Analysis of Progressive Collapse Mechanism of Steel Tube Concrete Column-Steel Beam Planar Frame

Literature Overview

This paper by Wang Jingxuan and Zhang Chengliang, published in the Journal of Lanzhou University of Technology (2019, Vol. 45, No. 6, pp. 127–132), funded by the National Natural Science Foundation of China (Grant No. 51708270), investigates the progressive collapse resistance of planar frames composed of steel tube concrete (CFST) columns and steel beams. Using ABAQUS finite element analysis, the authors studied the behavior of these frames under central column failure scenarios, examining the influence of different composite beam configurations and axial compression ratios on progressive collapse performance.

Core Technical Content

The fundamental finding is that CFST planar frames undergo a transition from a beam mechanism to a catenary mechanism during progressive collapse. This is consistent with established progressive collapse theory but is validated here specifically for CFST column systems with external ring plate joints.

The study reveals that a reasonable axial compression ratio limit has a positive effect on progressive collapse resistance, particularly during the beam mechanism stage. The presence of wing plates significantly improves initial stiffness, and in-plane reinforcement plays an important role during the catenary mechanism stage.

Technical Interpretation

From a steel tube and welding perspective, the external ring plate joint is a critical connection detail. The ring plate is typically attached to the CFST column by fillet or full-penetration welds, and the quality of these welds directly affects the frame's ability to redistribute loads during progressive collapse scenarios. The stress concentrations at the ring plate-to-tube interface represent potential initiation sites for crack formation under large displacement demands.

The finite element model must accurately capture the concrete-steel interaction within the CFST column, the weld behavior at the ring plate connections, and the composite beam behavior. The nonlinear material models for both steel and concrete, along with appropriate contact definitions, are essential for reliable predictions.

Engineering Practice Implications

For structural engineers designing CFST frames in high-rise or critical infrastructure applications, this study provides several actionable insights:

1. Progressive collapse analysis should be incorporated into the design of CFST frames, particularly for columns that could be subject to blast, impact, or construction-stage failures.
2. The axial compression ratio should be carefully controlled to balance gravity load capacity with progressive collapse resistance.
3. Connection design must account for large rotation demands during the catenary mechanism stage.
4. Wing plate reinforcement of composite beams is an effective strategy for improving initial stiffness and delaying the onset of catenary action.

The weld quality at ring plate connections deserves particular attention. Full-penetration butt welds with appropriate weld metal chemistry (matching the base steel grade) and proper post-weld treatment are recommended to ensure ductile connection behavior under large deformation conditions.

Study Insights

This paper contributes to the growing body of knowledge on progressive collapse resistance of CFST structures. The identification of the beam-to-catenary mechanism transition and the quantification of parameter effects provide practical design guidance. The emphasis on connection behavior highlights that progressive collapse resistance is not solely a member property but is fundamentally dependent on the integrity and ductility of structural connections.