Timber Flashcards
(28 cards)
What are the two types of tree
+describe
Coniferous-fast growing wood and have pines
Deciduous-slow growing wood and has leaves
Timber has a high ___ to ____ ratio
Strength to weight
Timber has good ____ insulation
Sound
Timber has good ____ resistance (might be unexpected)
Fire
What is the difference between hard and softwoods
Hardwoods come from deciduous trees and are denser
Softwoods come from coniferous trees are are looser (grain)
Timber is a ____ material due to growth rings
+ describe
Anisotropic-meaning that it is not the same in all directions
What is a knot
A knot is the point where a branch has joined a tree
Name five factors that affect the strength of timber
Species of tree
Geography of area
Age of tree
Variations within the tree
Moisture content
Growth effect
Statistical variation
What is growth effect
Rapid growth in tree causes some cells to be bigger than others causing reduced density and reduced strength
What are the three ways of grading timber
Visual
Proof
Mechanical
What is visual grading
The wood is inspected by eye for:
proportion occupied by knots
slope of the grain
width of growth rings
What is proof grading
+what is a disadvantage of it
Proof grading is when timber is tested via bending to see if it meets the required stress
However, this is wasteful as if it fails the test the timber snaps and also there is possibility for timber to weaken even if it passes
What is mechanical grading
Timber is fed into a machine continuously and passed between rollers where the middle roller applies a load, the resistance from the plank is measured and the strength is predicted
What is creep
Creep is a long term deformation causes by consistent prolonged loading over months and years,
it is also more pronounced with higher moisture content
What are some examples of laminated timber
Cross laminated timber (CLT)
Glued laminated timber (Glulam)
Laminated veneer lumber (LVL)
Nail-laminated timber (NLT)
What is laminated timber
+some advantages
Timber glued and clamped together
Distributes loads across member and
allows variety of shapes and sizes
What are some disadvantages of laminated timber
Glue can cause risk of fumes and sustainability issues
requires offsite manufacture so more planning needed
requires external cladding against weather or moisture
What does SIPS stand for and what is it
SIPS-Structurally Insulated Panels
It is two parallel faces with expanded polystyrene (EPS) in the middle
making it very good for insulation
What is plywood
Wood sheets peeled from a rotating log
and then glued together with perpendicular grain
What is chipboard
Wood chips from other manufacturing processes
glued together, not as strong
What is hardboard
Sawdust from manufacturing processes
glued together into sheets
What is blockboard
A thicker core (10-14mm) with
1 or 2 layers on veneer on either side of the core
Explain how timber is good in fire
Timber has a low thermal conductivity
Timber burns while steel buckles and concrete spalls
Timber has a known rate at which it burns which can be used to calculate how much will be lost in a fire and then add that amount on
Large timber structures are also harder to catch a light as fires usually aren’t big enough to consume the whole member
What are the conditions for a insect or fungi attack
Timber is subjected to over 20% moisture content
for long periods of time
(+when submerged can be attacked by marine borers)
