Experimental and numerical response analysis of a unilaterally constrained sdof system under harmonic base excitation

The pounding between adjacent systems can occur in different situations typical of civil engineering (base-isolated structures with limited seismic gap [1], equipment [3, 4] or bridges). The acceleration spikes, produced by the impact, can damage acceleration-sensitive equipment or lead to severe structural damage. These side effects can be mitigated inserting dissipative and deformable shock absorbers (bumpers) between the colliding systems, thus reducing the impact stiffness. In this work, the problem was studied considering a base-isolated single-degree-of-freedom (SDOF) system impacting against two symmetrically arranged bumpers, under harmonic base excitation [10–12]. Using a shaking table, a parametric experimental laboratory campaign was carried out, in which different values of peak table acceleration, total gap (distance between mass and bumpers) amplitude and different types of bumpers were considered. From the examination of some of the experimental results, it was possible to identify different scenarios that can occur varying the investigated parameters. These scenarios were found also numerically using a simplified nonlinear model, described in terms of dimensionless parameters. Although the model does not include all the nonlinearities involved in the real problem, some of the observations emerged analyzing the numerical results have found confirmation in the experimental outcomes.