Seismic risk of base isolated non-ductile reinforced concrete buildings considering uncertainties and mainshock–aftershock sequences

•A non-ductile RC frame building was hypothetically retrofitted using base isolation.•32 mainshock–aftershock records were used to calculate their seismic risks.•The influential uncertain parameters were identified through sensitivity study.•The base isolation can reduce the seismic risk effectively.•Seismic risk can be underestimated if aftershocks were not considered. Base isolation is a promising approach to retrofit seismically vulnerable buildings, but the supporting body of research on seismic risk mitigation through base isolation, particularly considering the associated uncertainties and mainshock–aftershock sequences, is deficient. Therefore, in this study seismic risk analysis was performed for an old non-ductile RC frame building before and after retrofit with base isolation. Various sources of uncertainty such as structural uncertainties, ground motions uncertainties and modeling uncertainties are discussed and propagated in the analysis procedure. A sensitivity study was also conducted to determine which structural parameters have the most significant impact on both the seismic demands of the un-retrofitted and base isolated building. A suite of recorded mainshock and aftershock ground motions was utilized to investigate the influence of considering aftershocks on the performance of these types of buildings. The study revealed that base isolation can greatly reduce the seismic risk for higher damage levels, as one would expect. More importantly, the results also indicated that neglecting aftershocks can cause considerable underestimation of the seismic risk.