Axial Compression Performance of Lattice Steel Skeleton Steel Tube Concrete Members

Literature Overview

This paper by Wang Xiantie, Li Bofan, Hou Xinyu, Han Junk, and Zhu Binrong from Xi'an University of Architecture and Technology investigates the axial compression performance of steel tube concrete (SRC) members with internal lattice steel skeleton reinforcement. Published in the Journal of Hunan University (Natural Science Edition) in 2022, the research was supported by the National Natural Science Foundation (Grant No. 51678474). The study systematically examines the effects of longitudinal stiffening ribs and lattice steel skeleton on SRC member performance through experimental testing and finite element analysis.

Core Technical Approach

The research employs a comprehensive experimental and analytical approach:

1. Experimental program: 4 groups of 8 specimens with varying internal configurations
2. Variable parameters: Presence/absence of longitudinal stiffening ribs and lattice steel skeleton
3. Testing method: Axial compression tests to failure
4. Numerical analysis: Full-process FEA simulation using ABAQUS
5. Design formula development: Axial compression capacity calculation formula for lattice steel skeleton SRC members

Key Technical Parameters and Findings

Interpretation of Technical Points

The "core column" mechanism identified in this research provides a fundamental understanding of how internal reinforcement enhances SRC member performance:

1. Core column formation: The lattice steel skeleton and internal concrete form a small "core column" within the larger SRC member.
2. Crack suppression: The core column delays or inhibits crack development in the core concrete by providing additional confinement.
3. Load capacity enhancement: The combined effect of the core column and the outer steel tube confinement creates a synergistic strengthening mechanism.
4. Ductility improvement: The internal reinforcement system provides additional deformation capacity before final failure.

The progressive capacity increases (4.65% → 10.53% → 21.12%) demonstrate that the reinforcement systems work additively but with some synergy between the stiffening ribs and lattice skeleton. The combined configuration provides more than the simple sum of individual contributions, suggesting interaction effects between the reinforcement systems.

Engineering Practice Integration

From a steel pipe manufacturing and welding perspective, this research has important implications for the fabrication of reinforced SRC members:

Lattice steel skeleton fabrication requirements:

Welding sequence for lattice skeleton installation:

1. Assemble lattice skeleton on flat ground with minimum distortion
2. Weld lattice skeleton to internal support structure (symmetric sequence)
3. Insert lattice skeleton assembly into outer steel tube
4. Weld stiffening ribs to inner tube surface (balanced sequence)
5. Close tube ends with end plates (symmetric welding)
6. Apply PWHT if required by material specification

Quality control considerations:

• The lattice skeleton joints are critical for overall performance; all critical joints require 100% UT inspection
• Residual stress from lattice skeleton welding should be measured and compared with allowable limits
• The interface between lattice skeleton and surrounding concrete requires careful consideration of bond strength; surface preparation of steel members before concrete placement is essential
• Weld distortion of the outer tube during lattice skeleton attachment welding must be controlled to maintain tube geometry within tolerance

Design formula validation: The developed axial compression capacity formula provides a practical design tool. Engineers should note that:

• The formula is based on experimental data from specific specimen configurations
• Application to different geometries requires appropriate scaling and verification
• The formula results are generally conservative (on the safe side), which is appropriate for structural design
• The formula should be used in conjunction with FEA for critical applications

Study Insights and Implications

The research provides several important insights for engineering practice:

1. Cost-effective strengthening: The lattice steel skeleton provides significant capacity enhancement (10.53%) with relatively modest additional steel usage. This makes it an economical strengthening option for existing SRC members or for new design optimization.
2. Synergistic reinforcement: The combined use of stiffening ribs and lattice skeleton provides 21.12% capacity increase, demonstrating that multiple reinforcement strategies should be considered together rather than in isolation.
3. Failure mode consistency: The observation that all specimens fail by overall buckling with varying degrees of outer tube bulging indicates that the reinforcement systems enhance capacity without fundamentally changing the failure mechanism. This consistency is beneficial for design predictability.
4. FEA methodology validation: The good agreement between FEA and experimental results validates the numerical modeling approach for use in design optimization and performance prediction. Engineers can use FEA to evaluate different reinforcement configurations without extensive physical testing.
5. Core column concept: The identification of the "core column" mechanism provides a physical basis for understanding and predicting the behavior of reinforced SRC members. This conceptual framework can be extended to other reinforcement configurations and loading conditions.

Reference Value and Outlook

This research contributes valuable experimental and analytical data for the design of reinforced SRC members. The developed capacity formula and validated FEA methodology provide practical tools for engineers. Future research directions include:

• Extension to eccentric compression and bending loading conditions
• Investigation of seismic (cyclic loading) performance of lattice steel skeleton SRC members
• Development of simplified design procedures for practical engineering application
• Long-term performance assessment including creep, shrinkage, and fatigue effects
• Optimization of lattice skeleton geometry and material properties for specific applications
• Integration with performance-based design methodology for SRC structures

The findings have particular relevance for the design of SRC columns in high-rise buildings, bridges, and industrial structures where enhanced axial capacity and ductility are required. As SRC technology continues to advance, the systematic understanding of reinforcement effectiveness provided by this research will contribute to more efficient and economical structural designs. The lattice steel skeleton concept represents a promising direction for enhancing SRC member performance without significantly increasing material usage or fabrication complexity.