SHMS-Based Fatigue Reliability Analysis of Multiloading Suspension Bridges

Long-span suspension bridges carrying both highway and railway have been built in wind-prone regions. The estimation of fatigue damage of such bridges under the long-term combined action of railway, highway, and wind loading represents a challenging task in consideration of randomness in multiple types of loading. This study presents a framework for fatigue reliability analysis of multiloading long-span suspension bridges equipped with structural health monitoring systems (SHMS), and the Tsing Ma suspension bridge in Hong Kong is taken as a case study. A limit-state function in the daily sum of $m$-power stress ranges is first defined for fatigue reliability analysis. Probabilistic models of railway, highway, and wind loading are established on the basis of the measurement data acquired from the SHMS. The daily stochastic stress responses induced by the multiple types of loading are simulated at the fatigue-critical locations of the bridge deck by using the finite-element method and Monte Carlo simulation (MCS) together with the loading probabilistic models established. The probability distribution of the daily sum of $m$-power stress ranges is estimated on the basis of the daily stochastic stress responses. The probability distribution of the sum of $m$-power stress ranges for a given time period is then evaluated in consideration of future traffic growth patterns. Finally, the fatigue failure probabilities of the bridge at the fatigue-critical locations are calculated for different time periods. The results demonstrate that the health condition of the Tsing Ma Bridge at the end of its design life will be satisfactory under current traffic conditions without growth but that attention should be paid to future traffic growth because it may lead to a much greater fatigue failure probability.