Fire-Resistant Steel Steel Tube Concrete Columns Fire Performance Analysis

Literature Overview

The paper by Liu Yixiang, Tong Gen-shu, and Zhang Lei from the College of Engineering, Zhejiang University, published in Steel Structures (Vol. 31, No. 3, 2016, pp. 35-39), addresses a critical gap in fire engineering research. While conventional steel tube concrete (STC) columns have been extensively studied for fire resistance, fire-resistant steel (FRS) encased STC columns remain under-researched in the Chinese literature. The authors employed ANSYS finite element software to simulate temperature field distribution under standard ISO 834 fire curves and numerically determined fire resistance limits, comparing results with experimental data. This work was funded under the "12th Five-Year" National Science and Technology Support Program (2012BAJ13B014).

Core Technical Content and Methodology

The study establishes a validated numerical framework for evaluating fire performance of circular STC columns. The key methodology involves:

Temperature field simulation: The ANSYS model accounts for thermal conductivity variations of both steel and concrete as functions of temperature. The thermal conductivity of carbon steel decreases significantly above 500°C, while concrete undergoes thermal cracking and spalling at elevated temperatures.
Fire resistance limit determination: The numerical approach solves for the time at which structural failure criteria are met—typically defined as loss of load-bearing capacity or excessive deformation.
Comparison between conventional and fire-resistant steel: The authors replaced standard carbon steel tubes with FRS tubes and quantified the improvement in fire resistance duration.

Parameter	Conventional STC Column	FRS-STC Column	Improvement
Material grade	Q235/Q345	Fire-resistant grade (e.g., 345F/460F)	Higher strength retention at 800°C
Yield strength retention at 600°C	~50-60%	~70-80%	~20-30% relative gain
Fire resistance limit (typical)	1.5-2.0 h	2.5-3.5 h	~50-75% increase
Thermal expansion coefficient	12×10⁻⁶/°C	12-14×10⁻⁶/°C	Slightly higher but manageable

Engineering Practice Integration

From a steel pipe manufacturing and welding perspective, this research has several practical implications:

Material selection for fire-exposed structures: Fire-resistant steels such as those conforming to EN 10225-2 (structural steels for fire resistance) or Chinese equivalents maintain higher strength at elevated temperatures. When specifying pipes for STC columns in high-rise buildings, the choice between Q345B and fire-resistant grades directly affects the required fire protection thickness.
Welding considerations for FRS pipes: Fire-resistant steels often contain higher alloy content (Ni, Cr, Mo) to maintain strength at high temperatures. This increases susceptibility to hot cracking during welding. Preheating temperatures of 100-150°C and controlled heat input are recommended for FRS pipe connections.
Fire protection strategy: The study demonstrates that using FRS can reduce the required fireproof coating thickness, which has economic and aesthetic advantages for architectural applications.

Key Insights and Reflections

The numerical results showing good agreement with experimental data validates the use of FEA for fire performance prediction, which is particularly valuable when full-scale fire tests are prohibitively expensive. However, I note that the study focuses on circular sections only; rectangular and square STC columns—which are more common in building frames—may exhibit different thermal-mechanical behavior due to non-uniform heat distribution. Furthermore, the long-term degradation of fire-resistant steel under cyclic thermal exposure (as in repeated fire scenarios or industrial environments) deserves further investigation. For pipe manufacturers, this research reinforces the market opportunity for fire-resistant steel grades in structural applications, provided that welding qualification procedures are properly adapted to the modified alloy chemistry.