Updating of structural failure probability based on experienced wave loading

This paper describes a simple generic model for calculating the failure probability of a structural system (jacket), and evaluates the effect of updating the probability of failure based on the experienced wave load on this structure. An existing structure in harsh weather areas are often claimed to be a safe structure after having survived some years exposed to environmental loading. This paper evaluates this statement by a practical method to assess how large loading the structure must have experienced to achieve a detectable change in the calculated overload failure probability. Also the effect of model uncertainties, reserve strength is evaluated and a simplified modelling of a possible gross error is included. Based on the model presented here, the example structure, modelled without gross errors, must have experienced a load level in the order of 1000 to 10 000 year loading in order to change the updated probability of failure significantly. If gross errors are included in the model, the experienced loading must exceed the 100 to 1000-year loading in order to conclude that a gross error is unlikely.