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A General Introduction to Wood Construction

A General Introduction to Wood Construction. Journal of Architectural Education. An Exploration of the Relationships between Houses and Forests in American History William Gould Sturges University of Oregon. There is a Supply & Demand Imbalance for Wood Products.

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A General Introduction to Wood Construction

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  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 >70bbf

  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 Today’s 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 >19% 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

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