Experimental Study on Axial Compression Performance of Hollow Steel Tube Concrete Long Columns

Literature Overview

Wang Hongwei, Xu Guolin, and Zhong Shantong conducted an experimental investigation into the axial compression behavior of hollow steel tube concrete (HSC) long columns, published in Industrial Construction in 2006. The study tested 11 specimens with both circular and square cross-sections, examining the influence of hollow ratio, slenderness ratio, and section shape on load-bearing capacity. This research is particularly significant for engineers considering the use of hollow steel tubes in composite column applications, where weight reduction and material efficiency are primary design objectives.

Test Program and Specimen Configuration

The experimental program was designed to systematically vary the key geometric parameters that influence the structural performance of HSC long columns.

The hollow ratio, defined as the ratio of the hollow core diameter to the outer tube diameter, is the critical geometric parameter distinguishing HSC columns from conventional SRC columns. Increasing the hollow ratio reduces the concrete volume and overall weight but simultaneously reduces the confinement effect and the effective cross-sectional area available for load transfer.

Key Experimental Findings

The most significant finding of this study is that the failure mode of hollow steel tube concrete long columns closely resembles that of empty steel tube long columns rather than that of solid SRC columns. This observation has profound implications for the design methodology and safety assessment of HSC structures.

When the hollow ratio is increased, the following trends were observed:

1. The load-bearing capacity decreases as the hollow ratio increases, due to the reduction in effective cross-sectional area and the diminished confinement effect on the concrete ring.
2. The slenderness ratio remains a dominant factor governing the failure mode, with higher slenderness ratios leading to more pronounced buckling behavior.
3. The square cross-section specimens exhibited different buckling characteristics compared to circular specimens, with local buckling of the flat faces being a potential failure mechanism.
4. The interaction between the steel tube and the concrete ring becomes less effective as the hollow ratio increases, because the concrete ring becomes thinner and more susceptible to local instability.

Comparison with Existing Codes and Formulas

The authors compared their proposed load-bearing capacity formula with the provisions of DL/T 5030-1996 (Technical Code for Thin-Walled Centrifugal Steel Tube Concrete Structures). The comparison demonstrated good agreement between the proposed formula and the experimental results, validating the feasibility of using the formula for practical design calculations of HSC axially compressed long columns.

Engineering Practice Considerations

From a steel pipe manufacturing standpoint, the use of hollow steel tubes in composite columns raises several practical considerations:

• Manufacturing precision of the inner hollow core is critical, as eccentricity of the hollow section relative to the outer tube wall can create localized stress concentrations.
• The welding quality of any internal partitions or stiffeners used to maintain the hollow core position directly affects the structural integrity.
• Corrosion protection of the inner hollow surface becomes more challenging and is essential for long-term durability.
• The selection of steel tube grade must account for the reduced confinement effect in hollow sections, potentially requiring higher-grade steel to maintain adequate safety margins.

Key Technical Points and Reflections

The finding that HSC long column failure resembles empty steel tube buckling rather than SRC crushing is a critical insight for structural engineers. It suggests that the concrete contribution to load-bearing capacity in hollow columns is more limited than in solid SRC columns, particularly for slender members. This has direct implications for the economy of using HSC versus conventional SRC in different structural applications.

The slenderness ratio effect in HSC columns is amplified compared to solid SRC columns because the moment of inertia reduction from the hollow core is proportionally larger than the cross-sectional area reduction. This means that HSC columns are more sensitive to slenderness and may require additional lateral bracing or increased wall thickness to achieve comparable stability margins.

The comparison with DL/T 5030-1996 highlights the importance of code development for specialized composite structures. As the application of HSC columns expands into new structural domains, the need for comprehensive design codes that cover the full range of loading conditions and geometric parameters becomes increasingly urgent.

Study Insights and Implications

This experimental study provides valuable data for the rational design of hollow steel tube concrete long columns. The systematic investigation of hollow ratio, slenderness ratio, and section shape effects enables engineers to make informed decisions about the applicability of HSC columns in specific structural contexts. The validation of the proposed load-bearing capacity formula against experimental data gives designers confidence in using the formula for practical calculations.

For steel pipe manufacturers, this research underscores the importance of dimensional accuracy and wall thickness uniformity in hollow steel tube production. The structural performance of HSC columns is highly sensitive to the geometric parameters of the steel tube, and manufacturing tolerances must be tightly controlled to ensure the design assumptions are met. The study also highlights the potential for material and weight savings through the use of hollow sections, which can be economically attractive in applications where transportation and erection costs are significant.