Experimental analysis of the performance of screwed connections for steel-timber composite beams

Abstract

The proposed research addresses the structural behavior of screwed connections in composite beams consisting of Cold-Formed Steel (CFS) profiles and timber boards. An experimental program consisting of 30 push-out tests involving six different models was conducted to evaluate the performance of different types of connection. The screw diameter and spacing were different in each model, and in one out of every five specimens of each model, the screws were installed with steel washers. Results indicate that the screws’ diameter influences the connection’s load-carrying capacity. Results also indicate that the spacing of screws influences the connection’s longitudinal shear flow: the larger the spacing between screws, the lower the longitudinal shear flow. Conversely, results from connections involving steel washers did not show any increase in load-carrying capacity or stiffness. The failure mode detected in the tested specimens resulted from the crushing of the Oriented Stranded Board (OSB) related to the rotation of the self-tapping screws. The typical failure mode, called "screw tilting", can be explained by analyzing the axial and transverse projections of the push-out force, where the latter causes crushing of the timber through contact pressure, and the former induces tension in the screw.