneven
4. Requires large space
5. Moisture cannot be brought to the desired level
6. Seasoned timber may have end split
7. Liable to be attacked by fungus and insects
 Artificial Seasoning

The drying of timber by exposure to high temperatures in a

closed chamber or by applying chemicals, steam and smoke is
termed as artificial seasoning
 Artificial Seasoning
Advantages
➢Rate of drying can be regulated
➢No chance of timber being attacked by fungus and insects
➢Takes short time
➢Desired moisture content can be attained during seasoning
➢Better control of air, temperature and humidity
➢Seasoning more uniform
➢No end splits
Methods of Artificial Seasoning

Smoking Kiln Seasoning

Boiling Chemical Seasoning

Steaming Electrical Seasoning

 Water Seasoning

➢Timbers and logs are immersed and allowed to remain in

water for a couple of days
➢Then dried in natural air.
➢In this process, the sap is diluted and is partly removed
 Characteristics of Good Timber
1. It should be strong, stiff, tough and durable.
2. It should be free from both natural and artificial defects
3. It should be radially sawn.
4. The annual growth rings should be regular, uniform and closely spaced.
5. 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. Dark uniform colour usually indicate strength and durabiliy of
timber.
6. When struck with a hammer, timber should give a clear sound. A dull
sound usually indicates in timber.
7. It should be obtained from the heart to a fully grown tres with straingth
and regular girth.
 Characteristics of Good Timber
8. The density of the timber should be high because heavier timbers are
always stronger and durable
9. It should have a good workability.
10. It should be elastic because this property is necessary in timber used
for carriage shafts, bows, sport goods etc.
11. It should be resistant to compression because this property is needed
when timber is used as struts, piles wheel spokes, posts, props, etc.
12. It should be fire resistant, ie.it should have low combustibility. A
dense timber offers greater resistance to fire than light and porous
one,
13. Timber should retain its shapes during the period of use
 Decay or Disease of Timber

Occurs due to fungal action

The fungi feeds on softwood and converts it into

powder

Decay does not occur either due to any chemical

action or due to fermentation of sap
 Decay or Disease of Timber

Alternate dry and wet conditions

Defective seasoning of timber

Main Causes of Presence of fungi and insects such

as marine borer, beetles, termite,
Timber Decay etc.

Lack of ventilation

Dark and damp condition

 Timber Rots
It is a sort of timber decay
During rot, disintegration of timber takes place and gases like
H2S and CO2 are generated

Dry Rot
Rot Types
Wet Rot
 Dry Rot
Disintegration of converted timber by the harmful effects of
certain fungi, which feeds on timber and converts it into dry
powder
Factors responsible are the same as those responsible for
decay
If some timbers are affected by dry rot, the best way is to cut
the affected portion
Dry rot may be prevented by using well-seasoned timber free
from sap, and the timber should be adequately ventilated by
fresh air
Detection: by tapping or scratching at one end and placing
the ear at the other end of log
 Wet Rot
It is the decomposition of timber caused by moisture
It is caused if alternate dry and wet conditions prevail around
the timber
Not caused by fungal attack
When unseasoned timbers are exposed to rain and wind, they
are liable to be attacked by wet rot
In wet rot, the timbers get converted into grayish brown
powder
Can be prevented by using well-seasoned timber; also using
tarred or painted timbers exposing to rain or water
 Preservation of Timber

Preservation indicates an increase in life by developing

resistance to insect attack, fungal infection and disease of
timbers
A preservative acts like a disinfectant
A seasoned timber, since dried, is hygroscope and to prevent
re-absorption of moisture and to impart immunity, the tissues
of dry/seasoned wood have to be soaked with some types of
preservatives
Seasoning, therefore, prepares a timber for preservative
treatment by driving away moisture and sap
 Preservation of Timber
i. Their toxicity and poisonous effects
ii. Permanency in their effect in treated
Choice of wood
Preservative iii. Should not be injurious to wood
is governed tissues
by iv. Cheaply available and safe to handle
v. Should allow a decorative treatment
vi. Should not disfigure exposed surface
of timber
vii. Non-inflammable
viii. Should have a good covering quality
 Methods of Preservation
1. Pressure Process
2. Non-Pressure Process( Hot & Cold Bath Treatment )
3. Superficial Process ( Painting By Preservatives )
4. Dipping Process ( Submerging in Tank)
 Artificial Wood

Veneer
Thin sheets of timber of superior quality
Obtained by rotating wooden logs of the timber against a sharp
knife of rotary cutter
Thickness 0.4 to 6.0 mm or even more
After removing from parent logs, they are dried in kiln to remove
moisture
Used for manufacturing of plywood
 Artificial Wood

Plywood
➢ Made from multiple veneers
➢ Veneers are taken in odd numbers and are placed one
above the other at right angles in successive veneers
➢ All veneers held together with the help of adhesives
➢ 3-ply, 5-ply, 7-ply, etc. are available; that is, veneers
are used in odd numbers in a plywood
 Artificial Wood

Advantages of Plywood

➢Suffers little expansion or shrinkage due to change in

moisture content
➢Light and available in large sizes
➢Available in decorative designs
➢Not liable to split and cracks
➢Easy to work with
➢Make use of costly timber in most economical manner
Laminated Board
Batten Board
Partex Board
 Important Varieties of Timber Available
in Bangladesh
1. Teak or Segun
2. Sal
3. Garjan
4. Gazari
5. Jarul
6. Sundari
7. Shisso
8. Shiris
9. Simul
10. Babul
11. Gamhari
 Important Foreign Timbers Imported in
Bangladesh
1. Burma Teak
2. Iron Wood
3. Pynkado
4. Mahogany
5. Pine
6. Ash
7. Hickory
8. Oak