Adjusting modulus of elasticity of lumber for changes in temperature
1999
Green, D.W. | Evans, J.W. | Logan, J.D. | Nelson, W.J.
This study evaluated the immediate effect of temperature on flexural modulus of elasticity (MOE) of green and dry nominal 2- by 4-inch (standard 38- by 89-mm) structural lumber at temperatures ranging from 150 degrees to -15 degrees F (66 degrees to 26 degrees C). For lumber at 12 percent moisture content (MC), a linear relationship was used to relate the increase in MOE to the decrease in temperature. For green lumber, MOE also increased with decreasing temperature. A segmented linear regression was developed to describe the change in MOE for temperatures from 150 degrees to 0 degrees F (66 degrees to -18 degrees C). The slope of this relationship was steeper below 32 degrees F (0 degrees C) than above this temperature. The actual MC of green lumber was not a factor above 0 degrees F (-18 degrees C). Below 0 degrees F, the increase in MOE with decreasing temperature was a function of both actual green MC and temperature. We discuss factors that cause this behavior in green wood at low temperatures and the use of an empirical model for describing the MOE-temperature relationship as a function of MC for frozen green lumber. The model is believed to be independent of softwood species and lumber grade. Relative to MOE at at 100 degrees F (38 degrees C), results of this research support the C(t) factors given in the National Design Specifications.
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