Vibration Analysis of Welded Tubular Structures Considering Local Joint Flexibility

Welded tubular structure is the backbone of offshore jacket platform. As a thin-walled structure, local joint flexibility (LJF) in a tubular structure is prominent, and it may produce significant effect on the dynamic performance for the overall structure. This study presents a simplified model to analyze the dynamic behavior of a steel tubular structure with LJF. The presented model simplifies a tubular structure into a frame model consisted of beam elements with considering the LJFs at the connections between any two elements. The LJF is simulated with a fictitious beam element (FBE). Methods for defining the dimensions of the cross section and the material properties of the FBE are provided. The accuracy of the presented method is verified through comparing with three dimensional (3D) finite element results on the vibration of a tubular structure. The tested results indicate that LJF has remarkable effect on the vibration of welded tubular structures, and the simplified model presented in this study can provide more accurate estimation compared to conventional rigid frame model.