Fire Resistance Performance and Load-Bearing Capacity Calculation of Double Steel Pipe Concrete Composite Short Columns

Literature Overview

This paper by Yang Qingtian, Duo Fei, Zhang Jinchuan, Hou Liqun, and Chen Shicai, published in the Journal of Architecture and Civil Engineering in 2024, investigates the fire resistance performance of double steel pipe concrete composite short columns. Supported by the National Natural Science Foundation of China (projects 51678016 and 52278471), the research establishes a refined numerical model of double steel pipe concrete composite short columns and validates it against experimental results from similar specimens. The authors comprehensively analyze the influence of parameters such as inner tube diameter-to-thickness ratio, outer tube diameter-to-thickness ratio, and the ratio of inner to outer tube diameters, as well as different cross-sectional combination forms including inner circular-outer circular, inner square-outer circular, and inner circular-outer square configurations.

Temperature Field Analysis and Theoretical Derivation

Based on heat conduction analysis theory, the authors derive the temperature field distribution formula for the cross-section of double steel pipe concrete composite short columns and subsequently correct the formula using finite element simulation results. The temperature field distribution is critical for determining the fire resistance performance because it directly governs the degradation of material properties at elevated temperatures. The derived formula provides a theoretical foundation for predicting how heat penetrates through the double steel tube and concrete layers during a fire event.

The simplified calculation formula for the cross-sectional temperature field under fire conditions and the load-bearing capacity calculation method based on equivalent temperature principles represent significant contributions to practical fire design methodology. These simplified formulas enable engineers to perform preliminary fire resistance assessments without resorting to computationally intensive finite element analyses, thereby streamlining the design process while maintaining acceptable accuracy.

Key Findings and Parameter Effects

The study demonstrates that double steel pipe concrete composite short columns possess good fire resistance performance. When the diameter remains constant, increasing the thickness of the inner steel tube benefits the fire resistance limit, and when the thickness remains constant, increasing the diameter of the inner steel tube also improves the fire resistance limit. Under conditions of identical load application and steel ratio, the fire resistance limits of double steel pipe concrete short columns with different cross-sectional combination forms differ insignificantly, although the double circular steel pipe concrete short column exhibits slightly superior fire resistance performance overall.

Accuracy Assessment of Proposed Methods

The proposed simplified calculation formula for the temperature field and the load-bearing capacity calculation method based on equivalent temperature demonstrate relative errors within 15 percent compared to finite element results. This level of accuracy is generally acceptable for engineering design purposes, particularly for preliminary design stages where rapid assessment is required. The 15 percent error margin should be considered when applying these simplified methods to critical structures where higher precision may be warranted.

Engineering Practice Integration and Reflections

From a practical standpoint, the findings have direct implications for the design of steel pipe concrete structures in fire-prone environments such as industrial facilities, underground structures, and offshore platforms. The preference for double circular configurations over mixed cross-sectional forms simplifies fabrication and welding procedures, as circular tubes are more readily available and easier to weld circumferentially. Engineers should note that the fire resistance performance is enhanced by increasing the steel content within the double tube configuration, which aligns with the general principle that steel provides thermal mass and structural continuity during fire exposure. The simplified calculation methods proposed offer a valuable tool for rapid fire safety assessments during the conceptual design phase, enabling early identification of potential fire resistance deficiencies before detailed design commences.