Base isolation technology, as a mature seismic mitigation method, demonstrates potential for enhancing seismic margins in nuclear power plant structures. This study investigates the seismic performance of isolated and non-isolated models for a diesel generator building in a nuclear power plant through shaking table tests. A 1/8-scale structural model was designed and tested under operational safety ground motion (SL-1), ultimate safety ground motion (SL-2), and beyond design benchmark ground motion (BDBE) seismic excitations. A finite element model considering different tensile and compressive stiffnesses of isolation bearings was established to simulate structural dynamic responses under test conditions. The results demonstrate that the test model design is effective, with the maximum isolation rate was close to 50%. The maximum displacement of the isolation layer meets the collision prevention ditch limit. Numerical simulations showed good agreement with experimental results in acceleration time histories, displacement time histories and bearing hysteresis curves. Additionally, the seismic isolation structure has a certain overturning effect in the test. To further optimize the base isolation scheme, numerical analyses incorporating dampers into the isolation layer were conducted, which demonstrated improvements in mitigating the rocking effect of the superstructure.

This paper validates the effectiveness of the modeling approach based on the finite element analysis of shaking table tests, establishing finite element models for both a base-isolated structure and a hybrid base-isolated structure designed to address overturning issues in the diesel engine building of a nuclear power plant. By using the Incremental Dynamic Analysis (IDA) method, a fragility analysis of the overturning resistance was conducted for both isolation systems. This study demonstrates that the hybrid base isolation scheme, which incorporates additional dampers, effectively enhances the structure’s overturning resistance and reduces the probability of failure. When evaluating the seismic fragility of the structure by using the TP value, which is related to the tensile stress of the isolation bearings, as a damage index, the results are more conservative compared with those obtained by using shear strain ($\gamma$). This highlights the importance of improving the tensile capacity of the isolation bearings in structural design. Furthermore, fragility assessment using $\gamma$ as a damage index can provide design references for the collision limit of the isolation moat in the base-isolated structure of the diesel engine building in nuclear power plants.