Application of broadband nonlinear targeted energy transfers for seismic mitigation of a shear frame: Experimental results

In an earlier work we showed computationally that it is possible to successfully employ nonlinear targeted energy transfers (TETs) for seismic mitigation. Moreover, we demonstrated that this passive strategy of seismic vibration control was feasible and robust. In this work, we report experimental validation of these results by performing a series of experimental tests with a three-story shear-frame structure under seismic excitation in the form of two different historic earthquakes. As in the computational part of this work, the experimental seismic mitigation design consists of either a single nonlinear energy sink or a combination of two nonlinear energy sinks (NESs) attached at floors of the test structure. We study the performance and efficiency of the NES(s) through a set of certain evaluation criteria. With a single vibro-impact NES (VI NES) applied to the top floor of the test structure, we find significant reduction of the response levels. To further improve the effectiveness of the seismic mitigation design, we consider a combination of two NESs-an NES with smooth stiffness nonlinearity at the top floor and a VI NES at the bottom floor of the test structure-and show dramatic reduction of the structural seismic response. Robustness of the proposed designs is addressed.