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CE 479: Design of Building Components and Systems Fall 2012 – J. Liu

CE 479: Design of Building Components and Systems Fall 2012 – J. Liu. Wood: Intro, Properties, Grades. OUTLINE. Introduction to Wood Properties Design Specifications Sizes, Grading. Introduction to Wood. Wood Members Species and Species Groups. Wood Members.

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CE 479: Design of Building Components and Systems Fall 2012 – J. Liu

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  1. CE 479: Design of Building Components and SystemsFall 2012 – J. Liu Wood: Intro, Properties, Grades

  2. OUTLINE Introduction to Wood Properties Design Specifications Sizes, Grading

  3. Introduction to Wood Wood Members Species and Species Groups

  4. Wood Members • Sawn lumber or solid sawn lumber • Wood members manufactured by cutting a member directly from a log • Glued laminated timbers • a.k.a. “glulams” • Laminated stock, glued and laid up to form larger wood members

  5. Wood Members • Wood poles/timber piles • Manufactured products • Plywood • Oriented strand board (OSB) • Structural composite lumber (laminated veneer or parallel strand lumber) • Fabricated components • Trusses • Wood I-joists • Box beams

  6. Sawn lumber – Basic size classifications • Dimension lumber • Smaller (thinner) sizes of structural lumber • Ranges from 2x2 through 4x16 • Any material with nominal thickness of 2 to 4 inches • Timbers • Larger sizes • 5 inch minimum nominal dimension • Practically speaking, smallest timber size is a 6x6

  7. Species and Species Groups • Structural designer uses lumber from a commercial species group rather than a specific species • Same grading rules, reference design values, grade stamps are applied to all species in a species group

  8. Species and Species Groups • Note: some groups have similar names; each is separate and distinct – different sets of reference design values • Douglas Fir-Larch and Douglas Fir-Larch (N) • Hem-Fir and Hem-Fir (N) • Spruce-Pine-Fir and Spruce-Pine-Fir (S) • (N) indicates a Canadian species group; (S) indicates USA species

  9. Species and Species Groups • Hardwoods and Softwoods • Hardwoods - broadleafed deciduous trees • Softwoods – narrow, needle-like leaves, generally evergreen, also known as conifers • “C is for Conifers” http://www.youtube.com/watch?v=FijQbZeTGNc • Large majority comes from Softwoods • Note: Douglas Fir-Larch and Southern Pine are classified as softwoods, but are relatively dense and have structural properties exceeding those of many hardwoods

  10. Typical Commercial Hardwoods Canadian Conseil Wood canadien Council du bois • Maples • Oaks • Birches • Elms • Walnut

  11. Typical Commercial Softwoods Canadian Conseil Wood canadien Council du bois • Spruces • Pines • Firs • Cedars • Hemlocks • Larches

  12. Properties Cellular Makeup Growth Characteristics (+ Guest Lecture R. Kristie) Moisture Content Shrinkage Specific Gravity Strength Other Properties, Decay (+ Guest Lecture R. Kristie)

  13. Interior of a Tree • Age • Conditions of growth • Structures • Some properties Canadian Conseil Wood canadien Council du bois

  14. Cellular Makeup Canadian Conseil Wood canadien Council du bois

  15. Cellular Makeup Canadian Conseil Wood canadien Council du bois

  16. Cellular Makeup Canadian Conseil Wood canadien Council du bois

  17. Cellular Makeup Canadian Conseil Wood canadien Council du bois

  18. Cellular Makeup Canadian Conseil Wood canadien Council du bois

  19. Cellular Makeup Canadian Conseil Wood canadien Council du bois

  20. Cellular Makeup Canadian Conseil Wood canadien Council du bois

  21. Cellular Makeup Canadian Conseil Wood canadien Council du bois

  22. Cellular Makeup Canadian Conseil Wood canadien Council du bois

  23. Cellular Makeup Canadian Conseil Wood canadien Council du bois

  24. Cellular Makeup Canadian Conseil Wood canadien Council du bois

  25. Cellular Makeup Canadian Conseil Wood canadien Council du bois

  26. Cellular Makeup Canadian Conseil Wood canadien Council du bois

  27. Cellular Makeup Canadian Conseil Wood canadien Council du bois

  28. Growth Characteristics • Include density, moisture content, knots, checks, shakes, splits, slope of grain, reaction wood, decay • Affect strength of lumber • Limits on size and number of defects permitted in a given stress grade

  29. Knots • Portion of a branch or limb that has been incorporated into the main body of the tree • Displace clear wood, cause slope of grain to deviate around them, therefore decreasing mechanical properties • Can cause stress concentrations and/or checking • Effect on tension and compression; greater effect on tension

  30. Checks, Shakes, Splits • Separations of wood fibers • (A) Checks = radial cracks • (C) Shakes = separation parallel to annual rings • (B) Splits = complete separation of wood fibers

  31. Slope of Grain • Deviation of wood fibers from a line that is parallel to edge of piece of lumber • Expressed as a ratio (e.g., 1:8, 1:15, etc.) • Measured over sufficient area to be representative of general slope of fibers; local deviations around knots disregarded

  32. Reaction Wood • Known as compression wood in softwood species • Abnormal wood that forms on underside of leaning and crooked trees • Hard and brittle • Unbalanced structure in wood • Not permitted in stress grades of lumber

  33. Moisture Content Canadian Conseil Wood canadien Council du bois

  34. Moisture Content • Moisture content in living trees comes from sap (water and dissolved mineral salts) • Can be as high as 200% in sapwood of some tress • May be 30% in heartwood of others • Held in wood in two ways: • Free water in the cell cavity • First to be driven off as wood dries • Bound water in the cell walls

  35. Moisture Content • Moisture content of lumber in service is much less than that of a living tree (can be 200 percent) • Equilibrium moisture content (EMC) • Average moisture content in service • Ranges between 7 – 14% • MC at time of construction will be higher than EMC of a building (perhaps 2 times higher)

  36. Moisture Content • Fiber Saturation Point (FSP) • Moisture content that corresponds to complete loss of free water • 100% of bound water remaining • No loss of bound water occurs above FSP • No volume changes or other changes in structural properties associated with change in MC above FSP

  37. Moisture Content

  38. Fiber Saturation Point (FSP)

  39. Above FSP Canadian Conseil Wood canadien Council du bois

  40. Below FSP Canadian Conseil Wood canadien Council du bois

  41. Shrinkage Canadian Conseil Wood canadien Council du bois

  42. Moisture Content Canadian Conseil Wood canadien Council du bois

  43. Shrinkage Canadian Conseil Wood canadien Council du bois

  44. Shrinkage Canadian Conseil Wood canadien Council du bois

  45. Shrinkage Canadian Conseil Wood canadien Council du bois

  46. Shrinkage • Shrinkage causes reduction in section properties, but reduction in MC increases structural properties • Drying of lumber in order to increase structural properties is known as “Seasoning” • “Seasoning” usually refers to a controlled drying process such as air or kiln drying

  47. Shrinkage

  48. Seasoning Checks

  49. Shrinkage Canadian Conseil Wood canadien Council du bois

  50. Moisture Content Canadian Conseil Wood canadien Council du bois

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