Structural Integrity Assessment of Offshore Jackets Considering Proper Modeling of Buckling in Tubular Members—a Case Study of Resalat Jacket

Abstract

In the present research, results of buckling analysis of 384 finite element models, verified using three different test results obtained from three separate experimental investigations, were used to study the effects of five parameters such as D/t, L/D, imperfection, mesh size and mesh size ratio. Moreover, proposed equations by offshore structural standards concerning global and local buckling capacity of tubular members including former API RP 2A WSD and recent API RP 2A LRFD, ISO 19902, and NORSOK N-004 have been compared to FE and experimental results. One of the most crucial parts in the estimation of the capacity curve of offshore jacket structures is the correct modeling of compressive members to properly investigate the interaction of global and local buckling which leads to the correct estimation of performance levels and ductility. Achievement of the proper compressive behavior of tubular members validated by experimental data is the main purpose of this paper. Modeling of compressive braces of offshore jacket platforms by 3D shell or solid elements can consider buckling modes and deformations due to local buckling. ABAQUS FE software is selected for FE modeling. The scope of action of each of elastic buckling, plastic buckling, and compressive yielding for various L/r ratios is described. Furthermore, the most affected part of each parameter on the buckling capacity curve is specified. The pushover results of the Resalat Jacket with proper versus improper modeling of compressive members have been compared as a case study. According to the results, applying improper mesh size for compressive members can under-predict the ductility by 33% and under-estimate the lateral loading capacity by up to 8%. Regarding elastic stiffness and post-buckling strength, the mesh size ratio is introduced as the most effective parameter. Besides, imperfection is significantly the most important parameter in terms of critical buckling load.

Keywords

Critical buckling load / Compressive behavior / Post-buckling strength / Local buckling / Tubular members / Jacket type offshore platforms