Fatigue assessment of multi-loading suspension bridges using continuum damage model

Long-span steel suspension bridges carrying both highway and railway have been built in wind-prone regions. The fatigue assessment of such bridges under the combined action of railway, highway, and wind loading represents a challenging task in consideration of uncertainties in both fatigue loading and fatigue resistance. This paper presents a framework for fatigue assessment of a long-span suspension bridge under combined highway, railway, and wind loadings using a continuum damage model. The continuum damage model (CDM) is first established based on continuum damage mechanics with an effective stress range and an effective nonlinear accumulative parameter to represent all of the stress ranges within a daily block of stress time history of the bridge. The CDM is then applied to estimate damage accumulation of the Tsing Ma suspension bridge at fatigue-critical locations, and the results are compared with those estimated by the linear Miner’s model. A limit state function for fatigue reliability analysis based on CDM is also defined by introducing proper random variables into CDM. The Monte Carlo simulation (MCS) is then adopted to generate the random variables and to calculate failure probability. Finally, the failure probabilities of the Tsing Ma Bridge at the end of 120 years are estimated for different loading scenarios. The results demonstrate that the fatigue condition of the Tsing Ma Bridge at the end of its design life depends on loading scenarios.