Friday, September 20, 2019

Timber in Building Construction

Timber construction is mostly used for green construction techniques in the modern industry. The wood used for building and engineering work is term as “timber”. Timber is one of the most important building materials since time immemorial & is widely available from trees’ trunks.
The trees are classified into two groups according to their growth, such as
  1. Endogenous
  2. Exogenic

Endogenous

These grow inward in a longitudinal fiber mask. These aren’t suitable for building purposes.
Ex. :- Coconut,bamboo

Exogenic

These grow outer in longitudinal fiber mask.These center in concerning adding layer after the layer.These are only useful for building purposes.

Here there is another classification of wood. That is,

  1. Soft wood
  2. Hard wood

Soft wood from coniferous. Hard wood is generally strong where resistance. They have good colour grains & good joinery in finish. These include Teek, Rose wood, Ork. The soft wood is softer than the hard wood. These include Mango Pein.


Defects in timber


  • Knots
  • Dead knots
  • Live knots
  • Heart shake
  • Star shake
  • Radial shake
  • Cup shake
  • Twisted fibers-These are made due to the wind.
  • Rupture
  • Warps-These are due to uneven drying of timber such as spring, bow cup & twist

Properties of the timber


It should be strong to resist the tension ,share ,bending , strength should be 700 – 1600 Nm-2 & compressive strength.
It should be also be durable.


Classification of timber


Super luxury class
(Ebony , Teak , Kaluwara , Kalu Madiriya , Nadun)

Luxury class
(Burutha , Milla , Halmilla, Mahogany)

Special upper class
(Jack wood, Kolon , Suriya Mara , Kohomba)

Special class
(Siyambala , Palu , Kumbuk, Akesiya)

Class one
(Muna mal , Hora (For piles),Wal del)

Class two
(Tuna , Ahela, Dunumadala, Ginisapu)

Class three
(Aldisiya, Ork, Ash, Turpentine, Birch, Pine, Redwood, Beach, Cempus, Ballaw)



Decay of timber


Wet rot

It is due to the decomposition of the timber case of damp & moisture. It also occurs when timber is subjected to wetting by raining & drying sun. The fungus of the timber are damaged & it starts to powder. The timber becomes dark, black & brownish & lose its strength

Dry rot

If the timber is stacked in such a place having no proper circular of air, then it is attacked by a fungus which act on it & rot the wood tissues & break down the cell walls. The wood becomes soft & discoloured & turns into spongy masks. The soft powder comes out when the wood is stacked on the ground.


Preservation of timber


Generally, all the timber are acted upon the white ants & insects, fungus, dry rot wet rot moisture, etc. which cause decay. Therefore at most necessary to preserve the timber again all types of decay for the safety & durability of the structure, furniture. The general method adapted for the preservation of timber is to poison the wood fungus in the form of preservation.

The preservation should be poisoned to the insects & white ants, but sate for humans. Generally, varnished paints & chemicals with pesticides are commonly used as a preservative. Also, there are various methods of application of preservation such as surface application, hot & cold method, pressure method etc. The timber should be successfully preserved by careful selection of the preservatives & proper method of application so as ensure safety. Increase life & better durability in the construction.




Seasoning of timber


Seasoning is the process of removing the sap & moisture in the fresh timber. The objectives & advantages of seasoning of timber are,
To reduce the moisture content to retain edges size shape

To increase the strength & durability

To increase the workability. It can be sawn to proceed easily.

To reduce the weight of timber & thereby the lower the prosper of transportation can be.

To minimize the defects like shrinkage, wrapping, splitting, cracking

To increase the resistance to the insects

To facilitate the application of preservatives such as varnish or paint




Methods of seasoning of Timber


Air seasoning

It is natural seasoning. Here the timber is sawn in different size shapes & stacked in sheds. It is protected by the sun, wind & rain. The timber pieces are stacked so that air circulates freely around them. After one or two years the timber will be season properly. It is the best method of seasoning. However, it consumed a lot of timber. The moisture content can be reduced to 15 %.

Water seasoning

The timber pieces are completely wet in water which time odd the slab devolves in water & come out of timber. The timber pieces are then taken out & allowed to dry in air. The timber season in this way doesn’t warm or crack. But the strength of this timber is less than air seasoned timber.

Kiln seasoning

The timber pieces are stacked in an air tagged place. Then hot air is allowed circulate around them. They by the moisture of timber is reduced to the required limit.

Vapor seasoning

The timber pieces are stacked in steel cylinders & vapor is passed at 1500c, thereby the moisture in timber is reduced to the required limit.

Electrical seasoning

In this method, the moisture content of the timber is reduced to the required limit by heating the timber bypassing the electric current. As it is costly not commonly used.




The usages of the timber

  • For furniture
  • For roof and ceiling structure ( doors, windows frame )
  • For piles
  • For flooring
  • Formwork & Shuttering


at

No comments:

Post a Comment