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Corrosion is one of important factor for securing the safety of steel bridges. In general cases, the corrosive environment of the steel bridge is evaluated as a site environment. However, even in one bridge, the corrosive environment greatly varies from part to part. This research aims to clarify the difference of corrosion environment for each part of plate-girder-bridge which has three main girders. At this bridge, anti-freezing agent is sprayed in winter. On site measurements were performed on five points on each girder, which are both sides of web, both sides of upper/lower part of bottom flange. These measurements points include two points where water leakage is scattered. Temperature, humidity, amount of airborne salt and amount of adhering salt have been measured. In order to comprehensively assess corrosive condition, exposure test was also performed. Observations were carried out for one year. From measurement results, it became clear that temperature and humidity were not uniform at all observation points. These were differed at the inside and outside of girder and upper part and lower part of web. Amount of airborne salt to each girder is strongly influenced by anti-freezing agent. On the upper surface of the lower flange of each girder, there are places where corrosion markedly progresses due to deposits and water leakage.

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To assess critical state of bridges, after-fracture-redundancy plays an important role. Therefore, it is necessary to make a correct prediction of redundancy. However, redundancy from numerical analysis is strongly influenced by various analytical conditions. This study aimed to clarify the influence of member connection modeling and shape of gusset plates on redundancy analysis of truss bridges. Redundancy were computed for three types of analysis model of truss bridge. Model A was a frame model of truss bridge, frame members were connected to each other rigidly as it is. On the other hand, in Model B and Model C, members were connected via gusset plates modeled by shell elements. Gusset plates in model B were rectangle and these of model C had curved shape. Using these three models, redundancies under different analytical condition and different gusset plate shape were compared. From the results of calculation, it was found that bending moment on truss members were strongly influenced by difference of member connection modeling. Computed results also indicated that the influence appears more strongly in damage state than normal state (non-damage state). This result suggested the necessity of accurate modeling of member connection. Furthermore, it was indicated that the redundancy of truss bridges could be improved by change in shape of gusset plates.