Chapter 3: Wood Flashcards
Protective layer around trunk
Bark
The center of the trunk, a small zone of weak wood cells, the first year’s growth
Pith
Source of new cells
Cambium
Dead cells that contribute to the structural strength
Heartwood
The direction of the long axes of the cells - changes appearance and physical properties
Grain
Cells are larger and less dense
Springwood/earlywood
Concentric bands of _____ and ______ make up the annual growth rings in a trunk that can be counted t determine the age of the tree.
Springwood; summerwood
Needlelike leaves that remain in cold weather, come from coniferous trees. Mostly in North America, fast growing, plentiful relatively inexpensive.
Softwoods
Most drop their leaves seasonally, come from broad-leafed trees. Slower growing, more expensive.
Hardwoods
Main microstructure:
- tracheids: large longitudinal cells
- rays: radial cells
Softwoods
More complex microstructure:
- fibers: longitudinal, small-diameter cells
- vessels/pores: longitudinal, large-diameter
Hardwoods
Most lumber for building structural frames come from _____. Furniture, cabinetry, interior paneling, flooring, and other fine woodwork are composed of _____ (and some denser _____).
Softwoods; hardwoods; softwoods
Comes from forests managed according to standards for long-term sustainability, resource conservation, etc. Protects the forest ecosystem and maintains long-term forest economic viability.
Environmentally certified wood
What are some wood certification programs and organizations?
The Forest Stewardship Council: certification program encompassing ecological, economic, and social purposes.
Forest Management Certification: applied to forests where trees are harvested.
Chain of Custody Certification: applied to the manufacturers and distributors that process the wood after it leaves the forest.
FSC Controlled Wood: certification that assures wood products were not illegally harvested or associated with other highly objectionable practices.
FSC Mixed Sources: label meaning the wood may include Chain of Custody, Controlled Wood, and recycled wood.
Lengths of squared wood for use in construction
Lumber
Logs
Roundwood
A circular saw or bandsaw
Headsaw
Judges how to obtain the maximum marketable wood from each log, and uses hydraulic machinery to rotate and advance the log in order to achieve the required succession of cuts
Sawyer
Lumber from softwood, significant portions of the growth rings are oriented roughly flat. Greater distortion during drying, more uneven.
Plainsawn
Lumber from softwood, the growth rings are consistently aligned at ~45 degrees or steeper. Less distortion during drying.
Quartersawn
When the cut produces an appearance where the rays appear prominently as contrasting elements.
Flecks/flakes
Lumber with growth rings that align roughly 30-60 degrees to the boards broader face
Riftsawn
The weight of the water in the wood as a percentage of the weight of the dry wood.
Moisture content
Water stored in the cell cavities
Free water
Water held more tightly within the cellulose of the cell walls
Bound water
Moisture condition, averages around 30%
Fiber saturation point
Final moisture condition
Equilibrium moisture content
The extent of drying
Seasoning
As wood dries below 30% moisture content, it shrinks mostly in _____, and only slightly in _____ (radial).
Cross-section; length
_____ lumber is lighter, stronger, and stiffer than _____ (or ______) lumber.
Seasoned; green, unseasoned
Faster than seasoning, requires more energy
Kiln drying
Moisture shrinkage along the length of the log - negligible
Longitudinal shrinkage
Shrinkage radially, many times larger by comparison
Radial shrinkage
Shrinkage around the circumference
Tangential shrinkage
Smoothed, more dimensionally precise, and safer to handle
Surfaced
High speed automatic machines for surfacing
Planes
Most lumber surfaced on four sides, for framing lumber
Surfaced four sides (S4S)
Often hardwoods are left with two rougher edges to be finished by the finish woodworkers, for finish lumber.
Surfaced two sides (S2S)
After seasoning, removes some drying distortions
Surfacing after seasoning (S-DRY)
Before seasoning, sometimes more economical. Best for wood species that don’t distort excessively as they dry.
Surfacing before seasoning (S-GRN)
What are the different types of growth characteristics?
Knots: in structure of tree; branches are joined at the trunk
Knotholes: holes left by loose knots dropping out of the wood
Decay
Insect damage
What are the different types of manufacturing characteristics?
Splits and checks: caused by shrinking stresses
Crooking, bowing, twisting, cupping: occur from non-uniform shrinkage
Wane: irregular rounding of edges of faces caused by sawing pieces too close to the perimeter of the log
Used to rare strength and stiffness properties of a piece of lumber, done visually or by machine
Structural grading
Inspectors examine, judge, and stamp each piece
Visually grading
An automatic device accesses the structural properties of the wood ad stamps a grade on the piece
Machine grading
Resistance to bending
Machine stress-rated
Rating by collections of individual wood species that are sufficiently similar in their properties that they may be used interchangeably
Species group/species combination
Ranking of visual qualities of lumber intended for flooring, trim, cabinetry, and other finish, nonstructural uses
Appearance grading
How are board feet measured (actual or nominal)?
Nominal
Wood produced in very thick sheets (~1/8-3mm in thickness or less)
Veneer
Produced by inserting a log into a large lathe and spinning the log knife edge
Rotary-cut/rotary-sliced veneer
Produced by pressing a log against a knife, without rotating the log
Sliced veneer
The log from which veneer is taken
Flitch
Arranged in the finished work in the same order in which they came from the log, so that grain patterns on adjacent pieces match as closely as possible
Sequenced
Large wood structural beams produced by joining many smaller strips of wood together with glue
Glue-laminated wood (glulam)
End joints between individual joints
Finger-jointed/scarf-jointed
Where would you find cross-laminated timber?
Walls, floors, roofs
Substitute composite laminated veneer lumber for the usually solid wood top and bottom laminations in the beam
Hybrid glulam beams
I-joists can span further than _____ _____.
Solid lumber
Structural panels laminated from solid lumber, which the orientation of members in each layer alternating from those above and below; the resulting panels are suitable for use as structural wall, floor, or roof components
Cross-laminated timbers (CLTs)
Greater than 50% plastic, durable, maintenance-free, decay-resistant, finish and structural
Plastic lumber
What are the advantages of cross-laminated timber?
- structural components can be produced in shapes and sizes not otherwise available
- quality can be carefully controlled
- lightweight
- structurally efficient
- high degree of prefabrication and rapid on-site assembly
Substitutes for solid lumber and are made from wood veneers or wood fiber strands and glue
Structural composite lumber (or engineered lumber)
Made from shredded wood strands, coated with adhesives pressed into a rectangular cross section, and cured under heat and pressure
Laminated strand lumber (LSL) and oriented strand lumber (OSL)
Made from thin wood veneer sheets; are as wide as the member is deep; glued and laminated into thicket members
Laminated veneer lumber (LVL)
Made from long, thin strips of wood veneer glued and pressed in a process similar to that for LSL and OSL, but wit the veneer strips arranged more uniformly parallel than the strands in those other products
Parallel strand lumber (PSL)
Manufactured wood members used for framing of both roofs and floors; I-shaped
I-joists
Made from blends of plastic with wood or agricultural fibers, usually in roughly equal proportions; may be prefinished
Wood-plastic composite (WPC)
What is an example of wood plastic composites?
Exterior decking, wood trim
Lumberlike products made entirely or mostly from plastic resins
Plastic lumber
Lumberlike products manufactured from recycled plastics
Recycled plastic lumber (RPL)
What is the most common material used in the manufacture of plastic lumber?
High-density polyethylene (HDPE): obtained from recycling postconsumer waste (milk jugs, detergent bottles, etc.).
Most commonly made from high-density polyethylene reinforced with glass fibers; can be formulated to be as strong as conventional solid wood, although less stiff and more prone to long-term creep under permanent loads.
Structural-grade plastic lumber (SGPL)
What are the three types of structural wood panels?
- Oriented strand board
- Particleboard
- Fiberboard
What are structural panel types (oriented strand board, particleboard and fiberboard) used for?
Sheathing on framed walls and roofs, and subflooring over floor framing
What are the differences in the three types of structural wood panels?
Oriented strand board: long shreds (strands) of wood compressed and glued into 3-5 layers. They are oriented in the same manner each layer. Strongest and stiffest.
Particleboard: different ranges of smaller wood particles than OSB that are compressed and bonded into panels. It is a base material for wood veneer and plastic laminate, or used as an underlayment panel, a smooth base for resilient flooring application.
Fiberboard: very fine-grained board made of wood fibers and sentencing resin binders. Mostly interior uses. More dimensionally stable and stiffer, and able to hold fasteners better. Most common type is medium-density fiberboard (MDF) used for cabinets, furniture, moldings, paneling, and many other manufactured products.
Chemical treatments are used to counteract two major weaknesses of wood:
Combustibility and susceptibility to attack by decay and insects
Placing lumber in a vessel and impregnating it under pressure with certain chemical salts that greatly reduce its combustibility; expensive; used in roof sheathing in attached houses and framing for nonstructural partitions, and other interior components.
Fire-retardant treatment
Used where decay or insect resistance is required, like with wood that is used in or near the ground; exposed to moisture; fences, decks, and marine docks; high termite risk areas.
Preservative-treated wood (also called pressure-treated wood)
What are the different types of wood fasteners?
Nails Screws Bolts Timber connectors Toothed Plates Sheet Metal and Metal Plate Framing Devices Wood Adhesives
What are the differences between nails, and screws and bolts?
Nails: inexpensive, fast and easy to install; may be driven by hand or nail gun; sized in pennies (d) such as 16d=3-1/2”; plain, uncoated steel (bright), galvanized (zinc, corrosion resistant) stainless steel, aluminum and copper
Screws and bolts: threaded fasteners; greater holding power than nails; bolts require pre-drilled holes; some screws require pilot holes, while some are self-drilling
Used in factory-produce lightweight roof and floor trusses; driven into wood with hydraulic presses, pneumatic (air) presses, or mechanical rollers; act as splice plates with a very large number of built-in nails.
Toothed plates
Manufactured for joining wood members or strengthening their joints; most common is joist hanger.
Sheet Metal and Metal Plate Framing Devices
Type of timber connector inserted in matching circular grooves to mate pieces of wood clamped together with a central bolt, providing greater capacity by spreading the load across a larger area of wood than can be done with one or a few bolts.
Split-ring connector
What are the different types of prefabricated wood components?
Trusses
Prefabricated panels
Factory-built housing
What are trusses?
Light wood members (2x4, 2x6) joined with toothed plates; have a long-span capability, and are rapidly erected on site.
What is factory-built housing?
Modular construction: constructed to local building code requirements, but factory-built and trucked to construction site.
