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.

Fire exposure can severely impair the load-bearing capacity of reinforced concrete (RC) structures by inducing thermo-mechanical damage and spalling. This study presents a coupled experimental and numerical investigation of RC beams (flexural members) and columns (axial members) subjected to ISO-834 fire conditions under sustained load. Transient heat transfer and structural analyses were performed sequentially in ABAQUS, using temperature-dependent material models (Concrete Damage Plasticity for concrete and elastoplastic steel) and realistic boundary conditions. The numerical model was calibrated and validated against laboratory tests on C30 beams and C40 cylinders. Results show that simulated stress–strain curves for columns and midspan deflection histories for beams closely match experimental data: peak strengths and ultimate strains agree within ∼10%, and deflection histories within ∼6%. Concrete properties remain almost unchanged up to ∼300 °C but degrade markedly at higher temperatures due to moisture loss and decomposition of hydrates. At ∼700 °C residual compressive strength falls below 30% of the ambient value. The validated FE model captures these coupled degradation mechanisms effectively. Key findings include the progressive formation of tensile cracks and spalling zones in heated regions, and the critical loss of flexural stiffness and reinforcement strength above 500 °C. These results underscore the importance of incorporating temperature-dependent material degradation and sustained loading in fire-resistance assessments. The proposed modeling framework provides a robust basis for performance-based fire design and parametric studies of RC structures under combined thermal–mechanical loading.

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.

This study develops a validated sequentially coupled finite element (FE) modelling framework for reinforced concrete (RC) beams subjected to ISO 834 standard fire exposure, with explicit consideration of temperature-dependent steel–concrete bond degradation. The thermal analysis first predicts transient temperature fields in concrete and reinforcement; these fields are then mapped to a mechanical model incorporating Concrete Damage Plasticity (CDP), temperature-dependent reinforcement properties, and nonlinear interface springs for longitudinal bond–slip. The revised model is strengthened by an explicit bond–slip constitutive relationship, a calibration procedure based on elevated-temperature bond data, and a mesh convergence assessment. The thermal simulation reproduced measured cross-sectional temperatures with typical deviations of 5–10%, while the mechanical analysis captured the overall deflection–time response, crack localization pattern, and failure-time range of 170–200 min. The results show that rapid stiffness loss and accelerated deflection are governed by the combined degradation of concrete compressive strength, steel stiffness/yield strength, and interfacial bond resistance, especially after reinforcement temperatures exceed approximately 600–700 °C. Concrete spalling was observed experimentally but was not explicitly simulated; its influence is discussed as a source of late-stage discrepancy and as a target for future hygro–thermal–mechanical modelling. The proposed framework therefore provides a transparent and reproducible tool for performance-based fire assessment of RC beams, particularly where bond deterioration cannot be represented by a perfect-bond assumption.

This study investigates the thermo-mechanical behavior and residual strength of full-scale reinforced concrete (RC) beams subjected to ISO-834 fire exposure, emphasizing temperature-dependent material degradation and bond-slip effects. A sequentially coupled numerical framework was developed in ABAQUS, integrating a temperature-indexed Concrete Damage Plasticity (CDP) model for concrete, elastoplastic steel constitutive laws, and a temperature-dependent bond-slip model implemented via nonlinear SPRING2 elements. The model explicitly accounts for post-peak concrete softening, steel yield degradation, and interface deterioration, and was calibrated against full-scale experiments. Experimental measurements included internal and surface temperatures, load–midspan deflection, and residual strength after natural cooling. The numerical results closely reproduce the experimental observations, with deviations of 7%–10% for both mid-span deflection and ultimate load. Key findings include: C40 concrete retains ~60% of its ambient compressive strength at 300°C–400°C; stiffness and peak load decrease by 30%–70% and 40%–50% at 600°C, respectively; residual load capacity drops to 20%–25% at 700°C. Steel yield strength decreases by ~50% at 600°C, and bond deterioration accelerates deflection and reduces residual capacity. This integrated numerical–experimental framework provides a validated predictive tool for post-fire performance assessment of RC beams, supporting fire-resilient design and structural safety evaluation.

Purpose: The purpose of this study is to develop and validate a temperature-indexed Concrete Damage Plasticity (CDP) model to analyze the thermo-mechanical behavior of reinforced concrete beams, slabs and columns under fire exposure. By integrating temperature-dependent material properties, this research aims to provide a comprehensive approach for evaluating the degradation of mechanical properties, including damage and strain, at elevated temperatures. The findings contribute to enhancing fire safety design practices, supporting Sustainable Development Goal (SDG) 9 (industry, innovation and infrastructure) and SDG 11 (sustainable cities and communities), by improving structural resilience to fire hazards. Design/methodology/approach: This study employs a temperature-indexed CDP model to simulate the thermo-mechanical behavior of reinforced concrete beams, slabs and columns exposed to fire. Numerical simulations are conducted using finite element analysis to assess the degradation of mechanical properties such as stress, strain and damage evolution under varying temperature conditions up to 800°C. Experimental data are used to validate the model's predictions. The approach integrates temperature-dependent material properties, providing a comprehensive framework for understanding the structural response to fire and offering insights for enhancing fire-resistant design in concrete structures. Findings: The findings of this study demonstrate that the temperature-indexed CDP model accurately predicts the thermo-mechanical behavior of reinforced concrete beams, slabs and columns under fire exposure. The model effectively captures the degradation of mechanical properties, including damage and plastic strain, at temperatures up to 800°C. Numerical simulations align well with experimental data, showing strong predictive capability, although minor discrepancies are observed at higher temperatures, particularly in deflection and strain. The research underscores the importance of refining temperature-dependent material properties for more accurate simulations of concrete behavior in extreme fire conditions. Originality/value: This study provides a novel approach by developing and validating a temperature-indexed CDP model for assessing the thermo-mechanical behavior of reinforced concrete under fire exposure. The model integrates temperature-dependent material properties, offering a comprehensive framework for simulating the degradation of concrete's mechanical properties across various structural elements. The originality lies in the model's ability to accurately predict damage, strain and stress evolution at elevated temperatures, filling a critical gap in structural fire safety design. This research advances fire-resistant infrastructure design, supporting more resilient and sustainable urban structures, contributing to SDG 9 and SDG 11.