Progressive Collapse Resistance of Square Steel Tube Concrete Column-External Ring Plate Composite Beam Joints

Literature Overview

This 2017 paper published in the Journal of Natural Disasters by Li Tianhao, Wang Wenda, and Wang Jingxuan from Lanzhou University of Technology investigates the progressive collapse resistance of square steel tube concrete (STC) column-external ring plate composite beam joints under middle column failure scenarios. The research employed ABAQUS finite element analysis to simulate the full progressive collapse process and performed parametric studies on key design variables. The work was supported by the National Natural Science Foundation of China (Grant 51268038).

Core Technical Mechanisms

The study identifies six distinct stages in the progressive collapse process of the composite joint:

1. Elastic stage: Initial load redistribution following column removal, with linear elastic response.
2. Elastic-plastic stage: Yielding of steel beam flanges and web, initiation of plastic hinge formation.
3. Arch effect stage: Floor slab develops arch action, providing additional load-carrying capacity through membrane compression forces.
4. Plastic stage: Full plastic hinge development in the steel beam, with significant lateral displacement.
5. Mixed mechanism stage: Transition from flexural to combined flexural-membrane mechanism.
6. Catenary effect stage: Steel reinforcement in the floor slab develops catenary action, providing ultimate tensile resistance through straight-line tension forces.

Key Technical Parameters and Parametric Analysis Results

The study specifically highlights that the floor slab arch effect can enhance the joint's initial load-bearing capacity, while the rebar tie action can strengthen the catenary effect. However, the effectiveness of the tie action depends critically on the shear connectors between the floor slab and the steel beam, making the design and construction quality of this interface a critical factor.

Engineering Practice Implications

For steel pipe and structural fabrication engineers, this study has several practical implications:

• Square steel tube column fabrication: Square steel tube concrete columns require precise fabrication to ensure proper fit-up with the external ring plate joint. The manufacturing tolerances for square tubes, including flatness, straightness, and wall thickness uniformity, directly affect the joint's load transfer efficiency and progressive collapse resistance.
• Welding of external ring plate joints: The external ring plate joint involves critical welds connecting the ring plate to both the column and the beam. These welds must be designed and executed according to high-quality welding procedures, typically requiring full-penetration butt welds with 100% ultrasonic testing (UT) inspection. The weld metal and heat-affected zone properties must match or exceed the base metal toughness, particularly at low temperatures.
• Steel beam section design: The parametric analysis confirms that increasing steel beam strength and section thickness significantly improves collapse resistance. In practice, this means that for progressive collapse-critical connections, engineers should specify heavier section steel beams with higher yield strength grades, such as Q345 or Q390 steel per GB/T 1591, or ASTM A572 Gr. 50/60 equivalent.
• Shear connector installation: The finding that shear connectors are essential for mobilizing the catenary effect underscores the importance of proper installation of headed studs or other shear connectors. In fabrication shops, stud welding must be performed in accordance with AWS D1.1 or ISO 2555, with proper bend tests to verify weld quality.

Finite Element Modeling Considerations

The ABAQUS analysis employed in this study requires careful attention to several modeling aspects:

The accuracy of the numerical model depends heavily on the material constitutive relationships, particularly the concrete damage model parameters and the steel hardening rules. Calibration against experimental data is essential for reliable predictions.

Critical Reflections

The study provides valuable insight into the progressive collapse mechanisms of composite joints, but several limitations should be noted. The analysis is quasi-static, which may not capture dynamic effects during progressive collapse events. The study focuses on middle column failure, which is one specific scenario; other scenarios such as corner column or edge column failure may exhibit different failure modes. Additionally, the study does not address the effect of steel tube concrete column damage or degradation on the joint's collapse resistance, which is relevant for structures subjected to fire, corrosion, or impact damage.

Study Insights and Reference Value

This research contributes to the growing body of knowledge on progressive collapse resistance in steel tube concrete structures. For engineers designing critical infrastructure such as nuclear facilities, military buildings, and high-rise commercial buildings, the findings provide actionable design guidance. The emphasis on the floor slab's role in progressive collapse resistance through arch and catenary effects suggests that the floor slab should be treated as an active structural element in progressive collapse design, rather than merely a gravity load-carrying component. The study reinforces the importance of robust detailing at all connections and the need for redundancy in structural systems.