This paper presents the nonlinear finite element analysis of the concrete platform that is suitable for offshore marginal oil fields in the Bo Hai of China. To simulate the process for crack growth of the prestressed concrete tank wall, layered finite element model is used. The"concrete layers are modeled by 20-node refined nonconforming isoparametric elements that have high accuracy, excellent computation efficiency and less sensitivity to mesh distortion. A new cracking criterion is used in the iteration process to improve the convergence. The result of nonlinear analysis is compared to the result of linear analysis, and the weak parts of the structure are suggested to be strengthened.
A multi-function removable concrete platform suitable for offshore in Bo Hai is developed by Dalain University of Technology (Yupu Song, 1997) and China Bo Hai Offshore Oil Corporation. The platform has three underwater prestressed concrete tanks to storage high pour point crude oil. The temperature difference between the two sides of the concrete tank wall is great. The concrete tank subjected to the temperature and wave load will get into the nonlinear state. It is important to make the nonlinear analysis of the platform and get the stress distribution and the process for crack growth. The nonlinear analysis of concrete platform without considering the reinforced bar and temperature stress was finished (Yupu Song, 1992). To consider the reinforced bar and the prestress, layered finite element model is used in this paper. Along the thick direction concrete is divided to six layers, and the truss element is used to represent to steel bar. The concrete layers are modeled by 20-node elements. Because the thickness of the element is very thin comparing to the length, the precision is an important problem.