Design method for steel structures in marine environment including the corrosion behaviour

Design Codes for steel structures, with among them Eurocode 3, are based on a semi-probabilistic approach. The statistical distribution of the main parameters governing the design leads to the definition of characteristic values, corresponding to an "a priori" accepted probability of occurrence. These characteristic values are then completed by safety factors including the effect of hardly quantified parameters. The effect of corrosion has still not been introduced in the semi-probabilistic approach : in Eurocode EN 1993-5 Piling, the effect of corrosion at the design stage has been implemented by corrosion rates depending on the water environment but without any statistical justification to these values. The goal of this project is to define corrosion design values according to the semi-probabilistic approach and to validate - a posteriori - the current values in Eurocode. This goal is achieved in three stages : collection and analyse corrosion data, development of statistical models of corrosion, integration of these latter in structural design. The corrosion process of steel in marine environments depends on numerous parameters : these parameters can be classified into endogenous parameters related to the steel material, exogenous parameters related to the environment and a dynamic component related to the time of exposure. A sensible modelling or marine corrosion should incorporate at least some of these parameters in order to better match the environmental conditions that are likely to be encountered. The multi-factorial prediction model and the simplified model that were developed in this project fulfil this requirement. Moreover, these models are based on a statistical approach that allows to assess the statistical influence of corrosion on the structural safety.