Zhuojin Pipe Fitting Co., LtdTemperature Field Analysis of Concrete-Filled Steel Tube Coal Gangue Concrete Columns Under Fire
Literature Overview
This paper by Li Guochang, Li Long, and Li Xiao (2022), published in the Journal of Shenyang Jianzhu University, investigates the temperature field distribution within concrete-filled steel tube (CFST) columns filled with coal gangue concrete under ISO-834 standard fire conditions. Coal gangue concrete is an environmentally friendly concrete that incorporates coal gangue, a mining waste material, as a partial replacement for natural aggregates. The study aims to provide a theoretical basis for evaluating the fire resistance performance of CFST columns using coal gangue concrete, which is particularly relevant for structures in mining regions where coal gangue is abundantly available and where fire safety is a critical concern.
Thermal Analysis Methodology
The authors developed a finite element heat transfer model using commercial software to simulate the temperature distribution within the CFST coal gangue concrete column under ISO-834 standard fire. The thermal analysis accounts for the heat transfer mechanisms of conduction, convection, and radiation within the composite cross-section.
| Thermal Parameter | Value / Range | Source |
|---|---|---|
| Fire temperature curve | ISO-834 standard | ISO 834-1 |
| Heating duration | 0–180 minutes | Typical structural fire analysis |
| Coal gangue concrete thermal conductivity | 0.8–1.5 W/(m·K) | Temperature-dependent |
| Steel tube thermal conductivity | 50–30 W/(m·K) | Decreases with temperature |
| Concrete specific heat | 880–1100 J/(kg·K) | Temperature-dependent |
| Fire exposure surface temperature | 0–1000 °C | ISO-834 curve |
The ISO-834 standard fire curve reaches approximately 580 °C at 30 minutes, 842 °C at 60 minutes, 945 °C at 90 minutes, and 1000 °C at 120 minutes. The temperature distribution within the column cross-section is highly non-uniform, with the outer steel tube experiencing the highest temperatures and the concrete core center experiencing significantly lower temperatures.
Key Findings and Parametric Analysis
The study examines the effects of heating duration, cross-sectional dimensions, steel ratio, and protective layer thickness on the temperature field:
| Parameter | Effect on Cross-Section Temperature | Effect on Fire Resistance |
|---|---|---|
| Heating duration (increase) | Increases core temperature | Reduces fire resistance |
| Cross-sectional dimension (decrease) | Increases core temperature | Reduces fire resistance |
| Steel ratio (increase) | Increases core temperature (steel conducts heat) | Reduces fire resistance |
| Protective layer thickness (increase) | Decreases core temperature | Improves fire resistance |
A significant finding is that the temperature field distribution of CFST coal gangue concrete columns is similar in pattern to that of conventional CFST columns, but the cross-sectional temperatures are consistently lower. This is attributed to the thermal properties of coal gangue aggregates, which have lower thermal conductivity than natural aggregates, resulting in slower heat transfer to the column core. The recommended fire protective layer thickness is approximately 15 mm, which is thinner than the typical 20–25 mm recommended for conventional CFST columns.
Engineering Practice Implications
The findings have direct implications for the fire design of structures using coal gangue concrete:
- Protective layer optimization: The reduced thermal conductivity of coal gangue concrete allows for thinner fire protective layers, potentially reducing material costs and structural weight.
- Temperature monitoring: In critical structures, temperature monitoring at the column core should be implemented to verify that the predicted temperature field matches actual conditions during fire events.
- Residual strength assessment: The lower core temperatures imply higher residual strength of both the steel tube and the concrete core after fire exposure, which may allow for repair rather than replacement in many cases.
- Code compliance: The fire resistance rating of CFST coal gangue concrete columns should be evaluated based on the specific thermal properties of the coal gangue concrete used, rather than applying conventional concrete fire design provisions directly.
The study also highlights the environmental benefit of using coal gangue concrete, as it diverts mining waste from landfills while providing improved fire performance. This dual benefit makes coal gangue concrete an attractive option for structures in mining regions.
Study Reflections
This research contributes to the growing body of knowledge on the fire performance of alternative concrete materials. The finding that coal gangue concrete provides better fire resistance than conventional concrete in CFST columns is counterintuitive at first glance, as coal gangue is a waste material. However, the explanation through reduced thermal conductivity is physically sound. One limitation of the study is that it focuses solely on the temperature field analysis and does not extend to the mechanical performance degradation of the column under fire. A complete fire design evaluation would require coupling the thermal analysis with a structural analysis that accounts for temperature-dependent material properties, thermal expansion, and potential spalling of the concrete core.
Conclusion and Outlook
The temperature field analysis of CFST coal gangue concrete columns under ISO-834 standard fire demonstrates that coal gangue concrete provides inherent fire resistance advantages over conventional concrete, primarily through its lower thermal conductivity. The recommended protective layer thickness of 15 mm is a practical and economical design guideline for engineers specifying coal gangue concrete in fire-exposed structural applications. Future research should extend this thermal analysis to include coupled thermo-mechanical analysis and experimental validation to fully establish the fire resistance performance of CFST coal gangue concrete columns for code-based design.