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Title: Stress Wave E-Rating of Structural Timber—Size and Moisture Content Effects
Author: Wang, Xiping;
Source: In: USDA Forest Service, Forest Products Laboratory, General Technical Report, FPL-GTR-226, 2013; pp. 38-46
Publication Series: Full Proceedings
Description: The objectives of this study were to investigate the influence of cross sectional size and moisture content on stress wave properties of structural timber in various sizes and evaluate the feasibility of using stress wave method to E-rate timber in green conditions. Four different sizes of Douglas-fir (Pseudotsuga menziesii) square timbers were tested using both stress wave and static bending methods at different moisture levels, ranging from green to dry conditions. As expected, stress wave velocity increased continuously as moisture content decreased through the whole moisture range studied. Master velocity-moisture relationships were established for Douglas-fir square timbers to convert stress wave velocity values from one moisture condition to any other moisture conditions. It was found that stress wave based dynamic MOE was generally higher than static bending MOE. However, the difference tended to be constant when moisture content was above the fiber saturation point (28%). This implied that green timber could still be sorted effectively based on dynamic MOE values even if there are moisture differences between individual pieces. The results also show that cross sectional dimension of square timbers has a significant influence on dynamic MOE. As the cross sectional size of square timbers increased, the MOE deviation increased also. This indicates that different sizes of timbers can not be graded together without making appropriate adjustments on dynamic MOE for size effect.
Keywords: Stress wave, structural timber, modulus of elasticity, moisture content, size
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Wang, Xiping 2013. Stress Wave E-Rating of Structural Timber—Size and Moisture Content Effects. In: USDA Forest Service, Forest Products Laboratory, General Technical Report, FPL-GTR-226, 2013; pp. 38-46
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