Plasticity theories are widely used for modeling the stress-strain relationship of concrete, especially confined concrete. Because of the nonhomogeneity and load path dependence of concrete material, no general rule is currently available for evaluation of the parameters for a plasticity model that suits different problems. One solution to the problem is to derive models for the parameters that are applicable to a certain category of problems from the experimental results. However, the derivation of parameters from test results is not straightforward due to coupling of the parameters in yield functions and experimentally obtained properties. An approach for deriving material parameters and characterizing yield surfaces from test results is developed in this work. This methodology is implemented in a special case of fiber-reinforced polymer (FRP) confined concrete under the framework of a linear extended Drucker-Prager (DP) plasticity model. The two material parameters for the yield surfaces, friction angle and cohesion, are decoupled from the yield function and evaluated using conventional compression test results. Models of the two parameters are derived. These results can be conveniently used for engineering applications. Furthermore, the interrelationship between the material parameters is theoretically studied with an energy method.
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