Seismic Risk Assessment of RC Framed Vertically Irregular Buildings

Abstract

The area of vertically irregular type of building is now having a lot of interest in seismic research field. Vertical irregularity arises in the buildings due to the significant change in stiffness and strength. The typical OGS and stepped types of irregularities are considered in the present study. For OGS buildings, the Magnification factors (MF) are suggested by the design codes. The present study focus on the performance of typical OGS buildings designed considering various magnification factors as well as the stepped type buildings with different geometry configurations using fragility analysis. The critical inter-storey drift is considered as an intensity measure. Various heights (6, 8 &10 stories) are considered for the present study. Fragility curves are developed for each type of buildings as per the methodology introduced by Cornell (2002). PSDM models are developed for each frames and the corresponding fragility curves are generated. It is observed that in terms of performance, a building with infill walls in all stories is equally comparable with an OGS framed building with MF of about 1.5. Performance of the OGS frame increases with the increase in MF, but it makes the adjacent storey vulnerable. The study is extended to the seismic reliability for all the considered buildings. The reliability is found out by combining a fragility curve with a seismic hazard curve of the region. The seismic hazard curve for the present study is chosen from the study conducted by Pallav et. al (2012). The performance of the buildings is assessed by comparing the reliabilities achieved with the target reliabilities suggested as per ISO 2394 (1998). It is observed that the frames without any infill walls failed to achieve the target reliabilities whereas the buildings with infill walls achieved the target reliabilities. The stiffness of infill walls is a significant factor that improves the performance of buildings during earthquakes.