An Analysis of Flexural Stiffness of 5-Ply Southern Pine Plywood at Short Spans Parallel to Face Grain


  • Evangelos J. Biblis
  • Yen-Ming Chiu


A method for predicting deflection of 5-ply plywood strips in small span-to-depth ratios has been verified experimentally. This method first transforms the cross section of 5-ply plywood into a homogeneous double-I-beam and then calculates shear deflection by equating the internal work with the external work of the bend double-I-beam. This method predicts shear deflection with an average error of 18% and total deflection at span-to-depth ratio of 24:1 with an average error of less than 6%. After considering the nonhomogeneity of southern pine veneer and the deviation of the plywood from the assumed ideal structure, the agreement between predicted and observed total deflection should be regarded satisfactory, particularly in the absence of another method by which deflection can be predicted more accurately. From the above method a simpler equation has been derived and experimentally verified for predicting shear deflection. This simpler equation is based on the assumption that shear deflections in any two beams of the same length, height, and moment of inertia, similarly loaded, are proportional to the summations of the shear stresses on their respective vertical sections.


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