Investigation of Thermal Effects on Nailed Connection of Mass Ply Panels

Mass ply panels (MPP), a relatively new mass timber product, has been utilized in several construction projects as diaphragm and wall panels. Connection for MPP is a crucial structural component that requires a better understanding. This article presents an experimental investigation into elevated temperature exposure–driven property degradation of MPP nailed connections, which is important for both the design of new structures in terms of fire resistance and the rehabilitation of structures partially damaged by fire. One control group and 32 exposure groups, which were combinations of eight elevated temperatures and four exposure durations, were investigated. The failure modes and yield strength of the nailed connection were analyzed as a function of elevated temperature and exposure time and compared with the prediction from the National Design Specification and existing literature. The results show a decrease of up to 45 percent in initial stiffness and ultimate load; meanwhile, there was no statistical evidence for the change in yield load in the majority of testing groups. Two analytical models, namely, multilinear regression and first-order kinetics model, were proposed to model the degradation of initial stiffness and ultimate strength. The kinetics model provided a better prediction and suggested that the initial stiffness and ultimate strength of the nail connection degraded over time at rates depending on the exposure temperature.