Finite Element Analysis of High-Strength Square Steel Tube Concrete Column with Sleeve Ring Plate Joint

Literature Overview

This 2021 paper by Li Guochang, Liu Xu, Zha Xiaoxiong, and Zhou Guangyi presents a novel beam-column joint design for high-strength square concrete-filled steel tube (CFST) columns connected to steel beams. The sleeve ring plate joint addresses two specific deficiencies identified in conventional connections: the separation between T-type connectors and the column wall under load, and the insufficient contribution of external ring plates to joint bearing capacity. The authors employ ABAQUS finite element analysis to investigate the low-cycle loading behavior of this new joint type, examining the influence of axial compression ratio, beam-to-column flexural capacity ratio, sleeve height, and sleeve thickness.

Joint Design Philosophy and Technical Innovation

The sleeve ring plate joint represents a significant departure from conventional CFST column connections. Traditional approaches to connecting steel beams to square CFST columns include internal diaphragms, external ring plates, and through-bolts, each with inherent limitations. Internal diaphragms require access to the column interior during construction, which becomes impractical when the concrete is already placed. External ring plates, while constructible, often fail to develop their full capacity due to the lack of effective load transfer from the beam to the ring plate.

The sleeve ring plate concept introduces an intermediate sleeve element that bridges the gap between the beam end and the column wall, creating a more continuous load path. The sleeve is designed to engage both the column wall and the beam end plate, distributing the concentrated beam forces over a larger area of the column wall and reducing the risk of local buckling or connector pullout.

Parametric Study Results

The parametric study reveals several important design guidelines:

The paper identifies the sleeve ring plate joint as a semi-rigid connection with good seismic performance and energy dissipation capacity. The semi-rigid classification is important for structural analysis, as it requires moment-rotation (M-θ) curves to be incorporated into the frame analysis model rather than assuming either fully rigid or fully pinned behavior.

The finding that changing the beam-to-column flexural capacity ratio through material strength modification affects the failure mode and seismic performance is particularly significant. When the beam flexural capacity is significantly lower than the column capacity, the joint behaves as a ductile beam-hinge system with the beam yielding in controlled plastic deformation. Conversely, when the column flexural capacity is reduced relative to the beam, the joint may experience premature column wall failure or sleeve buckling, leading to a more brittle failure mode.

Finite Element Modeling Considerations

The ABAQUS-based FE analysis in this paper incorporates several critical modeling aspects:

• Material nonlinearity for both steel and concrete using appropriate constitutive models
• Geometric nonlinearity to capture large deformation effects during low-cycle loading
• Contact interaction between the sleeve, column wall, and beam end plate
• Cyclic loading protocol simulating seismic conditions
• Concrete damage model accounting for cracking and crushing

The accuracy of the FE model depends critically on the contact formulation and the friction coefficient assumed between the sleeve and column wall. Insufficient friction leads to slip and separation, while excessive friction may overestimate the joint stiffness. Engineers should calibrate the friction coefficient based on surface preparation and welding quality at the sleeve-column interface.

Engineering Practice Implications

The recommended parameter ranges provide practical design guidelines for engineers specifying sleeve ring plate joints in seismic design. The axial compression ratio range of 0.4–0.6 aligns with general seismic design philosophy of limiting column axial loads to preserve ductility. However, in practice, the actual axial load on a CFST column is determined by gravity loads and seismic demands, and may exceed the recommended range in tall buildings or structures with heavy roof loads.

The sleeve dimensions (height 100–200 mm, thickness 6–10 mm) are relatively modest and should be readily achievable in fabrication. The sleeve can be fabricated as a separate component and welded to the column wall during construction, or it can be integrated into the column wall fabrication process. The key fabrication requirement is ensuring full-penetration welds between the sleeve and column wall to develop the required load transfer capacity.

From a welding quality control perspective, the sleeve-column wall weld is a critical detail that should be inspected using non-destructive testing (NDT) methods such as ultrasonic testing (UT) or phased array ultrasonic testing (PAUT). Incomplete weld penetration or lack of fusion at the sleeve-column interface can significantly reduce the joint capacity and ductility.

Key Questions and Reflections

The paper does not address the long-term durability of the sleeve ring plate joint under cyclic loading and environmental exposure. In seismic design, the joint must survive multiple loading cycles without progressive deterioration. Fatigue cracking at the sleeve weld toe or at the beam-to-sleeve fillet weld is a potential concern that requires further investigation through fatigue testing or fracture mechanics analysis.

Additionally, the paper focuses on the joint behavior under low-cycle quasi-static loading, which simulates the effects of a single major earthquake. The behavior under repeated moderate seismic events, which may be more common in practice, is not addressed. The accumulation of damage from multiple seismic events could affect the joint's residual capacity and post-earthquake functionality.

Study Insights and Implications

The sleeve ring plate joint concept represents a practical innovation that addresses real deficiencies in conventional CFST column connections. The finite element analysis provides a systematic basis for design recommendations, and the parametric study offers clear guidance on key design parameters. The classification of the joint as semi-rigid with good seismic performance positions it as a viable alternative for moment-resisting frame systems using CFST columns.

The broader implication is that connection design in CFST structures requires careful attention to the load transfer mechanisms between the beam, the column wall, and any intermediate elements. The sleeve ring plate concept demonstrates that introducing a well-designed intermediate element can significantly improve joint performance by creating a more effective load path and distributing stresses more uniformly. This principle can be extended to other connection types and structural systems.