Lecture 17 Flashcards
Wood
Many structural and non-structural applications
Where does the term lumber derive from?
Derived directly from logs and applies to wood products (Only solid pieces)
Advantages of wood?
High strength-to-weight ratio of lumber. No need for heavy equipment for lifting and hoisting building components. Low cost, Simple
What does a tree consist of?
Root structure, trunk, branches and leaves
Cambium Layer
Where cell division takes place, between bark and outermost ring
Heartwood
Interior dark colored region of tree trunk
Sapwood
Light colored region of tree trunk
What are the cells added during the wet and dry seasons called?
Earlywood and latewood
Two broad categories of lumber
Hardwoods and softwoods.
Hardwoods
Stronger than softwoods, flowering trees, hard broad leaves, deciduous, shedding and re-growing leaves
Softwoods
Do not bear flowers, hard broad leaves, typically deciduous
Isotropic
Having the same properties in all directions (Steel and concrete)
Anisotropic
Not having the same properties in all directions (wood)
Best direction in lumber
Stronger along the grain
Where does the conversion of logs into finished lumber take place
In lumber mills, located close to the forests
What are the four basic steps of the log to lumber process
- Transportation of logs from the forest to the mill
- Debarking of logs
- Sawing the debarked logs into lumber
- Surfacing lumber members smooth
Flat-sawing
Sawing of larger diameter log in two directions yield several pieces of dimension lumber and timbers. Or can be in one direction giving primarily dimension lumber
Quarter (radial) sawing of a log
More wasteful of wood than flat sawing
Drying of lumber
Lumber has to be dried (or seasoned) Seasoning implies a controlled rate of drying.
Fiber saturation point
The stage at which all the free water (cavity water) has evaporated and the bound water (cell water) has just begun to evaporate
How do you find the moisture content?
The weight of water in wood divided by the weight of oven dry wood multiplied by 100
Dry lumber vs Green lumber
Dry lumber (MC < 19%) Green lumber (MC>20)
Surfaced dry (S-DRY)
Piece of lumber (air or kiln) seasoned to a moisture content of 19% or less
Surfaced green (S-GRN)
If the moisture content at the time of surfacing is more than 19%
