Triaxial test for concrete under non-uniform passive confinement

Concrete in structures cannot be reliably simulated by computer under nonlinear triaxial stress state due to the lack of an appropriate constitutive relationship of concrete. When a continuum mechanics based constitutive model is adopted, users need to “adjust” its parameters to suit benchmark experimental results. Triaxial tests of concrete cubes are used to evaluate model parameters. As concrete is load path sensitive, model parameters are different under different stress conditions. Most existing triaxial tests of concrete are for active stress condition. This type of test is not suitable for passively confined concrete, such as fiber reinforced polymer (FRP) confined concrete. This problem is resolved by a unique and yet simple test method reported in this paper for conducting monotonic and cyclic compression tests. Detailed considerations for designing the test assembly are reported, particularly when considering factors that significantly affect test results such as friction from loading plates and measurement of three dimensional deformations.