Life-Cycle Cost of Bridges on Seismic Zones for Risk Management

Abstract

In this paper the acceptable failure probability and the risk of important bridges, located on seismic zones, are calculated throughout the expected cost of failure consequences. Also, the bridge expected life-cycle cost is formulated in terms of the bridge seismic hazard and the potential consequences of failure. These consequences include aspects arising from the physical loss of the bridge to the human casualties and economical cost of the loss of service, which are estimated in monetary terms. Current codes do not explicitly deal with this issue and in practice subjective estimations from experience are considered for some general cases. Bridge reliability is an essential component of risk and in this paper is estimated in a simplified way and applied to the structural types given in the examples. Monte Carlo simulation techniques are used to explicitly account for the uncertainties. Initial and failure cost curves are determined for all possible seismic intensities and expected life-cycle costs conditional to these intensities are obtained. The unconditional expected lifecycle cost is calculated by convolution of the conditional costs by the occurrence probabilities of these intensities, which are obtained from the seismic hazard curve of the given site. The procedure is illustrated throughout three reinforced concrete bridges located 1 on the soft soil of Mexico City and the other two on other sites with less seismic activity and different traffic volumes. The results may be extended to get risk management policies for bridges and to improve the current Mexican codes and to enhance the practices on bridge design and maintenance on seismic zones