Indonesia has had seismic codes for earthquake-resistant structure designs since 1970 and has been updated five times to the latest in 2019. In updating the Indonesian seismic codes, seismic hazard maps for design also update, and there are changes to the Peak Ground Acceleration (PGA). The Indonesian seismic design uses the concept of building performance levels consisting of Immediate Occupancy (IO), Life Safety (LS), and Collapse Prevention (CP). In relation to these performance levels, some cases have shown that buildings suffer from huge damage compared to their performance targets after an earthquake. Considering this issue, the current study aims to analyze the performance of the seismic isolation system design (isolated) on existing target buildings (fixed) and analyze seismic fragility with the PGA intensity according to Indonesia’s seismic hazard maps of 0.1–1.5g. The target building used in this study is a prototype design eight-story medium-rise residential building that uses the reinforced concrete moment frame structure. The analysis uses Nonlinear Time History Analysis (NLTHA) for the design and Incremental Dynamic Analysis (IDA) for seismic fragility. Both analyses use 11 selected ground motions based on soil classification, magnitude, fault distance, and earthquake source mechanism. The NLTHA results reveal that using a seismic isolation system can increase the target building's performance level from LS to IO. A comparison of the IDA results depicts a trend of significant performance improvement. That is, with the same performance level target and risk category, the isolated base structure can be used at 1.46–3.20 times higher PGA than the fixed base structure. The fragility analysis results show that the fixed base structure has a 30% safety margin and a 62.5% isolated base structure from the PGA design. The obtained results are useful for assessing existing buildings or considering a new building's performance.
Keywords: Seismic isolation, fragility curve, incremental dynamic analysis, performance level.