Web Buckling Performance of Carbon Steel Square Hollow Section Tubes

Literature Overview

This comprehensive experimental study by Chen Yu, Wang Chaoyang, Guo Xiaoying, Yin Hang, Xu Chang, and Guo Xiuquan investigates the web buckling behavior of carbon steel square hollow section (SHS) tubes under concentrated loads. Published in "China Civil Engineering Journal" (2015, Vol. 48, Issue 2, pp. 34-43), the research was conducted at Yangtze University and Huaqiao University with funding from the National Natural Science Foundation of China (Grants 51278209, 51478047). The study involved 50 test specimens with varying boundary conditions, loading configurations, bearing plate widths, and section heights.

Core Technical Content

The research addresses a critical structural design issue: the web buckling capacity of square hollow section tubes when subjected to concentrated forces, such as those transmitted from beams through connections. This is a fundamental concern in steel structure design where SHS tubes are used as columns or girders.

Test Configuration and Parameters

Failure Modes

The study identified distinct failure modes depending on the loading position:

• End concentrated loads: Web buckling initiates near the loaded corner, with plastic deformation spreading toward the adjacent flanges
• Internal concentrated loads: Web buckling develops from the load application point, with plastic hinge formation in the web mid-region

Key Experimental Results

Effect of Bearing Plate Width:

• Ultimate buckling capacity increases with increasing bearing plate width
• For bearing plate width of 50 mm and 100 mm: maximum capacity achieved at web thickness-to-height ratio of 18
• For bearing plate width of 150 mm: maximum capacity achieved at web thickness-to-height ratio of 12.55
• Minimum capacity observed at web thickness-to-height ratio of 24.67

Effect of Loading Configuration:

Strain Distribution: Strain measurement points in the mid-web region all entered the plastic range, ultimately forming plastic hinge zones, confirming the ductile nature of web buckling failure in carbon steel SHS tubes.

Standards Comparison and Design Implications

A critical finding of this study is the comparison between experimental results and existing design codes:

This finding has significant implications for structural safety and economy:

• The Chinese design code may lead to unsafe designs for SHS tube web buckling checks, potentially resulting in structural failures under concentrated loads
• The European code, while safe, leads to unnecessarily conservative designs that increase material usage and cost
• The proposed formula offers a balanced approach that accurately predicts the actual buckling capacity

Finite Element Verification

The FEA models developed in this study successfully reproduced:

• The experimental failure modes (web buckling patterns)
• The ultimate load-bearing capacities
• The load-displacement curve shapes

This confirms the reliability of FEA as a tool for predicting web buckling behavior and supports the use of numerical methods for design verification when code-based calculations are unavailable or questionable.

Engineering Practice Insights

From a steel pipe manufacturing and structural design perspective:

• The web thickness-to-height ratio is the most critical geometric parameter governing buckling capacity, directly affecting the slenderness of the web panel
• The optimal thickness-to-height ratio depends on the bearing plate width, meaning that connection design must be integrated with section selection
• Internal loading configurations provide higher capacities than end loading, suggesting that load introduction points should be positioned away from member ends where possible
• The formation of plastic hinge zones indicates that these members possess significant ductility reserve, which is beneficial for seismic design but must be accounted for in serviceability limit state checks

Key Questions and Reflections

1. How do residual stresses from the manufacturing process (roll forming or welding) of SHS tubes influence the web buckling capacity?
2. What is the effect of surface defects, such as dents or weld imperfections, on the initiation of web buckling?
3. How does the proposed formula perform for other cross-sectional shapes (rectangular, circular) or higher strength steel grades?
4. What are the implications for connection design when the code-based calculation is found to be unconservative?

Study Insights and Implications

This study provides essential experimental data that challenges existing design code provisions for SHS tube web buckling. The finding that the Chinese code is unconservative represents a potential safety concern that warrants attention from code committees and practicing engineers. The proposed formula offers a practical alternative that balances safety and economy. For steel pipe manufacturers, understanding the web buckling behavior is crucial for specifying appropriate wall thicknesses and for advising structural designers on the capacity of their products under concentrated loads. The comprehensive experimental database of 50 specimens provides a valuable resource for future code calibration and research into more complex loading scenarios, such as combined axial force and concentrated load, which is common in real structural applications.