Development of simplified method based on degree of irregularity to identify the seismic vulnerability of plan irregular reinforced concrete buildings

Irregular buildings are more vulnerable to seismic loading, depending on their degree of irregularity. Past studies quantify the degree of irregularity in vertically irregular buildings and study its correlation to seismic vulnerability. However, the past studies on plan irregular buildings were focused on evaluating the seismic performance only. The present study proposes a simplified method based on the degree of irregularity to identify the seismic vulnerability of plan irregular reinforced concrete (RC) buildings. Diaphragm discontinuity, reentrant corners, non-parallel systems, and torsional irregularity are different types of plan irregularities considered in the study. For each type of plan irregularity, numerical models are developed with varying degrees of irregularity. Numerical models are subjected to incremental dynamic analysis and maximum inter-story drift was recorded to develop fragility curves. It is found that the proposed simplified method can effectively identify the seismic vulnerability of the plan irregular RC buildings based on their degree of plan irregularity. It can help to identify the most vulnerable plan irregular RC buildings at the initial stage of large-scale seismic simulation, such as Integrated Earthquake Simulations of urban areas. This method can be used as a filtering method to select the most vulnerable plan irregular RC buildings that need detailed seismic analyses.