Fatigue failure has become one of the most significant concerns in offshore marine field. Offshore floating structures like transportation barges are subjected to cyclic loading during voyages because of chaotic sea environment. Random sea wave induces the cyclic stress in the structure, result in sudden local failure of the structure element. This may cause the loss of barge and costly offshore modules which are carried by the barge such as top sides, jackets. During its life time, barge experiences so many loading conditions, contributing to fatigue damage. At design stage, an adequate factor for safety has been considered for the loads encountered during its lifetime. But due to great uncertainties involved in fatigue failure, it is not possible to determine the fatigue life accurately. Among various existing methods available for the prediction of fatigue life, spectral fatigue method is considered to be more realistic approach by taking real sea state energy spectrum into account and is very convenient to use at the preliminary stage of design for the estimation of the fatigue life as compared to other methods. Here a study is made to find fatigue damage of the transportation barge based on spectral analysis.
Stochastic nature of the ocean environment is the main source of the fatigue demand for welded structural elements. Fatigue failure if not considered at design stage can produce precarious consequences on the floating structure. High tensile steel is extensively used in ship building to improve strength to weight ratio. But, usage of high tensile steel has not really enhanced the fatigue strength because of increase in hull stress level. Fatigue strength estimation broadly can be classified into two categories: (Xiang-chun Guo-qing and Hui-long, 2006) cumulative fatigue damage based on S-N curve and fracture mechanics method based on crack propagation.
