Buckling of Encased Elliptic Thin Ring

Abstract

This paper presents a new equation to obtain the ovality reduction factor for the buckling resistance of a rigidly encased thin ring under a uniform external load. The ovality reduction factor is used to relate the buckling pressure of a thin oval to that of a ring in its circular shape. A model for a thin ring subjected to shrink buckling is adapted for the analysis of a constrained ring under external pressure. The purpose of the research is to investigate the validity of the current design criteria of snug-fitting plastic liners, which are used to rehabilitate deteriorated underground pipes. The geometry of deformation of the ring's buckled portion is used to develop an equation to reduce the buckling capacity due to ovality. The proposed equation, which can be applied when the existing pipe has defects in shape, is shown to be much less conservative than the equation used in current practice.