Concrete confined by FRP material: a plasticity approach

Carbon fiber-reinforced polymer (FRP) material has proved to be more efficient than other composites when applied to concrete columns as an external reinforcement. Because of its enhanced durability characteristics compared to glass or aramid, and its relatively high E-modulus, carbon FRP shows a higher confining performance. The behavior of 22 cylindrical 200×320 mm specimens (height to diameter ratio 1.6) that are externally wrapped by carbon FRP sheets in low volumetric ratios (0.23–0.7%) is presented. The specimens are subjected to axial monotonic load until failure occurs. Carbon FRP confinement, even in low volumetric ratios, seems to considerably increase the strength and especially the ductility of concrete. A constitutive model based on plasticity theory is applied. The model proposed and applied to steel-confined concrete in this paper is modified and calibrated so as to incorporate the dilation characteristics of the FRP-confined concrete. The model provides the stress–strain curves of axially loaded circular columns that are confined by FRP reinforcement. It can be used in FRP tube-encased concrete as well as in FRP sheet-wrapped concrete. Satisfactory correlation of experimental and analytical results is observed.