Experimental and numerical investigation of base isolated SDOF system impact against bumpers under harmonic base excitation

During strong earthquakes, base isolated systems (buildings, bridges, strategic facilities, equipment etc.) can impact against the surrounding moat wall because of the deformation of the isolator if the available separation distance is limited. A possible mitigation measure is the interposition of shock-absorbers (bumpers). In this work some of the results of an experimental laboratory campaign are presented. The experimental tests were carried out to investigate the dynamic response of a base-isolated single-degree-of-freedom (SDOF) oscillator, excited by a harmonic base acceleration and symmetrically constrained by two unilateral deformable and dissipative bumpers. Three different peak values of table acceleration (A), four amplitudes of the total gap between mass and bumpers (G) and four types of bumpers (B) were considered. In this work the attention is focused on some characteristics of the dynamics with impact, such as force and time of contact between mass and bumpers, coefficient of restitution and energy dissipated by the bumpers during the impact. The results of the experimental tests were used to identify the parameters of stiffness and damping of a numerical model able to simulate the behavior of the system by using a general-purpose computer code.