Valutazione numerica del comportamento sismico e del fattore di struttura “q” di edifici in legno con pareti tipo XLam

In the X-Lam buildings, the energy dissipation capacity through inelastic behavior is concentrated in the connections between the wall panels and the footings. It has been possible to reproduce the behavior of wood-to-wood and wood-to-footings connections by properly combining several springs with simple work-hardening elasto-plastic constituent models in a complex macro-element. By using such nonlinear multi-springs connections in a finite element model it has been possible to reproduce the experimental results of monotonic and cyclic tests on single panels and plane walls as well as of a three-storey cross-laminated wooden building tested on a shaking table. The Xlam buildings modeling rests on the hypothesis that the nonlinear behavior of the wall is exclusively due to the (angular and hold-down) connections, whereas the XLam panels are always in the elastic field. The numerical simulations that have been performed have accurately reproduced the results of the experimental tests both in terms of shape of the force-displacement hysteresis curve and assessment of dissipated energy. The experimental tests carried out on a three-storey building tested on the shaking table have been numerically reproduced. The results of the nonlinear analysis in the time domain have confirmed the effectiveness of the numerical model in reproducing the behavior of the whole building. On the basis of these preliminary validations, the model has also been used to predict the displacements and forces on the structure subjected to seismic excitations and, therefore, their most appropriate ‘q ductility factor’. Two different approaches have been used. The first one calculates ‘q’ as the ratio between the acceleration leading the structure to a near-collapse condition and the acceleration leading the structure to the elastic limit. The second one defines the ‘ductility factor’ as the ratio between the base shear calculated for near-collapse seismic intensity in case of elastic response and in case of dissipative response of the connections. The results from such analyses confirm that the adoption of a ‘q’ factor equal to 3 is appropriate for the design of the examinated structures.