Beam–Column Connections with Concealed Steel Components in Timber Structures

Abstract

In timber structures, concealed beam-to-column connections may be attractive in ap plications where high load-carrying capacity must be combined with a seamless archi tectural expression. However, such connections are challenging to design, since the connection must provide sufficient resistance in both the steel components and the sur rounding timber. In particular, compression perpendicular to the grain in the beam-side contact zone may become governing in bearing-type solutions. This thesis investigates concealed beam-to-column connections in timber structures for high-load applications. Different concealed connection families were first reviewed and qualitatively screened with respect to load transfer, structural behaviour, and degree of concealment. Based on this screening, a bearing-type concept was selected for further study and developed in the form of an internal beam shoe integrated within the beam cross-section. The connection behaviour was then studied through a combination of analytical and numerical methods. Simplified analytical models were used to describe the principal load-transfer mechanisms and to provide reference quantities for validation of a nu merical model developed in Abaqus. The numerical analysis was used to investigate the force transfer to the timber column and to identify the governing steel components and fasteners. The results showed that the fasteners satisfied the governing shear, axial, and combined interaction checks for the studied load case, while the bearing plate was identified as the critical steel component due to local bending stresses. On the beam side, the unreinforced timber did not provide sufficient resistance against compression perpendicular to the grain. Reinforcement strategies were therefore stud ied analytically through parametric analyses and genetic-algorithm-based optimization. The results showed that fully threaded screws, rods with wood screw thread, and bonded in rods could increase the beam-side capacity sufficiently to carry the applied load, whereas wooden dowels could not. Among the feasible alternatives, screw reinforce ment was found to be the most efficient solution with respect to capacity increase and associated CO2-emissions.