Effects of increasing traffic loads on the fatigue reliability of a typical welded bridge detail

Fatigue reliability of bridge details needs to account for increased loads caused by the ever-increasing traffic flows and axle weights traversing a bridge. In this paper, a two-stage crack growth model and a failure assessment diagram, the latter accounting for the fracture event, are used to evaluate the reliability of a cover plate detail. A methodology is presented for tackling the case of evolving over time loads. To this end, different assumptions regarding the increase in the mean stress range, number of applied cycles and maximum loads are made. Accordingly, for each of the cases considered, the impact on the fatigue detail's reliability is determined. The results for these evolving load cases are compared with the case where loading remains constant over time. It is found that increase in the mean stress range contributes significantly towards the decrease in the detail's reliability. By comparison, the type of assumed growth pattern as well as increase in the maximum load and number of applied cycles affect the reliability results to a lesser degree.