Experimental Study of Cold‐formed Steel Screw Connections Failing in Block Shear

Abstract

Cold‐formed steel (CFS) structures, characterised by their lightweight and high strength‐to‐weight ratio, are increasingly used in steel‐framed structural systems in low‐ and mid‐rise buildings. Screw connections are commonly employed to join these CFS members because they are simple to install and allow rapid drilling through thin steel sheets. While the predominant failure modes in single‐screw connections are typically governed by tilting and/or bearing, group‐screw connections with closely spaced screws are highly susceptible to block shear failure. Currently, no national standards such as ANSI/SDI AISI S100:2024 or AS/NZS 4600:2018 provide design rules for group‐screw connections undergoing block shear failure, despite addressing this limit state in detail for group‐bolt connections. To address this gap, an experimental program on group‐screw (two‐ and four‐screw) connections was conducted at the University of Sydney to investigate their block shear behaviour across different CFS sheet thicknesses and screw spacings. The measured block shear resistances of the group‐screw connections were then compared against predictions specified for bolt connectors in ANSI/SDI AISI S100:2024 and AS/NZS 4600:2018. Experimental observations, supported by Digital Image Correlation (DIC), demonstrated that unlike group‐bolt connections where active shear planes are critical, group‐screw connections mobilise the gross shear plane. In certain instances, code‐based predictions were found to be overly conservative, highlighting the need for new design equations tailored to group‐screw connections failing in block shear. This paper presents a comprehensive discussion on the experimental observations and key findings.