Timber Note ( Btech- Civil Engineering Materials)

1. Civil Engineering Material
Presented by : Er. Jayant Chaudhary
MTech – Structural Engineering
MANMOHAN TECHNICAL UNIVERSITY
SCHOOL OF ENGINEERING
2nd Semester

2. TIMBER
• 4.1. Characteristics of good timber
• 4.2. Properties and uses
• 4.3. Seasoning of timber
• 4.4. Different methods for seasoning of timber
• 4.5. Common defects
• 4.6. Treatment of timber
• 4.7. Strength requirements
• 4.8. Commonly used timber for building construction in Nepal

3. INTRODUCTION
Hard and fibrous substance which forms a major part of the
trunk and branches of a tree is known as Wood. The wood
that is used for engineering purpose is called Timber.
Benefits of timber: -
• Efficient and fast installation
• Environment friendly
• Easy to craft with hand
• High salvage value
• Superior in thermal insulation, sound absorption and
electrical resistance
• High strength / weight ratio
Disadvantage : -
• Decay
• Readily combustible
• Variation in strength
• Moisture changes

5. FORMWORK
BEAM
COLUMN
SHEAR WALL

9. CHIR PINES DEODAR

10. TAEK SAL

11. SHISHUM

17. Characteristics of good timber
The principal characteristics of timber of concern are strength,
durability and finished appearance.
1. Obtained from heartwood area of tree and free from sap.
2. Narrow annual rings, closer the rings greater is the strength.
3. Compact medullary rays.
4. Dark uniform colour with uniform texture.
5. Sweet smell and a shining fresh cut surface.
6. When struck sonorous sound is produced.
7. Free from the defects in timber.
8. Heavy weight.
9. Low water permeability.
10.No woolliness at fresh cut surface.
11.Durable

18. Commonly used Timber in Nepal / Uses of Timber
Some of the examples are : -
1. Teak - high-end furniture, boat building,
2. Sal - furniture, bridge building, and railway sleepers.
3. Sissoo - furniture, flooring.
4. Deodar - furniture, and carving.
5. Pine - furniture, plywood .
6. Fir - plywood
7. Ash - used for sports equipment, tool handles, and furniture.
8. Yew - furniture, and carving.
9. Maple - used for flooring, furniture, and paneling.
10.Oak - used for flooring, furniture, and construction.
11.Chestnut - used for fence posts, furniture, and paneling.
12.Walnut - used for furniture, cabinetry, and decorative veneers.
13.Laurel - used for construction, furniture, and carving.
14.Magnolia - used for construction, furniture, and cabinetry.
15.Bamboo - used for scaffolding and other temporary structures.
16.Mango - cheap furniture, toys, cabinet works.
17.Kail - for making match boxes.
18.Benteak - for boats

27. SEASONING OF TIMBER
• Seasoning of timber is the process of reducing
or drying the moisture present in timber at
almost controlled condition to prevent the
timber from possible fermentation.
Objective of seasoning
• To prevent shrinkage, warping and cracking of
timber.
• To maintain the shape and size of timber.
• To reduce the weight of timber.
• To increase strength, durability and workability
of dimensional stability.
• Make it suitable for painting and applying
preservatives.
• To protect the timber from attack of insects,
vegetable growth,etc.
• To prevent possible fermentation of wood.

29. Air Seasoning
• Stacking of timber with free circulation of air.
• Cheap and simple.
• protected from direct sunlight and rain water by
constructing roof.
• Rate of drying is vey slow.
• Minimum 6 month or 2 to 4 years to dry out completely
depend on timber moisture content.
• It reduces the moisture content of the wood to 12-15%.
• It makes timber durable, tough and elastic.
• It is highly economical,
• Timber is likely to be attacked by insects and fungi.

30. Water seasoning
• When the log are placed in running water, the sap
from the cell can be easily washed out.
• In place of sap, the cell get filled with ordinary water.
• When such logs are taken out and placed for air
seasoning. It takes comparatively less time to become
dry.
• It takes 2 to 4 weeks to dry.
• Placing the log in water also saves them from unequal
shrinkage.
• Drying is uniform and chance of cracking and
warping is reduced.
• Elasticity and durability of timber is reduced. The
timber is rendered brittle.

31. Kiln seasoning
• This is the modern method of seasoning any type of timber
in short time.
• In this method timber is kept in a airtight chamber which
involves drying the timber in a specially designed kiln where
there is perfect control over temperature, humidiy and air
circulation.
• Initially the kiln is heated at low temperature, to avoid
cracking or splitting of timber and then gradually increase
the temperature.
• Fully saturated air (100% relative humidity) is passed at 35°C
to 38°C.
• It is a quick process. Wood takes between 4 days and a
week to be dried with this method.
• Moisture content can be reduced to any desired level.
• Stacking space required is less than the air drying.
• Less liable to attack of insects and fungi.
• Strength and dimensional stability is increased.
• It is costly process.
• Requires expert handling.

32. Seasoning by boiling
• A quick method of removing sap from
within the cells.
• Immersed in water and water is heated to
boiling temperature.
• Boiling for 4 to 5 hours.
• Sap is washed out,
• On placing in air such treated timber dries
quickly.
• Shrinkage is reduced but strength and
elasticity is also reduced.
• Hence, this method is rarely used.

33. Chemical seasoning
• Timber is treated with a chemical solution
like sodium chloride, sodium nitrate or Urea,
etc.
• such solution reduces the vapor pressure
on the surface of application.
• once such timber is exposed to natural
drying, it is the water form the inner cell
that moves to outer cell at lower vapor
pressure.
• It sets up vapour pressure gradient
between the inner and outer portion of
timber and causes uniform drying.
• Chemical seasoning enables the
timber to dry first from inside.
• Costly process
• Not attacked by insects and fungi

34. Electrical seasoning
• Dry wood is a bad conductor of electricity.
• But when a high alternating current is passed through
a piece of green timber, heat generated is enough to
dry out the moisture of the cell which do conduct
some electricity.
• In, this way the timber piece are dried quickly. The
time required is 5 to 8 hours.
• It is the most rapid method.
• Superior quality of timber can be obtained.
• This techniques involve costly equipments and even
the consumption of electricity is so high that the
process is uneconomical.
• Fibers of timber may split.

35. Treatment of Timber:
• It is done to increase the life of timber.
• To make more durable.
• To protect if from fungi, insects, etc.
• It doesn’t increase strength and doesn’t remove moisture.
Types of preservatives : -
• Cu treatment
• Chemical salts
• Coal tar
• Oil paints
• Acetic Anhydride Treatment

36. 1. As Cu treatment
• 1 part - Arsenic pentoxide (As2O5.2H2O)
• 3 part - Copper sulphate (CuSO4.5H2O)
• 4part - Potassium dichromate (Na2Cr2CO7 or
K2Cr2CO7)
• This solution is used to protect from white ants.
• 6 parts solution + 100 parts water = sprayed uniformly
over the timber surface.
• The timber is then allowed to dry for 6 weeks.
2. Chemical salts
• CuSO4, Nacl, NaF, etc applied over the timber
• To protect it from decay, insects, and fire.

37. 3. Coal tar
• Timber surface coated with coal tar
• Fire resistant
• unpleasant smell
• unsuitable for painting
• This is preferred in the wooden poles to be embedded in the
ground and parts of door and window frame to be built in the wall.
• However, the use of coal tar in the treatment of timber has
declined in recent years due to its carcinogenic effect.

38. 4. Creosote oil
• It is tar oil type (distillation of tar).
• It works as an antiseptic and poisonous for wood attacking fungi.
• Highly unpleasant smell.
5. Oil Paints
• 2 to 3 coats of oil paints are applied.
• Especially, solignum paint, mixed with colour pigments and
applied in hot state with brush.
• Preserve from white ants and are highly toxic.
• Preserve from moisture and make it durable.
• Dries much slower and provides a smoother finish
6. Acetic Anhydride Treatment
• It is used for protection of veneers, plywood
• minimises swelling and improves resistance to decay and attack by insects.