Yusuke TOMINAGA

Study on Simplified Evaluation Method of Stress at corroded area of steel I-girder with corrosion thinning on the lower flange

Eiji IWASAKI

The aging of social infrastructure in Japan, particularly bridges built post-1950, is a growing concern due to numerous reports of damage, primarily caused by corrosion in steel I-girder bridges. Corrosion, often found in complex areas like bearings, has also been reported in the interstices of girders. Despite the relatively low occurrence, corrosion in the interstices significantly impacts the bridges' load-bearing capacity by affecting their bending strength, a critical resistance mechanism. 
Therefore, the study aimed to develop a simplified method for evaluating stress in cases of corrosion-induced thinning of the lower flange in the interstage. Simplified method, such as using force balance condition equations, provide a means to estimate stress in corroded areas, they fail to account for stress disturbances near the boundary between healthy and corroded segments, especially with corrosion over a short length, leading to errors in stress distribution. In addition, the finite element analysis method, despite its accuracy, poses challenges due to the need for specialized software and time-consuming model creation and analysis. Therefore, we proposed a method to correct the corrosion zone stress obtained by the force balance condition equations. 
From the analysis results, equations were derived to calculate correction factors for both composite and non-composite girders, which could be multiplied with stress values obtained from force balance equations to adjust for changes in corrosion length. Comparisons between finite element analysis method and correction values indicated acceptable estimation accuracy, with errors typically within 6%. This suggests that the proposed method offers reliable estimation within the practical range of use in actual bridges, providing a pragmatic solution to address the impact of corrosion-induced deterioration on bridge performance.