Zhuojin Pipe Fitting Co., LtdFire Resistance Performance of Special-Shaped Steel Pipe Concrete Columns
Literature Overview
The paper by Wang Zhibin, Zhang Jianbin, Lin Zhiping, and Wang Bingkun, published in Progress in Steel Building Structures in 2021 (Vol. 23, No. 6, pp. 54–60), investigates the fire resistance performance of special-shaped steel pipe concrete (CFST) columns, including circular-end shaped and hexagonal cross-section configurations. The research was funded by the Fujian Provincial Natural Science Foundation (Grant 2017J01696) and the Quanzhou Science and Technology Program (Grant 2020N010s). The study establishes validated finite element models and examines the influence of protective layer type, protective layer thickness, cross-section shape, and cross-section perimeter on fire resistance limits.
Research Methodology
Finite element models of circular, square, circular-end shaped, and hexagonal CFST columns were developed and validated against existing experimental test results. Once validated, these models were used to conduct parametric studies on fire resistance performance under various design conditions.
| Column Shape | Cross-Section Characteristic |
|---|---|
| Circular | Constant radius, highest perimeter efficiency |
| Square | Flat faces, lower perimeter efficiency |
| Circular-end shaped (stadium) | Hybrid of circular and rectangular |
| Hexagonal | Six-sided polygon, intermediate efficiency |
The parametric study examined four key variables: protective layer type (thick-coating intumescent paint versus mortar), protective layer thickness, cross-section shape, and cross-section perimeter.
Key Findings
The research yielded several important conclusions regarding the fire resistance behavior of special-shaped CFST columns:
- Fire resistance limits increase with increasing protective layer thickness and cross-section perimeter
- Thick-coating intumescent paint provides superior fire protection compared to mortar
- Under equivalent slenderness ratio and cross-section perimeter conditions, circular-end shaped CFST columns exhibit higher fire resistance limits than circular CFST columns
- Hexagonal CFST columns demonstrate superior fire resistance compared to square CFST columns
- Fire resistance limits for failure about the strong axis are slightly lower than for failure about the weak axis
A significant practical conclusion is that based on the perimeter equivalence principle, circular-end shaped (or hexagonal) CFST columns can be treated as circular (or square) CFST columns for fire resistance design purposes.
Fire Protection Engineering Considerations
From a steel pipe fabrication and welding quality perspective, the fire resistance of CFST columns is influenced by several fabrication-related factors. The integrity of the steel pipe-to-steel pipe welds in multi-segment columns affects the structural continuity and therefore the fire resistance behavior. Any weld defects that reduce the effective cross-sectional area or create stress concentrations can compromise the column's load-bearing capacity at elevated temperatures.
The protective layer application must account for the geometry of the steel pipe surface, including any weld beads, fittings, and connection details. Weld beads on the external surface of the pipe can create uneven surfaces that affect protective layer thickness uniformity and adhesion. Proper weld finish, including grinding of external weld beads where required, is essential for achieving consistent protective layer performance.
| Factor | Effect on Fire Resistance |
|---|---|
| Protective layer thickness | Positive correlation |
| Cross-section perimeter | Positive correlation |
| Thick-coating intumescent paint | Superior to mortar |
| Circular-end shape vs. circular | Higher fire resistance |
| Hexagonal vs. square | Higher fire resistance |
| Strong axis failure vs. weak axis | Slightly lower fire resistance |
Study Insights and Reflections
This research provides valuable design guidance for the use of special-shaped CFST columns in fire-prone structural applications. The perimeter equivalence principle offers a practical and rational basis for extending fire resistance design methods from conventional circular and square sections to more geometrically complex configurations. The finding that circular-end shaped and hexagonal sections can outperform their circular and square counterparts, respectively, under equivalent perimeter conditions, opens up new possibilities for architectural design while maintaining or even improving fire safety performance. For engineers involved in the design and fabrication of steel pipe concrete structures, understanding these shape-dependent fire resistance behaviors is essential for selecting appropriate cross-section geometries, protective layer specifications, and quality control requirements that ensure adequate fire safety performance throughout the structural service life.