Numerical optimisation of novel connection for cross-laminated timber buildings

This paper presents Finite Element Analyses (FEA) on the performance of a novel hold-down connection, suitable for mass-timber buildings, consisting of hollow circular steel tubes, inserted in Cross-laminated Timber (CLT) panels. The FEA models, which account for nonlinear material properties of both timber and steel components, were validated against experimental results. The primary objective of this research was to optimise the connector geometry and material properties to achieve a target yield capacity of 85 kN. Considering a capacity-based design approach, where all the wood components remain elastic and only the steel tube deforms, a sensitivity analysis was performed to quantify the input-performance correlations. It was shown that the diameter (d) and thickness (t) of the tube, as well as the coupler diameter (c) were the main parameters influencing the yield capacity and overall performance of the connection. The subsequent optimisation resulted in an optimum detailing with d = 155 mm, t = 9.5 mm and c = 30 mm, and a required steel yield stress of approx. 800 MPa. With a load-carrying capacity of 98 kN, an elastic stiffness of 30 kN/mm, and a ductility of 9, the connection was deemed suitable for the design of resilient CLT buildings. Finally, it was shown that optimised detailing exhibited a robust performance in presence of uncertainties in the timber and steel material properties, as well as geometry of the detailing.