This article describes the use of fibre reinforced polymer composites to increase the strength of an isotropic metallic cylindrical shell against elephant’s foot buckling. This form of buckling ...occurs when a cylindrical shell structure is subjected to high internal pressure together with an axial force, such as those that may occur in tanks and silos. It is particularly relevant to tanks under seismic action. Although fibre reinforced polymer composites have been widely applied to different types of structures under several loading conditions, its use to strengthen thin steel cylindrical shells has been very limited. Here, a non-linear elasto-plastic finite element idealisation is used to explore the strengthening effect of a fibre reinforced polymer strip on a thin cylinder. The optimum size and position of the fibre reinforced polymer sheet were obtained and empirically formulated. This study has shown that the strength after repair is sensitive to minor changes in the fibre reinforced polymer parameters so that a close adherence to the optimum parameter values is very desirable.
Due to compressive loads, offshore flexible pipes may exhibit global and local instabilities and as a consequence structural failures. This work presents an experimental investigation concerning the ...local structural behavior of a real 2.5-inch flexible pipe under compressive load. Three instabilities events were observed in the experimental test: elephant’s foot buckling, birdcaging and wrinkling. Digital image correlation techniques, applied for the first time in this scenario, allowed a clear experimental assessment. Correspondence between axial compressive loads and observed instabilities is discussed. Linear elasticity formulations are used to explain the structural behavior, culminating on an instability diagram for elephant’s foot buckling deflagration, based on a von Mises stress yielding criterion.
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