Effect of hysteresis model on damage probability of R/C buildings

Fragility curves are useful tools for showing the probability of structural damage due to earthquakes as a function of ground motion indices. Generally, elastoplastic hysteretic model, which represents the hysteretic behaviour of structures, is used for construction of fragility curves. However, it is known that elastoplastic behaviour can not reflect the hysteretic behaviour of reinforced concrete structures under the effect of reversal loads.The purpose of this study is to investigate the possible effects of using a hysteretic model with strength and stiffness degradation on fragility curves.Two different types of sample buildings have been considered within the scope of this study. The first one represents the buildings with high ductility and yield strength and the latter represents the buildings with low ductility and yield strength. The pushover curves of sample buildings were obtained via pushover analyses. Then, those pushover curves were transformed to modal capacity diagrams by the help of modal parameters of first vibration mode of the sample buildings. Using 60 ground motion records, nonlinear time-history analyses of equivalent single degree of freedom systems were performed for each scaled elastic spectral displacement. The damage measure is maximum inter-story drift ratio and each performance level (immediate occupancy, life safety and collapse prevention) considered in this study has an assumed limit value of damage measure. Discrete damage probabilities were calculated using statistical methods for each considered performance level and elastic spectral displacement. Consequently, continuous fragility curves have been constructed based on the lognormal distribution assumption.According to the constructed fragility curves; it is observed that the difference between damage probabilities, obtained with bilinear and degrading models, becomes significant with increasing level of damage.