On the Ultimate Strength of Cylinders With U-Type Longitudinal Stiffeners

Results from an experimental and theoretical study of the cylinder with U type longitudinal stiffeners on buckling and ultimate strength are reported. In the experimental investigation, combined loading (axial, moment and shear) tests were conducted on longitudinally stiffened cylinders with sixty U-type stiffeners. In the theoretical investigation, FEM analyses by use of the computer program MSC/DYTRAN for the ultimate strength of the stiffened cylinder were conducted. From the parametric FEM analyses, it was clarified that the thickness of the cylinder and the stiffener exert decisive influences upon the buckling and ultimate strength. Introduction The utilization of a huge diameter stiffened cylinder for offshore structures which is shown in Fig.l gives the advantages of large stiffness, light weight and big buoyancy. Many projects using the stiffened cylinder are in various stages of design for offshore structures such as semi-submerged platform. Based on these necessity, Det Norske Veritas (DNV) investigated the buckling strength to issue regularly design code and recommendations "Buckling Strength Analysis, Classification Notes" for structural designs. [1] [2] In this paper, the authors carried out investigations into the buckling and ultimate strength of the stiffened cylinder. The ratio of diameter to thickness was D/t=2083. The U type longitudinal stiffeners (U stiffener) and H type circumferential ring stiffeners (H stiffener) were furnished on the cylinder by welding. The research program is composed of experiments and FEM simulation analyses. Experiment includes a series of static tests under combined compression, shear and bending. For FEM analysis, six models were employed to investigate the effects of the thickness of the panel, and one model was employed to simulate the buckling and ultimate strength of test model. Quite good agreements are observed between the experimental results and calculated FEM analysis.