ASD/LRFD Manual - American Wood Council

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ASD/LRFD MANUAL FOR ENGINEERED Wood Construction 15 The linear expansion coefficients across the grain (radial and tangential) are proportional to wood density. These coefficients are about five to ten times greater than the parallel-to-the-grain coefficients and are given as: Radial: e ⎡ − ⎣18 G 5. 5⎤ ⎦ 10 6 in./in. / ° F (M4.4-5) TE = ( ) + Tangential: ( ) e ⎡ − ⎣18 G 10. 2⎤ ⎦ 10 6 in./in. / ° F (M4.4-6) where: TE = ( ) + ( ) 4 G = tabulated specific gravity for the species. Table M4.4-2 Species Coefficient of Moisture Expansion, e ME , and Fiber Saturation Point, FSP, for Solid Woods Radial (in./in./%) Tangential (in./in./%) e ME Volumetric (in. 3 /in. 3 /%) Alaska Cedar 0.0010 0.0021 0.0033 28 Douglas Fir-Larch 0.0018 0.0033 0.0050 28 Englemann Spruce 0.0013 0.0024 0.0037 30 Redwood 0.0012 0.0022 0.0032 22 Red Oak 0.0017 0.0038 0.0063 30 Southern Pine 0.0020 0.0030 0.0047 26 Western Hemlock 0.0015 0.0028 0.0044 28 Yellow Poplar 0.0015 0.0026 0.0041 31 FSP (%) M4: SAWN LUMBER Table M4.4-3 provides the numerical values for e TE for the most commonly used commercial species or species groups. Wood that contains moisture reacts to varying temperature differently than does dry wood. When moist wood is heated, it tends to expand because of normal thermal expansion and to shrink because of loss in moisture content. Unless the wood is very dry initially (perhaps 3% or 4% MC or less), the shrinkage due to moisture loss on heating will be greater than the thermal expansion, so the net dimensional change on heating will be negative. Wood at intermediate moisture levels (about 8% to 20%) will expand when first heated, then gradually shrink to a volume smaller than the initial volume, as the wood gradually loses water while in the heated condition. Even in the longitudinal (grain) direction, where dimensional change due to moisture change is very small, such changes will still predominate over corresponding dimensional changes due to thermal expansion unless the wood is very dry initially. For wood at usual moisture levels, net dimensional changes will generally be negative after prolonged heating. Calculation of actual changes in dimensions can be accomplished by determining the equilibrium moisture content of wood at the temperature value and relative humidity of interest. Then the relative dimensional changes due to temperature change alone and moisture content change alone are calculated. By combining these two changes the final dimension of lumber and timber can be established. American Forest & paper association
16 M4: SAWN LUMBER Table M4.4-3 Coefficient of Thermal Expansion, e TE , for Solid Woods Durability e TE Species Radial (10 -6 in./in./°F) Tangential (10 -6 in./in./°F) California Redwood 13 18 Douglas Fir-Larch 1 15 19 Douglas Fir, South 14 19 Eastern Spruce 13 18 Hem-Fir 1 13 18 Red Oak 18 22 Southern Pine 15 20 Spruce-Pine-Fir 13 18 Yellow Poplar 14 18 1. Also applies when species name includes the designation “North.” Designing for durability is a key part of the architectural and engineering design of the building. This issue is particularly important in the design of buildings that use poles and piles. Many design conditions can be detailed to minimize the potential for decay; for other problem conditions, preservative-treated wood or naturally durable species should be specified. This section does not cover the topic of designing for durability in detail. There are many excellent texts on the topic, including AF&PA’s Design of Wood Structures for Permanence, WCD No. 6. Designers are advised to use this type of information to assist in designing for “difficult” design areas, such as: • structures in moist or humid conditions • where wood comes in contact with concrete or masonry • where wood members are supported in steel hangers or connectors in which condensation could collect • anywhere that wood is directly or indirectly exposed to the elements • where wood, if it should ever become wet, could not naturally dry out. This list is not intended to be all-inclusive – it is merely an attempt to alert designers to special conditions that may cause problems when durability is not considered in the design. American Wood Council
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66 M9: WOOD STRUCTURAL PANELS M9.3
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68 M9: WOOD STRUCTURAL PANELS Table
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70 M10: MECHANICAL CONNECTIONS M10.
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86 M11: DOWEL-TYPE FASTENERS M11.1
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88 M11: DOWEL-TYPE FASTENERS Americ
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90 M12: SPLIT RING AND SHEAR PLATE
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92 M13: TIMBER RIVETS M13.1 General
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94 M14: SHEAR WALLS AND DIAPHRAGMS
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100 M15: SPECIAL LOADING CONDITIONS
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102 M16: FIRE DESIGN M16.1 General
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104 M16: FIRE DESIGN Table M16.1-4
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106 M16: FIRE DESIGN Figure M16.1-2
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120 M16: FIRE DESIGN Poles and Pile
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132 M16: FIRE DESIGN Roof and Floor
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134 M16: FIRE DESIGN NER - 392 WTCA
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136 M16: FIRE DESIGN UL - P522 & P5
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140 M16: FIRE DESIGN Area Separatio
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156 M16: FIRE DESIGN Example 16.2-1
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American Forest & Paper Association
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