Shakedown Analysis of Ocean Engineering Structures Subjected to Repeated Dynamic Loads

Ocean engineering structures are frequently subjected to repeated dynamic loads caused by slamming of wave, impact of ice, dropped objects, collisions of store ship and grounding. Shakedown analysis is an extension of plastic limit analysis. Meanwhile, the dynamic strength analysis and shakedown analysis of offshore platform structure have an important place in ensuring the safety and reliability of ocean engineering structures under repeated dynamic loads. Therefore the shakedown analysis theory was introduced to the ultimate strength analysis of brace strut of semisubmersible drilling platform considering cyclic wave load. Based on the kinematic shakedown theorem, a theoretical method of shakedown analysis for typical ocean engineering structures under repeated dynamic loads was presented and compared with existing results to verify the reasonableness. According to the method of finite elastic-plastic theory, the strength of brace strut was analyzed through the overall model of semisubmersible drilling platform. Then based on the boundary conditions getting from the overall three-dimensional model, locally refined model of brace strut was obtained. By applying the theoretical method to shakedown analysis of brace strut under repeated dynamic loads, influence of shell thickness, stiffener thickness and stiffener spacing on shakedown limit were studied. The results show that the theoretical calculation method is consistent with the existing results. The limit load increases with the increase of shell thickness and stiffener thickness, while decreases with the increase of stiffener spacing.