Load Rating Based Maintenance Approach for Corrosive Twin I-Girder Railway Bridges in India

In Indian Railways, about 75% of the bridges are exceeding 60 years' life period and 80% of steel bridges population adopt simply supported twin I-girder structure. Corrosion has become one of the biggest challenge for maintenance of these old steel bridges. Currently the index called Condition Rating Number (CRN), utilized to assess the structural conditions and determine the maintenance strategy. CRN is a qualitative approach with individual bias in decision, therefore it is difficult to identify the prioritization of corrosion damages in same CRN category. In this study, a new approach based on load rating factor (LRF) for corrosion maintenance on typical twin I-girder bridges is proposed. Firstly, by considering frequently occurring corrosive location and the absolute maximum load effect, three categories of critical corrosive location and pattern are summarized. Secondly, LRF based on physical inspection is calculated using simplified theoretical approach and FEM approach. Various degree of corrosion is utilized to investigate the influence on the load capacity by incorporating the nonlinear phenomena such as buckling. It is found that the simplified approach is conservative enough to evaluate the structure practically within safety side. Finally, the practical decision flow regarding to the maintenance action is proposed, summarizing the relationship between the corrosion and the remaining load capacity by means of LRF. This approach is expected to provide not only an objective evaluation to load capacity of corrosive railway bridges, but also instructive information for the retrofit of structures with limited fund availability.