Reliability Analysis of River Bridge against Scours and Earthquakes

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This study proposes a bridge safety evaluation process against seismic and flood hazards. Because uncertainties in the scours, seismic hazard, and structural performance for a given seismic excitation are inevitable and important, reliability analysis is adopted. A scour prediction equation for a bridge with a complicated foundation system is developed and a probabilistic scour curve is constructed to measure the risk of scours using the Monte Carlo simulation. The seismic hazard is measured using the probabilistic seismic-hazard analysis. A series of nonlinear time-history analyses are performed to determine the structural performance under different peak-ground-acceleration values. SAP2000 is used to build the finite-element model wherein the soil is modeled using a bilinear link. A plastic hinge is predefined to simulate the nonlinear behaviors of the pier and caisson of the bridge. The displacement ductility is used to measure the structural performance and to construct the fragility curve for various limit states. The Nanyun Bridge located in central Taiwan is selected as an example to demonstrate the proposed safety-evaluation procedure. The results show that the probable scour depth of the Nanyun bridge is from 3 to 5 m. The failure probability considering the floods and earthquakes is insignificant. A deterministic design value, considering both the hazards, is provided for a given reliability target (e.g., β=3) to help engineers in their present design processes.

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