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 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

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