NUMERICAL ANALYSIS OF THE INFLUENCE OF SEISMIC EXCITATION INTENSITY ON THE RESPONSE OF A SDOF VIBRO-IMPACT ISOLATION SYSTEM

Impulsive seismic actions, such as near-fault earthquakes, can give rise to the occurrence of large displacements in isolated structures. The onset of large displacements can damage isolation systems, if they exceed the maximum allowable displacement limit, or increase superstructure accelerations and inter-story drifts, if the isolation floor impacts with adjacent structures. A methodology to mitigate these undesirable effects can be achieved by integrating the isolation systems at the base with dissipative and deformable devices, called bumpers, interposed between the structure and adjacent ones. These vibration mitigation systems are called Vibro-Impact Isolation Systems (V-IISs). In this work therefore, the dynamic response, from a numerical point of view, of single-degree-of-freedom V-IISs subjected to known seismic excitation was studied. V-IISs were designed in accordance with an optimal design criterion that relates the mechanical parameters of the damper to those of the bumpers, as well as to the seismic gap used. Analyses were conducted on optimally designed V-IISs by varying the intensity of the seismic action and the initial gap. The responses obtained are compared with both free to vibrate (free flight) and rigidly impacting (hard contact) systems. The quantities analyzed are the relative displacement and absolute acceleration of the mass, and the deformation and contact force of the bumpers. The results show, for typical periods of structure isolation, a considerable reduction in displacements versus a modest increase in accelerations, compared to free flight; while compared to hard contact, they show a considerable reduction in accelerations versus a modest increase in displacements. Therefore, these outcomings highlight the great potential of these new vibration mitigation systems with respect to seismic excitations.