Structural Behavior of CLT-Steel Composite Beams with Self-Tapping Screw Shear Connections

The use of timber–steel composite floor systems consisting of a timber floor slab connected to steel beams is increasing in North America. However, questions remain surrounding the performance of self-tapping screw shear connections, and there is an ongoing need to develop methods to determine their bending stiffness and moment-resistance. This paper discusses experimental results of the behavior of cross-laminated timber (CLT)-steel composite beams with self-tapping screws as shear connectors, and examines the influence of several parameters on their performance, including CLT orientation and continuity, screw spacing, and screwed-glued shear connections. Furthermore, the degree of composite action at serviceability and ultimate limit states was analyzed, and approaches to determine the effective bending stiffness and moment resistance of partially composite timber–steel beams are presented. Results of the study show that CLT-steel composite beams exhibit ductile behavior, and that taking advantage of partial composite action between the CLT and steel results in a moment resistance that is more than 2.4 times larger than that of the steel section alone. For screwed shear connections, the degree of partial composite action at service was 53% on average, whereas for screwed and glued connections it was 76%. Comparison of experimental results to the proposed design approaches demonstrated that the proposed methods could predict the stiffness and capacity of the composite beams to within 5% of the experimental result, on average.