Author(s)

A. Almasi

Abstract

In modern offshore installations, thin walled columns are used for energy absorption in accident situations. When this advanced offshore shock absorber is subjected to axial compressive load, plastic hinges are developed on the sides of column and the column crushes with repeatable patterns. It can absorb considerable impact energy due to large and continuous plastic deformation. This paper develops a new closed form, energy based, solution for the prediction of accurate collapse curves of plastic folding of square section columns under axial impact load. New formulations for square section tube plastic folding, with respect to contributions from hinge curvature, strain hardening, second force oscillation and sensitivity to imperfection, are presented. The behaviour of a column in dynamic load is investigated using a simplified model of an offshore impact with dynamic corrections, including strain rate modelling. Good agreement between experimental and theoretical load-displacement and velocitytime curves verifies the accuracy of the proposed formulation. Keywords: offshore shock absorbers, collapse, axial impact, square section column. 1 Introduction The design of offshore shock absorbers has great effect on the reliability of ships and offshore structures. When a relatively short thin-walled closed section column is subjected to an axial compressive load, horizontal and inclined yield lines are developed along the sides of the column and the column crushes with a repeatable pattern [1,2]. This type of crushing is known as \“Plastic Folding”. Fig.1 shows the plastic folding of a square tube [2]. The corresponding

Keywords

offshore shock absorbers, collapse, axial impact, square section column.