Shear Deflection of Wood Beams

Shear deflection contributes a major portion to total deflection in rectangular, box, and I-beams simply supported and centrally loaded. The author of this article considers the derivation of two equations for shear deflection and settles upon the elastic strain energy method. He discusses deflection of beams due to pure shear and pure bending and combines these concepts into one equation which accounts for both factors. The conjugate equation, accurately predicts beam stiffness under a wider range of conditions than previous equations. Using the new methods, the author demonstrates the relative contributions of shear and bending to the total deflection in beams. The shear contribution was shown to vary with the species ratio of elastic modulus to modulus of rigidity, E/G, and the beam ratio of span to depth. The shear influence will be the greatest as mentioned in low span to depth ratios, e.g. 8:1, box and 1- beams, and when the E/G ratio is large, e.g. approaching 50. Under these conditions, the shear contribution may approach or exceed 50 percent of the total deflection.

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