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

Authors

  • Evangelos J. Biblis
  • Yen-Ming Chiu

Abstract

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.

References

American Society for Testing and Materials. 1968. ASTM Standards, Part 16. D805-63. Philadelphia, Pa.nBiblis, E. J. 1965. An analysis of wood-fiberglass composite beams within and beyond the elastic region. Forest Prod. J., 15(2): 81-88.nBiblis, E. J. 1969. Flexural rigidity of southern pine plywood. Forest Prod. J., 19(6): 47-54.nBiblis, E. J. and Yen-Ming Chiu. 1969. An analysis of flexural elastic behavior of 3-ply southern pine plywood. Wood and Fiber, 1(2): 154-161.nMarch, H. W. 1936. Bending of a centrally loaded rectangular strip of plywood. Physics, 7(1): 32-41.nNewlin, J. A., and G. W. Trayer. 1924. Deflection of beams with special reference to shear deformations. National Advisory Committee for Aeronautics Rpt. No. 180. Washington, D. C.n

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Published

2007-06-19

Issue

Number 2 / Summer 1970

Section

Research Contributions

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