Buckling and Distortion Induced Fatigue of Curved Steel Plate Girders with Slender Webs

The slender webs of modern bridge plate girders are susceptible to buckling in both shear and bending regions. With each passing vehicle cycle, the out-of-plane web deformation due to buckling, fabrication and erection expands - a phenomenon sometimes referred to as ""web breathing"" - and results in stress concentrations at the intersections of welded elements such as stiffeners. This effect in horizontally curved plate girders is further exacerbated by the non-alignment of the internal forces resulting from major axis (vertical) moment, which push and pull the web out of its plane. While this may not significantly influence the nominal bending strength definition used in bridge design, the resulting fatigue crack potential might affect the service life and future maintenance costs. The objective of the work in which this paper is based is therefore to quantify the stress intensity at risers in curved steel bridge girders that result from the cumulative effects of fabrication, erection, and traffic loadings, and to relate that knowledge to the fatigue limit state. The stress magnitude quantification relies on multi-stage finite element modeling in which the deformation state of the full bridge structure modeled with shell elements is enforced onto high-resolution volume element submodels. Field measurements from fabrication through live load testing of an on-going bridge construction project with a radius of curvature of approximately 440 ft (134 m) are used for validation. Parametric studies using the submodeling technique define the predominant factors and recommendations for preventing and mitigating the fatigue concern are presented.

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