Fragility Function of Base Isolated Highway Bridges

This paper aims to use the performance-based evaluation approach to investigate the performance of highway bridges with isolation devices. Fragility functions of un-isolated and isolated bridges are derived and compared to study the efficiency of various isolation devices with different combination of strength and stiffness. A simplified 2D bridge model representing the transverse response of a typical highway bridge is adopted where the fiber section element is used for bridge columns while bilinear element is used for isolation devices. The fragility curves are derived by either PSDA or IDA method based on simulation results from the nonlinear time history analysis using 250 earthquake motion records. Damage criteria for both piers and isolation devices are established to relate the component response quantities to global damage states of bridges. Extensive parametric study is also conducted to evaluate the effect of mechanical properties of isolation devices on the damage probability of isolated bridges. The study identifies the optimum combination of mechanical parameters of isolation devices, which can serve as practical guide for isolation device designs.

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