Combined loading of angled screws in timber connections A study to evaluate the stiffness and load-carrying capacity of inclined screws

Abstract

Connections have a deciding role in the design of timber structures as they often present complex solutions and behaviour, which makes them critical areas during the design process. As wood has orthotropic properties the structural behaviour of connections becomes highly influenced by fastener- and force orientation. For connections with inclined screws, this behaviour is not fully reflected on in the current design standards. Therefore, the aim of this thesis is to study the combined loading of angled screws in timber-timber connections by evaluating the slip modulus and load-carrying capacity. The study investigates the behaviour of timber connections with inclined screws under various load scenarios and screw angles. The thesis utilizes experimental test results from previous studies, analytical equations from design standards and previous research, while the numerical part is carried out through finite element analysis in ABAQUS. The results of the study indicate that the slip modulus and load-carrying capacity of timber connections with inclined screws are underestimated by Eurocode 5 in general but especially when considering certain angles. This does still remain true with the second generation of Eurocode 5. The research does however demonstrate that the use of inclined screws can significantly increase the load-carrying capacity of timber connections, as well as the stiffness and improve their overall performance. Additional research on how to implement different load-to-grain angles is suggested to improve the perfomance further.