Failure Criteria and Wind-Induced Vibration Analysis for an Offshore Platform Jacking System

Abstract

Currently, the construction process of large offshore platforms worldwide involves building the topside and hull separately and then having them integrated. Jacking technology is emerging as a new integration method more suitable for offshore platform construction for its higher tonnage and larger scales compared with the lifting technology. Conventionally, an overlapped support tower (OST) is adopted to jack the topside to a predetermined height. However, with the OST’s increasing jacking height, the wind load effect becomes more significant, which in turn limits the OST height and applications. In this paper, failure criteria were developed for the OST based on the load types and structural characteristics of easy assembly and disassembly. Then a simplified method to simulate the OST was proposed. In addition, a finite element model (FEM) of the entire jacking system with the topside and OST (including 6 jacking towers, 8 strand cables and 23 bracing pipes) was established, and wind-induced vibration analysis was performed to ensure safety of the jacking system. The results show that the addition of the topside increases the torsional effect of the jacking system; the unfavorable wind angles are 0° and 15°, which should be paid much attention during the jacking operation. The recommended wind-induced vibration coefficients for the OST and topside are 3.0 and 4.0, respectively. The proposed method and simulation results of this study provide a reference for the jacking and integration design of similar offshore platforms.