Softening Instead of Strengthening for Seismic Rehabilitation

When rehabilitating existing structures for seismic loading, many engineers would first think of a strengthening approach. However, for the case of the large liquid gas tank described in this paper, it was more effective to soften the structure by shifting the fundamental frequency in the lower spectral region of the response spectrum of the seismic design event. As part of this softening approach, 26 high-damping elastomeric bearings were incorporated into the structural system. These rubber bearings are horizontally soft, which results in a decrease of the fundamental frequency from 2.3 Hz to 0.5 Hz. The drastic reduction in the seismic forces was confirmed by non-linear dynamic analyses in the time domain considering the hysteretic behaviour of the bearings.