Shear behavior and parametric analysis of steel-to-timber connections using coach screws

The mechanical performance of bolted steel-to-timber (ST) connections is significant influenced by the clearance between bolts and pre-drilled holes. As a potential alternative, coach screws, a type of partially threaded fastener, have been introduced for timber connections in recent years. To investigate the shear behavior of the ST connections with coach screws, a series of shear tests were conducted under various parametric configurations in this study, systematically examining the influences of screw diameter, pre-drilled hole diameter, penetration depth, and load-to-grain angle. The test results demonstrated that the shear stiffness and load-carrying capacity of the connections are significantly related to the screw diameter and load-to-grain angle. Increasing the screw diameter from 8 mm to 16 mm enhanced the shear stiffness and maximum load by 200% and 209%, respectively. Moreover, reducing the pre-drilled hole diameter and increasing the penetration depth improved the maximum load through enhancing the rope effect. Subsequently, the theoretical formulas to determine the shear stiffness and load-carrying capacity of the connections were derived based on the beam-on-elastic-foundation (BOEF) model and Eurocode 5 methods, respectively. Comparison of the results indicated that the proposed BOEF model could predict the shear stiffness with good accuracy. For the load-carrying capacity, the Eurocode 5 method provides conservative predictions due to its underestimation of the rope effect contribution, thereby ensuring a safety margin in design. • Shear tests on steel‑to-timber connections using coach screws. • Parametric analysis considering screw diameter, depth, and load angle. • Theoretical models for determining the stiffness of timber connection.