A Numerical Study of the Fire Resistance of Square Steel Tube Columns Embedded in Walls
Abstract
1. Introduction
2. FEM Building and Validation
2.1. FEM Building
2.2. FEM Validation
3. Simulation Results Analysis
3.1. Heat-Transfer Model
- (1)
- Along the wall-thickness direction, the non-embedded region of the SST column experiences a higher heating rate than that of the embedded region, i.e., points P4/P5 > points P1/P2/P3, and the temperature of point P5 is 14.7% higher than that of point P2 after 3 h of heating. The temperature variation trend is mainly due to the different heat-transfer mechanisms, with the non-embedded region of the SST column being directly affected by the heat radiation from the fire source, while the temperature rise of the embedded region is mainly through the heat conduction between the SST column and the walls. For the measurement points located on the embedded region of the SST column, the temperature of the measurement point near the middle of the wall (P3) is lowest, and as the measurement point approaches the wall edges, the temperature increases gradually, i.e., point P3 < points P1/P4, while for the measurement points located outside the walls, the pattern is reversed, i.e., point P5 > point P4. This is mainly due to the high thickness and relatively high thermal conductivity of the walls, which results in heat dispersion in the walls, and the measurement points near the walls are subject to the “cooling effect” by the walls.
- (2)
- Along the wall-length direction, the temperature of the measurement point near the wall is relatively low, as evidenced by the fact that point P1 < point P6, point P5 < point P7, and the temperature difference between point P1 and point P6 is greater than that between point P5 and point P7; this is attributable to the same underlying reasons previously discussed.
- (3)
- The wall effect results in a non-uniform temperature distribution along the SST column, and the degradation of the material’s properties varies across different positions within the column cross-section, resulting in material strength eccentricities. In practical engineering, considering the economic aspects and standard fire-protection requirements, it may be advantageous to reduce the fire-resistive coating thickness on the embedded region of the SST column.
3.2. Mechanical Model
3.2.1. Axial Deformation
- (1)
- Expansion phase (OA/OA’): At the initial heating, the overall temperature of the SST columns remains relatively low, which leads to minimal degradation of the material’s properties. Due to the high thermal-expansion coefficient of the steel, the columns undergo pronounced thermal expansion. During this phase, the deformation due to thermal expansion exceeds that of compressive deformation, resulting in an upward axial displacement of the columns. Under ideal fire conditions, the column experiences a more rapid temperature increase, resulting in a steeper slope of the axial deformation curve compared with that observed under actual fire conditions at this phase. As the columns temperature rises, the steel strength progressively deteriorates, accelerating the compressive deformation rate under axial loading, which is reflected in a gradual decrease in the slope of the Z-t curves. When the overall compressive deformation rate coincides with the thermal-expansion deformation rate, the Z-t curves attain their peak points (A/A’).
- (2)
- Compression failure phase (AB/A’B’): With the increasing temperature of the columns, degradation of the material’s properties becomes markedly pronounced. Concurrently, due to the initial defects and the stress redistribution induced by the thermal expansion, localized buckling or plastic deformation may manifest, resulting in a substantial reduction in the load-bearing capacity of the columns. During this phase, the overall compressive deformation rate significantly exceeds that of thermal expansion. According to the criteria for determining fire resistance outlined in Fire-Resistance Tests-Elements of Building Construction-Part 7: Specific Requirements for Columns GB/T 9978.1-2008 [39], for axial load bearing components, when the axial compressive deformation reaches 1/100 of its length, it is considered that the components undergo failure (B/B’).
3.2.2. Lateral Deformation
3.2.3. Stress Distribution
4. Parametric Analyses
4.1. Fire-Resistive Coating Thickness
4.2. Steel Tube Thickness
4.3. Steel Strength
4.4. Slenderness Ratio
5. Conclusions
- (1)
- Under ideal fire conditions, the temperature distribution across the whole cross-section of the SST column is uniform. However, when considering the wall effect, the temperature rise rate of the embedded region is considerably lower than that of the non-embedded region. Consequently, degradation of the material’s properties varies at different locations, resulting in eccentricity in the material’s strength.
- (2)
- The axial deformation trends of the SST column under ideal and actual fire conditions are consistent. In the initial heating, the temperature of the columns remains low, and the material’s properties exhibit minimal deterioration, resulting in significant thermal expansion. As the temperature escalates, the degradation of the material’s properties occurs, leading to an increased rate of compressive deformation and local buckling, which ultimately leads to the column’s failure. When considering the wall effect, the fire resistance of the SST column is enhanced by 25.3% compared with that under ideal fire conditions.
- (3)
- Under ideal fire conditions, the buckling direction of the SST column under failure is in the direction of the initial defect setting, whereas when considering the wall effect, the buckling direction of the SST column deviates toward the wall-thickness direction due to the eccentricity of the material strength induced by the non-uniform temperature distribution.
- (4)
- In a practical assembled steel-structure design, the thermal insulation effect of the wall should be considered. By reducing the fire-resistive coating thickness on the embedded region, the uniformity of stress distribution within the column can be ameliorated, which can ensure the fire resistance of the column members and reduce the cost at the same time. When a high load-bearing capacity is required, prioritizing an increase in the steel tube thickness over enhancing steel strength is advisable. Components with high slenderness ratios are more susceptible to local buckling and overall instability in fire conditions.
- (5)
- For the fire-resistance design of SST columns embedded in walls, when the demand for the fire-resistance level is Class I, it is recommended that the fire-resistive coating thickness on the embedded region be reduced to 10 mm, the steel tube thickness be no less than 8 mm and the load ratio and slenderness ratio not exceed 0.5 and 47.5, respectively.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
References
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T/°C | Yield Strength | Proportionality Limit | Elastic Modulus |
---|---|---|---|
20 | 1.000 | 1.000 | 1.000 |
100 | 1.000 | 1.000 | 1.000 |
200 | 1.000 | 0.807 | 0.900 |
300 | 1.000 | 0.613 | 0.800 |
400 | 1.000 | 0.420 | 0.700 |
500 | 0.780 | 0.360 | 0.600 |
600 | 0.470 | 0.180 | 0.310 |
700 | 0.230 | 0.075 | 0.130 |
800 | 0.110 | 0.050 | 0.090 |
900 | 0.060 | 0.0375 | 0.0675 |
1000 | 0.040 | 0.025 | 0.045 |
1100 | 0.020 | 0.0125 | 0.0225 |
1200 | 0.000 | 0.000 | 0.000 |
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Shen, W.; Wang, J.; Tan, S.; Wang, X.; Wang, T. A Numerical Study of the Fire Resistance of Square Steel Tube Columns Embedded in Walls. Fire 2025, 8, 122. https://doi.org/10.3390/fire8040122
Shen W, Wang J, Tan S, Wang X, Wang T. A Numerical Study of the Fire Resistance of Square Steel Tube Columns Embedded in Walls. Fire. 2025; 8(4):122. https://doi.org/10.3390/fire8040122
Chicago/Turabian StyleShen, Wanyu, Jian Wang, Siyong Tan, Xuehui Wang, and Tao Wang. 2025. "A Numerical Study of the Fire Resistance of Square Steel Tube Columns Embedded in Walls" Fire 8, no. 4: 122. https://doi.org/10.3390/fire8040122
APA StyleShen, W., Wang, J., Tan, S., Wang, X., & Wang, T. (2025). A Numerical Study of the Fire Resistance of Square Steel Tube Columns Embedded in Walls. Fire, 8(4), 122. https://doi.org/10.3390/fire8040122