Shaking table tests and numerical investigation of two-sided damping constraint for end-stop impact protection

During strong earthquakes, structural pounding may occur between the equipment and the surrounding moat wall because of the limited separation distance and the deformations of the isolator. A potential mitigation measure for this problem is the incorporation of collision bumpers. The aim of the paper is to study the experimental dynamic response and to formulate numerical model of a base-isolated SDOF oscillator excited by a harmonic base acceleration and symmetrically bounded by two unilateral deformable and dissipative constraints. Static tests have been first performed to determine the static characteristics and the support conditions of the bumpers, and successively, shaking table tests have been carried out to investigate two different configurations: the absence and the presence of bumpers. In both configurations, tests were carried out with the same type of excitation to the base. Different values of the table acceleration peak were applied, different amplitude values of the total gap between mass and bumpers were considered, and also two different types of bumpers were employed. The experimental dynamic responses in the absence and in the presence of bumpers have been compared, and the results obtained in the presence of bumpers have also been used to identify some characteristics of the dynamics with impact (force and time of contact between mass and bumpers, energy dissipated by the bumpers during the impact, and coefficient of restitution). A suitable model has been developed to numerically simulate the behavior of the system by using a general-purpose computer code, achieving a good agreement with the experimental results.