United States Department of Transportation
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Development of Advanced Grid Stiffened (AGS) Fiber Reinforced Polymer (FRP) Tube-Encased Concrete Columns: [Technical Summary].
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2013-03-01
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By Li, Guoqiang
[PDF-141.19 KB]
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Abstract:In recent years, the use of fiber reinforced polymer (FRP) tube-encased concrete columns for new construction and rebuilding of engineering structures has increased. The purpose in FRP tube-encased concrete columns is to replace the steel rebar by a corrosion-resistant laminated FRP shell. The FRP tube serves as a stay-in-place formwork during construction; during service, the tube confines the lateral expansion of the concrete core and transfers the core to a triaxial compressive stress condition. As a result, the compressive strength and ductility of the column are enhanced significantly. Also, owing to the inherent corrosion-resistance of FRP, it is maintenance-free, providing long-term cost benefit. However, it is found that the FRP tube only provides passive confinement to the concrete core such that the FRP tube cannot confine the concrete core before the concrete cracks/crushes. The reason for this is as follows: (1) Due to the orthopedic structural properties and various couplings, a FRP tube usually has a much larger radial (out-of-plane) Poisson’s ratio than that of the concrete core. Subjected to the same axial strain, the larger transverse Poisson’s ratio of the FRP tube leads to a radial deformation larger than that of the concrete core. Consequently, the FRP tube cannot confine the concrete core in this region, i.e., the first region or elastic region in the stress train curve. (2) For most FRP tubes, fibers are aligned towards the hoop direction in order to provide higher confinement. As a result, the axial stiffness of the FRP tube may be lower than that of the concrete core. A lower axial stiffness also translates to a higher transverse or radial deformation.
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