Effect of moisture cycling on truss-plate joint behavior

The structural performance of wood trusses, which are now commonplace in light-frame construction, is dictated in part by the mechanical properties of the truss-plate joints. However, little information exists quantifying the effect of environmental conditions on truss-plate joint properties. The main objective of this paper was to quantify the effect of moisture cycling on the mechanical properties of truss-plate joints. A secondary objective was to evaluate the possibility of retarding the degenerative effects of moisture cycling by means of an adhesive applied to the teeth of the truss plate immediately before assembly. The results indicate that mild moisture cycling decreases truss-plate joint strength and stiffness by approximately twice that of specimens subjected to a constant moisture content. More severe moisture cycling accelerated this decrease by a factor of about three. Addition of an adhesive to the teeth decreased plate backout and increased the mechanical properties of the truss-plate joints. The increase in initial stiffness caused by the adhesive was minimal after moisture cycling, and the improvement in ultimate load remained substantial even after eight severe moisture cycles.

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