BAA1312 : Engineering Material : Timber

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BAA1312 Engineering Material Timber
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How many legs do you see
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BAA1312 Engineering Material
Todays objectives

• Able to identify the structure of wood
• Able to identify the type of woods
• Able to explain the factors affecting the
  strength of timber

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BAA1312 Engineering Material
An Introduction Timber

• One of the earliest materials to be used in
  building.
• Still continues to play a major part in general
  building, particularly in furniture industry.
• Building parts such as Window Frame, Door Frame,
  Trusses, Wall Panel, Flooring etc using timber
  still in used.

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BAA1312 Engineering Material
An Introduction Timber (contd)
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BAA1312 Engineering Material
An Introduction Timber (contd)
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BAA1312 Engineering Material
An Introduction Timber (contd)

• Popular material in light construction because of
  
• simplicity in fabrication
• lightness
• reusability
• insulation from heat. sound electricity
• aesthetically pleasing appearance
• resistance to oxidation, acid attack salt
  attack and salt water
• environmental compatibility

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BAA1312 Engineering Material
An Introduction Timber (contd)

• Some problem associated with the used of timber
  are
• The material may be very variable due to natural
  defect.
• Possible distortion when its moisture content
  changes.
• Fungal and insect attack
• Not good as fire resistant
• Easy to creep under load

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BAA1312 Engineering Material
An Introduction Timber (contd)

• Nevertheless, with careful selection and
  appropriate use, timber and timber products
  constitute a very valuable range of building
  materials.
• But, Environmental consideration must taken into
  account

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BAA1312 Engineering Material
An Introduction Timber (contd)

• Root System The function
• Absorbing mineral transfer via the trunk to the
  crown
• as a anchorage or foundation to withstand wind
  force

• Growth Structure

• Crown The function
• Provide a large catchment area

• Trunk The function
• Provides rigidity, mechanical strength and
  height to maintain the crown at level above
  ground.
• Protects the growth cells and provides a two way
  transport system

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BAA1312 Engineering Material

• Annual Rings
• the growth of wood takes
• place continuously under
• the bark in the cambium
• layer resulting ring
• Width of ring depends
• on the rate of growth
• of the tree.

An Introduction Structure of Wood
Cambium Layer thin (microscopic) layer of wood
cells exists inside the bark
Bark a thin, rough and dense covering that
surrounds the trunk
Pith the center of the log surrounded by the
annual rings

• The number of rings approximately represents the
  age of the tree

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BAA1312 Engineering Material
An Introduction Structure of Wood (contd)
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BAA1312 Engineering Material
An Introduction Structure of Wood (contd)
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BAA1312 Engineering Material
An Introduction Structure of Wood (contd)

• Sapwood is the outer part and it contains
  living cells.
• The trunk place the role to convey a solution
  called sap to the leaves also to support the
  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.

• Heartwood is the inner part of the trunk is
  made 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.

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BAA1312 Engineering Material
An Introduction Type of Woods

• Hardwood
• Softwood

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BAA1312 Engineering Material
An Introduction Type of Woods - Hardwood
(contd)
Hardwood - trees with broad leaves that are shed
in winter Kayu Keras - Berdaun lebar dan
mempunyai biji benih berkulit - Contoh ???
- Mahogany, oak, maple, redwood, Teak, Keruing,
Jarrah
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BAA1312 Engineering Material
An Introduction Type of Woods - Softwood
(contd)

• Softwood - Any species that have needlelike
  leaves and that are generally
• evergreen.
• Kayu Lampung
• Berbentuk kon, daun berbentuk jejarum dan biji
  benih tidak berkulit
• Contoh ????

- pine, pokok getah,
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BAA1312 Engineering Material
An Introduction Characteristics of Timber

• Strength of timber is affected by various of
  factors

• Density - Ketumpatan
• Moisture Content - Kandungan Lembapan
• Temperature - Suhu
• Grain structure - Struktur ira
• Condition of growth - Keadaan pertumbuhan
• Position in tree - Kedudukan
• Defects - Kecacatan

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BAA1312 Engineering Material
An Introduction Characteristics of Timber
(contd) Factors affecting Timber Strength

• Density

• Density of wood is defined as the mass or weight
  per unit volume (kg/m3)
• Hardwood density range over 880 kg/m3, while for
  softwood below 720kg/m3.
• Timbers of young tree has a very low density
• Weight of timber reduced by drying while most
  strength properties are increased.
• The higher the density, so the higher its
  mechanical properties such as their stress and
  strength.

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BAA1312 Engineering Material
An Introduction Characteristics of Timber
(contd) Factors affecting Timber Strength

• Moisture Content

• Moisture content in a living tree varies with
  the 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
• Moisture content determined by oven-dry method or
  by electric moisture-meter method
• Moisture content mass of water present in as
  sample x 100
• mass of that sample when oven dry

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BAA1312 Engineering Material
An Introduction Characteristics of Timber
(contd) Factors affecting Timber Strength

• Temperature

• Strength of timber decreases, together with
  increasing temperature
• Permanent loss of strength may happen if wood is
  held at high temperature for a long period.

• 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 of the timber

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BAA1312 Engineering Material
An Introduction Characteristics of Timber
(contd) Factors affecting Timber Strength

• Defects

• Common defect are cracks, knots and slope of
  grain and occur principally during the growing
  period and the drying process.
• It can be classifieda) knotsb) shakec)
  splitd) check

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BAA1312 Engineering Material
An Introduction Characteristics of Timber
(contd) Defects in Timber

• Defect in Timber

• Defects can occur in timber at various stage
  during the growing period, during the conversion
  and during the seasoning.
• Conversion process by which size of the log is
  reduced to a size for use
• Seasoning the controlled process of the
  moisture content of timber to a level appropriate
  to its end use
• Defects can reducing its strength and its
  appearance

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BAA1312 Engineering Material
An Introduction Characteristics of Timber
(contd) Defects in Timber

• Knots

• Its natural defect, and reduce the strength of
  timber by interrupting the fibre continuity.
• Effect of knots depends on their position in the
  section.

Live Knot
Dead Knot
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BAA1312 Engineering Material
An Introduction Characteristics of Timber
(contd) Defects in Timber

• Knots

• Type of Knots
• Live Knot
• Intergrow Knot
• Dead Knot
• Enclosed Knot
• Arris Knot
• Splay Knot
• Margin Knot
• Edge Knot
• Face Knot

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BAA1312 Engineering Material
An Introduction Characteristics of Timber
(contd) Defects in Timber

• Shake

• Shake is the separation of the rings in a piece
  of wood that occurs as it dries. The wood can
  also 'peel' off around the rings, similar to the
  layers of an onion

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BAA1312 Engineering Material
An Introduction Characteristics of Timber
(contd) Defects in Timber

• Split

• Its a complete separation of wood fibers
  usually at the ends, throughout the thickness of
  lumber and parallel to the fiber direction.
• could affect the durability of timber.

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BAA1312 Engineering Material
An Introduction Characteristics of Timber
(contd) Defects in Timber

• Check

• A "Check" is a long crack that appears as the sap
  wood of a timber shrinks around the heart wood
  over time
• Checking is the appearance of cracks or splits in
  wood as the wood dries out over time.
• Checking is not a structural problem, and usually
  occurs only on one or two sides of a beam.

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BAA1312 Engineering Material
An Introduction Characteristics of Timber
(contd) Defects in Timber

• Check

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BAA1312 Engineering Material
An Introduction Characteristics of Timber
(contd) Defects in Timber

• Decay

• Whereas weathering is degradation of the wood
  surface, decay (also called rot) affects the full
  volume of wood.
• Decay is degradation caused by a variety of decay
  fungi that are capable of breaking down the
  structural components of wood for food.
• The fungi tunnel throughout the full volume of
  the wood, degrading the polymers that form the
  wood cells through a complicated biochemical
  process. Since these polymers give wood its
  strength, considerable loss of strength occurs
  long before visible damage is apparent. Wood
  decay fungi must have adequate moisture to grow.

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BAA1312 Engineering Material
An Introduction Characteristics of Timber
(contd) Defects in Timber

• Decay

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