Remaining Strength Estimation Methods of Plate Girders with Corrosion and the Practical Evaluations

Abstract

In steel plate girder railway bridges with open deck system, damage caused by local corrosion of the upper flanges under sleepers is well-known. This damage reduces ultimate strength of the main girders significantly (e.g., in the case of 50%-corroded upper flanges, approximately 30 percent reduction in bending strength). This paper presented a simple evaluation method for estimating the remaining strength of the plate girders that have local corrosion damage under sleepers. Remaining strength of the damaged plate girders can be calculated by taking into account both the remaining strength for local load (hereinafter referred to as “patch load”) that acts directly on the upper flanges under the sleepers, and the remaining strength for bending load that acts on the main beam itself. This new evaluation method using the equations proposed in this paper, is based on the idea that the remaining strength under pure bending load can be obtained as the minimum value of strengths calculated in light of the various buckling modes of the compression flange, while taking the thickness reduction due to corrosion into account. Thereafter, the remaining strength under patch load only can be calculated by using an equation which is further simplified based on Takimoto’s original equation. Finally, the remaining strength of the plate girder as a whole is obtained from the strength interaction curve between patch and bending loads. In addition, by comparing the estimated remaining strengths obtained through this method with those obtained from nonlinear Finite Element Method (FEM) analyses using full-scale beam models, it could be concluded that the simple evaluation method by using both new and original equations can estimate the remaining strength of plate girders with corroded flanges under sleepers with around 95 percent accuracy.