Investigation of hybrid thick steel-timber connections using novel self-drilling wing screws: Experimental tests and design formula

Self-drilling wing screws are commonly used in hardwood and composite board applications and offer a promising alternative to traditional bolts for connecting thick hot-rolled high-strength steel to timber in Australia and New Zealand because timber cracking is avoided during installation. Despite this potential, the shear behaviour of self-drilling wing screw connections in structural steel–timber systems has not yet been investigated. This study investigates the shear performance and load-carrying capacity of self-drilling wing screw connections between radiata pine timber and hot-rolled steel plates through an extensive experimental programme. Material characterisation included tensile coupon tests, screw bending tests, moisture content measurements, screw pull-out tests, and screw embedment tests to determine the mechanical properties of the steel, timber, and screws. A total of 70 connection tests were conducted with varying steel thickness (8–20 mm), timber thickness (15–45 mm), number of screws (1–3), and screw axis angle (45°–90°). The effects on load capacity, initial stiffness, and ductility were evaluated. Increasing the steel plate thickness from 8 mm to 15 mm increased the average shear capacity by approximately 25%, whereas increasing the timber thickness from 15 mm to 45 mm increased the capacity by 17% for single-screw and 32% for double-screw configurations. Comparisons with Eurocode 5 (2024) show significant inconsistencies: in some cases the design predictions are up to 30% conservative, while in others they overestimate the capacity by as much as 50%. To address these discrepancies, modified design equations based on Johansen yield theory are proposed to predict the shear capacity of self-drilling wing screw steel-timber connections. • 70 new Experimental tests on the novel self-drilling wing screws were conducted. • Parametric effects on load capacity, initial stiffness, and ductility were evaluated. • Eurocode 5 design guidelines were assessed. • New design equations based on Johansen yield theory were proposed.