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The bending stress analysis of wood beams in the plastic range is presented and a new theoretical method of predicting the ultimate load is developed. The method is based on the approach known as the bending theory of beams, but the pattern of stress distribution at failure in the critical cross-sectional area is now mathematically formulated on the basis of the stress-strain diagram obtained by the tests. The validity of the theoretical method is verified by a testing program using three full-size specimens. The test results agreed favorably with the theoretical predictions. The actual ultimate bending moment closely coincides with that obtained by the theory presented, as does the downward shifting of the neutral axis. Wood beams of any species can be computed by this theory if the mathematical equation for the stress-strain diagram is known. This theory is verified through tests on glue laminated beams using wood of the best quality.
Borislav D. Zakić (Mon,) studied this question.