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Timber
The Material Timber is one of the most important building materials, Timber is self renewing and trees have always exerted significant effects on people and the environment. Timber is essentially component of building constructed in all other materials –generally as scaffolding or levers or Specifically as centering for masonry , formwork for lining for concrete or fixing for steelwork.
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Qualities of Wood THE MATERIAL WOOD IS:
Strong Light Easily handled, worked, &
shaped Fastened quickly & economically Recyclable Biodegradable A renewable resource http://www.frontdesk.co.in/forum/
Undesirable Characteristics of Wood
Not perfectly straight Affected by moisture Has growth defects But can be protected from:
Splitting & warping Burning Decaying Attack by Insects http://www.frontdesk.co.in/forum/
Tree Composition Bark Cambium Sapwood Heartwood Pith
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Tree Growth Springwood (earlywood)
Faster growth Cells larger and less dense
Summerwood (latewood) Slower growth Cells smaller and denser
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TWO TYPES OF WOOD Generally, two types of trees provide wood: ď Ž HARDWOOD
Hardwood is produced by trees that have broad leaves - lose them in winter - reproduce them in spring. Species are oak, pecan, walnut, ash, cherry, birch, Teak etc. Slow growth. ď Ž SOFTWOOD Softwood is the type that comes from trees that have needles, are evergreen, do not lose them in winter. Species include pine, fir, spruce, larch, cedar, etc. Fast growth. Much more plentiful than hardwoods. http://www.frontdesk.co.in/forum/
CLASSIFICATION OF TIMBER IS 399 : 1963 Zonal Distribution : India is divided into five zones for convenience in tabulating the information on timber. The zones are:
Zone I -Jammu & Kashmir, Punjab, Himachal
Pradesh, Uttar Pradesh, Haryana
and Rajasthan.
Zone2 -Assam, Manipur, Tripura, West Bengal, Bihar, Orissa, Mizoram, Arunachal Pradesh, Nagaland, Sikkim, Bhutan, Andamans.
Zone 3 -Madhya Pradesh, Vidharbha areas of Maharashtra and north east part of Andhra Pradesh (Godavari Delta area).
Zone 4 -Maharashtra (except Vidharbha area), Gujarat, and north west part of Karnataka.
Zone 5 - Tamil Nadu, Pondicherry, Andhra Pradesh (except Godavari Delta area), Kerala and Karnataka (except north west part). http://www.frontdesk.co.in/forum/
Engineered Wood
Wood used in construction includes products such as chipboard, hardboard, medium-density fibreboard (MDF), oriented strand board (OSB). Such wood derivatives are widely used: wood fibers are an
important component of most paper, and cellulose is used as a component of some synthetic materials. Wood derivatives can also be used for kinds of flooring, for example laminate flooring. http://www.frontdesk.co.in/forum/
Timber Structures
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Grading of timber
Defects that affect the strength of timber
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SHRINKAGE When water in the cell cavities of wood
evaporates, there’s no reduction in the cross sectional dimensions of lumber can be observed. But when the wood dries further, water is driven off the cell walls, leading to decrease in the dimensions & shrinkage of wood. The amount of shrinkage is proportional to the amount of water removed Shrinkage is not equal in all direction http://www.frontdesk.co.in/forum/
SKETCH SHOWING DIFFERENTIAL SHRINKAGE IN THE TANGENTIAL AND RADIAL DIRECTIONS AS PER IS CODE 3629-1986 M- Intermediate between ‘R’ and ‘T’.
R - Best for dowel and planks ( structural )
D- Discarded for joists and beams.
C- Showing circular shrinkage. B- Best for joists and beams.
T- Not good for structural planks. http://www.frontdesk.co.in/forum/
SHRINKAGE ďƒź The least of shrinkage is along the length of the
board. ďƒź Repeated wetting & drying, plus the accompanying expansion & contraction, weakens the wood and finally promotes decay
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SEASONING It is a process of controlled drying of lumber to
improve its structural properties. It could increase in strength characteristics, lowering of shrinkage in service, improvement in decay resistance, reduction in weight and better workability. Seasoning also required to prepare lumber for preservative treatment.
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SEASONING ďƒź There are 2 methods of drying
a) air drying b) kiln drying ďƒź Air drying procedure is cheaper than kiln drying where the lumber is stacked in open-sided sheds so as to promote drying without artificial assistance. ďƒź Kiln drying employs a heated, ventilated and humidified oven where the humidity is essential to control the rate of evaporation of moisture from within the lumber. http://www.frontdesk.co.in/forum/
SEASONING
ďƒź There are only 3 factors that affect the
drying process : a) temperature b) relative humidity c) air circulation
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TREATMENT & DURABILITY It refers to long term performance of the
material. Wood can be durable if it well seasoned and kept in dry place, immersed in water or buried in the ground. Heartwood of all species has a very good resistance. Sapwood is susceptible to decay if not used properly in construction. http://www.frontdesk.co.in/forum/
Preservative treatment of wood in marine environment http://www.frontdesk.co.in/forum/
Decay in a poorly constructed building envelope http://www.frontdesk.co.in/forum/
Wet column bases
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TREATMENT & DURABILITY Seasoning followed by the use of an effective waterproofing technique will render most wood species resistant to attack by wooddestroying. Paints, stains or waterproofing chemicals are used to make lumber waterproof. Even though stains & waterproofing chemical can penetrate farther into the wood than paints but none of it is effective when wood is in contact with ground. To protect lumber that is in contact with ground or is susceptible to decay, the wood need to be chemically treated. http://www.frontdesk.co.in/forum/
PRESERVATIVE TREATMENT Wood need to be chemically treated because:
a) To prevent destruction from fungi and insects b) To inhibit combustion This kind of treatment done by injecting chemicals, under
pressure, into the wood fibers and is called “pressure treatment” or “preservative treatment”. Treatment to prevent destruction from fungi & insects is carried out with 1 of 3 classes of chemical such as “ Organic solvent preservatives , Tar oil preservatives (example; Creosote) & Waterborne preservatives http://www.frontdesk.co.in/forum/
PRESERVATIVE TREATMENT Proper seasoning is required prior to the
treatment. The ease with which preservatives can be injected into woods depends on density & structure of wood, chemical composition of cell walls, cross-sectional dimensions of lumber and moisture content. Sapwood is more easily impregnated and absorbs more preservatives than heartwood. http://www.frontdesk.co.in/forum/
PRESERVATIVE TREATMENT ď Ž Among the techniques that can be used for
application of this preservatives are: a) Brushing or spraying b) Dipping c) Double vacuum process d) Pressure impregnation e) Diffusion process
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DECAY & DESTRUCTION Untreated timber may decay or destroyed. Decay happen due to attack by fungi. Early stage of decay / fungal attack
a) dramatic decrease in some mechanical properties b) very little loss in component volume c) limited changes in appearance Advanced fungal attack a) wood is brittle & weak b) destruction can be readily recognized http://www.frontdesk.co.in/forum/
DECAY & DESTRUCTION Elements needed for fungal growth are:
a) proper temperature b) moisture content over 19% c) oxygen d) food (wood fiber) Elimination of any one or more of these will effectively control the growth of fungal organisms. Dry rot is a type of decay caused by house fungus that can live in seasoned lumber in somewhat dry condition. http://www.frontdesk.co.in/forum/
DECAY & DESTRUCTION Dry Rot is most serious of all fungi attack
because once established, it can spread rapidly & the spread may be extensive before visible signs appear. Wet Rot is fungal deterioration that occurs in excessively wet lumber.
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Dry rot is most serious of all fungi attack http://www.frontdesk.co.in/forum/
ď Ž Dry Rot http://www.frontdesk.co.in/forum/
Wood uses BEECH
Furniture, tool handles, benches
A straight grained hardwood. Very easy to work with. OAK Very tough, light brown in colour. Difficult to work.
High quality furniture, ships and veneers
ASH Open grained, easy to work.
Tool handles and sports equipment.
MAHOGANY Easy to work, reddish brown in colour.
TEAK
Furniture, veneers and window frames.
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Indian Standards (IS CODE) for Timber IS CODE
Title
399:1963
Classification of commercial timbers and their zonal distribution (revised)
1150:2000
Trade names and abbreviated symbols for timber species (third revision)
4970:1973
Key for identification of commercial timber (First revision)
1978: (Part 1) : 1986
Methods of testing small clear specimens of timber: Determination of moisture content (second revision)
(Part 2) : 1986
Determination of specific gravity (second revision)
(Part 3) : 1986
Determination of volumetric shrinkage (second revision)
(Part 4) : 1986
Determination of radial and tangential shrinkage and fibre saturation point (second revision)
(Part 5) : 1986
Determination of static bending strength (second revision)
(Part 6) : 1986
Determination of static bending strength under two point loading (second revision)
(Part 7) : 1986
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Determination of impact bending strength (second revision)
Indian Standards (IS CODE) for Timber IS CODE
Title
1978:
Determination of compressive strength parallel to grain (second revision)
(Part 8) : 1986 (Part 9) : 1986
Determination of compressive strength perpendicular to grain (second revision)
(Part 10) : 1986
Determination of hardness under static indentation (second Revision)
(Part 11) : 1986
Determination of shear strength parallel to grain (second revision)
(Part 12) : 1986
Determination of tensile strength parallel to grain (second revision)
(Part 13) : 1986
Determination of tensile strength perpendicular to grain (second revision)
(Part 14) : 1986
Determination of cleavage strength parallel to grain (second Revision)
(Part 15) : 1986
Determination of nail and screw holding power (second revision)
(Part 16) : 1986
Determination of brittleness by izod impact (second revision)
(Part 17) : 1986
Determination of brittleness by Charpy impact (second revision)
(Part 18) : 1986
Determination of torsional strength (second revision)
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Wood in bending and compression
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Wood in bending and compression
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