Fire Resistance of Square Reinforced Stainless Steel Tube Concrete Columns with Embedded Cross-Section Steel

Literature Overview

The study conducted by Liu Yanzhi, Deng Jiqian, and Tan Qinghua from Hunan University and the National University of Defense Technology investigates the fire resistance performance of square reinforced stainless steel tube concrete (RSSTC) columns with embedded cross-section steel profiles. Published in the Journal of Architecture and Civil Engineering (2019, Vol. 36, No. 3, pp. 66-73), this research addresses an important structural engineering challenge: improving the fire resistance and ductility of stainless steel tube concrete columns while simultaneously reducing the consumption of expensive stainless steel material. The work is supported by the National Natural Science Foundation of China (Grant No. 51408212) and the Hunan Provincial Natural Science Foundation Youth Fund (Grant No. 2018JJ3058).

Structural Configuration and Design Rationale

The proposed RSSTC column configuration integrates an embedded cross-shaped steel profile within a square stainless steel tube filled with concrete. This hybrid design leverages the complementary properties of stainless steel, carbon steel, and concrete. Stainless steel offers superior corrosion resistance and maintains relatively better mechanical properties at elevated temperatures compared to carbon steel, but its high cost limits widespread application. By embedding a cross-section steel profile, the design reduces the stainless steel usage while enhancing structural performance.

Finite Element Analysis and Validation

The authors employed finite element (FE) simulation to analyze the fire resistance behavior of the RSSTC columns. The FE model was validated against experimental data on temperature distribution and fire resistance performance, ensuring the reliability of the numerical predictions. The validated model was then used to investigate the temperature history, axial displacement-time relationships, typical failure modes, and section internal force redistribution under various load ratios.

The key finding is that the embedded steel profile enhances both axial and lateral stiffness of the column at elevated temperatures. The failure mode of the RSSTC column is characterized by axial compressive failure, which is a ductile and predictable mode of collapse. This is in contrast to potential buckling failures that could occur in conventional stainless steel tube concrete columns under fire conditions.

Load Ratio Effects and Performance Enhancement

A critical finding of this research is the relationship between the fire load ratio and the improvement in fire resistance performance. Under low fire load ratios, the embedded steel profile bears a portion of the load that would otherwise be transferred from the stainless steel as its material properties degrade with increasing temperature. This load redistribution mechanism allows the stainless steel to undergo greater temperature-induced material degradation without immediate structural failure.

The improvement in fire resistance is most pronounced at lower load ratios. As the load ratio decreases, the embedded profile has greater capacity to redistribute loads, effectively extending the time to failure. This behavior is particularly advantageous for structures designed with higher safety margins, where the service loads are well below the ultimate capacity.

Engineering Practice and Design Implications

From a structural engineering practice perspective, this research offers several important implications:

1. Material optimization: The RSSTC configuration allows designers to reduce stainless steel usage while maintaining or improving fire resistance, which is economically significant given the high cost of stainless steel.
2. Load redistribution: The embedded cross-section profile provides a mechanical pathway for load redistribution during fire exposure, which enhances structural reliability.
3. Failure mode control: The predictable axial compressive failure mode facilitates more straightforward structural assessment and design.
4. Load ratio sensitivity: Designers should consider the expected load ratio when selecting between conventional SSTC and RSSTC columns, as the benefits are most pronounced at lower load ratios.

The cross-section steel profile serves as an internal reinforcement that does not interfere with the concrete placement or the stainless steel tube forming process. However, the connection between the embedded profile and the stainless steel tube must be carefully detailed to ensure composite action during both normal service and fire conditions. Welding or mechanical fastening of the embedded profile to the tube should be designed to maintain integrity at elevated temperatures.

Study Insights and Reflections

This research represents a thoughtful approach to structural optimization that balances material efficiency with safety performance. The concept of using embedded steel profiles to enhance the fire resistance of stainless steel tube concrete columns is particularly relevant for applications in harsh environments where corrosion resistance is paramount, such as marine structures, chemical processing facilities, and infrastructure in aggressive atmospheric conditions. The numerical methodology employed provides a robust framework for parametric studies that would be prohibitively expensive through experimental means alone. The validation against experimental data lends credibility to the findings and supports their application in engineering design. The study underscores the importance of considering load ratio effects in fire design, as the benefits of composite action are most pronounced when the structure operates well below its ultimate capacity—a condition that aligns with good engineering practice and adequate safety factors.