timber 1 Flashcards
what are some general properties of timber?
renewable, good fire resistance, no waste, no energy use
what can cause imperfections in timber?
moisture, fungal attacks and creep
what are the 2 types of tree? + explanation
endogenous: inwards trunk growth (bamboo, palm)
exogenous: outward trunk growth (hardwood and solfwoods)
what is a hardwood?
produced from tree with seed from fruit
harder, and slower growth
(oak, beech)
what is softwood?
produced from cone bearing trees
softer and faster growth
(pine, spruce)
what is balsa?
a hardwood that behaves like a softwood
name the parts of the trunk
heart pith- soft issue
heart wood- no living cells
sap wood- wet (fungal attacks occur)
what are the two ways timber can be sawn?
plain sawn
quarter sawn
list the different types of timber natural defects
sloping grain: grain not ring pattern
rate of growth: early wood has small density
wane: rounded trunk intrudes sawn sections
heart shake: splits in near the center of the trunk
what do the different types of knots indicate?
live knots: some on the branch is enclosed within the tree
dead knots: when the branch drops off
how do knots affect strength
the smaller the knot the stronger
sawn timber has to be seasoned, what is meant by seasoned?
making sure there’s not too much or too little moisture
how can timber be seasoned?
air drying: stacking them and leaving them to dry
kiln drying: put in a controlled environment when air is heated
what is anisotropic behaviour and how does it relate to timber?
when the strength of the material varies depending on its positioning. the strength of timber in one position in different to that on another (because of the layers)
how is timber in tension?
brittle
how is timber in compression?
ductile
what is the initial and final failures of timber when it bending
initial failure: the creasing in compression
final failure: snapping in tension
what is meant by pre-stressed timber?
when the compression strength is reduced
