New S-N curves for details in bridges with steel truss tubular superstructure
The promotion of tubular structures in bridge construction is a meaningful goal since these are aesthetic, lead to structurally efficient systems as well as sustainable ones. Good fatigue design of the tubular superstructure is a key factor to ensure safety of these bridges. The present paper present the results of several research studies carried out to determine the fatigue strength, i.e. S-N curves for design, of different welded joints and details typical in tubular trusses. The details considered are butt joints between a tube and a cast steel tube part, and by extension between different tubes, as well as K-joints. The paper summarizes the experimental investigations carried out within the research studies, giving the specimen geometries and loading conditions. It also includes information about specimen fabrication and non-destructive inspection of the welds by Ultrasonic techniques. The test results are first presented and commented, then detail categories for typical butt joints used in bridge constructions are given. The test results on K-joints are presented in the way. The size correction factor rules for larger joints, as well as the rules for misalignment/eccentricity, which both reduce fatigue strength, are presented and discussed. The paper shows that detail classifications identical or better then given in the codes can be adopted for the details presented.