A wooden house. Image credit designrulz.com

A wooden house. Image credit designrulz.com

ZIMSEC O Level Combined Science Notes:Timber properties and timber structures

  • Wood is a popular material in the construction industry
  • Wood is light and has a high strength/mass ratio
  • Light, strong beams/trusses are a priority in the building of houses
  • Wood is suitable for this type of structure because it is tough and flexible
  • Wooden beams are safer in a fire when compared to say steel beams provided the wooden beams are treated with fire retardant
  • This is because the wooden beams will only char but retain their shape and keep their position and much of their strength
  • A steel beam may expand and buckle tearing the building apart
Annual Rings. Image credit hobbithouseinc.com

Annual Rings of hardwood(left) and softer wood (right). Image credit hobbithouseinc.com

  • As trees grow they produce annual rings
  • These annual rings give the grain marks
  • They show where the tree’s very strong fibres laid down at various times in its life
  • Hardwoods grow at a slower rate and thus have annual rings that are closer together
  • The closer together the wood’s grain is the stiffer/ the wood is
  • Examples of hardwoods(close grains) are mukwa, mahogany and wattle
  • Softwoods (broad grains) include pines and poplar
  • They are usually lighter in color
  • Planks are cut longitudinally (along the length of the tree)
  • This is because the fibres of the tree are strong in tension
  • Cutting the tree across the grain would create weak spots and the planks would crack along the grain

To access more topics go to the Combined Science Notes page