Experiments and Stress-Strain Model of Concrete Confined by UHPC Materials

Compressive behaviors of 12 stub normal-strength concrete (NC) columns were experimentally investigated, which were confined by ultra-high performance concrete (UHPC) jackets. The governing influencing factors consisted of the thickness of the UHPC jacket, shape of specimens, and compressive strength of the core concrete. Generally, the UHPC jacket greatly improved the ductility of the stub columns. The final failure pattern transferred from crushing for concrete stub columns to the expansive crack of the UHPC jacket for UHPC-confined stub concrete columns. Moreover, the thickness of the UHPC jacket was found to greatly affect the compressive strength of specimens. In particular, the circular UHPC-confined stub columns, of lower-strength core concrete, were prone to gain more increments in compressive strengths. Debonding of the UHPC-NC interface was observed in the rectangular and square UHPC-confined stub columns. Enlightened from experimental observations, an analytical model is proposed to predict the axial stress-strain behavior of UHPC-confined concrete columns. It is noteworthy that the UHPC-NC interfacial behavior is identified and accounted for. The accuracy of the analytical model is validated by the reported experimental results. The model provides a useful tool to predict the axial strain-stress relation of UHPC-confined concrete columns in closed-form expressions for design-oriented purposes.