Advanced modelling of CLT wall systems for earthquake resistant timber structures

Cross-Laminated Timber (CLT) is gaining a significant popularity among the structural products as a sustainable alternative to steel and concrete. In comparison with those traditional building materials, CLT has a low carbon footprint and provides comfortable living conditions; moreover, the high strength-to-weight ratio, the prefabrication process and the erection speed are additional key points of its broad diffusion. Determining the load-carrying capacity of lateral load-resisting systems made of CLT panels (such as CLT wall systems, i.e. CLT walls with mechanical connections) is crucial for both the static and seismic design of CLT structures. However, a calculation method has not yet been included in Eurocode 5 (EN 1995-1-1:2004/A2 2014). Nowadays, the load-carrying capacity of CLT wall systems is determined with forcebased design procedures. However, since the analysis neglects the connections stiffness, those methods do not ensure that the wall system behaves in accordance with the design assumptions. Furthermore, simplified methods neglect some contributions that might affect the response of a CLT wall system, like the friction between the wall and the element that is restrained to and the effect of the overlaying floor. Based on the above-mentioned issues, this paper proposes a new numerical model of a CLT wall system. The model schematizes the CLT panel as an elastic orthotropic element, while the connections (i.e. hold-downs, angle brackets, and screws) are simulated as non-linear hysteretic springs. The interaction between the CLT panel and the foundation, and between the wall element and the CLT floor restrained on top of it, were specifically addressed in the development of the model. The study presented herein is carried out considering the experimental tests results obtained by Gavric et al. (2015a-2015b-2015c). At first, experimental and numerical results are compared. A parametric study is carried out afterwards, (a) by varying the vertical load applied on top of the CLT wall, (b) by modifying the aspect ratio of the timber panel, and (c) by simulating a CLT floor screwed on top of the wall. Results are collected in diagrams and compared with a simplified design procedure commonly adopted by practicing engineers and discussed by Pozza et al. (2016b), highlighting how those contributions influence the elastic stiffness and the load-carrying capacity of a CLT wall system.