Several examination on the static bending tests methods of wood using todomatsu (Japanese fir)

We examined the methods of measuring the bending properties of wood using todomatsu (Abies sachalinensis Fr. Schmidt) by elementary bending theory. Three- and four-point bending tests were conducted under various span/depth ratios, and the load, deflection, loading point displacement, and strain at the bottom of the center were simultaneously measured. The load-deflection, load-loading point displacement, and load-strain relations were regressed into Ramberg-Osgood?s function. Young?s modulus, proportional limit stress, and bending strength were calculated by substituting the parameters obtained by the regression into the equations derived from elementary bending theory. By comparing the obtained properties with each other, we examined an appropriate method for measuring the bending properties based on elementary bending theory. The results are summarized as follows: 1) regarding the measurement of Young?s modulus, a strain gauge was effective for reducing the influence of span/depth ratio even in the small span/depth ratio range; when the strain gauge was not used, the four-point bending test with measuring the deflection at the center was most effective because the span/depth ratio range where Young?s modulus was stably obtained was larger than those obtained from the other methods.; 2) the proportional limit stress was greatly influenced by the method of measuring deflection, and, in contrast, the influence of span/depth ratio on the proportional limit stress was less significant than that on Young?s modulus; 3) the influence of span/depth ratio on the bending strength was less significant than that on Young?s modulus; and 4) the load-deflection relation under four-point bending using a specimen whose span/depth ratio is larger than 20 is recommended for consistent determination of the bending properties based on elementary bending theory.

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