Local Buckling Behavior of PBL-Stiffened Rectangular CFST Axial Compression Columns

Literature Overview

This paper by Zhang Ning, Liu Yongjian, and Li Hui (2017), published in the Journal of Architecture and Civil Engineering, investigates the influence of PBL (Perforated Steel Plate) stiffeners on the local buckling performance of rectangular concrete-filled steel tube (CFST) axial compression columns. The study is supported by the National Natural Science Foundation of China (Project No. 51378068) and the Ministry of Transport Construction Science and Technology Project. The authors employ the energy method to derive the buckling coefficient formula for the steel tube, introduce relative stiffness expressions for both PBL and stiffeners, and analyze their interaction on the buckling mode.

Core Technical Content

The research addresses a critical practical problem in structural engineering: how to improve the local stability of rectangular CFST columns through the strategic use of PBL stiffeners. The energy method is applied to derive the steel tube buckling coefficient formula, which serves as the analytical foundation for the entire study. The key innovation lies in introducing relative stiffness calculation formulas for both PBL stiffeners and rib stiffeners, and then analyzing the interaction relationship between these two stiffening mechanisms on the buckling mode.

The paper discusses the ultimate buckling mode of PBL-stiffened steel tubes, the ultimate buckling coefficient, and the maximum allowable relative width-thickness ratio limits. The results demonstrate that PBL stiffeners can significantly improve the local stability of steel tubes. The buckling coefficient k increases with the increase in PBL stiffener stiffness, reaching an ultimate buckling coefficient of 42.68. The PBL connectors can reduce the wavelength of longitudinal plate buckling, while the stiffeners have an opposite effect on this wavelength.

Key Technical Parameters and Results

The findings indicate that after installing PBL stiffeners, the maximum relative width-thickness ratio limit of the steel tube can reach 184, and the strength degradation curve after plate buckling shows a slower decline trend. The strength values gradually improve as the PBL stiffness increases. This represents a substantial improvement over unstiffened rectangular CFST columns, where the width-thickness ratio limits are typically much more restrictive.

Standards and Engineering Practice Implications

From a welding and fabrication perspective, the PBL connector system involves the cutting and welding of perforated steel plates to the interior of the steel tube before concrete filling. The welding quality of these internal connectors is critical to ensuring the structural integrity of the composite member. The PBL stiffeners essentially act as internal shear connectors that transfer stresses between the steel tube and the confined concrete, while simultaneously providing local buckling resistance to the steel plates.

In terms of applicable standards, the design of CFST columns falls under GB 50936-2014 (Code for design of concrete-filled steel tubular structures) and related codes. The width-thickness ratio limits specified in these standards are typically conservative for unstiffened sections. The research findings suggest that with proper PBL stiffener design, significantly higher width-thickness ratios can be tolerated, which has direct implications for material economy and constructability.

Study Insights and Reflections

The paper provides valuable analytical tools for the design of PBL-stiffened CFST columns. The energy method approach offers a systematic framework for understanding how different stiffening mechanisms interact, which is essential for optimizing the stiffener layout and geometry. However, the analytical results should be validated against experimental data for practical design applications. The interaction between PBL connectors and rib stiffeners on buckling wavelength is particularly interesting — the opposing effects suggest that a balanced combination of both stiffening types may be optimal for maximizing the buckling resistance while controlling the buckling mode shape.

For engineering practice, the key takeaway is that PBL stiffeners are an effective and efficient means of enhancing the local buckling resistance of rectangular CFST columns, particularly when large width-thickness ratios are desired. The derived buckling coefficient formulas and width-thickness ratio limits can be directly incorporated into design calculations, provided that the fabrication and welding quality of the PBL connectors are rigorously controlled.