This article presents guidelines developed by the Research Institute of Roads and Bridges for estimating the loss of the load capacity and determining the time between failures of steel road bridges resulting from corrosion. Mathematical relationships which enable the determination of load capacity and durability of bridge structures were discussed. Reduction coefficients required to calculate the percentage decrease of the load bearing capacity of the corroded structure and reduction coefficients that are significant in determining the degree to which lifespan of the structure is shortened were defined. Mathematical algorithms of presented method made it possible to obtain information, that are necessary for further maintenance and possible modernization of the bridge in Wisla.
The following article discusses the problem of durability of girders made of structural steel S355 affected by corrosion. It presents the Polish procedure for calculating the time between failures of steel elements of bridge and durability factors necessary to estimate the impact of corrosion on the durability of steel road bridges. According to the presented procedure, two real bridges of steel structure were analysed. The bridges selected for analysis are located in extremely different corrosive environments in Poland. This bridges were built in different areas of the country which are characterized by different (mountain, urban) aggressiveness of the environment. The objects of the analysis differ in terms of corrosion type occurring on the bearing system. Their age is also different which has a significant impact on their safety.The results obtained allowed to determine the time when, with the existing corrosion damage, failures may occur.