what are the 3 sub systems for timber?
- Root system
- Trunk
- Crown
what are the 3 characteristics of timber?
- strength
- Appearance
- durability
Name 4 natural defects of timber
- Knots
- Fungi
- Cracks
- overgrowth
Name 3 types of Knots that are found
- Live
- Dead
- Enclosed
What are Knots?
Branches that become enclosed within growing trunk
What are cracks?
Fissures which disrupt continuity of of timber
3 types of cracks?
- Star heat shake
- cup/ring shake
- Radial shake
Defects of fungal decay are?
- Dote
2. Punk
What is dote?
White streaks/ patches
called pocket rot
LITTLE DETERIORATION
What is punk?
Progressive decay, can cause softening
softening of centre- brittle heart, spongy heart, punky heart
what causes blue stain?
Sap stain. they feed on sugars left over from sap
what is reaction wood?
timber where one side is in compression
what situations does reaction wood form in?
on slopes
in windy areas
is reaction wood strong?
no. brittle and prone to shrinkage. Can distort
defects of preparation of wood?
- conversion
2. seasoning
what is seasoning?
Drying of wood
how can distortion occur if seasoning defect happens?
- excessive drying
- uneven drying
- exposed to wind/ rain
what is mechanical stress grading?
- applying TRANVERSE load over successive short lengths
- machine records MAX deflection, converts to mod of elasticity
- compares relationship between stiffness and strength
advantages over visual grading of mechanical stress grading?
- non destructive
- more reliable
- lower factors of safety
