Axial Compression Performance of Steel Pipe-Confinement High-Strength Concrete Core Composite Short Columns

Literature Overview

This research by Ji Jing, Wang Yang, Chen Xiaokun, Jiang Liangqin, Zhang Wenfu, Zhang Yunfeng, Yuan Chaoqing, and Liu Yingchun, published in 2017 in the Journal of Northeast Petroleum University, presents a comprehensive study on the axial compression behavior of steel pipe-confined high-strength concrete core columns with heterogeneous strength distribution (SGCC). The work was supported by multiple funding sources including the National Natural Science Foundation of China (51178087) and was conducted at the Key Laboratory of Disaster Prevention and Protection Engineering of Heilongjiang Province. The study addresses an important structural engineering challenge: how to optimize the composite action between steel pipes and high-strength concrete cores while managing the strength mismatch between inner and outer concrete zones.

Structural Configuration and Design Parameters

The SGCC (Steel pipe-Guarded Concrete core) system represents an innovative approach to composite column design. The fundamental concept involves a steel pipe embedded within a larger concrete section, where the concrete inside the pipe is of higher strength grade than the surrounding concrete. This creates a heterogeneous strength distribution that leverages the confinement effect of the steel pipe on the high-strength core while maintaining a conventional concrete exterior.

The parametric study investigated 36 specimens with the following design variables:

Finite Element Methodology

The study employed ABAQUS finite element software to establish models for 18 of the 36 specimens. Key modeling considerations included:

• Material nonlinear constitutive models: Appropriate models for confined concrete behavior were selected to capture the triaxial stress state within the steel pipe
• Mesh size sensitivity: Optimal element dimensions were determined through convergence studies
• Validation approach: Finite element results were compared against experimental test data to verify model accuracy

The constitutive modeling of confined high-strength concrete is particularly challenging because conventional models (Mander, Kent-Park) were developed for normal-strength concrete and may not accurately predict the behavior of high-strength concrete under confinement. The steel pipe provides a more uniform confinement pressure than discrete stirrups, which fundamentally alters the stress-strain response of the enclosed concrete.

Key Results and Performance Characteristics

Axial Load-Bearing Capacity

The parametric study revealed that the following parameters have significant influence on axial load-bearing capacity:

1. Confinement index (ξ): Higher confinement indices lead to substantially increased load capacity, as the steel pipe provides more effective lateral restraint to the high-strength concrete core.
2. Outer concrete stirrup ratio (ρ_v): Increased stirrup density in the outer concrete zone improves overall column ductility and ultimate capacity.
3. Steel pipe concrete rate (η): A larger proportion of the cross-section occupied by the steel pipe-confined core results in higher load capacity.

Stiffness and Ductility

The elastic stage stiffness was found to be primarily governed by the confinement index and the steel pipe concrete rate. The ductility performance showed a similar trend, with higher values of these parameters correlating with improved energy dissipation capacity.

Simplified Design Formula

Based on the superposition principle, the authors introduced an axial load-bearing capacity reduction factor and developed a simplified calculation formula for SGCC column axial capacity. This formula accounts for:

• The composite action between the steel pipe and confined concrete
• The contribution of the outer concrete zone
• The interaction effects between different material zones
• The reduction factor for non-ideal composite behavior

Standards and Code Comparison

Engineering Application Considerations

The SGCC system offers several advantages for practical engineering applications:

1. Material optimization: Using high-strength concrete only within the steel pipe confines reduces material costs while maximizing structural efficiency.
2. Formwork efficiency: The steel pipe serves as permanent formwork for the inner concrete, reducing construction time and eliminating the need for temporary formwork in that zone.
3. Ductility enhancement: The confinement effect of the steel pipe on the high-strength core prevents brittle failure and promotes ductile behavior even with high-strength concrete.
4. Seismic performance: The improved ductility and energy dissipation capacity make this system suitable for seismic regions.

FMEA Analysis of Potential Failure Modes

Applying a Failure Mode and Effects Analysis approach to the SGCC system:

Study Insights and Reflections

This research makes a meaningful contribution to the field of composite column design by addressing the practical challenge of heterogeneous concrete strength distribution. The development of a simplified design formula based on the superposition principle with a reduction factor represents a pragmatic approach that balances theoretical accuracy with practical usability. However, several aspects warrant further consideration: the long-term behavior under sustained loads (creep and shrinkage effects on the composite action), the behavior under combined axial and bending loads, and the fire resistance characteristics of the SGCC system. The parametric study provides a solid foundation, but full-scale testing of multi-story frames incorporating SGCC columns would be necessary before widespread engineering adoption.