Development of extended Drucker–Prager model for non-uniform FRP-confined concrete based on triaxial tests

Extended linear Drucker–Prager (DP) model has been a proper choice to capture the stress-strain of cylindrical concrete columns confined by fiber reinforced polymers (FRPs). However, most existing DP models calibrated by uniform active/passive tests are unsuitable for concrete under non-uniform passive confinement. This paper aims to calibrate the key parameters i.e., friction angle, plastic dilation angle and hardening needed for the DP model based on tri-axial test results on concrete cube subjected to non-uniform confinement. The effect of friction angle parameter is isolated from the hardening parameter within the yield function while the friction angle is defined as a function of concrete grade and hardening as a function of lateral confinement stiffness ratio. Here, the plastic lateral strains of non-uniform confined concrete, which could be obtained in cyclic tests but were usually left aside, are used to define a function for plastic dilation angle which works compatibly with the yield parameters. The resultant extended DP model could capture the stress-strain behaviour of concrete under both uniform or non-uniform passive pressure as well as the variable flow rules and different load paths occurring across the section of FRP-confined non-circular concrete.