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A General Introduction to Wood Construction

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Title: A General Introduction to Wood Construction


1
A General Introduction to Wood Construction
2
Journal of Architectural Education
  • An Exploration of the Relationships between
    Houses and Forests in American History
  • William Gould Sturges
  • University of Oregon

3
There is a Supply Demand Imbalance for Wood
Products
  • In 1986 we consumed 57.2 Billion Board Feet (bbf)
    of Wood Products, yet only 70 was Produced
    Domestically
  • This is 40 greater Consumption than in the 50's
    and 60's
  • The Trend is Getting More Acute
  • In 2040, the estimates are gt70bbf

4
Forests
  • Provide
  • species habitat
  • watershed protection
  • biological gene banks
  • medicine i.e.. taxol

5
Primeval Forests 1620
6
Primeval Forests 1850
7
Primeval Forests 1989
8
Population Density Maps 1776, 1876, 1976
9
Annual Housing Unit Production
10
Iroquois Longhouse
11
Iroquois Longhouse
  • Minimal Impact on the Forest
  • High Density Configuration
  • Same Quantity of Wood as Todays SF Detached
    BUT...
  • they housed 50 - 60 people compared to today's
    average family of 2.5 persons

12
Log Cabin
13
Log Cabin
  • First Response to Housing Need
  • Forests were Viewed as an Impediment to
    Agriculture
  • 9216 in3/lf

14
Timber Framing
15
Timber Framing
  • Coincided with the Development of Sawmills
  • Maine ca. 1620
  • Water Powered
  • Mortise and Tenon
  • Labor Intensive
  • 6210 in3/lf

16
Balloon Framing
17
Balloon Framing
  • Coincided with the Development of
  • Steam Powered Sawmills
  • Machine Made Nail
  • 4234 in3/lf

18
Western Platform Framing
19
Western Platform Framing
  • Coincided with the Development of Veneer Panel
    Products
  • early 1900's
  • 1368 in3/lf

20
Wood Use per Lineal Ft of 8' High Wall
Source Jerry Finrow, The Conflict between
Dwelling and the American Forest. A Revolution in
Basic Cultural Values
21
Energy Consumption of Common Building Materials
Mining, Processing, and Transporting
Combined Concrete Contributes 3 of Greenhouse
Gases
22
Strategies for the Future
  • Sustainable Forests
  • Create Housing with Less Demand

23
Sustainable Forest Farming
  • Forest Stewardship Council (FSC)
  • Limit Timber Removal to Prevent Decline in
    Quality/Quantity
  • Provide Variety of Ages
  • Allow Trees to Mature Fully
  • Maintain Plant and Animal Habitat
  • Protect the Soil

24
Create Housing w/ Less Demand
  • Recycle
  • Don't Over-design
  • Engineered Wood Products
  • Higher Density Configurations

25
Wood Construction Topics
  • Wood Botany
  • Lumber
  • Panels Products
  • Engineered Wood Products

26
Tree Structure
  • Bark
  • Cambium Layer
  • Sapwood - conduction, storage and support
  • Heartwood - support only
  • Growth (Annual) Rings
  • Late Wood - summer/fall, small, densely packed
    cells
  • Early Wood - spring, large cells

27
Cross Section through a Tree
28
Wood Botany
  • Two Major Groups
  • Coniferous
  • Deciduous

29
Coniferous
  • Softwoods (not a measure of hardness)
  • Gymnosperms - naked seeds
  • Evergreen e.g. Douglas fir, larch, pine
  • Narrow leaf
  • Coniferous trees lack vessels

30
Deciduous
  • Hardwoods (not a measure of hardness)
  • Angiosperms - covered seeds
  • Shed leaves annually
  • Broadleaf e.g. oak, maple, cherry
  • Deciduous trees have vessels for support and
    conduction of nutrients

31
Wood is Anisotropic
  • An anisotropic material has physical properties
    that are different with respect to their three
    major orthogonal planes

32
Three Major Planes
  • Longitudinal - along the length of the log
  • Radial - with respect to the center of the log
  • Tangential - with respect to the growth rings

33
Wood is Hygroscopic
  • An hygroscopic material has an affinity for water
    molecules which causes swelling and shrinking as
    the material reaches equilibrium with its
    environment

34
Wood is Viscoelastic
  • enough is enough!

35
Moisture Content
  • the weight of water as a percentage of the weight
    of an oven dry sample of wood
  • freshly cut lumber can range from 30 to200

36
Fiber Saturation Point
  • the point at which the cell cavities are empty
    but the cell walls are full of water
  • approx. 28 MC

37
Moisture Content
38
Wood Product Moisture Content
39
Shrinkage Relative to the Major Planes
40
Manufacture of Sawn Lumber
41
Surfacing
  • S4S, surfaced four sides
  • S-Green, surfaced at gt19 MC
  • S-Dry, surfaced at 19 or less

42
Categories of Dimension / Stress Rated Framing
Lumber
43
How Do We Determine the Strength of Lumber
44
Visual Grading by Certified Graders
  • based upon tested strength of clear sample
  • reductions in strength (grade) made based upon
    defects, grain direction etc

45
Grade Stamps
46
Machine Testing
  • every board is tested and stamped according to
    results

47
Machine Stress Rated Lumber
48
In-Grade Testing
  • North American In-Grade Testing Program, 1977
  • testing of 70,000 full size pieces (1 million
    board feet)
  • created a database of empirical design values
  • Bending values went up for narrows and high
    grades, down for wides and lower grades

49
Engineered Wood Products
50
Engineered Wood Products
  • attempt to improve the basic properties of lumber
  • strength
  • appearance
  • dimensional stability
  • cost
  • use fast-growing, low-density wood species in
    combination with plastic resins

51
Engineered Wood Products
  • potential disadvantages
  • out-gassing from formaldehydes
  • deterioration under certain conditions
  • FRT plywood
  • appearance

52
Engineered Wood Products
  • Sheathing and Decking
  • Main Structural Members
  • Stress Skin Foam Panels

53
Sheathing and Decking
  • Plywood
  • Oriented Strand Board (OSB) and Waferboard

54
Main Structural Members
  • Light Frame Trusses
  • Glue Laminated Lumber (Glulam)
  • Laminated Veneer Lumber (LVL)
  • Parallel Strand Lumber (PSL)
  • Prefabricated Wood I-Joists

55
Light Frame Trusses
  • Flat Plate Connectors
  • Stamped metal plates hydraulically pressed into
    wood to make connections
  • Suitable for floors and roofs
  • Proprietary Connectors
  • Wood Top and Bottom Chord
  • Fab. Steel Element for Web w/ Integral Fastener
  • Split Ring Connector
  • For Custom-Designed, Field-Fabricated Trusses
  • Increase Effective Area of Joint

56
Glue Laminated Lumber (Glulam)
  • Old Technology
  • Headers, Beams, Girders and Columns
  • Strength Depends on Wood Species and Quality
  • Limitless Variety of Straight and Curved
    Configurations

57
Glulam Manufacture
58
Laminated Veneer Lumber (LVL)
  • Based on Plywood Technology
  • Headers, Beams and Girders
  • Sized to Flush Frame with Platform Framing
  • i.e. 1 3/4" x 9 1/4"
  • Fb 2800 psi, E 2,000,000 psi

59
LVL Manufacture
60
Parallel Strand Lumber (PSL)
  • Based on Cross between Plywood OSB Technology
  • Strands are up to 8' long and 1/2" thick
  • Headers, Beams, Girders and Columns
  • Sized to Flush Frame with Platform Framing
  • i.e. 1 3/4" x 9 1/4"
  • Potential Applications in Finish and Cabinet Work

61
PSL Manufacture
62
Prefabricated Wood I-Joists
  • Profile Similar to Steel Beams
  • Top and Bottom Flanges Resist Compressive and
    Tensile Stresses Respectively
  • Solid Wood
  • LVL
  • Glulam
  • Web Resists Shear Forces
  • Plywood
  • OSB

63
Stress Skin Foam Panels
  • Walls, Floors and Roofs
  • Foam Core Bonded to Structural Skin
  • Modular Design Principles
  • Joints between Panel Are Key to Usability

64
Joint Types
  • Dual Spline e.g. R-Control
  • Special Piece e.g. Ray-Core
  • Stud
  • Cam Lock

65
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