As the result of safety factors considered in load and resistant values for the design of new offshore platforms, a higher resistance compared to the 100 year return period environmental loading, is achieved in the structure. This type of design is usually performed using linear methods of structural analysis. In this case the structure practically has a high reserve capacity which is disregarded in the design phase but may be considered in special cases. One of these important cases is when an existing structure is assessed and evaluated after elapse of its structural life. In this case using the platforms reserve capacity, through a non-linear analysis such as push-over, would be logical and economic. In this paper initially the factors affecting a platform non-linear analysis and methods for considering non-linear characteristics of structures will be discussed. Then the results of an investigation on the behavior of three Persian Gulf platforms due to wave loading using the non-linear push over analysis method of USFOS software are presented. Finally, the results of these analyses are compared with the API RP2A’s assessment criteria [1].

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