Axial compressive behaviour of circular UHPC-confined concrete columns

UHPC-confined concrete columns have garnered significant attention in civil engineering. However, the axial compressive behavior of circular UHPC-confined concrete columns with an emphasis on the confinement mechanism of UHPC on core concrete has not been fully understood. To investigate this confinement mechanism, focusing on the stress-strain relationship of UHPC-confined concrete, axial compression tests are conducted on circular UHPC-confined concrete columns. Test results demonstrate that UHPC improves the compressive strength and deformation capacity of the core concrete column. Based on the established experimental data, prediction equations are proposed for the compressive strength and corresponding strain of the circular UHPC-confined concrete, and a stress-strain model is developed to predict the compressive behaviour of such confined concrete. The predicted results agree well with the experimental data. Finite element (FE) analysis of interfacial stress indicates that the tensile strength of UHPC is fully utilized. Parametric FE analysis reveals that as UHPC thickness and core concrete strength increase, the strength of UHPC-confined concrete columns undergoes positive reinforcement, whereas ductility first rises and then declines. The increase in UHPC tensile strength and steel fiber content exerts have a positive impact on both the strength and ductility of such columns. Under the same volume fraction, straight steel fibers are superior to hooked-end steel fibers in enhancing ductility.