Component Level Fragility Estimation for Vertically Irregular Reinforced Concrete Frames

Seismic fragility functions are essential for performance-based seismic design of structures. Global demand parameters, such as peak roof displacement or maximum drift over the height of the building, are commonly used to estimate seismic fragility. However, in case of buildings with vertical irregularities, the global demand parameters may not suffice since maximum demand in such building is mostly concentrated at the level of irregularity. The current study focuses on one of the most common forms of vertically irregular reinforced concrete (RC) buildings, known as open ground story buildings, where irregularity lies at the ground story. Nonlinear dynamic analyses of RC frames subjected to a number of ground motions, each scaled-up for different PGA, are carried out to estimate the component level and global drift demands, also known as engineering demand parameters (EDPs). Seismic fragilities developed for the frames based on both the component and global EDPs are presented. Finally, the importance of component-based fragilities for estimation of seismic fragility of irregular frames is emphasized. The component level EDP-based fragility is found to be effective in predicting the actual damage scenarios in such buildings observed during past earthquakes.