A temperature-indexed concrete damage plasticity framework for thermomechanical analysis of concrete structures

Abstract This study develops an integrated experimental–numerical framework to investigate the behavior of reinforced concrete (RC) cylinders under thermal–mechanical coupling across 20–800 °C. Laboratory tests, including heat-after-force (residual) and thermo-mechanically coupled loading paths, were conducted to capture temperature-dependent degradation of stiffness, strength, strain localization, and damage evolution. Detailed spatial fields of displacement, principal strain, and damage were obtained and analyzed to identify cracking/spalling precursors and the transition from quasi-brittle to low-strength, high-deformation compression. A temperature-indexed concrete damage plasticity (CDP) model was implemented in Abaqus/Standard with full thermal–mechanical coupling, calibrated against the multi-temperature stress–strain responses. The model reproduces the experimental trend (20 to 800 °C) with high fidelity ( R 2 ≈0.94), capturing both global and local phenomena, including the influence of axial thermal gradients and boundary constraints on deformation localization. Results highlight a practical threshold at 500–600 °C beyond which mechanical deterioration accelerates and damage spreads and reveal that damage evolution becomes more distributed with increasing temperature, requiring larger strains to reach equivalent damage states. The validated numerical model and findings inform more accurate post-fire residual capacity assessments, recommending temperature-dependent constitutive laws with reduced initial damage slope and enlarged ultimate strain and treating perimeter tensile-strain bands as critical spalling initiation zones.