Seismic Performance of Rectangular Concrete-Filled Steel Tube Column-Steel Beam Joints

Literature Overview

This study by Jin Gang, Ding Jiemin, and Chen Jianbin from the Architectural Design and Research Institute of Tongji University, published in Building Structures in 2007, presents the results of low-cycle reversed loading tests on nine joint specimens connecting rectangular concrete-filled steel tube (CFST) columns with steel beams. The research investigates the seismic performance of three joint types: internal diaphragm joints, anchor bolt joints, and T-shaped joints, with emphasis on the influence of steel ratio and column wall thickness on joint behavior.

Experimental Results and Key Findings

The nine joint specimens demonstrated good elastoplastic deformation capacity and energy dissipation capability, with full hysteresis loops indicating stable energy absorption under cyclic loading. At maximum bearing capacity, most specimens exhibited column rotation angles (story drift ratios) exceeding 1/100, which is a critical seismic performance threshold. When bearing capacity degraded, the hysteresis loops did not show significant pinching, indicating that the joints maintained stable load-carrying capacity even after entering the plastic range.

The internal diaphragm joint demonstrated significantly higher bearing capacity compared to the anchor bolt joint, with the steel ratio and column wall thickness being the dominant factors. However, the internal diaphragm joint exhibited lower ductility than the anchor bolt joint. The T-shaped joint showed better compression-bending performance than tension-bending performance, which is an important consideration for seismic design where asymmetric loading can occur.

Finite Element Analysis and Design Implications

ANSYS finite element analysis was conducted to simulate and verify the experimental results, providing additional insight into the stress distribution and failure mechanisms within the joint. The numerical analysis confirmed the experimental observations and provided a basis for extrapolating the results to different joint geometries and loading conditions.

From a steel pipe manufacturing and structural engineering perspective, the column wall thickness is a critical parameter that directly affects joint performance. Thicker-walled CFST columns provide greater resistance to local buckling and improved load transfer capacity at the joint region. The steel ratio, defined as the ratio of steel cross-sectional area to total cross-sectional area, is another key parameter that influences both the bearing capacity and the ductility of the joint. Engineers must carefully balance these parameters to achieve an optimal combination of strength and ductility for seismic applications.

Engineering Practice and Seismic Design Considerations

The finding that internal diaphragm joints offer higher bearing capacity but lower ductility, while anchor bolt joints provide better ductility, has direct implications for seismic design strategy. In high-seismicity regions, ductility is often prioritized over strength, suggesting that anchor bolt joints may be preferred for critical structural elements. However, in regions with moderate seismic demand, the higher bearing capacity of internal diaphragm joints may be acceptable if the reduced ductility is compensated through other means, such as increased column wall thickness or additional reinforcement.

The T-shaped joint's asymmetric behavior under compression-bending versus tension-bending loading highlights the importance of considering loading direction in seismic design. In practice, this means that T-shaped joints should be designed with additional attention to the tension-bending case, where performance is weaker.

Study Insights and Implications

The research provides valuable experimental data and analytical insights into the seismic behavior of CFST column-steel beam joints, which are critical components in moment-resisting frames. The comprehensive evaluation of three joint types under low-cycle reversed loading offers engineers a basis for joint selection based on the specific seismic design requirements of a project. The combination of experimental testing and finite element analysis provides a robust validation framework that enhances confidence in the design recommendations. For steel pipe manufacturers and structural engineers, this study underscores the importance of column wall thickness and steel ratio as key parameters in CFST joint design, and highlights the trade-off between bearing capacity and ductility that must be carefully managed in seismic design.