Residual ultimate strength formulations of locally damaged steel stiffened cylinders under combined loads

This paper aims to derive new simple and consistently reliable residual strength equations for predicting the residual ultimate strength of steel dented stiffened cylinders under combined axial compression and radial pressure including hydrostatic pressure. For this, two types of the stiffened cylinders, namely, stringer- and/or ring-stiffened cylinders, which are generally main components of offshore marine structures used in semi-submersibles, submarines, tension legs of platforms (TLPs), and other various types of floating offshore structures, are investigated. Firstly, the various collision damage scenarios which illustrated the collision accidents of offshore stiffened cylinders with supply vessels or floating subjects, were analysed. Then, a finite element modelling of the stiffened cylinders was developed using a commercial software package ABAQUS/Explicit after being validated against available test results. Next, rigorous parametric studies on full-scaled design examples of stiffened cylinders were carried out by changing the design variables. Based on the rigorous case of the study results, new simple design equations, which are used to predict the ultimate residual strength of the damaged stiffened cylinders under combined loads are proposed through a regression study. Finally, the accuracy and reliability of the proposed equations have been compared with available test data and a nonlinear finite element analysis (NFEA). These equations can be useful for the initial design stage of stiffened cylinders under the risk conditions of offshore structures in the case of collision incidents.