Temperature Field Analysis of Steel Tube Coal Gangue Concrete Columns Under Standard Fire

Literature Overview and Research Motivation

The paper by Li Guochang, Li Long, and Li Xiao (2022), published in the Journal of Shenyang Jianzhu University, investigates the thermal behavior of steel tube coal gangue concrete (STCGC) columns under ISO 834 standard fire conditions. Coal gangue, a byproduct of coal mining and processing, is an abundant waste material whose use as a concrete aggregate represents both an environmental benefit and a technical challenge. By replacing natural aggregate with coal gangue in the concrete core of steel tube columns, this research explores whether the thermal properties of coal gangue concrete can enhance the fire resistance of STC columns. The study is supported by the National Natural Science Foundation of China (Grant 51938009) and was conducted at the School of Civil Engineering, Shenyang Jianzhu University.

Thermal Analysis Methodology and Parameter Study

The authors establish a finite element thermal transfer model using commercial analysis software to simulate the temperature distribution within STCGC columns subjected to the ISO 834 standard fire curve. The model accounts for the heat conduction through the steel tube, the heat conduction through the concrete core, the convective and radiative heat transfer from the fire environment to the steel tube outer surface, and the temperature-dependent material properties of both steel and coal gangue concrete. A parametric study is conducted to evaluate the influence of heating duration, cross-sectional dimensions, steel ratio, and fire protection layer thickness on the temperature field.

The results demonstrate that as heating time increases, the temperature throughout the cross-section rises progressively, with the steel tube outer surface reaching temperatures close to the fire environment temperature within the first 30 minutes. The concrete core temperature rises more slowly due to the thermal insulation effect of the concrete itself and any applied fire protection layer. As the cross-sectional dimension decreases, the surface-to-volume ratio increases, leading to more rapid heat penetration and higher core temperatures. Similarly, reducing the fire protection layer thickness accelerates heat transfer to the core.

Comparison with Ordinary Steel Tube Concrete Columns

A particularly significant finding is the comparison between STCGC columns and ordinary steel tube concrete (STC) columns. The temperature field distribution patterns are qualitatively similar, but the STCGC columns exhibit consistently lower core temperatures throughout the fire exposure duration. This thermal advantage is attributed to the lower thermal conductivity of coal gangue concrete compared to ordinary concrete, which reduces the rate of heat transfer from the steel tube to the concrete core. The lower thermal conductivity of coal gangue aggregates, combined with the porous structure of coal gangue particles, creates additional thermal resistance within the concrete matrix.

Based on the thermal analysis, the authors recommend a fire protection layer thickness of approximately 15 mm for STCGC columns to achieve acceptable fire resistance performance. This recommendation is significant because it suggests that STCGC columns may require less fire protection than ordinary STC columns to achieve equivalent fire resistance ratings, offering potential cost savings in fire protection materials and application labor.

Study Insights and Practical Recommendations

This research contributes valuable thermal data for the fire design of STCGC columns, a material system that has received relatively limited attention in fire engineering literature. The finding that coal gangue concrete provides inherent thermal insulation benefits is encouraging for the promotion of waste material utilization in construction. However, engineers should note that the fire resistance of a column is not determined by temperature alone; the mechanical properties of both steel and concrete degrade at elevated temperatures, and the fire resistance rating depends on the residual load-bearing capacity at the relevant temperature. Therefore, the thermal analysis presented in this paper must be complemented by mechanical analysis at elevated temperatures to determine the actual fire resistance rating.

From a practical standpoint, the recommended 15 mm fire protection layer thickness should be validated through full-scale fire tests or validated numerical models that include temperature-dependent material properties and the potential for concrete spalling. Engineers should also consider the long-term durability of coal gangue concrete in fire-exposed conditions, as the thermal cycling during and after a fire event may affect the bond between the steel tube and the concrete core. The thermal expansion mismatch between steel and coal gangue concrete at elevated temperatures could lead to debonding or cracking, which would compromise the composite action and reduce the column's residual strength.