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ABSTRACT
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 150o to - 15degF (66o to 26oC). 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 150deg to Odeg F (66deg to -18deg C). The slope of this relationship was steeper below 32F (0C) than above this temperature. The actual MC of green lumber was not a factor above 0F (-18oC). Below OoF, 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 100oF (38oC), results of this research support the Ct factors given in the National Design Specifications ( 1).
Historically, tests of lumberproperties have been conducted in a laboratory under constant conditions of temperature and humidity, which allow the effect of temperature to be separated from the generally greater effect of moisture content (MC). Increasingly, however, tests are being conducted in the field under ambient conditions. For example, bending tests of visually graded lumber in the U.S. Ingrade testing program have been conducted in the field using portable equipment (18). Wood temperatures at time of test ranged from about Oo to 90oF (-18o to 32C). Such test results must be corrected to room temperature to obtain meaningful results.
In the United States, mechanical grading is a two-step process. First, a machine is used to measure a mechanical or physical property and growth characteristics are visually assessed to sort the lumber into proposed grades. Second, the mechanical grades are initially qualified by test, and proof-testing is then performed daily to verify one or more of the assigned properties. Two approaches to mechanical grading...