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LIFE IS BEAUTIFUL SO APPRECIATE IT

ASSALAMUALAIKUM & GOOD MORNING

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TIMBER

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Timber is one of the most popular material

in light construction because of :a) simplicity in fabrication

b) lightness

c) reusability

d) insulation from heat. sound & electricity

e) aesthetically pleasing appearance

f) resistance to oxidation, acid attack & salt

attack and salt water

g) environmental compatibility

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STRUCTURE OF WOOD

Cambium Layer

Bark

Pith

Annual Rings

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STRUCTURE OF WOOD

Bark is a thin, rough and dense covering

that surrounds the trunk.

Cambium is a thin (microscopic) layer ofwood cells exists inside the bark.

The growth of wood takes place continuously

under the bark in the cambium layer resulting

ring knowns as Annual ring.

Width of ring depends on the rate of growth

of the tree.

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Pith is the center of the log surrounded by

the annual rings. The number of rings approximately

represents the age of the tree.

Heartwood is the inner part of the trunk ismade of dead tissue which primary function is

to provide mechanical support to the tree.

Heartwood that is the older wood is darker,

drier and harder than the outer part.

Sapwood is the outer part and it contains

living cells.

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The trunk place the role to convey a solution

called sap to the leaves & also to supportthe

crow at such a height as to ensure a

sufficiency of air & light.

As one layer of woods succeeds another, the

cell in the layers die, cease to function for

food storage and only useful to give the tree

stiffness.

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Heartwood & Softwood

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Hardwood Trees

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Softwood Trees

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FACTORS AFFECTING STRENGTH OF

TIMBER Density

Moisture Content

Temperature

Grain structure

Position in tree Condition of growth

Defects

Creep

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DENSITY

Density of wood is defined as the mass or

weight per unit volume.

Moisture in wood has a very large effect onthe specific gravity as well as the density.

Timbers of young tree has a very low density,therefore reduced stresses used for suchmaterial.

Weight of timber reduced by drying while

most strength properties are increased.

The higher the density, so the higher itsmechanical properties.

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MOISTURE CONTENT

Moisture content in a living tree varies withthe species.

Even in the same species, variation in moisture

content depends on the age & size of the tree

and its location.

Mechanical properties of wood influenced by

moisture content but modulus elasticity is less

affected by changes in moisture

Strength of wood increase as the moisture

content decreases

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Moisture content determined by oven-dry

method or by electric moisture-metermethod

Drying of timber from the green condition

as cut to constructional usable content ofsay, 18% moisture content will cause

shrinkage.

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TEMPERATURE

Strength of timber decreases, togetherwith increasing temperature

Permanent loss of strength may happen if

wood is held at high temperature for a longperiod.

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POSITION IN TREE

In the early trees life, wood often tends to

become stronger with increasing distance

from the pith

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CONDITION OF GROWTH

Environmental factor such as height above

the sea level, temperature, type of soil,

rainfall, spacing between the trees have

effect on the strength of the properties ofthe timber

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DEFECTS

Common defect are cracks, knots and slopeof grain and occur principally during the

growing period and the drying process.

It can be classified:a) knots

b) shake

c) split

d) check

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Knots

It is a cross-section or longitudinal sectionof a branch that was cut with the lumber

It could affect the mechanical properties ofwood

Also allow stress concentration to occur

Effect of knots depends on their position inthe section.

Knots are harder, denser and possessdifferent shrinkage characteristics thanthose of wood tissue.

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Live Knots Dead Knots

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Shake

Shakes are lengthwise separations in thewood occurring between and parallel toannual rings

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Split

Its a complete separation of wood fibersusually at the ends, throughout the

thickness of lumber and parallel to the fiber

direction.

could affect the durability of timber.

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Check

Its a lengthwise separation of woodoccurring across or through the annual ring

usually as a result of seasoning.

It can occur anywhere on a piece oflumber.

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TIMBER DEFECTS

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DECAY or DESTRUCTION

Decay is a decomposition of the woodsubstances caused by fungi

Wood suffered fungal attack can becomes

brittle or weak.Destruction is done by insects or marine

borers

Termites normally found in warmer climates &wood beetles in conditions of high humidity

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WORK HARD AND ACHIEVE YOUR GOAL IN LIFE

TRY TO UNDERSTAND AND AVOID MEMORIZING NOTES