Fatigue and reliability analysis of long-span suspension bridges with SHMS

Many long span suspension bridges have been built but they are often subject to multiple types of dynamic loads, especially those located in wind-prone regions and carrying both trains and road vehicles. To ensure the safety and functionality of long steel suspension bridges, fatigue and reliability assessment must be performed from time to time during their service life. In this regard, structural health monitoring systems (SHMS) have been installed in a few suspension bridges, but it is not clear how to make use of SHMS for fatigue and reliability assessment. This study thus focuses on fatigue and reliability analysis of long suspension bridges under multiple types of dynamic loads by integrating computer simulation with the measurement data from SHMS and by taking the Tsing Ma suspension bridge in Hong Kong as an example. A comprehensive framework based on the finite element method is first proposed for the dynamic stress analysis of long suspension bridges under combined action of wind, railway, and highway loads. The proposed framework is then verified by using measurement data of both structural responses and load conditions recorded by SHMS installed in the bridge. To apply the framework for the fatigue analysis of multi-loading suspension bridges, two major simplifications have to be made to produce an engineering approach for efficient computation of dynamic stress time histories. The computational accuracy and efficiency of the engineering approach are also verified through numerical simulations and field measurements. Subsequently, a general computational procedure is proposed for the fatigue analysis of a multi-loading suspension bridge over its design life, which is used to compute the cumulative fatigue damage induced by either individual type of dynamic load or multiple types of dynamic loads. Finally, a framework for fatigue reliability analysis is developed to estimate fatigue failure probabilities at fatigue-critical locations of a multi-loading suspension bridge for different time epochs. This study narrows down the gap currently existing between structural health monitoring technologies and structural condition assessment practices.