Determination of the fundamental period of CLT buildings via incremental elastic-non linear dynamic analyses

The evaluation of the proper period of vibration is one of the crucial issues in the analysis and seismic design of buildings and is influenced by a number of variables contributing in the definition of the global rigidity and therefore the seismic susceptibility of the structure. In the case of multi-storey X-Lam buildings connection elements play a key role since they are responsible of most of the dissipative and deformative capacity of the structure. The present work aims to investigate the influence of the connection elements typically used to avoid the rocking of the seismic-resistant walls (i.e. hold-down elements) on the fundamental period of multi-storey XLam buildings. A nonlinear numerical model capable of faithfully reproducing the rocking behavior of X-Lam wall system (i.e. accounting for the interaction between the vertical applied loads and the hold-down connection activation) is developed and validated on experimental dynamic tests. The model is used to assess the principal vibration period of a selected case study by means of incremental dynamic analyses. Results from the experimental tests and from the performed analyses demonstrate that when the X-Lam wall system is subjected to significant vertical loads (capable of avoiding the overturning of the walls) the principal vibration period is not affected by the connection stiffness. On the contrary, when negligible vertical loads are applied to the X-Lam wall the principal vibration period is controlled by the hold-down connection stiffness. Finally, the numerical model is also used to characterize the principal vibration period of the case study at different level of the top-displacement adopting seismic input with variable frequency. Results from numerical analyses confirm the strong correlation between the value of principal vibration period and the phenomenon of hold-down connection activation showing an increase of the period increasing the top building displacement.