Design Guide for Confined Concrete Columns Based on Plasticity Theory

Although concrete is a quasi-brittle material, it transforms to a ductile and strain-hardening one under significant confinement. Therefore, plasticity theory is applicable to confined concrete and has been widely used to model the behavior of concrete under triaxial compression in recent years. Currently, the material parameters of a plasticity model are often determined by adjusting their values to match the resulting responses of structures to available benchmark results. Clearly, determination of the parameters directly from compression tests of concrete is a more rational way. However, evaluation of material parameters from test results is not straightforward due to the coupling of parameters in the yield function and physically obtained properties. A novel approach for evaluating material parameters and characterizing yield surfaces from test results is developed in this work. Using this approach and a test database, models of the material parameters are derived that can be easily implemented into commercial software for engineering applications. Furthermore, an energy method is used to derive the interrelationships among material parameters, from which the existing understanding on their relationships is extended. These relationships are subsequently used to derive critical confinement levels of columns that correspond to strain-hardening, ductile, or strain-softening response curves, which can be conveniently used for column jacketing design.