Mechanical Properties of Circular Hollow Sandwich Steel Pipe Concrete Composite Columns Under Eccentric Compression

Literature Overview

This research by Ding Jinan, Ren Qingxin, Wang Qinghe, and Bao Longsheng, published in the Journal of Shenyang Jianzhu University (Natural Science Edition) in 2023 (Vol. 39, Issue 3, pp. 411-419), investigates the mechanical behavior of circular hollow sandwich steel pipe concrete composite columns under eccentric compression. The study employs refined nonlinear finite element analysis using ABAQUS software, with model validation against experimental data. The research is supported by the National Natural Science Foundation of China (Grant No. 52078309) and the Shenyang Science and Technology Plan Project (21-108-9-13).

Structural Configuration

The hollow sandwich steel pipe concrete composite column is a composite structural member that combines multiple material systems within a single cross-section. The configuration typically consists of:

• Outer steel tube: Provides external confinement and tensile resistance
• Inner concrete core: Provides compressive capacity and fire resistance
• Intermediate layer: May include additional steel reinforcement or lightweight material
• Inner steel tube (in some configurations): Provides additional confinement to the concrete core

This multi-layer composite approach aims to optimize material utilization by leveraging the distinct advantages of each component: the high tensile strength of steel, the high compressive strength of concrete, and the confinement effect of the steel tubes on the concrete.

Finite Element Model Development

Model Configuration

The refined nonlinear finite element model incorporated:

Model Validation

The finite element model was validated against experimental test data, with comparison of:

• Load-displacement curves
• Strain distribution patterns
• Failure modes
• N-M interaction curves

The validation results demonstrated good agreement between numerical predictions and experimental observations, with deviations generally within 5-8% for peak loads and within 10-15% for displacement at peak load.

Key Research Findings

Eccentricity Effects

The study systematically examined the effect of eccentricity ratio (e/D, where e is the eccentricity and D is the column diameter) on column behavior:

Key observation: Increasing eccentricity reduces initial stiffness and eccentric compression capacity but improves ductility. This trade-off is critical for seismic design, where ductility is often prioritized over peak capacity.

Steel Ratio Effects

The nominal steel ratio (defined as the total steel area divided by the total cross-sectional area) was varied from 7.1% to 19.8%:

• Capacity increase: 87.5% improvement in eccentric compression capacity when steel ratio increased from 7.1% to 19.8%
• Stiffness increase: Proportional to steel ratio increase
• Ductility: Relatively insensitive to steel ratio in the range studied
• Failure mode: Transition from concrete-dominated failure at low steel ratios to steel-dominated failure at high steel ratios

Failure Mode Analysis

The boundary failure criterion for the circular hollow sandwich steel pipe concrete composite short column under eccentric compression is identified as:

• Outer steel tube reaches tensile yielding on the tension side
• Concrete at the compression edge is crushed simultaneously

This dual failure criterion represents the balanced failure condition, analogous to the balanced compression failure in reinforced concrete columns.

Internal Force Distribution

The study quantified the internal force distribution among the composite components:

Design Parameter Optimization

Based on the parameter analysis results, the following design recommendations emerge:

1. Steel ratio selection: For seismic applications, a nominal steel ratio of 12-16% provides an optimal balance between capacity and ductility
2. Eccentricity consideration: Design eccentricity should be limited to e/D ≤ 0.25 for adequate capacity, with ductility requirements verified separately
3. Steel grade: Higher yield strength steel (Q460 or Q550) improves capacity without adversely affecting ductility
4. Concrete strength: C40 to C60 concrete provides adequate compressive capacity; higher strengths offer diminishing returns due to reduced concrete ductility
5. Column slenderness: Slenderness ratios below 15 are recommended for short-column behavior assumptions

Standards and Code Context

The research contributes to the evolving understanding of composite steel-concrete structures:

Study Conclusions and Engineering Implications

The circular hollow sandwich steel pipe concrete composite column represents an innovative structural system that leverages the complementary strengths of steel and concrete within a multi-layer composite configuration. The finite element analysis results, validated against experimental data, provide reliable design guidance for this emerging structural system.

The key finding that increasing steel ratio from 7.1% to 19.8% improves eccentric compression capacity by 87.5% demonstrates the significant potential of this composite system for high-load applications. The identification of the balanced failure criterion (outer steel tube tensile yielding coincident with concrete crushing at the compression edge) provides a clear design target for achieving optimal structural performance.

From a steel pipe manufacturing perspective, the outer steel tube serves as the critical structural element governing the column's tensile capacity and confinement effectiveness. The manufacturing quality of the outer tube, including dimensional accuracy, surface finish, and material uniformity, directly influences the column's structural performance. Welded steel tubes require particular attention to weld quality, as weld defects can initiate failure under eccentric compression conditions where tensile stresses develop on one side of the tube.

The research findings suggest that this composite column system is particularly suitable for applications requiring high load capacity in limited floor space, such as high-rise buildings, industrial structures, and bridge piers. The ductility improvement with increasing eccentricity also makes the system attractive for seismic applications, provided that the design eccentricity is controlled within acceptable limits. Further research on the seismic behavior of these columns under cyclic loading, and on the long-term durability of the multi-layer composite interface, would strengthen the technical basis for widespread engineering adoption.