Seismic fragility assessment of existing reinforced concrete buildings in Patna, India

Assessment of seismic fragility of reinforced concrete (RC) buildings requires appropriate consideration of uncertainty in aleatory and epistemic sources. Aleatory uncertainty is typically attributed to randomness in ground motion records, while epistemic is due to the uncertainties in structural modelling. The present work focuses on obtaining the variability functions and fragility curves by considering those uncertainties for low, mid and high rise RC buildings in Patna, India, which is a region of high seismicity. Modelling uncertainties requires consideration of material, geometrical, and design as random parameters. These parameters mainly comprise material strength, storey height, plan, typology, design provisions, and various irregularities. In this study, the selection of the random parameters is purely based on the investigation of buildings in the Patna region. Considering the multiple combinations of random parameters, the buildings are modelled and analysed using nonlinear static (NLS) pushover analysis. The monotonic load in a triangular pattern is applied for NLS analysis to get pushover curves. The pushover curves are subsequently converted into capacity curves considering the dynamic characteristic of the first mode of vibration. The obtained capacity curves are utilised to derive the variability in the capacity spectrum for different categories of RC buildings. Subsequently, variability due to randomness in ground motion records is determined by generating several artificial (comprising near field and far field) ground motions considering the seismotectonic map of the region. Thence, by accounting for both the uncertainties, lognormal variability functions are determined, and seismic fragility assessment is performed for different building categories in Patna, India. Furthermore, the seismic vulnerability of existing buildings can be determined based on the obtained fragility curve.