Eccentric Compression Behavior of Circular-Ended Steel-Concrete Short Columns

Literature Overview

This 2019 study by Wang Fengqin, Wang Jingfeng, and Shen Qihan from Hefei University of Technology (Journal of Hefei University of Technology, Vol. 42, No. 11, pp. 1521-1529) investigates the eccentric compression performance of circular-ended steel-concrete short columns. Funded by the National Natural Science Foundation (Grant 51478158) and the Ministry of Education New Century Excellent Talents Program (NCET-12-0838), this research addresses a relatively novel cross-sectional geometry that offers potential advantages over conventional circular and rectangular steel-concrete columns.

Core Technical Content

Circular-Ended Cross-Section Geometry

The circular-ended cross-section combines the benefits of circular and rectangular sections. The circular ends provide uniform confinement and eliminate corner stress concentrations, while the flat sides between the circular arcs allow for easier connection to beam flanges and facilitate formwork construction. This hybrid geometry represents an engineering compromise between structural efficiency and constructability.

Numerical Modeling Approach

The authors employed ABAQUS finite element software to establish numerical models of circular-ended steel-concrete eccentrically compressed short columns. Key modeling considerations include:

The numerical model was validated against experimental results, confirming its accuracy in predicting load-displacement responses and failure modes.

Parametric Study Results

The parametric analysis examined the influence of multiple variables on eccentric compression performance:

Effect of Eccentricity Ratio (e/D):

• As eccentricity increases, the failure mode transitions from symmetric local indentation to asymmetric failure with excessive rotation at the eccentric end.
• The axial load capacity decreases while the maximum moment capacity initially increases then decreases beyond a critical eccentricity.
• The interaction curve (P-M relationship) was fitted based on numerical results.

Effect of Section Area:

• Larger section areas increase both axial load capacity and maximum moment capacity proportionally within the studied eccentricity range.

Effect of Steel Strength:

• Higher steel yield strength contributes to increased load-bearing capacity, particularly in the lower eccentricity range where steel tube contribution is more significant.

Effect of Concrete Strength:

• Higher concrete compressive strength improves axial capacity but has a diminishing effect on moment capacity at high eccentricities.

Effect of Diameter-to-Thickness Ratio (D/t):

• Higher D/t ratios reduce both axial and moment capacities due to increased susceptibility to local buckling of the steel tube.

Failure Modes Identified

The research identifies two primary failure modes for circular-ended steel-concrete short columns under eccentric compression:

1. Local indentation with end bulging: Occurs at moderate eccentricities where the steel tube locally deforms inward on the compression side while bulging outward at the column ends. The circular geometry distributes this deformation around the cross-section perimeter.
2. Excessive eccentric-end rotation: Occurs at high eccentricities where the compression zone experiences severe crushing, leading to large rotations at the eccentric end and eventual loss of load-carrying capacity.

Standards and Design Considerations

The P-M interaction curves derived in this study provide essential input for developing design provisions for circular-ended steel-concrete columns. Currently, most design codes (GB 50017, AISC 360, Eurocode 4) provide interaction curves for circular and rectangular sections but lack specific provisions for circular-ended geometries. This research fills that gap by providing the fundamental data needed for code development.

For practical design, engineers should note that the circular-ended section generally provides 5-15% higher eccentric compression capacity compared to equivalent circular sections due to the additional flat-sided area, while maintaining the uniform confinement characteristics of circular geometry.

Engineering Practice Integration

This research has direct applications in:

• Design of composite columns in seismic regions where eccentric loading is unavoidable
• Development of prefabricated composite column systems with standardized circular-ended cross-sections
• Retrofitting of existing steel columns with concrete infill in circular-ended configurations

The numerical methodology presented can be adapted for parametric studies of other hybrid cross-sectional geometries, making it a valuable tool for structural engineers exploring innovative composite section designs.

Key Insights and Reflections

The circular-ended cross-section represents a promising evolution in composite column design, but its adoption requires comprehensive research on connections, fabrication, and long-term behavior under sustained loading. The parametric study methodology employed—combining validated finite element models with systematic parameter variation—provides a template for investigating other non-standard composite sections. The fitted P-M interaction curves should be incorporated into future revisions of Chinese national standards for steel-concrete composite structures, and the authors' recommendation for further experimental validation at larger scales is well-founded before full code adoption.