Zhuojin Pipe Fitting Co., LtdTemperature Field Analysis of Rectangular Steel Tube Concrete Columns Under Single-Side Fire Exposure
Literature Overview
The paper by Yang Hua, Lü Xuetao, and Zhang Sumei (Harbin Institute of Technology, 2010) addresses a critical but under-explored aspect of fire engineering for composite structures: the thermal behavior of rectangular steel tube concrete (SRC) columns subjected to one-sided fire loading. Published in the Journal of Tianjin University (Vol. 43, No. 5, pp. 392-399), this work was funded by the National Natural Science Foundation of China (Grant No. 50708028) and the Heilongjiang Province Postdoctoral Research Foundation (Grant No. LBH-Q07048). The study employs finite element analysis using ANSYS to establish a temperature field calculation model and validates results against prior experimental data.
Core Technical Content
The fundamental insight of this research is that single-side fire exposure produces a markedly different temperature distribution compared to the conventional four-sided fire scenario that dominates most fire design codes. Under one-sided fire, the overall cross-sectional temperature remains significantly lower, resulting in reduced material degradation and consequently improved fire resistance performance. However, the temperature distribution exhibits single-axis symmetry, which induces initial deflection and additional eccentricity—phenomena fundamentally distinct from four-sided fire conditions.
Key Parameters and Their Influence
| Parameter | Influence Level | Technical Observation |
|---|---|---|
| Heating time | High | Temperature gradient increases progressively; longer exposure leads to deeper heat penetration |
| Steel content ratio | Moderate | Higher steel ratio provides thermal mass buffering but accelerates local heating at steel-concrete interface |
| Cross-section width | High | Wider sections develop more uniform interior temperatures; edge effects become less dominant |
| Aspect ratio (H/W) | Moderate | Affects heat transfer path length and thermal gradient directionality |
| Fireproof coating type | High | Different coatings exhibit distinct thermal conductivity and emissivity characteristics |
| Fireproof coating thickness | High | Primary control variable for reducing steel tube surface temperature; thicker coatings delay temperature rise significantly |
Engineering Practice Implications
From a steel pipe manufacturing and structural engineering perspective, this research carries several important implications. First, the finding that single-side fire produces lower overall temperatures suggests that steel tube concrete columns with rectangular cross-sections may possess inherent fire resistance advantages in certain fire scenarios—particularly in cases where fire originates from one direction due to compartmentation failures or external fire exposure.
The induced eccentricity under asymmetric heating is a critical concern for structural integrity. During fire exposure, differential thermal expansion between the heated and unheated faces creates bending moments superimposed on the axial load. This is analogous to the residual stress and distortion phenomena encountered in welding processes, where asymmetric heat input leads to warping and residual deformation. Engineers must consider this coupled thermal-mechanical response in fire design calculations.
The parametric study reveals that fireproof coating thickness and type are the most effective design levers for controlling temperature fields. In practice, this aligns with industry experience where intumescent coatings and thermal barrier coatings are applied to steel structures. For rectangular steel tubes specifically, the heat transfer from the exposed face through the steel wall to the concrete core is the governing mechanism, and the concrete's low thermal conductivity serves as a natural insulator for the interior regions.
Critical Reflections
The study's reliance on ANSYS finite element modeling with validation against experimental data provides a solid technical foundation. However, several practical considerations warrant attention:
- The thermal properties of steel and concrete are temperature-dependent, and accurate material property databases at elevated temperatures remain a challenge in practice.
- The assumption of uniform fire loading on the exposed face may not represent real fire scenarios where flame impingement creates localized hot spots.
- The interaction between thermal gradients and the confining effect of the steel tube on concrete deserves further investigation—particularly regarding potential steel-concrete interface debonding at elevated temperatures.
- For steel pipe manufacturers, the study highlights the importance of steel tube wall thickness uniformity, as variations in wall thickness directly affect heat transfer rates and ultimately the fire performance of the composite member.
Study Insights
This research bridges the gap between conventional four-sided fire design assumptions and realistic fire scenarios involving asymmetric heating. The conclusion that single-side fire conditions are generally less severe in terms of overall temperature but more complex in terms of induced eccentricity represents a nuanced understanding that should inform both fire design codes and practical engineering decisions. For structural engineers specifying steel tubes for composite columns, the parametric findings provide actionable guidance on optimizing cross-sectional dimensions and protective coatings to achieve target fire resistance ratings.