Wood

Showing the versatility in Wood Construction
Fig. 1: The Versatility of Wood Construction

From Wikipedia, "Wood is an organic material found as the primary content of the stems of woody plants, especially trees, but also shrubs." Wood in the form of lumber and timber, has been a widely used structural component for centuries in building shelters, houses, and boats, . Modern day wood design application includes: shear walls, wood panels, plywood, glue-laminated lumber, and various other uses. Wood is now used by engineers, who use technical analysis and design data to create modern day structures. Per weight, wood is stronger than both concrete and steel.

Wood is unique in the sense that it is non-homogenous, so similar to concrete depending on the type and condition of wood you can lose strength. Also, unlike concrete, wood will get weaker over time. Numerous factors are also used to determine the strength of wood (including a factor for time, size, temperature, etc.)

The American Wood Council has created the National Design Specification (NDS) for wood design. The most common Design Code currently being used by the IBC is the 2005 NDS.

Wood Analysis Practices:

The different types/categories of Wood:

Wood types can be broken down into two categories, species and types. A few of each have been provided below:

Species:

  • Douglas Fir (most common)
  • Birch
  • Oak
  • Redwood

Types:

  • Sawn Lumber
  • Glued-Laminated Timber (GluLams for short)
  • Composite Lumber
  • Chipboard
  • Oriented Strand Board (OSB)

Common Wood Properties [1]:

Common Wood Properties include (english units):

  • Douglas Fir
    • E = 1,600-1,900 ksi
    • γ = weight density = 30-35 lb/ft3
    • ρ = mass density = 0.9-1.1 slug/ft3
  • Oak
    • E = 1,600-1,800 ksi
    • γ = weight density = 40-45 lb/ft3
    • ρ = mass density = 1.2-1.4 slug/ft3
  • Southern Pine
    • E = 1,600-2,000 ksi
    • γ = weight density = 35-40 lb/ft3
    • ρ = mass density = 1.1-1.2 slug/ft3

Common Wood Properties include (metric units):

  • Douglas Fir
    • E = 11-13 GPa
    • γ = weight density = 4.7-5.5 kN/m3
    • ρ = mass density = 480-560 kg/m'^3
  • Oak
    • E = 11-12 GPa
    • γ = weight density = 6.3-7.1 kN/m3
    • ρ = mass density = 640-720 kg/m'^3
  • Southern Pine
    • E = 11-14 GPa
    • γ = weight density = 5.5-6.3 kN/m3
    • ρ = mass density = 560-640 kg/m'^3

References:

  1. Gere, James M. "Mechanics of Materials, Sixth Edition",2004

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