Progressive Collapse Resistance Analysis of CHS-CFT Column-H Steel Beam Annular Plate Joints with Different Configurations

Literature Overview

This paper by Shi Yanli, Li Tianhao, and Wang Wenda from Lanzhou University of Technology, published in Journal of Natural Disasters (2017, Vol. 26, No. 3, pp. 28-38), investigates the progressive collapse resistance of circular hollow section concrete-filled steel tube (CHS-CFT) columns connected to H-steel beams through external annular plate joints. Using ABAQUS finite element analysis, the authors simulate the complete progressive collapse process under a central column failure scenario and systematically evaluate how joint configuration variations influence collapse resistance performance.

Core Technical Findings

The study addresses a critical structural safety concern: the ability of a building frame to prevent progressive collapse following the sudden loss of a primary structural element. The annular plate joint is a common connection type for CFT columns to steel beams, and its behavior under extreme loading conditions is essential for ensuring structural robustness.

Three Configuration Variables Analyzed

The research identifies three key configuration variables that influence progressive collapse performance:

Annular Plate Extension Dimension

The annular plate extends radially from the CHS column surface to provide a bearing surface for the beam connections. The study found that varying the extension dimension shifts the location of plastic hinge formation but does not significantly improve overall progressive collapse resistance. This is an important finding because it suggests that the annular plate dimension should be optimized for constructability and economy rather than solely for collapse resistance enhancement.

Beam Configuration and Catenary Action

The catenary action mechanism is a key post-yield load redistribution mechanism in progressive collapse resistance. The beam configuration directly influences how effectively this mechanism develops:

• Expanded-flange joints: Recommended because the expanded flange provides additional load path and enhances the beam's ability to develop catenary action through tensile membrane effects
• Reduced-flange joints: Not recommended because flange reduction weakens the tension resistance needed for catenary action development
• Web-opening joints: Acceptable when clear height constraints exist, though with some reduction in collapse resistance capacity

Joint Core Zone and Weld Integrity

The joint core zone is the region where the beam, annular plate, and column intersect. The configuration of this zone critically affects the welding integrity at the beam-column connection. Brittle fracture of welds in this zone can initiate progressive collapse even before significant catenary action develops. The recommended gusset plate reinforcement approach provides additional load path continuity and reduces stress concentrations at critical weld locations.

Engineering Practice Integration

Retrofitting Existing Structures

The paper provides valuable guidance for retrofitting existing buildings to improve progressive collapse resistance. The recommendation to weld horizontal stiffeners or bracket supports (明牛腿) to existing structures is particularly practical because:

• It can be implemented without major structural modifications
• It provides significant improvement in progressive collapse performance
• It is compatible with most existing joint configurations
• It requires minimal disruption to building occupants

Design Implications for New Construction

For new construction projects involving CHS-CFT columns with annular plate joints, the following design priorities should be considered:

1. Beam configuration selection: Prioritize expanded-flange connections for maximum catenary action potential
2. Joint core reinforcement: Always incorporate gusset plate reinforcement to prevent brittle weld failure
3. Annular plate sizing: Optimize for fabrication economy and constructability rather than collapse resistance
4. Weld quality control: Ensure high-quality welding at beam-column connections, particularly at the joint core zone

Welding Process Considerations

From a welding engineering perspective, the joint core zone presents significant challenges:

• Multi-layer multi-pass welding is required to fill the joint geometry
• Thermal distortion must be controlled to maintain joint alignment
• Heat-affected zone properties must be managed to prevent brittle fracture susceptibility
• Post-weld heat treatment may be required for high-strength steels

The recommendation against reduced-flange joints also has implications for welding sequence and access. Reduced flange connections create complex geometries that are difficult to weld and inspect, increasing the risk of weld defects.

Key Reflections and Study Insights

The systematic parametric study approach adopted in this research is commendable, as it isolates the influence of individual configuration variables on progressive collapse performance. The finding that annular plate extension dimension has minimal effect on collapse resistance is counterintuitive but practically useful, as it allows designers to optimize this dimension for other objectives.

The emphasis on catenary action as the primary progressive collapse resistance mechanism is well-founded. In the post-yield phase following column failure, the beams must develop sufficient tensile resistance to form a catenary that spans the gap left by the failed column. The beam configuration directly controls this capability, making it the most critical design variable.

One area that warrants further investigation is the interaction between the three configuration variables. The study analyzes each variable independently, but in practice, they interact in complex ways. For example, the effectiveness of gusset plate reinforcement may depend on the beam configuration selected.

Reference Value and Outlook

This research provides actionable design guidance for engineers working with CHS-CFT column systems. The recommendations are practical and implementable, making them immediately applicable to both new construction and retrofitting projects. Future research should investigate the effects of material properties (steel grade, concrete strength) on progressive collapse performance, extend the analysis to multi-story frames, and develop simplified design equations that incorporate the configuration factors identified in this study. The findings also highlight the importance of welding quality and joint detail design in ensuring structural robustness under extreme loading conditions.