Nonlinear finite element method models for ultimate strength analysis of steel stiffened-plate structures under combined biaxial compression and lateral pressure actions—Part I: Plate elements

For design and strength assessment of various types of structures such as ships, offshore platforms, land-based structures, and aerospace structures, it has been realized that ultimate limit states (or ultimate strength) are much better basis than the allowable working stresses. Within the framework of ultimate limit state design and strength assessment, the primary task is to determine the level of imposed actions which causes the ultimate limit states. The aim of the present study is to develop some useful insights on nonlinear finite element method application for ultimate limit state assessment of steel stiffened-plate structures subject to combined biaxial compression and lateral pressure actions. As an illustrative example, outer bottom stiffened-plate structures of 100,000 ton class double-hull oil tankers are considered. The present study consists of two parts; Part I deals with plate elements surrounded by stiffeners or support members, and Part II treats stiffened panels, where some important factors of influence such as structural dimensions, initial imperfections, loading types and computational techniques in association with ultimate limit states are studied. For ultimate limit state computations, ANSYS nonlinear finite element method together with ALPS/ULSAP semi-analytical method is employed. Important insights developed from the present study are documented.