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

Literature Overview

Published in Industrial Construction in 2006, this paper by Wang Hongwei, Xu Guolin, and Zhong Shantong presents experimental results from eleven hollow steel tube concrete (HSC) long columns subjected to axial compression. The specimens included both circular and square cross-sections, with varying hollow ratios and slenderness ratios. The study was conducted jointly by Harbin Institute of Technology and Hangzhou Zhongdian Electric Power Engineering Technology Research Institute, indicating a strong connection between academic research and power industry engineering practice. The primary objective was to investigate how hollow ratio, slenderness ratio, and cross-sectional shape influence the load-bearing capacity and failure modes of HSC long columns.

Experimental Configuration and Key Parameters

The experimental program comprised eleven specimens with the following key parameters:

The hollow ratio is the most distinctive parameter in this study. Unlike conventional SRC columns with fully filled concrete cores, HSC columns contain an internal void that reduces self-weight while maintaining structural performance. This is particularly attractive for applications where weight reduction is critical, such as tall chimneys, transmission towers, and industrial pipe racks.

Failure Mode Analysis

A key finding of this study is that the failure mode of HSC long columns closely resembles that of empty steel tube long columns, characterized by overall buckling rather than local concrete crushing. This observation is significant because it implies that the hollow ratio has a limited effect on the failure mechanism of long columns—the dominant failure mode is governed by the overall slenderness and the steel tube's flexural rigidity rather than the concrete's compressive strength.

The experimental results showed that as the hollow ratio increased, the load-bearing capacity decreased, but the rate of decrease was less than proportional to the reduction in concrete area. This indicates that the steel tube continues to carry a significant portion of the axial load even when the concrete core is partially removed. The slenderness ratio emerged as the dominant parameter controlling the ultimate load capacity, consistent with classical column theory.

Standards Comparison and Code Applicability

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 revealed good agreement between the proposed formula and experimental results, validating the practical applicability of the design approach. This is an important contribution because, at the time of publication, design codes for HSC structures were not yet fully developed, and engineers lacked reliable design tools.

From a welding and pipe fabrication standpoint, the hollow steel tube concrete column requires careful attention to the manufacturing process. The steel tube must be formed and welded with sufficient dimensional accuracy to ensure proper concrete placement and void formation. For seamless steel tubes, the wall thickness uniformity is critical; for welded pipes, the weld quality directly affects the column's buckling resistance. Any weld defect—such as incomplete fusion, undercut, or excess reinforcement—could serve as a stress concentration site that initiates local buckling under axial compression.

Engineering Practice Connection

In pipeline engineering, hollow steel tube concrete columns find application in elevated pipe racks, particularly in chemical and petrochemical plants where self-weight reduction is desired to minimize foundation costs. The experimental findings directly inform the design of such structures: engineers can select an optimal hollow ratio that balances weight savings against strength reduction, while ensuring that the slenderness ratio remains within acceptable limits for the intended service life.

The observation that HSC long columns fail similarly to empty steel tubes has important implications for inspection and maintenance. Non-destructive testing (NDT) protocols for these structures should focus on detecting local buckling, weld defects, and corrosion thinning of the steel tube, rather than on assessing concrete integrity, which is secondary in the failure mechanism of long columns.

Key Questions and Reflections

A notable gap in the study is the absence of long-term loading tests. The axial compression tests were presumably short-duration, and the long-term behavior—particularly the interaction between concrete creep and steel tube buckling—remains unexplored. For pipeline support structures that must maintain alignment over decades of service, the long-term stability of HSC columns deserves dedicated investigation.

Another reflection concerns the practical challenges of constructing HSC columns in the field. The internal void must be maintained during concrete placement, which requires formwork or spacers that are subsequently removed. Any residual debris or incomplete void formation could alter the load distribution between the steel tube and concrete, potentially reducing the effective hollow ratio and the associated weight savings.

Study Insights and Implications

This experimental study provides valuable data for the design of hollow steel tube concrete long columns, confirming that they can achieve satisfactory structural performance with significant self-weight reduction. For engineers in the pipeline support industry, the key insight is that hollow ratio selection should be driven primarily by slenderness considerations rather than concrete area optimization. The validated design formula offers a practical tool for preliminary design, but engineers should remain aware of the limitations regarding long-term behavior and construction quality control.