Seismic vulnerability assessment of a continuous steel box girder bridge considering influence of LRB properties

Bridges are one of the most crucial facilities of transportation networks. Therefore, evaluation of the seismic vulnerability of bridge structures is perpetually regarded topic for researchers. In this study, we developed seismic fragility curves for a continuous steel box girder bridge considering the effect of different levels of mechanical properties of lead rubber bearing (LRB) devices including initial stiffness and yield strength on the seismic performance of such structure. A powerful framework for an earthquake engineering simulation, OpenSees, is used to perform nonlinear analyses of the bridge model. In order to construct fragility curves for this structure, a set of 20 ground acceleration records is adopted and various scales of the peak ground acceleration (PGA) from 0.1 to 1.6 g are considered. Besides, a series of damage state of the bridgeis defined based on a damage index, which is expressed in terms of the column displacement ductility ratio. Fragility analyses result reveals that reducing the initial stiffness of LRBs reduces the seismic vulnerability of bridge piers and vice versa. Meanwhile, the changes of the yield strength of LRBs have trivially effected on the seismic behaviour of the bridge piers. On the other hand, the short pier has performed more susceptibly than those of the high pier in both seismically-isolated and non-isolated bridge cases. Lastly, the results in this research also indicate that the bridge structures equipped with seismic isolation devices (e.g. LRBs) significantly mitigated the damages due to earthquakes.