Zhuojin Pipe Fitting Co., LtdTemperature Field Simulation of Steel Tube Concrete Composite Columns Under Fire Exposure
Literature Overview
Gong Yufa, Qi Xiang, and Zhang Xuan (2017), published in Journal of Liaoning Technical University (Natural Science Edition, Vol. 36, No. 12, pp. 1284–1287), present a finite element analysis of the temperature field distribution in steel tube concrete composite columns subjected to fire. The study employs ABAQUS software to establish a three-dimensional thermal model, validated against existing experimental data, and investigates the influence of time, fire-exposed surface, and position coefficient on temperature distribution.
Core Technical Approach
Thermal Model Development
The finite element model incorporates the following thermal parameters for steel and concrete:
| Parameter | Steel | Concrete |
|---|---|---|
| Thermal conductivity (W/m·K) | 50–60 (temperature-dependent) | 1.5–2.5 (temperature-dependent) |
| Specific heat (J/kg·K) | 600–750 | 1000–1200 |
| Density (kg/m³) | 7850 | 2400 |
| Emissivity | 0.7–0.9 | 0.9–0.95 |
| Thermal expansion coefficient (1/K) | 12×10⁻⁶ | 10×10⁻⁶ |
The model accounts for convective and radiative heat transfer at the fire-exposed surface, with boundary conditions following the ISO 834 standard fire curve or equivalent.
Validation Against Experimental Data
The numerical results were compared with previously published experimental data, demonstrating high agreement between predicted and measured temperature profiles. This validation confirms the reliability of the thermal model for parametric studies.
Parametric Analysis Results
Influence of Time
Temperature gradients within the column section increase with fire exposure duration. The peak temperature at the fire-exposed surface rises rapidly in the first 30 minutes, followed by a more gradual increase. The interior concrete core temperature lags significantly behind the surface temperature due to the insulating effect of the steel tube and the thermal mass of the concrete.
Influence of Fire-Exposed Surface
The position and extent of the fire-exposed surface significantly affect the temperature field distribution. Full-surface exposure produces the highest temperatures and largest gradients, while partial exposure results in asymmetric temperature fields that can induce significant thermal bending moments.
| Exposure Condition | Peak Surface Temperature (°C) | Core Temperature (°C) at 60 min | Maximum Gradient (°C/mm) |
|---|---|---|---|
| Full surface exposure | 700–800 | 200–300 | 15–25 |
| Three-sided exposure | 650–750 | 150–250 | 12–20 |
| Two-sided exposure | 600–700 | 100–200 | 10–18 |
| One-sided exposure | 550–650 | 80–150 | 8–15 |
Position Coefficient Analysis
The position coefficient, which characterizes the relative location of measurement points within the cross-section, reveals that temperature distribution is highly non-uniform. Points closer to the fire-exposed surface experience significantly higher temperatures, while the thermal penetration depth increases with time.
Engineering Practice Integration
Fire Resistance Design Implications
- The steel tube acts as both a structural element and a thermal barrier, but at temperatures exceeding 550°C, steel strength degradation becomes critical.
- Concrete spalling risk increases when surface temperatures exceed 300°C, particularly in high-strength concrete.
- Thermal expansion mismatch between steel and concrete can induce internal stresses that may lead to debonding at the steel-concrete interface.
Protective Measures
Based on the temperature field analysis, the following fire protection strategies are recommended:
- Apply fire-resistant coatings to the steel tube exterior to delay temperature rise.
- Use high-temperature concrete grades with improved thermal stability for the core.
- Design for thermal cracking by incorporating controlled joints or flexible connections.
Key Questions and Reflections
A significant limitation of this study is the focus on thermal analysis alone, without coupled thermo-mechanical analysis. In practice, the temperature field directly influences the mechanical behavior, including strength degradation, creep, and thermal expansion. Future research should integrate thermal and structural analyses to provide comprehensive fire resistance predictions.
Additionally, the study does not address the effect of fire protection systems (sprinklers, fire barriers) on the temperature field, which is critical for real-world applications.
Study Insights and Implications
This research provides a validated numerical framework for predicting temperature field distributions in steel tube concrete composite columns under fire. The parametric analysis offers practical guidance for engineers designing fire-resistant composite structures. The key insight is that the steel tube, while providing structural confinement, also accelerates heat transfer to the concrete core, necessitating careful consideration of thermal protection measures in fire design. Engineers should treat the temperature field as a primary design input rather than a secondary verification step.