Modified plastic-damage model for passively confined concrete based on triaxial tests

Plasticity-based models are used as the constitutive relationship of concrete under passive confinement of fiber reinforced polymers (FRPs). Triaxial cube tests are needed for adjusting the parameters included in a model. Most of the existing plasticity models are developed from actively confined tests or by uniform passively confined column tests. Methods for developing a plasticity model based on non-uniform passively confined concrete tests and applied to non-uniform passive confinement are rare and needed. This study reports more than one hundred triaxial concrete cube tests under uniform and non-uniform passive confinement. Six grades of concrete were tested under monotonic and cyclic compression loads. The lateral stiffness ratio was the main parameter for designing the tests. Using the reported tests, a new approach is devised for deriving parameters of a plastic-damage model for practical application to concrete structures under non-uniform passive confinement. The lateral stiffness ratio is found to be a key factor for plasticity model parameters involving dilation angle, hardening rule, and damage variable. Based on the test results and using finite element analysis (FEA), explicit empirical models are developed for the plasticity parameters. FEA analyses using the developed plasticity-damage model performs well compared with test results.