Axial Compression Performance of High-Strength Square Steel Tube-Concrete-Circular Steel Tube Composite Short Columns

Literature Overview and Research Significance

The paper by Li Xiaoli and Chen Li from Northeast Petroleum University (Journal of Northeast Petroleum University, ISSN 2095-4107, Vol. 45, Issue 1, 2021, pp. 112-122) presents a comprehensive parametric study of High-Strength Square Steel Tube-Concrete-Circular Steel Tube (HSCS) composite short columns under axial compression. This innovative composite cross-section concept combines a high-strength square outer tube with a circular inner tube and concrete infill, representing an advancement in composite structural design. The classification TU398 confirms its structural engineering focus.

Research Methodology and Design Parameters

The study employs a rigorous numerical approach with 27 full-scale specimens designed through parametric variation. The control parameters include:

The methodology includes material constitutive model selection, mesh rationality analysis, and validation against existing experimental specimens to ensure prediction accuracy before conducting the parametric study.

Key Findings and Technical Analysis

Load-Bearing Capacity Trends

The parametric analysis reveals clear trends in axial compression performance:

1. Increasing outer tube width significantly increases load-bearing capacity due to greater cross-sectional area and moment of inertia
2. Increasing wall thickness of both tubes enhances capacity through improved confinement and direct load-carrying contribution
3. Higher tensile strength of both inner and outer tubes leads to substantial capacity improvement
4. Higher concrete compressive strength contributes positively to overall column capacity
5. Increasing void ratio reduces capacity, with the optimal void ratio recommended at 0.1 to 0.3

Void Ratio Optimization

The finding that the optimal void ratio ranges from 0.1 to 0.3 is particularly significant from a materials engineering perspective. This range represents the balance between:

• Material economy (lower void ratio means less concrete and less steel)
• Structural efficiency (adequate concrete infill for composite action)
• Confinement effectiveness (sufficient concrete to engage both tubes)

Constitutive Model and Calculation Expression

The authors develop a calculation expression for the axial compression load-bearing capacity of HSCS composite short columns with high prediction accuracy, suitable for engineering practice. The accuracy validation against experimental data demonstrates that the numerical model captures the essential mechanics of the composite system.

Steel Tube Manufacturing Implications

From a pipe fabrication standpoint, this research highlights several important considerations:

• High-strength steel tubes require careful control of heat treatment to achieve the specified tensile strength without sacrificing ductility
• The square tube geometry demands precise corner radius control to avoid stress concentrations
• Wall thickness uniformity is critical for consistent composite action between steel and concrete
• Surface finish of the inner tube surface affects the bond strength with the concrete infill

The selection of appropriate steel grades for both the outer square tube and inner circular tube requires balancing strength requirements against formability during tube manufacturing. High-strength grades (such as Q460 or Q550 per GB/T 1591) may require specific heat treatment schedules to achieve the desired mechanical properties while maintaining adequate toughness for the composite application.

Engineering Practice Integration

The HSCS composite column concept offers several advantages for practical applications:

• The dual-tube configuration provides enhanced confinement compared to single-tube CFST columns
• The square outer tube facilitates frame connections while the circular inner tube optimizes material efficiency
• The void ratio parameter allows design flexibility for different load requirements
• The system can be tailored for seismic applications by selecting appropriate ductility characteristics in the steel tubes

For welding operations at column connections, the high-strength steel grades require preheating and controlled cooling to prevent cracking in the heat-affected zone. The welding procedure specification should account for the elevated carbon equivalent of high-strength grades and include appropriate post-weld heat treatment if required.

Study Insights and Implications

This research demonstrates that the HSCS composite column concept offers a promising alternative to conventional CFST columns with potentially superior load-bearing capacity. The systematic parametric approach provides clear design guidance, particularly regarding the optimal void ratio range. For engineers in our field, the key insight is that the steel tube component quality — including dimensional accuracy, mechanical property uniformity, and surface condition — directly influences the composite system performance. The calculation expressions developed in this study should be validated through full-scale testing before widespread adoption in design codes. Future work should address the behavior of these composite columns under combined loading conditions and seismic loading, where the interaction between the two tube layers becomes even more critical.