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

Nonlinear dynamic response of a base-excited SDOF oscillator with double-side unilateral constraints

The aim of this paper was to study the dynamic response of a single-degree-of-freedom (SDOF) oscillator exited by a base acceleration and constrained by two unilateral constraints (bumpers). The coupled equations of motion are formulated in dimensional and dimensionless form for the case in which both SDOF oscillator and bumpers exhibit a nonlinear behavior. Two possible states characterize the system’s response: flight, when the mass of the oscillator is not in contact with the bumper, and contact, when the mass touches the bumper. When the system is in the flight state, the independent time evolution of the bumpers’ response is also considered in equations of motion. In the numerical investigations, a viscoelastic SDOF oscillator and viscoelastic perfectly plastic bumpers subjected to a harmonic base excitation are considered. First, the transient versus steady-state dynamic response is considered, and afterward the only steady-state dynamic response is studied by means of pseudo-resonance curves of maximum absolute acceleration and relative displacement excursion of the SDOF oscillator. Furthermore, the continuation technique is applied in some cases in order to highlight in the system’s dynamic response hysteresis ranges, jumps between multi-periodic orbits, and super-harmonics. The dynamic analysis with and without bumpers is compared to observe how unilateral constraints modify the dynamic response of the SDOF oscillator with respect to the absence of bumpers and when their presence may be beneficial with respect to response mitigation

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