Temperature Field Characteristics of Steel Tube Concrete Composite Columns Under Standard Fire

Literature Overview

This study by Xiang Kai and Wang Guohui from the Tianjin Fire Research Institute of the Ministry of Public Security investigates the temperature field distribution in steel tube concrete composite columns subjected to ISO 834 standard fire exposure. Published in the Journal of Natural Disasters in 2015, Volume 24, Issue 1, pages 133-140, the research was funded by the Twelfth Five-Year National Science and Technology Support Plan Project (2011BAK03B0104) and the National Natural Science Foundation of China (Grant 51408134). The work comprises 8 fire tests on composite columns with varying cross-sectional dimensions, cross-sectional types, and steel tube volume ratios, supplemented by finite element numerical analysis.

Core Technical Points

The experimental program systematically varied multiple parameters to establish their influence on the internal temperature field of steel tube concrete composite columns during fire exposure. The key findings regarding temperature field behavior are presented below:

The finite element numerical model was validated against experimental results and used for parametric analysis. The model identified fire duration, cross-sectional size, and fire exposure mode as the three primary factors controlling the temperature field distribution in steel tube concrete composite columns.

Interpretation of Technical Findings

The finding that cross-sectional size has a more significant effect on internal temperature than steel tube volume ratio is particularly important for fire-resistant design. This suggests that increasing the overall column dimension is more effective for fire protection than increasing the steel tube wall thickness, which has implications for economic optimization of fire-resistant structural design. The square section outperforming the circular section at equivalent characteristic dimensions can be attributed to the larger surface-to-volume ratio and more uniform heat distribution geometry of the square cross-section.

The relatively minor effect of steel tube volume ratio on internal temperature is somewhat counterintuitive, as one might expect the steel tube to act as a thermal barrier. However, the steel tube's high thermal conductivity means that it rapidly transfers heat to the core concrete, effectively becoming part of the thermal mass rather than serving as an insulating layer. This finding has important implications for fire design, as increasing steel tube thickness alone may not significantly improve fire resistance.

Engineering Practice Integration

In practical fire-resistant design of steel tube concrete composite columns, engineers should prioritize cross-sectional dimension optimization over steel tube thickness modification when the primary objective is to maintain core concrete temperature within acceptable limits during fire exposure. The ISO 834 standard fire curve provides a well-established benchmark for fire resistance testing, and the experimental data from this study can be directly applied to verify fire resistance ratings for similar column designs. The finite element model developed in this research provides a valuable tool for predicting temperature field distributions under various fire scenarios and geometric configurations, enabling engineers to optimize column design for fire safety without relying exclusively on physical testing.

For code compliance purposes, the temperature field data can be used to determine the effective fire resistance duration of steel tube concrete composite columns under specific loading conditions. The temperature at critical locations, particularly at the steel tube inner surface and at the center of the concrete core, governs the residual strength of the column at elevated temperatures and should be monitored during fire testing.

Study Insights and Implications

This research provides essential experimental data for the fire-resistant design of steel tube concrete composite columns, a structural system that is increasingly adopted in modern construction for its superior structural efficiency. The key insight is that fire resistance of these columns is primarily governed by geometric factors rather than material proportion adjustments, which offers a clear and practical design strategy for engineers. The combination of physical testing and numerical simulation provides a comprehensive understanding of the thermal behavior that can be leveraged for both code development and practical design applications. Future research should extend to consider the effect of fire protective coatings and the structural response of these columns under combined thermal and mechanical loading conditions.