A Temperature-Indexed Concrete Damage Plasticity Model Incorporating Bond-Slip Mechanism for Thermo-Mechanical Analysis of Reinforced Concrete Structures

This study investigates the thermo–mechanical behavior of C40 concrete and reinforced concrete subjected to elevated temperatures up to 700°C by integrating experimental testing and advanced numerical modeling. A temperature-indexed Concrete Damage Plasticity (CDP) framework incorporating bond–slip effects was developed in Abaqus to capture both global stress–strain responses and localized damage evolution. Uniaxial compression tests on thermally exposed cylinders provided residual strength data and failure observations for model calibration and validation. Results demonstrated a distinct two-stage degradation regime: moderate stiffness and strength reduction up to ~400°C, followed by sharp deterioration beyond 500°C–600°C, with residual capacity at 700°C reduced to ~20%–25% of the ambient value. Strain–damage analyses revealed the formation of a peripheral tensile strain band, which thickened and propagated inward with increasing temperature, governing crack initiation and cover spalling. Supplemental analyses highlighted that transverse reinforcement improved ductility and damage distribution at moderate temperatures (~300°C), but bond deterioration and steel softening beyond ~600°C substantially diminished confinement effectiveness. The proposed CDP model accurately reproduced experimental stress–strain curves (R2 ≈ 0.94–0.98 up to 600°C; ≈0.90 at 700°C), with peak stress errors within 7%–10% and energy absorption captured within ~12%. These findings confirm the robustness of the temperature-indexed CDP framework for simulating fire-damaged reinforced concrete and provide practical guidelines for post-fire assessment, spalling detection, and fire-resilient design of structural members.