Seismic fragility of 3-span RC-slab overpass bridges according to pushover and response spectra analysis

This paper presents results of numerical analysis of a generated population of bridges of one structural type in various structural configurations. The investigated bridge type is a three-span highway overpass with slab deck and reinforced concrete piers with rectangular cross-section. Almost 20.000 configurations of this bridge type were calculated used linear response spectra analysis and single-mode pushover analysis. Due to application of simple numerical models, results were achieved in reasonable time and are intended to be used as first estimates of structural behavior to help with decision whether more detailed analysis should be performed. The paper compares results of the two analysis methods using evaluation of deviations considering the whole bridge population, showing 50% and 90% confidence intervals. The difference between the two analysis methods was most prominent for bending limit state on structures with low reinforcement ratios. Seismic performance of bridges was evaluated in terms of PGA at full utilization of limit states. Approximation formulas were derived by linear regression, using fundamental structural properties as the only parameters, and their accuracy was evaluated.