Estimating local modulus of elasticity in a beam from bending measurements: an overview
2007
Bechtel, F.K. | Hsu, C.S. | Hanshaw, T.C.
Bending modulus of elasticity measurements have been useful and profitable for decades in the sorting of dimension lumber for its structural quality. Bending and tensile strengths of lumber are known to be correlated with modulus of elasticity. Previous research indicates that knowledge of elasticity properties on shorter spans may improve the correlation with strength. However, for practical reasons, bending spans cannot be as short as the desired measurement resolution. It is expected, therefore, that the optimal estimation method of the present work will be applied in the machine stress rating (MSR) process for more accurate sorting of dimension lumber into MSR grades. We describe a method for estimating local modulus of elasticity along the length of a beam. A sequence of measurements from overlapping bending spans, such as those obtained in equipment for MSR lumber production, is processed using a new concept called "span function." The method is feasible in real-time, and the primary requirement for its implementation with high-speed, production-line equipment is additional software. Tests indicate that the method may be immediately applicable in reducing measurement noise in the MSR process, thereby improving grading accuracy. Further, it is likely that improved grading algorithms will be developed that make use of local elasticity properties. Because of the large throughput volume of modern MSR machinery, the profit increment from reduced measurement noise alone has the potential for funding the research into better grading algorithms.
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