Investigation On Bending Ultimate Strength Of Offshore Platform Steel Containing Random Corrosion Pits

Offshore platforms are often served in extremely harsh marine environment, in which corrosion can cause significantly impact on the safety of structure. The maximum load is an important index to evaluate the safe capacity of offshore platform. With the development of computer technology, the nonlinear finite element method involving elastoplastic and large deformation is applied to the ultimate strength analysis of ships and offshore platforms. Considering the random of corrosion for offshore platform steel structures, stochastic finite element method becomes an effective method to study the safety of offshore platforms.This thesis relies on China 981 offshore platform project and WDH370 steel is treated as the research object. The effect of corrosion on the bending ultimate strength of steel structure is intensively studied in this thesis. The main contents of this thesis are as follows.1. The random corrosion plate model is established by MATLAB. The MATLAB program can create FEM model of plates with corrosion pits, and bilinear elastic-plastic stressstrain curve of WDH370 steel is set up in ABAQUS with the capacity of elastic-plastic and large deformation.2. The ABAQUS results and effective data are automatic imported to the designated EXCEL electronic form by PYTHON program. The finite element calculation is accomplished with the main program in MATLAB. Thus, one command can carried out a number of stochastic finite element calculation.3. The corrosion plate with different corrosion rate and different yield ratio was numerically studied. The moment-rotation curve, ultimate moment and displacement are extracted. The statistical relationship between the corrosion rate, yield ratio and the bending stiffness reduction is finally obtained.4. Some bending experiments of steel are carried out in our lab. Finally, a quantitative relationship between the corrosion rate and the residual flexural ultimate strength is obtained as results.The numerical results show that the proposed numerical method is reasonable, effective with high precision. A number of numerical are obtained and these data are dealed with statistics tools in MATLAB, so that the relation between the bending ultimate strength of plate and the corrosion rate is established. The results show that the proposal method has potential application to evaluate the safety of offshore platform structure.