Introduction to civil engineering (timber) Note

2.  Wood suitable for building or other engineering
works is called timber
 When it forms a part of a living tree, it is called
standing timber
 When the tree has been felled, it is called rough
timber
 When it has been sawn to various market forms such
as beams, battens, planks etc, it is called converted
timber

3. Classification of Trees
Trees can be divied into the following groups
 Endogenous
 Exogenous

4. ENDOGENOUS:
 Trees which grows inward in a longitudinal fibrous
mass, such as canes, bamboo, palms etc
EXOGENOUS:
 Trees which grows outward from the centre in
approximate concentric rings across the longitudinal
section of the stem. Each ring representing a layer
deposited every year. Extensively used in engineering
works.

5. LOCAL TIMBER
 Types of Local Timber
 Hardwood
 Heavy Hardwood
 Medium Hardwood
 Leightweight harwood
 Softwood

6. Heavy Hardwood
Medium Hardwood

7. Lightweight Hardwood
Softwood

8. Classification of Wood-
Based Aspects of Botany,
Density, Durability and
Strength.

9. Group Name Density Durability and
Strenght
Heavy
Hardwood
Gred A
Cengal
Balau/
Selayan batu
Kekatong
Merbau
Resak
Tembusu
993kg/m3
1027kg/m3
847kg/m3
9.979N/mm2
11.38N/mm2
9.17N/mm2
4.9-11.45N/mm2
8.00N/mm2

10. Group Name Density Durability and
Strenght
Medium
Hardwood
Gred B
Kempas
Keruing
Kapur
Tualang
926kg/m3
926kg/m3
791kg/m3
875kg/m3
7.52N/mm2
4.34-9.17N/mm2
6.74N/mm2
8.0N/mm2

11. Group Name Density Durability and
Strenght
Lightweight
Hardwood
Gred C
Nyatuh
Jelutung
Meranti
Ramin
Sepetir
Kayu getah
758kg/m3
707kg/m3
657kg/m3
707kg/m3
2.65N/mm2
3.38N/mm2
5.93N/mm2
4.69N/mm2

12. Group Name Density Durability and
Strenght
Softwood
Gred D
Damar
minyak

13. Standard-Size Wood Production
Process
No. Name size
1.
2.
3.
4.
5.
6.
7.
Timber
Column
Beam
Plank
Batten
Small Batten
Strip board
Pieces of wood from the trees or
branches that are not sawn.
100 mm x 100 mm - 150 mm x 150 mm
Thickness> 100 mm x width> 150 mm
Thickness 12 mm - 37 mm x width> 150
mm
Thickness 37 mm - 100 mm <150 mm
Thickness 20 mm - 37 mm x 25 mm - 75
mm
Thickness <20 mm x width <100 mm

14. MATED OF SAWING TIMBER

16. Procedure for Drying / Seasoning
of Wood
 The process of removal of moisture content from wood
so as to make it useful for construction and other uses
 Wood must be dried up moisture content less than
15% then suitable for use in construction work
 The wood drying process is a step that must be done
before the wood can be used.

17. The purpose of drying
 increase the strength, durable and with good
work.
 reduce the likelihood of broken wood,
contracting and warping..
 prevent the wood from insects and fungi.
 weight, cost-effective delivery.
 More easy to preserving, painting and polishing.
 making it easier to burn, if used as firewood.

18. Naturally Drying Methods (
Pengeringan secara semulajadi )
 The traditional method of seasoning timber was to
stack it in air and let the heat of the atmosphere and
the natural air movement around the stacked timber
removes the moisture. The process has undergone a
number of refinements over the years that have made
it more efficient and reduced the quantity of wood
that was damaged by drying too quickly near the ends
in air seasoning.

19.  The basic principle is to stack the timber so that plenty
of air can circulate around each piece. The timber is
stacked with wide spaces between each piece
horizontally, and with strips of wood between each
layer ensuring that there is a vertical separation too.
 Air can then circulate around and through the stack, to
slowly remove moisture. In some cases, weights can be
placed on top of the stacks to prevent warping of the
timber as it dries.

20. Kiln Drying Methods

21.  Kiln drying of lumber is perhaps the most effective and
economical method available. Drying rates in a kiln
can be carefully controlled and defect losses reduced
to a minimum. Length of drying time is also greatly
reduced and is predictable so that dry lumber
inventories can often be reduced. Where staining is a
problem, kiln drying is often the only reasonable
method that can be used unless chemical dips are
employed.

22. WOOD PRESERVATION
Protecting products of timber from deterioration(
fungi) decomposition or damage due to pest attacks
Wood must have the following characteristics before
preservatives are applied to it:
 Wood must be well seasoned
 Wood must be cut to size before applying preservatives

23. There are 3 main classeses of
preservatives
 Oily substances insoluble in water
 Water – soluble salts
 Salts carried in volatile solvent other than water

24. Methods of Applying Wood
Preservatives
Painting & Dipping
 Simplest method
 Preservatives applied by mean of brush (several times)
 Timber can also be immersed in tank full of liquid
(preservative)
 Penetration should hardly exceed (1/16 inch)
 Duration of immersion and temperature of
preservative solution ►increased ►to increase
penetration

25. Pressure Process(Full Cell Process)
 A higher degree of penetration can be obtained by forcing
the preservative into the wood
 Timber placed inside a chamber
 Air drawn out to create a vacuum
 Thus the cells are completely (almost) empty to receive the
preservative
 Preservative material may be creosote oil or zinc chloride
 Preservatives pumped under a pressure of 100 to 200 psi at
120oF
 The excess preservative is removed by creating a low
vacuum
 Timber preserved by this method are used in piles in
saltish water, poles, sleeper

26.  The Empty Cell Process
 Similar to the full cell process but no initial vacuum is
created
 No attempt is made to remove the air from the cells
 The preservatives applied under a pressure of 200 psi
 The excess preservatives drains away
 A deeper penetration of preservatives ►achieved

27. Wood defects:
 Defects in wood can be broadly classified into two
categories which are as follows:
(A) NATURAL DEFECTS (Knots, Shakes, Cross grain,
Compression)
(B) OTHER THAN NATURAL DEFECTS ( External
Factors )

28.  Definition of Natural Defects
Natural defects are defects that occur within the growing
tree and which can infl uence the strength and visual
appearance of the surface of the timber. They are
sometimes referred to as structural defects.
Most structural or natural defects have little effect on the
growing tree, but they can degrade the timber cut from
it.
Not all trees are suitable for structural use and those that
are must conform to certainquality checks before it is
acceptable for use in the building industry.

29. Structural defects
 Knots.
 Shakes.
 Waney edge.
 Encased bark.
 Growth rate.
 Resin pockets.
There are other defects, which will effect the use and
acceptability of timber. These defects are usually the
result of incorrect seasoning methods or fungal and
insect attack.

31.  Knots
Knots are formed as a result of the tree’s habit of
forming branches. All branches are an integral
part of the trunk of the tree, and when the tree is
cut and converted into timber, the branches are
exposed on the faces of the timber.
There are two kinds of knots:
 Live knots.
 Dead knots.

32.  Live knots
Live knots are knots which are bonded into the
surrounding wood. They are tightly encased and do not
contain any rot or dead wood.
 Dead knots
Dead knots are knots which separated from the surrounding
wood by the bark of the branch which once protected it. They
are usually the result of damaged branches which have died
and become encased within the trunk over the years. Very
often some of these knots become loose in their sockets and
are known as ‘loose dead knots’. These types of knots are a
potential hazard when machining timber as they often
disintegrated and fl y out of the machine, sometimes causing
injury to the eyes.

35.  Shakes
Shakes are large cracks (a parting of the wood
tissue) in the log caused by uneven stresses being
set up, which may increase as the timber dries.
Shakes follow the two main directions of
weakness in the timber:
 Between the growth rings.
 Along the line of the rays.
Shakes occur in:
 The growing tree.
 At the time of felling.
 During drying or seasoning.

36. There are two main types of shakes.
 Heart or star shake.
 Ring or cup shake.
 Heart shake
Wood tissue separates due to uneven stress forming a
crack.
 Star shake
This occurs where several shakes radiate from the
centre region.
 Ring or cup shake
This type of shake follows the line of the growth ring.
The split occurs between two growthring and is the
result of uncontrolled seasoning.

38.  External Factors
Types of external defects:
(a) Warping: The distortion in converted timber caused
departure from its original plane usually during seasoning period
is called warping. Warping can be culping, bowing, twist, string.
(b) Check, Split and Shakes: These are the examples of
separation or ruptures of the wood along the grain. These three
forms differ in whether the crack is confined to the interior of the
wood or extends to the surface.
(c) Stain: Fungi causing stain in wood, when it feeds only on
food materials stored in the sapwood. In this case, fungi do not
attack the heart wood which normally does not contain food
material within the cell. Stain defect does not affect strength
properties of wood. For example: Ceratocystis.

39. (d) Decay: This is observed due to wood destroying
or wood rotting fungus of wood. These fungi nourish
cell wall material and break down the cell structure
and enzymatic activities. Decay fungi attack both
sapwood and heartwood. This defect reduces the
strength properties of wood.
(e) Insects: Insects borers and termites together
constitute one of the most destructive biological
agencies causing defects in timber. Some insects infest
standing trees others infest felled logs before
conversion or converted timber. The damage is visible
in the form of tunnels and wood dust packed galleries
in timber.

40. Wood defects:
 Knots ( buku )
 Slope of grain ( ira serong )
 Wane (ira menurun )
 Shake (rekah)
 Splits and cracks ( terbelah dan retak )
 Insect attact
 Decay ( reput )

45. Wood production
 Plywood
 Particle board
 Fiber board
- softboard
- MDF
- hardboard

46. Wood finishing
Wood finishing refers to the process of
embellishment and protecting the
surface of a wooden material.

47. Types And use Of Wood
Finishing
 Wax – a finish that is commonly used as the final layer
for a smooth, flat and shiny.
 Shellac - is the most commonly finishers used on
wood. Shellac is a natural resin produced from insect
called lac bug excrement.
 Lacquer – consisting of resin types ( nitro-cellulose )
its is transparent, quick dry , lacquer is dissolved with
thinner.
 Paint – Liquid paint binder containing materials and
natural immune and smooth.

48. Types of Solvents And Its Use
 Turpentine – to dissolve the paint and cleaning
 Spirit – as a solvent to dissolve shellac
 Thinner – to dissolve the paint
 Kerosene – to dissolve lacquer

49. Wood Joints
 What is a joint?
A joint is the juncture of two pieces of wood that are
connected together. The connection may be made by
fasteners, like screws or nails, by glue, by interlocking
parts, or by any combination of these. A joint may
stand on its own, or may be reinforced by hardware,
glue blocks, dowels, biscuits or other methods.

50.  Names of joints
As with most things, a joint may have more than one
name. People in different trades often use different
names for the same joint. People from different places
sometimes have different names for the same joint.
The names used here are common to cabinet and
furniture makers.

51.  Strength of joints
 In evaluating the strength of a joint you should
consider the following:
1. If the joint is secured by mechanical fasteners, a joint
that positions the fasteners so that the main force on
them is a shearing force will be stronger.
2. If the joint is secured by glue, a joint with more
gluing surface will be stronger, as long as increasing
the gluing surface doesn't decrease the size of the
members too much.
3. A locking joint is one that interlocks mechanically,
so that separating the members in at least one
direction requires actually breaking one of the
members. Locking joints are generally stronger than
non-locking joints.

52.  Butt Joints
 Mortise and Tenon Joints
 Dado Joints
 Rabbet joints
 Dovetail Joints
 Splice Joints
 Edge Joints
 Other Joints
 Lap Joints
 Miter Joints

53. Butt joints

54. Lap or halved joints

55. Tee half joint

56. Mitre joints

57. Rebate joints

58. Stopped rebate joint

59. Tongue and groove joints

60. Tenon and mortise joints

61. Dovetail joints