Load path dependence for passively and actively confined high-strength concrete

Abstract

The assumption of load path independence has been instrumental in developing analysis-oriented stress-strain models for FRP-confined concrete. However, there remains no consensus on this assumption when applied to high-strength concrete (HSC). An axial stress gap is typically observed between active and passive confined HSC cases, even when their confinement conditions and deformations are identical. To address the existing research gap, this study conducted experimental tests on a series of HSC specimens under various levels of active and passive confinement. These tests aimed to assess the influence of the stress disparity between the two confinement mechanisms. Cyclic loading was also applied to the confined HSC specimens to derive damage indices (plastic strain, tangent unloading stiffness, and reloading stiffness) and to establish their relationship with the stress gaps. The findings revealed that the stress gap identified from different confinement types increases with the strength of the concrete. It also varies with the axial strain, exhibiting a trend that initially increases and then decreases. The test results further indicated that the presence of this stress difference is a response to internal damage within the concrete. Specifically, under different confinement paths, a reduction in the plastic strain difference that characterizes the damage will lead to a decrease in the stress gap. Moreover, under large deformations, the severe internal damage condition in concrete also reduces the damage differences for HSC experiencing different load paths, which in turn diminishes the stress gap. These insights provide a deeper understanding of how different confinement mechanisms affect the material properties of HSC under various load paths.