Seismic performance of indoor substation RC frames with combined base isolation techniques

In order to investigate the seismic performance of indoor RC substations with combined base isolation technique under far-field earthquakes and near-fault earthquakes, a 1/4 scaled three-story RC frame model was prepared for shaking table tests. Three different model configurations were considered, namely the non-isolated model (control model), the mono-isolated model (model with lead rubber bearings), and the combined isolated model (model with lead rubber bearings and viscous dampers). Scaled transformers and GISs were also installed on the model floors to consider the influence of the electrical equipment. Typical far field and near fault seismic waves, in this study the El Centro wave and the ChiChi wave, respectively, up to a PGA of 0.44 g were used as exci-tations. It was found that LRBs worked desirably for the RC model under the El Centro wave while less effective under the ChiChi wave. The acceleration responses (roof), the inter-story shear force (1F) and the inter-story drift (2F) were reduced by use of the LRBs at most by 21%, 51% and 26%, respectively, with respect to the non-isolated model under the El Centro wave. However, under the ChiChi wave irregular torsional behavior was observed and the isolation layer displacement reached 88% of the limit value. Combined use of LRBs and VDs effectively reduced the seismic responses of the RC model under the ChiChi wave. In particular, the isolation layer displacement was reduced by 15% and the torsional displacement ratio was reduced to less than 1.15, with respect to the model with LRBs only. Considerable equipment-structure interaction was found in the RC indoor substations and increased the acceleration and the displacement responses by up to 21% and 22%, respectively, given the position and mass of the equipment in this study. Besides, the LRBs and VDs were found to be effective to reduce the equipment-structure interaction.