Seismic Vulnerability Assessment of RC Buildings with Plan Irregularities using Pushover Analysis

Earthquakes are the most dangerous and unpredictable forces in nature. Seismic behaviour of structures is always an area of concern and requires special attention from structural designers. Presence of plan and vertical irregularities further complicates the seismic behaviour of the structures and also makes the structures more vulnerable to seismic forces. Pushover analysis, which is gaining popularity as an effective tool to quantify the seismic vulnerability of structures, is a good method of analysis to deal with structures with irregularities. In the present study, an attempt is made to study the seismic vulnerability of buildings with plan irregularities using pushover analysis. In the present study 3 storey, 6 storey and 9 storey structures of regular configurations as well as varying amount of irregularities has been modelled and analysed. ETABS, an efficient FE analysis tool, has been used for the analysis. The modelling and loading considerations are according to relevant Indian codes while pushover analysis has been carried out according to FEMA and ATC codes. The parameters compared involve base shear carrying capacity, displacement capacity, performance point and the status of hinges formed. An attempt was also made to study and quantify the improvement in the seismic capacity of the structure by strengthening it using shear wall elements. The results of the analysis revealed that the structures with plan irregularity are more vulnerable to seismic forces compared to regular structures. Irregular structures possessed much lower base shear capacity compared to regular structures and the states of hinges formed were also at higher damage states. The introduction of shear walls proved to be an effective solution against the plan irregularity. The structures strengthened with shear walls exhibited tremendous improvement in the base shear carrying capacity (3 to 5 times) and also overall ductility of the structures. The improved states of hinges formed during pushover analysis also indicated the lesser vulnerability of irregular structures with shear walls.