Retrofitting to Alleviate Effects of Corrosion in Cross Girders Under Inner Rail of Curved Railway Bridges

The main railway line which spans from Colombo Fort to Badulla, is one of the nine railway lines of Sri Lanka Railways (SLR). The track alignment of the upcountry section (Rambukkana to Badulla) of the main line was defined about 150 years ago and it has a number of bends with sharp curves. Curved railway bridges are the bridges having railway bends on the bridge to bring gradual change of track direction. When considering with the total number of curved railway bridges, around 75% of curved bridges are located in the upcountry section of the main line. Corrosion of the cross girders beneath the inner rail of a railway bend is the most common problem encountered in curved bridges in the main line. In this study, the reason for corrosion of cross girders of curved railway bridges was investigated through a detailed study of two corroded curved truss bridges in the upcountry section of the main railway line. Current strength of bridge materials and its microstructure were investigated with in-situ hardness measurements and microscopic examination, respectively. Validated numerical models were developed and model results showed that cross girder location beneath the inner rail experienced the highest stresses. These higher stresses are the most logical reasons for corrosion initiation of the cross girders. Further, four repair options were proposed to upgrade these two bridges and their respective numerical models were prepared and analysed. Option 1 is the introduction of the trough section which is the common practice of SLR. Option 2 is the increase of web thickness by welding a steel plate on to the web of the cross girder. Option 3 is the attaching of two steel plates to the top and bottom flanges of cross girders. Option 4 is the combination of Options 2 and 3. Repair Option 1 was not feasible since analysed results showed higher stresses than those of the existing bridges. Options 2, 3 and 4 showed lower stresses than those of existing bridges. Considering the economical and practical aspects of railway operation, it was concluded that Option 2 (increasing web thickness only) is the optimum repair option for the strengthening of corroded curved railway bridges.