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Lare Section D Materials-Wood
Properties of Wood
24
Architecture
Professional
08/16/2008

Additional Architecture Flashcards

 


 

Cards

Term

Materials - Wood

Softwoods

Definition
  • Key species: Douglas fir, West Coast Hemlock, Redwood, Pines, Cedars, Spruce
  • Used as structural & framing lumber, sheathing, roofing, subflooring, exterior siding, flooring, trim, interior paneling

 

Term

Materials - Woods

Hardwoods

Definition

Key species: maple, oak, poplar, birch, beech, cherry, black walnut, basswood, hickory, gum, ash

Lumber used for flooring, cabinets, furniture

Term

Materials - Wood

Moisture Content

Definition
  • amount of water contained in wood (expressed as % relative to weight of oven-dried wood)
  • unseasoned (green/fresh cut) = very high MC
  • seasoning reduces MC significantly
Term

Materials - Wood

Moisture Content & Seasoning

Definition
  • Seasoning lumber increases strength; reduces shrinkage, checking, warping in service; reduces susceptibility to fungus rot in storage; improves capacity to accept pressure preservative treatment
Term

Materials - Wood

Air Drying

Definition
  • 12-15% moisture content
  • dried by exposure to air over period of several months
  • usually used for dimension or lower grades of lumber
  • complete air drying of larger, structural timbers usually impractical
Term

Materials - Wood

Kiln Drying

Definition
  • 6 - 19% moisture content
  • dried in kiln under controlled temp. to achieve desired MC
  • hastens drying time and kills stain, decay fungi, insects
  • used primarily for appearance grades or finished lumber where dimensional stability and appearance are important
  • for hardwoods, air drying in yards often combined with kiln drying
Term

Materials - Wood

Equilibrium Moisture Content

Definition
  • Point of equilibrium between moisture in lumber and surrounding air
  • To ensure wood will experience only minor dimensional changes during use, specification of lumber stock should be as close as possible to MC the lumber will reach in use
  • Consider temp. & humidity of location
  • Especially important for doors, etc. that require proper fit between wood elements
Term

Materials - Wood

Strength

Definition

Ability of wood to resist loading depends on strength, orientation in the structure, and cross-sectional dimension of the member

 

 

Term

Materials - Wood

Tensile Strength

Definition
  • Ability to resist stretching or stresses imposed parallel to grain
  • Reduced by knots, splits, checks, other defects
  • Tensile strength of wood perpendicular to grain is very low and very high parallel to grain
Term

Material - Wood

Compressive Strength

Definition
  • ability to resist loads that are crushing to members
  • cs parallel to grain 2-5x greater than cs perpendicular to grain
  • important relative to vertical or horizontal load-bearing members
Term

Materials - Wood

Fiber Stress in Bending

Definition
  • ability of horizontal load-bearing member to carry max. load in bending without causing fibers at extreme top (most compression) and bottom (most tension) to fail
Term

Materials - Wood

Modulus of Elasticity (E)

Definition
  • measure of stiffness
  • ability of member to resist deflection
  • ratio of the amount by which material will deflect in proportion to applied load
  • used in load-bearing calculations to determine size of horizontal members
Term

Materials - Wood

Horizontal Shear Stress

Definition
  • ability of wood fibers at top half of bending member (in compression) to resist shearing horizontally from fibers in bottom half (in tension)
  • horizontal shearing stresses largest at each end of a beam along the central (neutral) axis
  • avoid installing bolts along this plane
Term

Materials - Wood

Grain

Definition
  • direction of fibers in lumber as consequence of natural growth or sawing
  • close grain: tightly spaced annual growth rings with small pores
  • coarse grain: widely spaced rings with large pores
  • coarse-grained woods accept stains preservatives, paints, surface sealers better than close-grained woods
  • cross grain: slope of grain defect from aberrant growth or improper sawing; weakens lumber
  • straight grained lumber is strongest; fibers oriented parallel to longitudinal axis of the piece
Term

Materials - Wood

Insect & Decay Resistance

Definition
  • Termite-resistant species: redwood, bald cypress (tidewater red), Eastern red cedar,
  • Fungi/decay-resistanc species: bald cypress (tidewater red), cedars, redwood, black locust, black walnut
Term

Materials - Wood

Decay

Definition
  • Fungi: molds, stain, dry rot, soft rot
  • Most decay in wood occurs when moisture content >30%
  • Fungal decay does not occur in permanently submerged water (fungi need oxygen)
  • Pressure-treated wood should be used where a member will be embedded in moist ground
Term

Materials - Wood

Preservative Treatment

Definition

Three major classes:

  • Water-borne
  • Oil borne
  • Creosote

American Wood Preservers Assoc (AWPA): standards and certifications

Term

Materials - Wood

Water-Borne Preservatives

Definition
  • Used to pressure treat lumber
  • leave wood clean, odorless, easy to paint
  • present less environmental hazard than other preservatives

 

Term

Materials - Wood

Water-Borne Preservatives

Definition
  • ACA - ammoniacal copper arsenate: ok for ground or water contact
  • CCA - chromated copper arsenate: ok for ground or water contact; limited marine application
  • ACC - acid copper chromate: ok for ground or water contact, resistant to marine borer
Term

Materials - Wood

Oil-Borne Preservatives

Definition
  • Can be used any application except contact with salt water
  • often prohibited for use where it will come in contact with people
  • Penta designated toxic environ. hazard

 

 

Term

Materials - Wood

Creosote Preservative

Definition
  • used where protection against wood destroying orgs high priority, painting not req'd, and odor not a concern
  • potential hazard for  human exposure
  • creosote-tar mixtures: marine/saltwater apps; pilings for shore dwellings
  • creosote-petroleum mixtures: economical but not used for marine installations

 

Term

Materials - Wood

Lumber Classification

Definition
  • American Lumber Standards Committee (PS20-70 American Softwood Lumber Standards) establishes basic principles for grading lumber
  • Grade: slope of grain; natural & manufacturing defects; number, tightness & location of knots
  • Common grade: suitable for general construction
  • Select grade: higher quality surface for painting or natural finishes

 

Term

Materials - Wood

Lumber Classification: Uses

 

Definition
  • Yard lumber: ordinary construction, general building purposes
  • Structural lumber: 2 in. or more nominal thickness; aka stress graded lumber
Term

Materials - Wood

Lumber Classification: Size

Definition
  • Lumber sized & spec'd as nominal (size before shrinkage and planing) Dressed dims smaller - except length (shrinkage longitudinal to grain is negligible)
  • Boards: <2 in. thick, 2 in. or more wide; sheathing, flooring, roofing, finish, trim, siding, paneling
  • Dimension lumber: 2-4 in. thick, 2 in wide or more; used principally for structural elements
  • Timbers: >5 in x 5 in: beams, stringers, posts, caps, sills, girders, purlins, other members
  • Most dimension lumber & timbers are stress graded
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