Stiffness Characterization of Single Lap Shear Screw Fastened Connections Using Finite Element Modeling

Cold-formed steel (CFS) connections are commonly fastened using self-tapping self-drilling screws. Though screw manufacturers typically provide the strength of their screws, the stiffness of these connections is typically not reported. While modern design codes are strength-based, stiffness is increasingly necessary to characterize cold-formed steel system response in seismic applications. The full force-displacement response of the fastened connections is required for energy dissipation analysis. Historically, researchers and engineers have conducted experimental testing to determine connection behavior. However, repeatedly conducting this type of experiment is time consuming and expensive. This work aims to create robust finite element models that can successfully predict the force-displacement response of single lap steel-to-steel shear connections, without requiring tests. Five models of single lap screw connections were created using the finite element program ABAQUS/CAE. The thickness of the two CFS plies used in the connection varied for each model. These models were validated using experimental results of identical screw connections. Stiffness is the focus of the work herein, though strength results are also provided. During the development of the models, it was found that the contact parameters defined between the screw and the CFS plies had the most significant effect on the connection stiffness. To further investigate the effect of each contact parameter on the stiffness of the models, a parametric study was also conducted. In general, the results of the modelling program showed good agreement with the stiffness found in the tests. This work represents a promising first step in finite element characterization of cold-formed steel fastened connections