Confinement Model of Concrete with Externally Bonded FRP Jackets or Posttensioned FRP Shells

A design-oriented confinement model for square and rectangular columns confined with bonded fiber-reinforced polymer (FRP) jackets, and shape-modified square and rectangular sections confined with posttensioned FRP shells is developed. The proposed design model for FRP-confined concrete columns is based on the bilinear four-parameter formulation by Richard and Abbott. The axial compressive strength of FRP-confined concrete is obtained using concrete plasticity theory based on the five parameter Willam and Warnke model. The ultimate axial strain of FRP-confined concrete is obtained from a strain-based approach depending on either passive or active confinement; the ultimate axial strain is based on the concepts of secant concrete modulus and strain dependent stiffness established by Pantazopoulou and Mills. Comparisons of the proposed stress-strain model with uniaxial compression experiments for columns with bonded FRP jackets or posttensioned FRP shells, performed by the writers and other researchers, show satisfactory agreement for the entire stress-strain curve.