Integrated Fatigue Life Evaluation Method for Members in Riveted Steel Truss Bridges

Abstract

The riveted steel truss bridge, which is commonly subjected to railway traffic loads, suffers from a potential severe threat of fatigue failure. Therefore, it is imperative to evaluate its fatigue performance. An integrated fatigue life evaluation method is proposed, and three main improvements are included: (1) fatigue evaluation is conducted with a consideration of both the stress ratio effect and load sequence effect; (2) a modified rainflow method maintaining the load sequence is introduced to consider the load sequence; and (3) a whole-range modeling methodology is applied to extend the partially known S-N curve to an S-N curve applicable to the whole range of fatigue regions, which is essential when considering the load sequence effect. To illustrate the effectiveness of the proposed method, the long-term monitoring stress data of an old riveted steel truss bridge are used in the analysis. The fatigue conditions of the monitored members are investigated, the effects of both the stress ratio and load sequence are analyzed, and a key point of fatigue life evaluation is proposed. It is shown that the longitudinal beam of the deck is the critical fatigue member among all monitored members, the stress ratio effect differs with member type and measured point, fatigue life evaluation results are obviously influenced by the effects of both the stress ratio and load sequence, and the load sequence effect is greater than that of the stress ratio effect on the fatigue life evaluation. The proposed integrated method lays a solid foundation for fatigue life evaluation of members in riveted steel truss bridges, which can provide meaningful guidance for maintenance. At the same time, sufficient attention should be devoted to the optimal sensor layout for fatigue life evaluation, which is vital for assessing a structure’s life cycle performance.