3501-12 - WOOD AS A CONSTRUCTION MATERIAL Classification of...

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WOOD AS A CONSTRUCTION MATERIAL • Classification of Trees • Structure of Wood • Properties of Wood • Grading of Wood • Preservation of Wood •P lyw ood • Other Wood Products Classification of Trees (1) EXOGENOUS Grows ________ by adding new cells in a layer between the existing wood and the bark. (a) ___________ - conifers or cone-bearing e.g. Pine, Spruce, Fir, Hemlock, Cedar, Cypress, Redwood (b) _____________ - broad-leafed, mostly deciduous e.g. Oak, Maple, Ash, Walnut, Hickory, Poplar, Gum, Birch (2) ENDOGENOUS Grows ___________ by adding new cells to the old. e.g. Bamboo, Palm Wood Structure • ________ Wood cells • ____________ (15 to 30 % ) Cellulose provides __________________ & elastic property of wood. Lignin cements the cellulose together to provide
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cambium layer heartwood sapwood pith bark medullary ray Cross Section of a Tree Cambium Layer- Layer of new cells beneath the bark. (This is the _______ region of the tree) Pith- ___________ ring Heartwood- ________ inner portion, relatively darker in color. (More resistant to decay as compared with sapwood) Sapwood- __________ outer portion, relatively lighter in color. Medullary Ray- Group of cells in the ______ ________ , adding strength to the radial direction. Two growth regions in an annual ring: (1) Early Wood (Springwood) - Inner _______ ___________ layer, which grows in the spring and grows relatively faster. (2) Late Wood (Summerwood)- outer ______ layer, which grows in the summer and grows relatively slower. Rate of Growth: Measured by the number of annual growth rings per distance (rings/inch) along a line perpendicular to the rings across a right section of the tree. The wood is relatively ________ when the rate of growth is___________.
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Properties of Wood (1) DENSITY Solid wood substance ( cellulose ) Specific gravity= 1.5 Wood ( with air-filled cavities ) Specific gravity = 0.3 - 0.9 ( A function of moisture content ) (2) MOISTURE CONTENT Wood contains moisture in 2 forms: a) ______________________ in the capillaries of cell walls. b) _________________ in cell cavities. Fiber-saturation point: moisture content at which the cell walls are __________ & _________________ exists; 25 - 30%. Ranges of moisture content:
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3501-12 - WOOD AS A CONSTRUCTION MATERIAL Classification of...

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