Web Stress Development Mechanism Critical for the Fatigue Limit State in Horizontally Curved Steel Bridges

Although the nominal strength of modern steel bridges that involve increasingly slender elements has been well defined through extensive research and testing, fatigue concerns have not been thoroughly investigated. The out-of-plane displacements of slender webs result in secondary bending stresses at the web boundaries connections, i.e., flange and stiffeners. The so-called web breathing phenomenon potentially leads to fatigue crack initiation at the web boundary connections and has been studied for straight girders. Curved steel girders experience large deflection and rotations during construction and service that can intensify the web breathing effect. In addition, the curvature-induced lateral forces pushing and pulling slender curved webs develop mechanisms that can lead to critical web boundary stresses that do not typically occur in straight bridges. This paper aims to define the slender web behavior of composite curved steel bridges essential for the fatigue limit state. It focuses on capturing the distortion-induced web stresses from the construction stage through service using 3D finite element analyses. An advanced technique was applied to simulate the non-composite and composite stages to quantify the continuous web stress development due to geometric nonlinearities. Three different web panels under high shear, high moment, and high shear-moment combination were studied. The stress ranges due to the AASHTO fatigue truck is presented for composite bridges with varying curvature radii. The mechanism involved in curved bridges is defined and the stress magnitudes are compared to that of equivalent straight bridges to understand the role of curvature in intensifying the critical fatigue stress ranges.

Automated summary

This paper focuses on the fatigue behavior of slender web in composite curved steel bridges and aims to understand the influence of curvature on critical fatigue stress ranges. By using 3D finite element analyses, the distortion-induced web stresses during construction and service are captured. The role of curvature in intensifying the critical fatigue stress ranges is investigated by comparing with equivalent straight bridges.