Cold-formed steel screwed connections with dimples: Numerical investigation and design proposal

In recent years, screwed connections with dimpled holes have widely been adopted in cold-formed steel (CFS) framing to facilitate screw installation and enhance overall fabrication efficiency. These connections typically utilise self-tapping screws to fasten directly into steel sheets through pre-punched holes. Experimental investigations on single-lap CFS screwed connections with and without dimpled holes were recently conducted and are presented in a companion paper by the authors. The results demonstrated that the inclusion of dimples enhances both the ultimate shear strength and stiffness of screwed connections. Comparisons between experimental data and code-based predictions highlighted the need for new design provisions for dimpled screwed connections in shear, which are currently not included in existing design standards. This paper presents detailed finite element (FE) models, incorporating three-dimensional geometries of self-tapping screws with spiral threads to realistically simulate the interaction between screws and dimpled holes. The non-linear numerical models, developed in ABAQUS/Explicit, were calibrated against experimental results. A parametric study using the validated FE models was then performed to examine the effects of screw diameter, dimple depth, and sheet thickness combinations on shear performance. Based on the combined experimental and numerical results, new design equations are proposed for shear-loaded CFS screwed connections with dimpled holes, particularly governed by the bearing limit state. Finally, a reliability analysis was performed to evaluate the safety and accuracy of the proposed design formulations in accordance with the ANSI/SDI AISI-S100:2024 specification and the combined AS/NZS-4600:2018 and NCC 2019 standards, providing comprehensive design guidance for screwed connections with dimpled holes. • Cold-formed steel screwed connections with pre-punched dimpled holes were investigated. • FE ABAQUS models were developed to simulate single-lap shear tests on screwed connections with dimples. • A parametric study was conducted to examine the effects of screw diameter, dimple depth and sheet thickness. • New design equations were proposed based on the combined experimental and numerical results. • A reliability analysis was performed to evaluate the safety and accuracy of the proposed design formulations.