Probabilistic fatigue life analysis of welded steel plate railway bridge girders using S-N curve approach

In this article, a generalized procedure for estimating probabilistic fatigue life of steel plate railway bridge girders with welded connections, considering plate breathing and a loading spectrum, is presented. The procedure combines the probabilistic S-N curve with Palmgren-Miner's fatigue damage accumulation rule. One of the features of the study is determination of effect of the modeling error associated with the S-N curve on estimation on the fatigue life of bridge girders. Expressions for probability density functions of number of cycles to failure and accumulated fatigue damage are obtained in the closed form and Monte Carlo simulation, for the cases of without and with modeling error considered in fatigue life estimation, respectively. The use of the proposed procedure is illustrated by considering two railway plate girder bridges designed according to Indian Railway Standards. From the results obtained, it is noted that plate breathing is an important mechanism to be considered while estimating the fatigue life of the railway bridges. The results of the present investigation clearly bring out the importance of carrying out fatigue reliability analysis of different bridge spans, while establishing railway line reliability (as reliability of the weakest span would govern the line reliability).