Timber

Question 1

What direction is timber compressive strength strongest?

Answer 1

parallel to the grain (longitudinal)

Question 2

Why are knots undesireable

Answer 2

the grain direction is changed creating a point of weakness due to the change in stress distribution.

Question 3

Types of defects
(all used for grading of plywood)

Answer 3

• split (moisture)
• check (moisture)
• slope of grain
• pitch pocket
• compression wood (grew on a hill)
• knot (from branches, control by pruning)

Question 4

Moisture Content

Answer 4

is the ratio of the weight of water in a given piece of wood to the weight of the wood when it is dry.

dry - below 16%
wet - above 16%

Question 5

Machine stress graded (MSG)

Answer 5

Strength of the piece of timber is assigned based on a relation between deformation and strength or force and strength previously determined

Question 6

Visually Stress graded (VSG)

Answer 6

strength is assigned based on knot sizes

Question 7

maximum stress state of timber is limited to

Answer 7

elastic response

Question 8

k1 load duration factor

Answer 8

accounts for how timber members subjected to a constant load for a long period of time tend to fail at a lower load than if the load had been applied for a short period of time

Question 9

k4 load sharing factor

Answer 9

allows for the reduction in variability for a system that shares load between four or more elements, compared to an individual element

Question 10

k8 stability factor

Answer 10

accounts for lateral stability of the beam (flexural torsional buckling)

Question 11

critical flange

Answer 11

Flange which would deflect the furtherest laterally during buckling.

Question 12

Explain nominal bearing

Answer 12

checks to see if the load or reaction causes crushing of the timber.

Bearing strength = Load being transferred/contact area

Question 13

k3 factor

Answer 13

increases the effective bearing area - When a member is loaded in compression perpendicular to the grain the timber cells are compressed. Because the cells are continuous, the cells help to spread the load along the member.

Question 14

potential failure modes of compression members

Answer 14

crushing and buckling

Question 15

what variables govern deflection of a beam

Answer 15

• span (L)
• load
• elastic modulus (E)
• bending stiffness (I)

Question 16

what does amount of creep depend on

Answer 16

• MC
• duration of load
• type of loading (bending or axial)

Question 17

k2 factor

Answer 17

duration of load factor for deformation (accounts for creep)

Question 18

why should external corners always be braced in each direction?

Answer 18

these areas attract high forces under wind or seismic action

Question 19

bracing lines should not be placed more than X meters apart

Answer 19

6m
5m for subfloor