Zhuojin Pipe Fitting Co., LtdFire Protection Coating Thickness for Fire-Resistant Steel Concrete Filled Tube Columns
Overview of the Study
The paper by Liu Yixiang, Tong Genzhu, and Zhang Lei, published in the Journal of Zhejiang University (Engineering Science) in 2015, investigates the fire protection coating thickness required for fire-resistant steel concrete-filled tube (CFT) columns under fire conditions. The research was funded by the National Science and Technology Support Program (Grant No. 2012BAJ13B04). The study systematically examines the thermal and structural performance of circular and square CFT columns made with fire-resistant steel under standard fire exposure, providing practical design formulas for fire protection coating thickness determination.
Methodology and Parametric Analysis
The authors employed ANSYS finite element software to simulate the temperature field distribution in both circular and square CFT columns subjected to standard fire temperature-time curves. Multiple fire protection systems were evaluated: thick-type intumescent fire-resistant coatings and cement mortar for circular columns, and autoclaved aerated concrete (AAC) boards with cement mortar for square columns.
| Column Type | Fire Protection System | Parameters Varied |
|---|---|---|
| Circular CFT column | Thick-type intumescent coating, cement mortar | Concrete strength, steel ratio, eccentricity, tube size, fire resistance rating, slenderness ratio, steel grade |
| Square CFT column | AAC board, cement mortar | Same as circular |
The numerical model accounted for the temperature-dependent mechanical properties of both the fire-resistant steel and the concrete infill. The steel ratio, defined as the ratio of steel cross-sectional area to total cross-sectional area, was varied to capture the influence of steel contribution on fire resistance. The load eccentricity ratio was varied to simulate realistic moment demands on columns in frame structures.
Key Findings on Coating Thickness
The most significant finding of this study is that fire-resistant steel CFT columns require substantially less fire protection coating thickness compared to conventional steel CFT columns. The required coating thickness for fire-resistant steel columns is approximately one-third to one-half of that required for conventional steel columns. This reduction is attributed to the superior high-temperature strength retention of fire-resistant steel, which maintains higher yield strength at elevated temperatures compared to conventional structural steel grades.
The authors developed three practical calculation formulas for determining the required fire protection coating thickness for different column configurations and fire resistance ratings. The calculated results from these fitted formulas showed small errors compared to the full theoretical calculation results, validating the simplified approach for engineering design purposes.
Engineering Practice Integration
The findings of this study have direct implications for structural fire design practice. The reduction in required coating thickness translates into several practical benefits: reduced construction costs associated with fire protection materials and application labor, increased usable building space due to thinner coatings, and reduced overall structural weight. For engineers specifying fire protection systems, the following considerations are relevant:
- Fire-resistant steel grades such as those conforming to EN 10225 or equivalent Chinese standards should be specified where fire resistance is a critical design consideration.
- The choice of fire protection material depends on the column geometry: intumescent coatings are suitable for circular sections where uniform application is achievable, while AAC boards provide better protection for square sections with flat surfaces.
- The slenderness ratio of the column significantly affects fire performance, as slender columns are more susceptible to buckling under reduced material strength at elevated temperatures.
Study Reflections and Recommendations
This research makes a valuable contribution to the rational design of fire-resistant CFT columns by demonstrating the quantitative benefit of using fire-resistant steel. The development of simplified calculation formulas is particularly useful for practical design, as it eliminates the need for full finite element analysis in routine design situations. However, engineers should note that the study is based on numerical simulation rather than full-scale fire testing, and validation through physical fire tests would further strengthen the confidence in the proposed design formulas. Future research should extend the investigation to include connections between fire-resistant steel CFT columns and beams, as connection behavior under fire conditions is often the governing factor in structural fire design.