Study on the influence of base shear distribution on the seismic response of base-isolated split-foundation structures

Split-foundation structures with base isolation have multiple isolation layers due to their uneven foundation heights. This complexity adds challenges to the seismic isolation design of split-foundation structures. In this paper, two special parameters, namely the shear non-uniformity factor phi and the ratio of shear non-uniformity factor Gamma, were proposed. Response spectrum analysis and time history analysis on base-isolated split-foundation structures with varying phi and Gamma were conducted to investigate their seismic response and damping effect. The results indicate that phi primarily affects the seismic response in the lower stories and the upper embedding story. When phi is too small or too large, it results in an uneven isolation effect. Moreover, when the base shear ratio beta z exceeds 0.5, the distribution of plastic hinges is significantly affected by the variations in phi. Additionally, the story shear and story drift ratio of lower stories in the along-slope direction are generally greater than that of the corresponding story of the non-isolated structure. Therefore, in the seismic isolation design of the split-foundation structure, the base shear at different embedding ends should be reasonably assigned. Special attention should also be given to the adverse effects in the along-slope direction.