Seismic mitigation of a benchmark twenty-story steel structure based on intermodal targeted energy transfer (IMTET)

This study investigates a new intermodal targeted energy transfer (IMTET) concept for rapid, effective, and purely passive seismic mitigation of a benchmark large-scale model of a twenty-story steel structure. IMTET is based on extremely rapid nonlinear scattering of seismic input energy from low to high frequency modes of a building. This effect is achieved by introducing strategically placed, local strong vibro-impact nonlinearities that are generated by contacts of the building floors with a relatively light, yet stiff, auxiliary core structure. Accordingly, the performance of IMTET is studied here, with the benchmark structure realized through a set of previously established performance criteria. The seismic loads are simulated based on records from three historical earthquakes, namely the 1995 Kobe, 1994 Northridge, and 1940 El Centro. To assess the robustness of the proposed passive nonlinear mitigation mechanism, the clearance distributions as well as the core structure parameters, are optimized for a specific seismic excitation (Kobe). Subsequently, the optimized design is tested against the two other historical earthquake records to demonstrate the effectiveness of the IMTET for these cases as well. The numerical results show that the vibro-impacts rapidly, robustly, and almost irreversibly redistribute the seismic input energy from low to high frequency structural modes, thus realizing a highly effective passive earthquake protective system. In addition, when optimized, this new concept can be realized fully passively, without the need to add any mass to the building, and at the cost of only moderate increases in the resulting floor accelerations and local stresses. In addition, the nonlinear vibro-impacts between the floors and the core structure reduce the seismic input energy to the building compared to the no core case, adding an additional benefit to the seismic mitigation approach. Therefore, the IMTET methodology for seismic mitigation has the potential to significantly enhance the seismic performance of building structures.