Pushout Tests on Steel-Timber Connections Using Self-Tapping Screws

This paper presents an experimental investigation to evaluate the connection performance of self-tapping wood screws for use in steel-timber composite construction. Monotonic pushout tests were conducted on cross-laminated timber (CLT) made from Southern Yellow Pine species that was fastened to a hot-rolled wide flange steel section using three different brands of self-tapping wood screws available in the US construction market. The ultimate load and relative slip of the connection was measured to make design recommendations for using self-tapping screws in steel-timber composite floor systems. Additional testing parameters included: fastener length, fastener spacing to investigate group effect, panel layup orientation to investigate loading screws in different wood grain orientations, and edge distance to investigate potential panel side failure modes. Experimental results revealed that screw geometry at the steel-timber interface is critical for developing a plastic hinge to reach higher connection strengths and deformation capacities. Results are compared with design yield mode equations and to previous studies, and a simplified calculation method for predicting the ultimate connection strength of mechanical fasteners used in steel-timber construction is proposed.