Fatigue Performance Evaluation and Cold Reinforcement for Old Steel Bridges

Fatigue and corrosion damage in existing old steel bridges are accumulated continuously in service stage, probably leading to structural failure. One old welded steel bridge and one old riveted steel bridge are taken as examples for structural performance and safety evaluation. A large number of out plan deformation-induced long fatigue cracks were found at the connection plates connecting the bottom flange of end cross-frames and main girders of the two old steel bridges, and serious corrosion damage was found at such details of the old riveted steel bridge. Cold reinforcement techniques of drilling stop holes and bonding and bolting steel plates were adopted to strengthen the old steel bridges. Fracture mechanical models using the short-term monitoring data were established to assess the fatigue lives before and after the reinforcement, considering the coupling effect of fatigue and corrosion, and the evaluation results indicate that corrosion and fatigue coupling is very significant for old steel bridges. Monitoring and evaluation results show that bonding and bolting steel plates leads to about 90% reduction in the maximum tensile stress and about 8 times fatigue lives extension, while drilling stop holes can only temporarily arrest the crack growth. Additionally, the future maintenance strategies recommendations are provided.