Eccentric Compression Performance of Circular Hollow Sandwich Steel Tube Concrete Composite Long Columns

Literature Overview

This study by Wang Jianchao, Wang Xingyu, and Ren Qingxin (Shenyang Jianzhu University, published in Journal of Shenyang Jianzhu University, 2024, Vol. 40, No. 4, pp. 647-657) investigates the eccentric compression performance of circular hollow sandwich steel tube concrete composite long columns using ABAQUS finite element analysis. The study examines the effects of slenderness ratio, eccentricity ratio, concrete strength, longitudinal reinforcement ratio, and outer steel tube diameter on load-deflection and load-moment curves, and proposes a bearing capacity calculation method based on superposition theory. The work was supported by the National Natural Science Foundation of China (52108235).

Core Technical Content

Parametric Study Results

Load-Deformation Stages

The eccentric compression behavior of the composite long column can be divided into three stages:

1. Elastic stage: Both the steel tube and concrete core deform elastically under combined axial and bending loads.
2. Elastic-plastic stage: The outer steel tube yields on the compression side while the concrete core remains largely elastic.
3. Plastic stage: Both the steel tube and concrete core undergo significant plastic deformation, with the load-moment curve approaching a plateau or showing gradual reduction.

Technical Analysis

Hollow Sandwich Construction Advantages

The hollow sandwich construction, where a concrete-filled steel tube is placed inside an outer hollow steel tube, offers several structural advantages:

• The outer hollow steel tube provides additional lateral confinement and bending resistance without adding significant self-weight.
• The concrete core contributes axial load capacity and enhances the overall stiffness of the column.
• The hollow interior reduces self-weight compared to a solid section of equivalent outer diameter, which is particularly beneficial for long columns where self-weight buckling is a critical concern.

Slenderness and Eccentricity Interaction

The study demonstrates that both slenderness ratio and eccentricity ratio are the primary factors governing the eccentric compression behavior. The interaction between these two parameters is critical: a column with high slenderness ratio is more sensitive to eccentric loading because the additional bending moment amplifies the P-delta effect, leading to a more pronounced reduction in bearing capacity. The finding that increasing the eccentricity ratio from 0.2 to 0.6 causes a 50.3% reduction in bearing capacity underscores the importance of accurate eccentricity estimation in design.

Engineering Practice Implications

Design Methodology

The proposed bearing capacity calculation method based on superposition theory provides a practical tool for engineers. The superposition approach considers the individual contributions of the outer steel tube, the concrete core, and the longitudinal reinforcement to the total bearing capacity. This method offers the advantage of conceptual clarity and ease of implementation, though engineers should be aware of its limitations when applied to columns with very high slenderness ratios or large eccentricities where interaction effects become more pronounced.

Fabrication and Assembly Considerations

For the practical construction of hollow sandwich steel tube concrete columns:

• The inner concrete-filled tube and outer hollow tube must be concentrically aligned during assembly to prevent eccentric loading of the inner tube.
• Spacers or connection rings should be used to maintain the gap between the inner and outer tubes during construction.
• The welding or mechanical connection between the inner and outer tubes should be designed to ensure composite action while accommodating differential thermal expansion.
• Quality control should include dimensional verification of both tubes, alignment checks during assembly, and NDT of all welds connecting the inner and outer components.

Material Selection

The choice of steel grade for both the inner and outer tubes should be considered in conjunction with the concrete strength. Higher concrete strength increases the axial capacity of the core but does not significantly affect the buckling behavior of the steel tubes. The outer steel tube diameter is identified as a significant parameter, suggesting that optimizing the outer tube diameter can provide the most efficient use of material for enhancing eccentric compression capacity.

Study Insights and Reflections

This study addresses an important structural element—the hollow sandwich steel tube concrete composite long column—that offers a promising solution for applications requiring high load capacity with reduced self-weight. The finding that eccentricity ratio has a more pronounced effect on bearing capacity than slenderness ratio is consistent with the general understanding of eccentrically loaded members, but the quantified values provide useful data for design. The proposed calculation method, while based on a relatively simple theoretical framework, shows good agreement with finite element results, which is encouraging for practical application. However, the study is limited to finite element analysis, and experimental validation with physical specimens would be valuable to confirm the predicted failure modes and ductility characteristics. The hollow sandwich concept has potential applications in long-span structures, tall buildings, and bridge piers where weight reduction is a critical design consideration.