Lecture 18 Flashcards
How does wood change?
Wood shrinks across the grain not along the grain. Lumber cross section changes due to the relative humidity of air. Quarter sawn shrinks unifromly, flat sawn lumber cups, bows, or twists
What is lumber surfacing done by?
Surfacing is done by high-speed planing machines
What does lumber surfacing do?
Smoothes lumber, round off the edges, and makes it more square, removing some of the distortions that occurred during the seasoning process
What is lumber that was surfaced before seasoning called?
S-GRN (surfaced green)
Softwoods
Originating from north American forests, fast growing, plentiful, inexpensive, soft, easily workable
Hardwoods
Harvested from around the world, slower, denser, more expensive
Three classifications of softwood lumber
Board lumber (or boards), dimension lumber, and timbers
Most commonly used lumber
2x (two-by)
Dimension lumber is available in lengths of..?
8ft, 10ft, 12ft, and so on up to 28ft
Lumbers strength and appearance
Not same degree of uniformity as steel or concrete
When axis runs parallel to grain, stronger.
What reduces strength in lumber?
Knot in a member, if grain doesnt run parallel to the axis
Knots in members
Weaker, stronger when near longitudinal axis
What is a check?
A check is a seperation of wood fibers along the rays (perpendicular to growth rings)
What is a shake?
A separation of wood fibers along the growth rings
What is a split?
A split occurs at the ends of a member and is a complete separation of wood fibers through the entire end
What is a wane?
A wane is the absence of wood or the presence of bark at the corner or the edge of a piece that results from the sawing process
Lumber grading
Each piece of lumber used for structural framing is graded and stamped
What do higher structural grades mean?
Fewer defects and when left exposed are generally also more attractive
Appearance grading
Appearance grading is always performed visually
What is bio-deterioration?
Cause by living organisms that use wood as food
What are the two groups of organisms that consume wood?
Fungi (fungal decay, decay of wood or rotting)
Insects (termites, water based wood eating insects, and carpenter ants)
Termite control
For wood members not buried in the ground, maintain distance between ground, soil barrier with chemical soil treatment, natural decay resistant, termite shield, inspection and remediation
What is preservative treated lumber?
Most effective and commonly used method of achieving termite protection. Must be toxic to organisms but non-damaging to wood.
Three types of preservatives to protect lumber
Creosote, oil-borne preservatives, waterborne preservatives
What is FRTW
Fire-retardant treated wood is lumber of plywood that has been pressure treated with chemicals that retard the development of fire.
