The Effect of Reinforcing Plate on the Stiffness of Elastomeric Bearing for FPSO

Abstract

The marine elastomeric bearing consists of an elastomer and several reinforcing inserted plates. Unlike land bearings that are to absorb high-frequency vibration during earthquakes, offshore elastomeric bearings are to support topside-module weight while efficiently absorbing wave-induced hull motions. The bearing is to receive three loads: compression, shear, and bending, and providing sufficient stiffness to resist the loads by inserting an adequate number of reinforcing plates is a major design issue for marine bearings. The stiffness of elastomeric bearings is largely influenced by the ratio of height to the area of the bearing and the number of laminated reinforcing plates. In this study, for the given size of the elastomeric bearing, the effect of the number of reinforcing plates on its compression, shear, and bending stiffness is investigated by using ANSYS Mechanical APDL, a commercial structural FE (finite element) analysis program. First, full analysis is done for the compression, shear, and bending stiffness with increasing respective displacements and the number of reinforcing plates from 0 to 8. The numerical results are partly validated by authors’ experimental results. Based on the numerical results, several empirical formulas are suggested for the variation of the three stiffnesses as a function of the number of reinforcing plates. Next, the design of the elastomer bearing for a representative FPSO (Floating Production Storage and Offloading) operated in the North Sea is conducted according to the required load and displacement conditions. Then, the adequate number of reinforcing plates for the case is determined and the results are shown to satisfy all the required safety factors for various required loading conditions.