Timber%20and%20Wood%20Products

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Timber and Wood Products

• Basic material properties and characteristics.

By Engr. Abbas Qureshi
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Timber in history

• Timber is one of the oldest building materials
  known.
• It has been used in buildings in most parts of
  the world for thousands of years.
• In low energy ages, timber was the natural
  material of choice.

Melbournes Exhibition Building 1880
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Timbers potential today

• Timber is a light construction material with a
  high strength to weight ratio.
• Economic and easy to use, it is available as a
  structural and appearance product, and suitable
  for a wide range of uses.

Hardwood in a drying yard
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The timber American Wood Council

• Only one primary building material comes from a
  renewable resource, cleans the air and water
  utilizes nearly 100 of its resource for
  products is the lowest of all in its energy
  requirements for its manufacturing creates fewer
  air and water emissions than any of its
  alternatives and is totally reusable, recyclable
  and 100 .
• And it has been increasing in US net reserves
  since 1952, with growth exceeding harvest in the
  US by more than 30.

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The nature of timber

• Timber is a natural product, drawn from the wood
  in the trunks of trees.
• Its character is consistent with the species of
  tree and the form and growth over time of the
  wood in it.

Regrowth in a native forest
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Definition

• Wood suitable for building or other engineering
  purposes is called timber
• Standing timber part of a living tree
• Rough timber part of a felled tree
• Converted timber sawn to various forms like
  beams, battens and planks, etc.
• Dressed timber- sawn timber which has been placed
  and worked to the required condition.
• Clear timber- timber free from defects.
• Structural timber- timber used in framing and
  load bearing structures.

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Classification of Trees

• Endogenous. Grow inwards.
• Grow in longitudinal fibrous mass like palm,
  cane, bamboo, banana, etc. Except bamboo
  unsuitable for engineering purpose.
• Exogenous. Grow outwards.
• Conifers. Evergreen trees yielding soft wood.
  Deodar, chir, fir, kail, pine, etc. Distinct
  annual rings, straight fibers, light color,
  resinous and light weight
• Deciduous. Flat broad leaf trees yielding hard
  wood. Oak, teak, shishum, poplar and maple.
  Indistinct annual rings, non-resinous, dark in
  color and heavy weight

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Structure of Timber

• Tree Crown, Trunk, Roots
• Cross section of a tree
• Bark (outer and inner) outermost protective
  layer of cells and woody fibers that splits and
  peels off
• Cambium outermost one ring between the bark and
  sap wood not yet converted into wood
• Sap wood outer annual rings that transmit sap
  from root to branches
• Heart wood innermost rings surrounding pith
• Pith or Medula first formed portion of stem of
  tree, initially to convey sap
• Annual rings
• Medullary rays thin horizontal veins from bark
  to pith to carry sap inwards

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Tree growth

• Spring season
• Salt and water solution sucked by the roots
• Under sunlight absorbs CO2 from air
• Viscous solution is called sap
• Autumn season
• Sap descends under the bark and leaves a thick
  layer
• Sap layer transformed into wood as cambium layer
• New layer added each year as annual ring
• Sap carried through medullary rays from bark to
  interior

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Tree growth

• New wood on outside of tree
• oldest wood on the inside
• youngest wood on the outside
• diameter largest at the base
• one ring (layer) per growing season

• Tree in forest grows toward light
• trunk is straight
• lower branches die
• leaving small knots in wood

• Bark protects wood from damage
• the tree sheds bark each year

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Major parts of tree
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Major parts of tree
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(No Transcript)
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Production of wood
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Heartwood and Softwood
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Hard and Soft Wood Characteristics

• Property Soft Wood Hard Wood
• Color Lighter Darker
• Growth Faster Slower
• Weight Lighter Heavier
• Density Low High
• Annual Rings Distinct Indistinct
• Heart wood Indistinguishable distinguishable
• Sap wood
• Strength Strong along grains Strong along
• across grains
• Conversion Easy Difficult
• Resinous Exists in pores Does not exist
• Examples Chir, Fir, Conifer Teak, sal, shisham

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Characteristics of Good Timber

• Obtained from heartwood area of tree and free
  from sap
• Should have straight and close fibers
• Dark uniform color with uniform texture
• When struck sonorous ringing sound is produced
• Narrow annular rings, closer the rings greater is
  the strength
• Compact medullary rays
• Sweet smell and a shining fresh cut surface
• No clogging of saw teeth during sawing
• Free from the defects like dead knots, shakes
  etc
• Heavy weight
• No woolliness at fresh cut surface
• Bright and smooth surface when planed

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Defects in Timber during growth

• Shakes separations between annual rings
• Star shake radial splits or cracks wider on
  surface and narrow inwards, due to severe heat
  and frost action
• Heart shake radial splits in heartwood due to
  shrinkage
• Cup shake curved split among annual rings. Also
  ring shake
• Twisted fibers wind turning the trunk and
  twisting fibers
• Rind gall growth of sapwood layer over wounds
• Upsets crushing of transverse fibers due to
  winds
• Foxiness yellow or red stains as sign of decay
• Doatiness speckled stain indicating start of
  decay due to over maturity or bad ventilation
• Druxiness Whitish spot or streaks indicating
  early decay
• Coarse grains wide annual rings due to rapid
  growth

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Defects in Timber(Figs.)
Knots
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Defects in Timber(figs).
Cup shakes
Rind galls
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Defects in Timber knots

• Knots root of small branches buried in mother
  branch annual rings. This modifies the tissues in
  elliptical or concentric circles . Knot disturbs
  the homogeneity , strength and workability of
  wood.
• Dead or loose knot - separable
• Live or sound knot inseparable
• Size based classification
• Pin knot under 12 mm
• Small knot 12 to 20 mm
• Medium knot 20 to 40 mm
• Large knot over 40 mm
• Form based classification
• Round knot
• Spike knot

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Live Knot and Dead Knot
Live Knot
Dead Knot
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Defects in Timber knots

• Quality based classification
• Sound knot hard and solid as surrounding wood
• Decayed knot contains advance decay, softer
  than surrounding wood
• Encased knot annual rings fail to grow into
  fibers of surrounding wood
• Tight knot a knot so securely fastened that it
  holds its position in finished product
• Occurrence based classification
• Single knot wood fibers deflect around one knot
• Cluster knot wood fibers deflect around two or
  more knots as one unit
• Branch knot two or more knots radiating from
  one common center

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Defects in Timber
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Defects in Timber
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Defects in Timber - Diseases Decay

• Diseases
• Dry rot fungus turns timber to dry powder
• Wet rot decay due to alternate wetting and
  drying
• Decay
• Decay due to fungal and bacterial attack
• Damage due to insects
• Termites, white ants
• Beetles powder post beetles, long horn beetles,
  ambrosia beetle, furniture beetles, death watch
  beetles
• Carpenter ants
• Damage due to rodents

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Seasoning of Timber

• Seasoning extraction of moist sap under
  controlled conditions (as nearly as possible at a
  uniform rate) from all parts of timber, and to
  leave inextricable moisture uniformly distributed
  throughout
• Irregular drying causes irregular shrinkage
  leading to warping and shakes formation
• Seasoning methods
• Air or natural seasoning timber stacked in
  ventilated shady place. Slow process takes six
  months
• Kiln or artificial seasoning steam chamber with
  controllable temperature and humidity. Rapid 4-5
  days.

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Seasoning of Timber(Artificial)

• Water Seasoning - The logs of wood are kept in
  running water. The sap, sugur, and gum are
  leached out. The logs are then kept out in air to
  dry.
• Chemical or Salt seasoning- A water Chemical(
  salt, urea) is applied to the timber for
  seasoning. It reduces the moisture due to the
  difference in vapour pressure of chemical and
  pure water. It reduces the internal stress which
  are the causes of defects as checks.

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Seasoning of Timber(Artificial)

• Electric Seasoning- The logs are placed in such
  a way that their two ends touch the electrodes.
  Current is passed , wood resists the flow of
  current. During this heat is generated which
  results in drying of timber.

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Seasoning of Timber
Air /Natural seasoning
Kiln Seasoning
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Seasoning of Timber

• Air Seasoning
• Slow process
• Simple and economical
• Difficult to reduce moisture content below 15 to
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• Timber more prone to fungi and insect attack
• More stacking space needed
• Stronger timber is obtained

• Kiln Seasoning
• Quick process
• Technical and expensive
• Moisture reduced to any desired level
• Timber less prone to fungi and insect attack
• Less stacking space needed
• Timber obtained is comparatively weaker

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Seasoning of Timber (Objectives)

• Reduce the shrinkage and warping after placement
  in structure.
• Increase strength, durability, and workability.
• Reduce its tendency to split and decay.
• Make the timber suitable painting.
• Reduce the weight of timber.

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Seasoning of Timber

• Preventing drying of logs
• Felled tree roughly squared and sawn
• Ends sealed to prevent rapid evaporation of
  moisture
• Logs kept completely submerged in running water
• Stacking of square logs
• Stacked under shade, free from weeds and debris
• One and nine stacking method
• Close crib stacking method - logs, poles, planks
• Open crib stacking method - logs, poles, planks

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Moisture and drying in wood cells
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Benefits of drying

• Drying timber increases its
• strength
• stiffness
• stability
• durability
• ease of fastening.
• It is ideally dried to a moisture content in
  equilibrium with its service environment.

Checking the moisture content
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Timber Preservation

• Preservation is protection of timber from attack
  of insects and internal decay
• Perfect seasoning is the best form of timber
  preservation
• Charring ground embedded ends of posts.
  Quenching post ends in water after charring in
  wood fire. Prevents dry rot and attack of worms
• Tarring coating with tar or pitch

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Timber Preservation

• Painting application of paint coat on dry
  timber to provide good appearance and protection
  from attack by white ants
• Creosoting application of creosote oil on
  railway sleepers, piles and electricity poles.
  Bad color, bad smell, stains plaster
• Wolman salt creosote and salt in water. NaF,
  ZnCl, MgSiF, CuSO4
• Ascu treatment application of powder chemicals
  arsenic pentaoxide, blue vitriol, potassium
  dichromate
• Fire proofing timber made fire resistance by
  soaking in NH4SO4, NH3Cl, NH4PO3, NaAs, ZnCl

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Tests of Timber

• Specific gravity
• Volumetric shrinkage
• Radial and tangential shrinkage
• Static bending strength
• One point loading test
• Two point loading test
• Impact bending strength

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Tests of Timber

• Compressive strength
• Parallel to grain
• Perpendicular to grain
• Hardness under static indentation test
• Shear strength test
• Tensile strength test
• Parallel to grain
• Perpendicular to grain

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Tests of Timber

• Cleavage strength test
• Brittleness test
• Izod impact test
• Charpy impact test
• Torsional strength test
• Moisture content test
• Oven drying method
• Electrical moisture meter method
• Distillation method

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Tests of Timber

• Moisture content test
• Specimen 5 cm x 5 cm x 2.5 cm
• Specimen weighed fresh as W0
• Oven dried at 103 2 C till no weight change
  noted. Dry weight W1
• Percentage of moisture content
• (W1 W0) / W0 x 100

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Tests of Timber

• Specific gravity test
• Specimen 5 cm x 5 cm x 15 cm
• Specimen weighed fresh as W1 correct to 0.001 gm
• Specimen volume measured to 0.01 cm3
• Specimen end coated with paraffin wax and air
  seasoned to 12 moisture content
• Weight and volume again noted as Wr Vr
• Oven dried at 103 2 C till weight constant
• Weight and volume noted as W0 and V0

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Tests of Timber

• Specific gravity test
• Specific gravity at test W1/V1
• Standard specific gravity W0/V1
• Oven dry specific gravity W0/V0
• Moisture content r (Wr-W0) / W0 x 100

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Wood Products

• Veneers
• Plywood
• Lamina Boards
• Fiber Boards
• Block Boards
• Batten Boards

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Wood Products

• Veneers
• Thin sheets of wood peeled off, sliced or sawn
  from a log of wood having attractive or artistic
  grain arrangement
• Sheet thickness from 0.4 mm to 6 mm
• Walnut, teak and rosewood veneers used in
  plywood, lamina boards and batten boards

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Timber products veneer

• Thin layers of solid wood sliced or peeled from a
  log and dried.
• High quality material is used as a decorative
  finish.
• Lower grade material is used to make plywood and
  similar products.

Veneer leaf
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Wood Products

• Plywood
• Under pressure gluing together of veneer plies in
  odd number to make 3 mm to 6 mm thick sheet
• Grains of alternate layers at right angle to each
  other
• Outer plies called face plies or faces
• Used for covering or paneling of walls, doors,
  furniture and shuttering

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Timber products plywood

• Layers of veneer glued together so that the grain
  direction alternates between layers.
• Usually produced in sheets.
• Very good in a structure, as a lining and as a
  flooring surface.

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Wood Products

• Plywood Advantages
• Better appearance
• Stronger than same thickness wood
• Elastic and may be bent to give any shape
• Not much affected by climatic changes
• Uniform strength in all directions
• Available in large sizes not possible in wood
• Almost negligible shrinkage and expansion
• Does not split under nails

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Properties are variable

• Drying (seasoning) shrinkage
• Strength hardness
• Durability
• Appearance

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Wood products
Lamin board
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Wood products
Block boards
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Wood products
Fiber board
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Fiber board anchoring
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Wood products
Hard board
Melamine hard board
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Timber shrinks as it dries

• It shrinks at different rates in different
  directions.
• Once dry, it will expand contract to be in
  equilibrium with changing local conditions.

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Shrinkage in sawn sections

• Tangential shrinkage is the highest
• So, the growth rings tend to shorten as the
  timber dries.

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Timber dries at different rates

• Pines have a porous cell structure
• They can be dried very quickly.
• Turnaround time from saw to store can be as low
  as a week.
• Hardwoods have a non-porous cell structure
• The moisture must diffuse through the cell wall.
• Drying can be very slow.
• It must be done carefully.

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Grain, strength stiffness
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Summary of characteristics

• Timber is a natural material
• Each piece is unique in fibre, texture and colour
• Its strength is dependant on the properties of
  the wood and the slope of the grain
• It takes up and gives up moisture
• It expands and shrinks as it does so
• It deteriorates in line with exposure

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Timber products

• Timber is available in a wide range of products
  and species including
• Solid sawn, moulded and laminated timber
• Veneer
• Plywood and
• Wood panels.

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Timber products sawn

• Hardwood or softwood.
• Solid timber cut from a log and dried.
• It is a versatile material used for moulding,
  frames and exposed structures.
• Size is restricted.

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Timber products mouldings

• Hardwood or softwood.
• Solid seasoned timber milled to a wide variety of
  shapes.

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Timber products glue laminated

• Small pieces of timber glued together to form a
  larger element.
• Used as both a structural and finishing element.
• Size is limited only by transport capacity.

beam
bench top
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Timber products curved glulam

• Glue laminated material can be curved.

Curved bar
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Timber products wood panels

• Panels made from wood or wood fibres bound
  together with glue, or other binder
• Particleboard
• Medium Density Fibreboard (MDF)
• Hardboard
• Core board

MDF sheet
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Jointing

• Timber is a highly versatile material that can be
  shaped and joined easily.

Half housed
Mortice and tenon
Housed
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Jointing methods
Dowel
Biscuit
Overlap
Fixing blocks
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Conclusions

• Timber is a natural product.
• It has been used for centuries.
• Skilled use and understanding of the material can
  yield excellent results.