Review of Special-Shaped CFST Columns and Beam-Column Joint Configurations

Literature Overview

This review paper, published in the Journal of Beijing University of Technology (Vol. 47, No. 9, 2021, pp. 1083-1094) by Ye Quanxi, Hao Fang, Xue Bingyong, Li Tongdong, Zhu Lin, and Liu Liyue from Hebei Water Resources and Electric Power University, Tsinghua University, and the Hebei Provincial Key Laboratory of Geotechnical Engineering Safety and Deformation Control, provides a comprehensive overview of the development and current state of research on special-shaped concrete-filled steel tube (CFST) columns and their associated beam-column joints. The work was supported by the Hebei Provincial Higher Education Science Research Plan Young Top-notch Talent Project (BJ2018062) and the Hebei Provincial Higher Education Science Research Plan Project (ZC2016142).

Classification of Special-Shaped CFST Columns

The review identifies four primary categories of special-shaped CFST columns based on two fundamental design philosophies: enhancing the lateral restraint that the outer steel tube provides to the internal concrete, and improving the stability of individual steel plate elements within the column limb. This classification framework is particularly useful for engineers who need to select an appropriate column type for a given structural application.

The multi-chamber CFST column is particularly noteworthy because it divides the internal concrete into multiple independent compartments, each of which is individually confined by the surrounding steel. This design approach can significantly improve the ductility and energy dissipation capacity of the column under seismic loading, as each chamber can deform independently without compromising the integrity of the others.

Beam-Column Joint Innovations

The review classifies beam-column joints for special-shaped CFST columns into two broad categories based on the relative position of the load-transmitting member with respect to the column limb steel tube: internal type (load-transmitting member inside the steel tube) and external type (load-transmitting member outside the steel tube).

The internal type joints are generally preferred because they allow the steel tube to provide lateral restraint to the beam connection, enhancing the joint's ductility and load-carrying capacity. However, internal joints present significant fabrication challenges, including the need for precise welding inside confined spaces and the difficulty of ensuring adequate weld quality and accessibility for inspection.

The external type joints, while easier to fabricate and inspect, may not fully exploit the confining effect of the steel tube and may require additional structural elements to ensure adequate joint strength and ductility. The review identifies several innovative joint configurations, including through-bolt connections and internal diaphragm connections, which offer different trade-offs between fabrication complexity and structural performance.

Research Gaps and Future Directions

The review identifies several critical areas where further research is needed. First, the seismic performance of special-shaped CFST columns under multi-directional loading has not been adequately studied, which is a significant concern given that real earthquakes produce complex, multi-axial loading patterns. Second, the long-term durability of special-shaped CFST columns in aggressive environments, particularly regarding corrosion of the internal steel components and the concrete-steel interface, requires further investigation.

Third, the review notes that the interaction between the internal restraint elements (such as tie rods and stiffeners) and the surrounding concrete under cyclic loading has not been fully characterised. This interaction is critical because it governs the column's ductility and energy dissipation capacity, which are the primary design parameters for seismic-resistant structures.

Fourth, the fabrication and welding quality of special-shaped CFST columns remains a significant challenge. The complex geometry of these columns, with their multiple internal chambers, tie rods, and stiffeners, creates numerous weld joints that must be carefully designed, fabricated, and inspected. Engineers must develop and validate welding procedures that can accommodate the confined geometries and ensure consistent weld quality throughout the fabrication process.

Engineering Practice Implications

For engineers involved in the design and fabrication of special-shaped CFST columns, this review provides a valuable framework for selecting appropriate column types and joint configurations based on the specific structural requirements of the project. The classification of columns into four types based on two fundamental design philosophies offers a clear decision-making framework that can be applied to a wide range of structural applications, from high-rise buildings to industrial facilities and infrastructure projects.

The review also highlights the importance of considering fabrication feasibility and weldability when selecting a column type. Engineers should engage with fabrication specialists early in the design process to ensure that the selected column configuration can be manufactured to the required quality standards, particularly for complex joints involving multiple steel components and internal restraint elements.

In conclusion, this review provides a comprehensive and well-organised overview of the current state of research on special-shaped CFST columns and their beam-column joints, identifying key innovations, classifying existing solutions, and highlighting critical areas for future research, thereby serving as an essential reference for engineers and researchers working in the field of composite structural engineering.