Remaining fatigue life estimation of corroded bridge members

This paper presents a method to estimate remaining fatigue lives of railway bridge members subjected to time-dependent corrosion. The method addresses effects of material loss due to general (uniform) corrosion and fatigue strength degradation of material due to corrosive environment. The method mainly consists of stress history, which is obtained by considering the effect of time-dependent loss of material, full-range S-N curve, which represents the corrosive environment, and sequential law, which takes the loading sequence effect more precisely in to account than Miner's rule. Initially, nonlinear behaviour of material loss over time (i.e. time-dependent growth of corrosion wastage) is discussed, and hence, necessary formulae to calculate time-dependent cross-sectional properties are comprehensively presented. Then finite element analysis-based procedure is clearly proposed to predict stress histories of corroded members. A technique is introduced to obtain the full-range S-N curve for the corroded structural detail. The concept of sequential law is summarized with the algorithm, and then the proposed method is applied to predict the remaining fatigue lives of the corroded members of a railway bridge. The predicted remaining lives were compared with the previous method-based estimations, and comparisons reveal the range of 16-47% reduction of fatigue lives of critical members when time-dependent corrosion is taken into account. Also, the results reveal that the corroded members of smaller cross-sectional area are most vulnerable for fatigue damage. Finally, significance of the proposed method is confirmed.