Poundings of seismically isolated buildings during strong earthquakes

Seismic isolation reduces the induced seismic loads, particularly in low- to medium-rise buildings, by avoiding resonance, with the predominant frequencies of earthquake excitations, thanks to flexibility introduced at the isolation level. This earthquake resistant design approach significantly decreases the shear forces, interstory deflections, and floor accelerations of a building, avoiding damage of its structural and non-structural elements as well as damage of its contents. The size of the seismic gap, which must be provided around a seismically isolated building, in order to facilitate the expected large relative displacements at the isolation level, is usually finite, due to practical limitations, giving rise to the possibility of poundings of the building with adjacent structures during strong earthquakes. Therefore, understanding how the effectiveness of seismic isolation is affected from potential poundings of seismically isolated buildings with adjacent structures due to strong ground motions is vital. This research work aims to address this issue using numerical simulations and parametric studies in an effort to investigate how the maximum floor accelerations, story shear forces and interstory deflections of these buildings are affected by impacts and the relevant design parameters and conditions. Numerical simulations demonstrate that poundings may substantially increase floor accelerations, especially as the stiffness of the impact is increased, and, hence, may cause damage to the contents of a seismically isolated building, significantly reducing the effectiveness of seismic isolation. In addition to the presentation of results from parametric studies for some of the influencing conditions, the possibility of using bumpers, as a practical measure to mitigate the adverse effects from potential poundings, is considered.