Shear Performance of Connectors in Steel–CLT Hybrid Floors: Influence of Fastener Configuration and Flange Knurling

Steel-timber hybrid floors provide many benefits to construction by matching two materials that both have speed of construction goals as well as sustainability efforts. This pairing has led to many steel-timber hybrid buildings being constructed. However, even though these designs are being constructed, there are knowledge gaps as it pertains to stiffness of the floors for serviceability limit states (e.g., vibration) and diaphragm design for seismic or wind applications. Much of these knowledge gaps fall in the range of limited understanding of the fundamental mechanisms of composite action between steel and mass timber, particularly cross laminated timber (CLT). This paper summarizes experimental testing of novel shear connectors, screws inserted through the CLT into the top flange of the beam, screws inserted through the bottom flange of the steel beam into the CLT, and through bolts, under direct shear loading demands. The connectors were tested with and without knurling of the top flange of the beam to increase friction. The results of the experiments were analyzed for strength, stiffness, and ductility and compared to similar connectors that have been tested throughout the world. The results demonstrate that while through bolts have the highest strength capacity, they have the lowest stiffness of the connectors and that knurling increases the capacity of the connectors but decreases the ductility of the connectors, similar to other top flange treatments explored by other researchers.