Stress strain relationship of FRP-confined concrete for hollow columns

Past studies demonstrated the structural efficiency of FRP-confinement for reinforced concrete (RC) columns to increase their strength and ductility in axial compression [1-4]. Numerical and analytical models were developed to predict the stress-strain behavior of FRP confined concrete [5-8] and recommendations were provided to practitioners for design of FRP-retrofitted RC columns. Scientific studies related to FRP-confinement of hollow-core RC columns are very limited at the moment; a few data reporting properties of RC hollow-core columns under seismic forces are available [9-11]. This clashes with the thousands of applications all over the world in which bridge piers are designed as hollow-core columns to maximize the structural efficiency in terms of strength/mass and stiffness/mass ratios. In this work both solid and hollow-core concrete prisms and cylinders were tested under uniaxial compression to study the influence of various experimental parameters on the effectiveness of FRP jackets applied to concrete columns subjected to uniaxial compression loading. The investigated parameters were the concrete strength, the fibers type, the number of wrap layers, the column shape and dimensions and, for prismatic sections, the corner radius and the cross-sectional aspect ratio. On the basis of the experimental results obtained, a nonlinear finite element model was developed, obtaining a good correlation between the experimental and the numerical data in terms of stress-strain curves and ultimate load.