Seismic vulnerability assessment of regular and irregular concrete structures using fragility curves

One of the basic problems in seismic design of buildings is appropriate configuration of their plans to prevent an increase in torsional moments due to irregularity. Nowadays, usage of irregular plans because of having a specific plan and beautiful appearance is increasing. The existence of irregularities in the structure during an earthquake causes torsion of structure, which leads to the intensification of seismic displacements and forces on structure. In this study, the seismic behavior of regular and irregular reinforced concrete structure with the number 3, 6 and 9 stories under ten records for incremental dynamic analysis have been evaluated. To this purpose, indexes such as maximum drift, residual drift, base shear and response modification factor have been compared. Fragility curves, using the threshold of damage state of RC structure according to HAZUS in both regular and irregular structures have been investigated. The results indicated that by increasing irregularity, maximum drift, residual drift base shear and probability of damage are increased. The response modification factor is also reduced as irregularity increases. Furthermore, by increasing the number of stories and rate of irregularity, the damage percentage of structure is increased. Therefore, design of irregular structures in plan is not recommended as much as possible