Wood & Timber Materials Flashcards
Where do softwoods come from?
cone-bearing (coniferous) trees
Describe the cell structure of softwoods.
relatively simple
Describe the grain structure of softwoods.
plain grain structure
Where are softwoods typically sourced?
North American forests
What are some advantages of softwoods? (4)
- fast-growing
- plentiful
- relatively inexpensive
- easily worked
What are softwoods used for? (5)
- structural wood products
- finish trim
- shingles
- siding
- flooring
Are all softwoods soft?
no - Douglas Fir is a softwood but is harder than some hardwoods
Where do hardwoods come from?
from broad-leafed (deciduous) trees
Describe the cell structure of hardwoods.
more complex
Describe the grain structure of hardwoods.
more interesting
Where are hardwoods typically sourced?
around the world
What are some advantages and disadvantages of hardwoods?
- advantages: denser, with a greater variety of colors and figure
- disadvantages: slower growing, generally more expensive than softwoods
Why is wood the most sustainable of construction materials? (4)
- wood is the only major structural material that is renewable
- in North America, annual tree growth exceeds the volume of harvested trees
- manufactured wood products efficiently use waste
- if the wood frame of a building is kept dry, it can last indefinitely
What sort of strength does wood possess?
wood has both tensile and compressive strength
What natural factors can affect wood strength? (3)
- direction of grain
- species
- presence of knots or other defects
What man-made factors can affect wood strength? (5)
- duration of load
- moisture content
- chemical treatments
- temperature
- size and shape
Why are timber engineering properties often unique?
they’re relative to the grain orientation
What do the mechanical properties of timber often depend upon, and why? (2)
- mechanical properties depend on load direction
- mechanical properties along the longitudinal axis are usually greater than those along the radial and tangential axis
What are the five steps of sawn wood production?
- sawing into desired shapes
- seasoning
- surfacing
- grading
- preservative treatments
What is the difference between plainsawn and quartersawn wood?
- plainsawn: growth rings roughly parallel to wider face of board
- quartersawn: growth rings close to perpendicular to wider face of board
What are some pros and cons of plainsawn lumber?
- pros: most economical sawing method; produces maximum yield of useful pieces
- cons: lumber experiences greater distortion during drying process
What are some pros and cons of quartersawn lumber?
- cons: requires more handling of the log during sawing; not as efficient, generates more waste
- pros: lumber is more dimensionally stable; produces more pleasing grain figure
Why is kiln drying, or seasoning, generally preferred to air drying?
kiln drying uses more energy but it is faster and produces more stable, uniform lumber
Why is lumber dried/seasoned?
seasoned lumber is lighter, stronger, and stiffer than green, or unseasoned, lumber
