Static Performance Analysis of Rectangular Steel Tube Truss with Concrete-Filled Compression Chord Tubes

Literature Overview

The paper by Liu Yongjian et al. (2008), published in Journal of Architecture and Civil Engineering (Vol. 25, No. 4, pp. 65-72), investigates the static performance of rectangular steel tube trusses with concrete-filled compression chord tubes. Supported by the National Western Transportation Construction Science and Technology Project (2006318812112), the Ministry of Transport Applied Basic Research Plan (2006319812130), and the Ministry of Education New Century Excellent Talent Support Program (NCET-06-0855), the research was conducted by Chang'an University Highway College and Jiangsu Provincial Transportation Science Research Institute.

Finite Element Analysis Methodology

The study employed nonlinear finite element analysis considering both material nonlinearity and geometric nonlinearity. The analysis examined:

• Stress and deformation distribution under nodal loading
• Plastic development and propagation
• Failure modes and ultimate load capacity
• Comparison between empty tube and concrete-filled tube configurations

The rectangular steel tube truss was modeled with concrete filling applied only to the compression chord tubes, while tension chord tubes remained unfilled. This selective filling strategy optimizes material usage while enhancing structural performance.

Key Findings

The critical finding is that the empty compression tube node represents the capacity bottleneck of the entire truss system. The failure mode is characterized by excessive plastic deformation at the empty tube node, which leads to premature structural failure.

Technical Discussion

From a steel structure design perspective, several important aspects emerge:

1. Stress concentration at nodes: Rectangular steel tube truss nodes inherently have stress concentrations due to geometric discontinuities. The empty tube nodes exhibit particularly severe stress concentrations that initiate plastic deformation at relatively low load levels.
2. Concrete confinement effect: Filling compression tubes with concrete provides lateral confinement that:

• Increases the compressive strength of the steel tube
• Delays local buckling
• Reduces stress concentration effects
• Improves overall ductility

1. Selective filling optimization: Filling only compression tubes with concrete is an efficient approach because:

• Compression members are more susceptible to buckling
• Tension members do not benefit significantly from concrete filling
• Material cost is reduced while performance is enhanced

1. Nonlinear behavior: The consideration of both material and geometric nonlinearity is essential for accurate prediction of truss behavior, particularly near the ultimate limit state where large deformations and extensive plasticity develop.

Engineering Practice Implications

For engineers designing steel tube truss structures:

• Empty compression tube nodes should be identified as critical weak points requiring careful design
• Concrete filling of compression members significantly improves structural performance and should be considered for critical truss applications
• The "bottleneck" concept is important — the overall truss capacity is governed by the weakest component, not the average capacity
• Nonlinear analysis is essential for accurate assessment of steel tube truss behavior, particularly for seismic and impact loading applications

The study provides valuable guidance for optimizing steel tube truss designs by strategically applying concrete filling to compression members. This approach can significantly improve structural efficiency while maintaining constructability and cost-effectiveness.

Study Insights

This research highlights the importance of understanding component-level behavior in determining overall structural performance. The identification of empty compression tube nodes as the capacity bottleneck demonstrates that structural optimization requires attention to local behavior, not just global analysis. The concrete filling strategy represents a practical engineering solution that leverages the composite behavior of steel and concrete to enhance structural performance. For highway and bridge engineering applications, where steel tube trusses are increasingly used for their lightweight and constructable advantages, this research provides important design guidance for achieving optimal structural performance through selective composite design.