A Nonlinear Numerical Model for the Assesment of the Seismic Behaviour and Ductility Factor of X-Lam Timber Structures

This paper reports the development of a three-dimensional finite-element model suitable for the investigation of the seismic response of massive timber structures and for the determination of their “ductility factor q”, which is defined as the factor used for design purposes to reduce the forces obtained from a linear analysis, accounting for the non-linear response of a structure. In the X-Lam buildings, the capability of energetic dissipation through inelastic behavior is concentrated in the connections between the panels and footings. The development of a specific non linear spring element, able to represent the hysteretic response of load-displacement curves of such connections, is reported in this paper. By using the non linear spring in a finite element model has been possible to reproduce the experimental results of monotonic and cyclic tests on single panels and plane wall and also of a three-storey cross-laminated wooden building tested by means of a shaking table. All the results from the numerical models fit well with that from the experiments. Supported from these preliminary validations, the model has been also used to predict the displacements and forces on the structure subjected to seismic excitations and therefore their most appropriate ‘ductility factor q’