Ships And Marine Engineering Structure Ultimate Strength Analysis

The thesis investigates a methodology of computing the ultimate strength of a box girder structure based on the simple non-linear finite element analysis. First, the cross section of a boxlike girder is discretized into stiffened elements and corner elements, then the FEM(Finite Element Method) program is compiled to calculate the curve between stress and strain of every stiffened element. At last the Fortran program is compiled to calculate the moment-curvature relationship of the box girder structure based on the progressive collapse mechanism, and the peak values as its ultimate strength are identified.The FEM program is compiled considering not only material and geometrical nonlinearities but also the initial deflection and lateral loading to calculate the stress-strain relationship of a stiffened panel. This method has the advantages of high precision, wide application and uniform format, it can calculate all kinds of stiffened panels, such as cracked and damaged stiffened panels. At the same time the post-collapse behaviour of the stiffened panel can also been get.The Fortran program is also complied to calculate the ultimate strength of the box girder structure based on the results about stress-strain relationship of stiffened panels calculated by FEM. The program computes the ultimate strength of two classic box girder models very efficiently. Results are compared with experimentally available values for the box girder models, good agreements are found between the results obtained by the current program and the actual collapse values. The results also demonstrate that the program is effective and credible.At last, the program is applied to calculate the ultimate longitudinal bending moment of a large platform, which broken off at one normal operation. Defects of the platform structure are found based on the results by the program, such as the bottom longitudinal stiffeners and bulkheads have very low buckling stress, which reduce the overall ability to resist the destroy.