Constitutive model for the axial stress-strain response of a steel-reinforced concrete core confined with a UHPC jacket

This study develops a closed-form analytical model to predict the axial stress-strain behavior of cylindrical concrete columns under multi-layer confinement provided by ultra-high-performance concrete (UHPC) jackets and internal steel reinforcement. The formulation is derived from fundamental mechanical principles, incorporating lateral pressure equilibrium and deformation compatibility across the constituent layers: the UHPC jacket, concrete cover, transverse steel, and concrete core. Nonlinear constitutive laws for all materials are integrated into the framework. The model’s accuracy is validated against experimental data, demonstrating a high correlation with measured responses. The results indicate that the analytical model exhibits good performance, with an average absolute error (AAE) ranging from 0.037 to 0.072 and peak load ratios (R) falling between 0.988 and 1.046. Complementary three-dimensional nonlinear finite element analyses corroborate the experimental findings and provide further insight into the complex failure mechanisms. Ultimately, the results confirm that the proposed analytical model offers a reliable tool for predicting the compressive behavior of this composite column system. • Analytical model was developed to predict compressive behavior of UHPC-TSR confined concrete columns. • Mechanics-based framework was established in multi-layer confinement systems. • The peak stress formulation for UHPC-TSR confined concrete was calibrated through regression analysis of experimental data. • Nonlinear FEM model was developed to simulate the damage progression of composite column systems.