Progressive Collapse Resistance of Full-Infill-Wall Concrete-Filled Steel Tube Composite Frames

Literature Overview

This comprehensive study by Wang Jingxuan, Yang Yong, and Sun Yanhao from Lanzhou University of Technology, published in the Chinese Journal of Civil Engineering in 2022, addresses progressive collapse resistance in concrete-filled steel tube (CFST) composite frames with full infill walls. The research was funded by the National Natural Science Foundation of China (grants 52068047 and 51708270) and the Gansu Provincial Youth Science and Technology Fund (20JR5RA437). The work fills an important gap in progressive collapse research by investigating the contribution of non-structural infill walls to the post-failure load-bearing capacity of CFST composite frame structures.

Research Methodology and Experimental Design

The experimental program involved removing the middle column from CFST column to profiled steel plate composite beam frames, followed by monotonic vertical static loading on the remaining structure. This approach simulates the loss of a primary vertical load-bearing member, which is the initiating event in progressive collapse scenarios. The specimens were instrumented with strain gauges at critical sections to capture strain development throughout the loading process. The authors also developed refined finite element models using ABAQUS/Implicit to validate and extend the experimental findings, particularly to investigate the influence of different infill wall opening ratios on collapse resistance.

The progressive collapse resistance mechanism in these structures involves the transition from the initial beam mechanism to the catenary (tension chord) mechanism as displacements increase. The presence of infill walls modifies this transition by providing additional lateral confinement and diaphragm action, which redistributes loads to adjacent structural elements.

Key Findings and Technical Analysis

The load-displacement relationship curves of the full-infill-wall CFST composite frames exhibited four distinct stages: the elastic stage, the elastic-plastic stage, the crack development stage, and the failure stage. The infill walls contributed positively to the collapse resistance capacity but reduced the overall ductility of the structure. This trade-off between strength and ductility is a critical consideration in progressive collapse design, as ductility provides the deformation capacity necessary to prevent sudden collapse initiation.

The finite element modeling approach using ABAQUS/Implicit was validated against experimental results, demonstrating the reliability of the numerical framework for parametric studies. The parametric analysis of different infill wall opening ratios revealed that the opening ratio significantly influences the initial stiffness, peak load, and displacement ductility of the structure. Higher opening ratios generally reduce the beneficial contribution of the infill walls, bringing the structural behavior closer to that of bare CFST composite frames.

Welding and Fabrication Considerations

From a fabrication and welding perspective, CFST composite frames with infill walls present unique challenges. The connection between CFST columns and profiled steel plate composite beams typically involves welded connections, often with bolted end plates or welded shear connectors embedded in the profiled steel plate. The quality of these connections directly influences the catenary mechanism development, as the tension chord action requires reliable load transfer through the beam-column connections.

The welding of CFST columns, particularly at the column splice locations and base connections, must maintain the integrity of the concrete-steel composite action. Any defects in the column welds can compromise the load redistribution capacity that is essential for progressive collapse resistance. The use of full-penetration groove welds with appropriate filler metal selection, such as E7018 or equivalent low-hydrogen electrodes, is critical for maintaining the toughness and ductility of the welded joints.

Engineering Practice Integration

The findings of this study have direct implications for progressive collapse design codes and practice. Current design approaches primarily focus on enhancing the beam mechanism and catenary mechanism capacity of the superstructure beams, often neglecting the contribution of non-structural elements such as infill walls. This research demonstrates that infill walls can provide meaningful contributions to collapse resistance, particularly in the early stages of progressive collapse development. However, the reduction in ductility associated with infill walls must be carefully considered, as insufficient ductility can lead to brittle failure modes that defeat the purpose of progressive collapse design.

In engineering practice, the design of CFST composite frames for progressive collapse resistance should incorporate the following considerations: first, the infill wall contribution should be quantified through detailed analysis rather than ignored; second, the reduction in ductility due to infill walls should be compensated through adequate detailing of beam-column connections; third, the welding quality of all critical connections must be verified through rigorous non-destructive testing to ensure reliable load transfer during the catenary mechanism development.

Study Insights and Reflections

This study represents a significant advancement in progressive collapse research by incorporating the often-overlooked contribution of non-structural elements. The experimental and numerical approaches adopted are rigorous and well-validated, providing a solid foundation for future research. The observation that infill walls increase collapse resistance but reduce ductility highlights the inherent trade-offs in structural design and the need for balanced design approaches. For welding engineers involved in CFST composite frame construction, this research reinforces the importance of maintaining high welding quality standards, as the progressive collapse resistance of the entire structure depends on the reliability of welded connections under extreme loading conditions.