Cyclic behaviour of typical metal connectors for cross-laminated (CLT) structures

An extended experimental programme on typical cross-laminated (CLT) connections was performed at IVALSA Trees and Timber Institute. The paper discusses the results of monotonic and cyclic tests in shear and tension (pull-out) carried out on hold-downs and steel angle brackets used to anchor the wall panels to foundations or to connect wall panels to floor panels. Mechanical properties such as strength, stiffness, energy dissipation, impairment of strength and ductility were evaluated and are critically discussed in the paper. Significant ductility and energy dissipation was attained in most of the tests. Nevertheless, brittle failure modes were observed in some tests, indicating the need for introduction of capacity based design principles for CLT connections. The overstrength factors, which are needed for capacity based design, were also evaluated for the different types of connection tested. A comparison between the test results and the analytical formulas provided by current codes of practice and new proposals is also provided. The approach developed by Uibel and Blass gives slightly more accurate CLT metal strength predictions compared to the existing formulas in Eurocode 5. Both approaches lead to very conservative results. However, analytical models for the prediction of CLT metal connectors' stiffness significantly overestimate the experimental values. Therefore, it is recommended that currently only experimental strength and stiffness values of hold-downs and angle brackets be used in seismic analyses. Some proposals to improve the mechanical performance of metal connectors in terms of strength and stiffness are also given based on this experimental and analytical study.