Fire performance of moment-resisting concealed timber connections reinforced with self-tapping screws

Recent research shows that the two predominant failure modes encountered in concealed wood-steel-wood bolted connections at ambient temperature are perpendicular-to-grain tensile splitting and row shear out [1]. The study presented in this paper aims to investigate the fire performance of these connections but with self-tapping screws (STS) acting as perpendicular-to-wood grain reinforcement along with applying fire protection to the metal components, e.g., head and nut of steel bolts and connecting steel plates, of the connections. Two full-size glulam beam end connections were tested experimentally at elevated temperatures while being loaded perpendicular to wood grain to develop bending moment on the connection. Two connection configurations, each involved four steel bolts arranged in two different patterns, were examined. In both fire tests, the connection assemblies were exposed to elevated temperatures that followed the CAN/ULC S101 standard time-temperature curve [2] and each connection configuration was loaded to 100% of the ultimate design load of the weakest connection configuration. The experimental results showed that the influence of the self-tapping screws was significant as it helped in avoiding the occurrence of wood splitting or row shear out, and thus resulted in increased time to failure of the connections in standard fire condition.