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    Author(s): J. E. Winandy; P. K. Lebow; W. Nelson
    Source: (Research paper FPL ; RP-568):20 p. : ill. ; 28 cm.
    Publication Series: Research Paper (RP)
    Station: Forest Products Laboratory
    PDF: Download Publication  (794 KB)


    This report describes the development of a test method and predictive model to estimate the residual bending strength of fire-retardant-treated plywood roof sheathing from measurement of screw-withdrawal force. The preferred test methodology is described in detail. Models were developed to predict loss in mean and lower prediction bounds for plywood bending strength as a function of a screw-withdrawal force. Our analysis of fire-retardant-treated plywood from three different studies, each with various fire-retardant-treatment, processing, plywood thickness, and exposure temperature groupings, clearly indicated that different fire-retardant-treatments and plywood thicknesses could not be grouped into a single buniversalc model. Nevertheless, some grouping was possible; parameter estimates for several grouped fire-retardant formulations and plywood thicknesses are reported for mean trends and lower prediction boundaries. Although the models were shown to acceptably predict plywood bending strength, additional work is needed to expand these models to address the effects of plywood quality, wood temperature, and moisture content at time of test.

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    • This article was written and prepared by U.S. Government employees on official time, and is therefore in the public domain.


    Winandy, J. E.; Lebow, P. K.; Nelson, W. Predicting bending strength of fire-retardant-treated plywood from screw-withdrawal tests. (Research paper FPL ; RP-568):20 p. : ill. ; 28 cm.


    Plywood, Bending strength, Screwed joints, Fire retardants, Fire retardant treatment, FRT plywood

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