Manufacturing, Testing and Modeling of Advanced Filament Wound Grid Stiffened Composite Cylinders

Abstract

Advanced Grid Stiffened (AGS) structures are a kind of FRP composites that are being extensively used in many engineering fields because of their inherent advantages. Hence it is of utmost importance to understand the basic mechanism of these structures in order to develop better models and to find ways to improve their efficiency. This thesis discusses the manufacturing technology used viz. the filament winding technique to fabricate grid stiffened composite cylinders. A step by step procedure of the fabrication process of grid cylinders is explained. The confinement effectiveness of the AGS cylinders is evaluated by filling them with concrete and subjecting the specimens to uniaxial compression tests. The results from the experiments show that the grid stiffened cylinders have more load carrying capacity than the normal FRP pipes. The stiffeners in the grid structures increase the structural capacity and also prevent the global buckling of the grid cylinders. It is seen that the skin wound at a certain angle provides satisfactory lateral confinement to the grid structure and the desired composite action is achieved between the grid structure and the skin. The AGS structures are able to effectively confine the concrete, thereby increasing their strength multi-fold. To validate the results obtained from the experiments a 3-D finite element model of the grid stiffened cylinder was developed using ANSYS. The nonlinear behavior of the materials used in the experiments was incorporated into the FEA model by considering the appropriate stress-strain relationships. The behavior of the confined concrete composite cylinder was modeled using a non-associative Drucker-Prager plasticity criterion. The validated FEA model was used to perform a parametric analysis. Several design parameters were identified that seem to have an effect on the load carrying capacity of the grid structures. These parameters were then varied using the FEA model to evaluate the structural behavior of the cylinders and the results were analyzed to efficiently design high strength grid stiffened composite cylinders. Finally a discussion of the results from both the experiments and the FEA model are presented and general conclusions are drawn.