Seismic evaluation of RC bridge pier using analytical fragility curves

This paper aims to evaluate the seismic vulnerability of a RC bridge pier using analytical approach that involves numerical modelling of structure, nonlinear analyses on the model and preparation of damage ranks for different damage states. In addition, simplified method to develop fragility curves for a typical highway bridge pier using nonlinear modelling at element and material levels has been discussed in this study. An existing two-span PSC box girder bridge has been chosen to carry out the analysis. Beam with hinges model for element modelling, reinforcing steel and concrete 01 models have been adopted for steel and concrete materials, respectively. Nonlinear static analysis and time history analyses were carried out to evaluate the capacity of pier, and corresponding responses of pier were studied under different ground motion intensities. By assuming log-normal distribution, fragility curves were constructed in longitudinal and transverse directions. In longitudinal direction, the probability of exceeding slight, moderate and extensive damage states is 73.9%, 65.2% and 58.5%, respectively, at 2.5 g (g = 9.81 m/s(2)) peak ground acceleration (PGA) and the probability of collapse at 2.5 g is 50%. In transverse direction, the probability of exceeding slight, moderate and extensive damage states is 91.7%, 98.2% and 80.75%, respectively, at PGA 3 g, and the probability of collapse is 59.8% in this direction. This simplified method discussed in the present study is useful to construct fragility curves for bridges in India which fall in the same group and similar characteristics. Fragility curves are particularly useful in assessing the seismic vulnerability of bridge piers in highly seismic-prone areas of India where seismic retrofit of bridges and pre-earthquake planning are becoming more prevalent.