Multiaxial fatigue assessment of complex steel connections: A case study of a vertical-lift gussetless truss bridge

Abstract Civil engineering structures grow more complex as engineers push innovation boundaries. Load complexity, costs, construction and maintenance efficiency, among other things, can lead to unique designs that are often excluded in current design codes and evaluation standards. Fatigue-induced damage is currently one of the most common damage types experienced by ordinary and complex civil engineering structures subjected to cyclic loading such as bridges. However, current fatigue evaluation and design standards provide limited guidance on how to approach complex welded connections. Uniaxial and multiaxial methods for the evaluation of fatigue life using strains histories are compared for the assessment of a welded gussetless truss connection of the Memorial Bridge, a vertical-lift bridge connecting Portsmouth, NH and Kittery, ME. As expected, using both approaches result in sufficient remaining fatigue life. However, it is demonstrated that commonly used uniaxial fatigue analysis methods can be insufficient in complex structures that experience variable amplitude, multiaxial, and non-proportional loading. Multiaxial non-proportional stresses experienced by a complex connection can cause a decrease in remaining fatigue life estimates. This paper presents assessment tools and a method for the evaluation of fatigue life of complex welded connections using strain time histories.