Stress-strain behavior of actively and passively confined concrete under cyclic axial load

Monotonic stress-strain relationship of actively-confined concrete has been used as the base model to establish analysis-oriented stress-strain model of fiber reinforced polymer (FRP) confined concrete. This approach is based on the assumption that the axial stress and strain of FRP-confined concrete are the same as those of actively confined concrete under the same confinement pressure and lateral strain. In this study, an experiment was conducted to verify this assumption for concrete subjected to cyclic loading. A total of 31 actively confined and FRP-confined concrete cylinders were tested. The results indicate that this assumption is not applicable to concrete under cyclic loading; a gap was found between the envelop curves of the two types of confined concrete. In addition, the test results also reveal that confinement pressure significantly affects both reloading modulus and plastic strain which are the main factors controlling cyclic behavior of confined concrete.