Mechanical characterization of connections in seismic resistant Cross-Laminated Timber structures

Cross-Laminated Timber (CLT) structures are assembled with massive timber panels that are fastened together and to the horizontal elements (the foundations and the intermediate floors) with step joints and mechanical connections. Due to the high in-plane stiffness of CLT, the seismic behaviour of those structures markedly depends upon the connections used. The mechanical behaviour of lateral load-resisting systems made with CLT panels and typical connection systems was the focus of a large body of research, especially in Europe and North America. Furthermore, full-scale shaking table tests were carried out on several multi-storey buildings, demonstrating a significant ductility and energy dissipation under seismic loading. In contrast with the significant findings associated to those research projects, specific calculation methods have not yet been included either in Eurocode 5 (static design) or in Eurocode 8 (seismic design). Nowadays, the design is done using simplified calculation methods that neglect the connections stiffness and introduce some simplifications on their mechanical behaviour. The mechanical characterization of typical connection systems for CLT structures (e.g. with angle brackets and hold-downs, nailed and bolted to the wall and floor panels) is an expensive and time-consuming process, since requires the execution of a large number of tests. Therefore, to limit the need of experimental testing to a minimum, significant effort should be devoted to develop advanced numerical models capable to predict their load-displacement response and failure mechanisms. In the scope of this thesis, an extensive experimental programme was carried out on nailed steel-to-timber joints in CLT. The experimental results were used as input to assess the reliability of currently available calculation methods and to develop capacity-based design principles for nailed steel-to-timber joints in CLT (i.e. the overstrength factor and the strength degradation factor). In addition, analytical methods and numerical models capable to predict the mechanical properties and energy dissipation at different building levels (single fastener joint, connection, and wall system) were developed. Experimental results obtained during previous research projects served also for calibration of non-linear analyses, which were used to extend the test results to different configurations of technical interest. Outcomes of the parametric studies provided better understanding of the seismic behaviour and energy dissipation of typical connection systems for CLT buildings. It was concluded that the numerical models presented within this thesis are a sound basis to investigate the seismic behaviour of CLT buildings. However, future research is required to further verify and improve these predictive models.