Effect of moisture cycling on mechanical response of metal-plate connector joints with and without an adhesive interface

Abstract

Wood trusses are frequently located in light-frame structures where they are subjected to significant shifts in moisture conditions.

However, little is known about the effects of moisture cycling of the wood members on the mechanical behavior of metal-plate connector (MPC) joints. Thus, the primary objective of this study was to quantify the effect of wood moisture content fluctuations on MPC joint behavior. A secondary objective was to investigate maintaining interfacial integrity between the metal-plate teeth and wood by applying an epoxy adhesive at the interface and noting the changes in mechanical performance of MPC joints. Results of this study indicate that moisture cycling significantly affects the mechanical performance of MPC joints. Some of the decline in mechanical performance could be attributable to pIate "backout." It was shown that in addition to a decrease in mechanical performance, moisture-cycled specimens probably have an altered stress transfer mechanism as exhibited by load-slip traces. Initial stiffness of the load-slip traces is most drastically affected by moisture cycling, but ultimate load and load-at-0.015-inch-slip were also affected. Addition of an adhesive interface between the teeth and wood appears to increase the mechanical performance of MPC joints. However, the apparent increase in mechanical performance could not be quantified due to the lack of identically matched specimens. The degrade of ultimate load and load-at-0.0l5-inch-slip of MPC joints with an adhesive interface was similar to that of standard MPC joints. Initial stiffness of MPC joints with an adhesive interface degraded more rapidly than standard MPC joints, probably due to weakening of the adhesion between the teeth and wood. Addition of an adhesive to the tooth-wood interface resulted in less variability of mechanical properties when compared to standard MPC joints, with this variability remaining constant regardless of number and severity of moisture cycles.