Precise Evaluation of Structural Reliability against Fatigue Damage

It is normal practice to consider 100 years environmental condition for the assessment of existing jacket type platforms. Metocean criteria are mostly specified in terms of factors relative to loads caused by 100-year environmental conditions and reserve strength ration which is defined as the ratio of a platform's ultimate lateral load carrying capacity to its 100 – years environmental condition lateral loading RSR=Q u Q d indicates the structural integrity against extreme conditions. Related wave hights are usually considered for storm conditions in In-place analysis and design of offshore platforms. It is usual to consider platform structure in its perfect existing conditions in both analyses. On the other hand the design fatigue lige should be at least twice the service life which is normally less than 100 years. Therefore a well designed offshore platform may loss some joints due to accumulative fatigue damage within 100 years time span while it is not taken in to account in the normal procedure for integrity assessment of existing platform.