Zhuojin Pipe Fitting Co., LtdAxial Compression Test and Bearing Capacity Calculation of Cross-Shaped Multi-Cavity Composite Lightweight Steel Tube Concrete Column
Literature Overview
This study presents experimental and analytical investigations on cross-shaped multi-cavity composite lightweight steel tube concrete (SC) columns under axial compression loading. The innovative cross-section geometry, featuring multiple internal cavities within a steel tube frame filled with lightweight concrete, represents a significant advancement in structural efficiency. By combining the high strength of steel tubes with the reduced weight of lightweight concrete and the geometric efficiency of multi-cavity cross-sections, the research targets the dual objectives of maximizing load-bearing capacity while minimizing structural self-weight.
Cross-Section Geometry and Material Properties
The cross-shaped multi-cavity column section comprises external steel tubes arranged in a cruciform pattern, with internal cavities creating a hollow-core lightweight structure. The section properties are characterized by the following typical parameters:
| Parameter | Typical Range | Design Consideration |
|---|---|---|
| Overall section dimension | 300–600 mm | Span-to-depth ratio |
| Steel tube wall thickness | 4–10 mm | Buckling resistance |
| Concrete core thickness | 50–150 mm | Confinement effectiveness |
| Number of cavities | 2–4 | Weight reduction vs. stability |
| Steel tube grade | Q345/Q355 | Yield strength 345–355 MPa |
| Lightweight concrete density | 1400–1800 kg/m³ | Weight optimization |
| Concrete compressive strength | C30–C50 | Confined concrete performance |
The multi-cavity configuration introduces complex stress distribution patterns within the section. Unlike conventional solid SC columns, the hollow cavities create stress concentration zones at the cavity boundaries, requiring careful analysis of the interaction between the steel tube walls and the concrete infill. The lightweight concrete, typically composed of expanded clay aggregate or foamed concrete, provides reduced self-weight but may exhibit lower confinement effectiveness compared to normal-weight concrete.
Axial Compression Performance
The axial compression behavior of the cross-shaped multi-cavity SC column progresses through distinct stages:
- Elastic stage: Linear stress-strain response with uniform stress distribution across the section
- Elastic-plastic transition: Progressive yielding of steel tube walls and micro-cracking in lightweight concrete
- Plastic stage: Full section yielding with confined concrete reaching peak strength
- Post-peak stage: Gradual strength degradation as cavities begin to collapse and steel tubes buckle
The experimental results demonstrate that the cross-shaped multi-cavity column achieves a load-bearing capacity of 85–95% of a conventional solid SC column of equivalent outer dimensions, while reducing self-weight by 25–40%. This represents a significant structural efficiency improvement, particularly relevant for high-rise buildings where self-weight directly impacts foundation design and seismic response.
Bearing Capacity Calculation Methodology
The proposed bearing capacity calculation method accounts for the following factors:
- Confined concrete strength enhancement due to steel tube restraint
- Geometric efficiency of the multi-cavity cross-section
- Local buckling resistance of individual steel tube walls
- Interface bond strength between steel tube and lightweight concrete
- Slenderness ratio effects on overall column stability
The bearing capacity formula incorporates a confinement effectiveness coefficient that varies with the cavity configuration and the steel tube-to-concrete thickness ratio. For columns with slenderness ratios below 15, the confinement effect is most pronounced, with confined concrete strength enhancements of 1.5–2.5 times the unconfined strength. As slenderness increases beyond 25, overall buckling becomes the governing failure mode, and the confinement benefit diminishes.
Fabrication and Welding Challenges
The fabrication of cross-shaped multi-cavity SC columns presents unique welding challenges. The cruciform arrangement requires precise alignment of intersecting steel tube sections, with tolerance requirements of ±0.5 mm for centerline alignment. The recommended welding approach involves:
- Root preparation using beveled edges at 60° included angle
- GTAW for root pass to ensure full penetration in tight junctions
- SMAW or FCAW for filling and capping passes
- Post-weld inspection using MT and RT to verify weld integrity at all intersections
The welding sequence must be carefully planned to minimize distortion. A symmetric welding pattern, progressing from the center outward, helps maintain dimensional accuracy. Preheating at 100°C is recommended for wall thicknesses exceeding 8 mm to prevent cold cracking in the HAZ.
Study Insights and Engineering Implications
The research provides valuable data for the practical application of cross-shaped multi-cavity SC columns in modern structural engineering. The combination of lightweight concrete and multi-cavity geometry offers a promising solution for weight-sensitive applications, including long-span bridges, high-rise buildings, and industrial facilities with strict self-weight limitations. The proposed bearing capacity calculation method, validated against experimental data with deviations within ±10%, provides a reliable basis for design implementation.
However, the research also highlights areas requiring further investigation, particularly the long-term durability of lightweight concrete under cyclic loading and the fatigue behavior of the multi-cavity section under variable amplitude loading. These aspects are critical for the widespread adoption of this innovative column type in demanding structural applications.