Vulnerability assessment of RC buildings with irregularities using probabilistic analysis

Abstract

Modern construction comprises of large number of reinforced concrete structures with geometric irregularities. Even though these types of structures have good serviceability and aesthetic appearance, such structures show high vulnerability during earthquakes. The present study investigates the performance of multistorey RC buildings, with different irregularities under seismic excitations, using Pushover analysis. Fragility curve, defined as the probability of reaching or exceeding of a specific damage state under a seismic excitation, provides an estimate of possible damage during occurrence of an earthquake. Four structural models of multi storey reinforced concrete buildings with different configurations consisting of bare frame with plan irregularity, setback frame, set back frame with shear wall without openings and set back frame with shear wall with openings are considered. Three-dimensional models of the structures with different geometric irregularity are generated and pushover analysis of each model is carried out using the software ETABS. The capacity curves generated using pushover analysis are transformed into bilinear curves and the roof displacement at the yield and ultimate levels are obtained. The procedure asper ATC-40 is followed to find the performance point from this nonlinear analysis. Later the damage probability is calculated based on the damage state levels, and curves of fragility are generated. To quantify the damage of the structure using fragility curve, damage state levels are fixed as Slight, Moderate, Extreme and Collapse Damage Level. The results of pushover analysis indicate the effect of enhancement of the stiffness of the setback frame by providing shear wall without openings, but no significant effect in terms of stiffness and ductility while including shear wall with openings. Based on the damage state level chosen and fragility analysis of the four structural models, the structural system with setback frame with shear wall without openings has shown better performance.