Progressive Collapse Analysis of Steel Tube Concrete Composite Frame with Infill Walls

Literature Overview

The paper by Wang Jingxuan, Yang Yong, and Shen Yajun, published in the Journal of Zhengzhou University (Engineering Science) in 2021, investigates the progressive collapse resistance of steel tube concrete (SRC) composite frames with masonry infill walls. Progressive collapse, also known as disproportionate collapse, refers to the phenomenon where the failure of a single structural element triggers a chain reaction leading to the collapse of the entire structure. This is a critical safety concern for public buildings, and understanding how infill walls influence the collapse resistance of SRC frames is essential for robust structural design. The study employs ABAQUS/Explicit nonlinear dynamic analysis to simulate the collapse process following the sudden removal of a central column, modeling the full range of material behavior including steel, concrete, and masonry infill.

Core Technical Content and Modeling Approach

The numerical model is built using ABAQUS/Explicit, which is particularly suitable for capturing the dynamic, nonlinear behavior during progressive collapse events. The material constitutive models are carefully selected: the steel follows an elastic-perfectly plastic model with strain hardening; the concrete uses a concrete damaged plasticity model; and the masonry infill is modeled with appropriate brittle fracture criteria. The interaction between structural members and the infill wall is modeled through contact constraints that allow for sliding and separation while maintaining compression transfer. The model is validated against experimental data from previous researchers, confirming the accuracy of the simulation approach.

Collapse Mechanism Stages

The study identifies three distinct stages in the progressive collapse process: the beam mechanism stage, the catenary mechanism stage, and the failure stage. During the beam mechanism stage, the adjacent beams redistribute the load from the failed column through flexural action. As the deflection increases, the beams develop axial tension forces and transition into the catenary mechanism, where tensile resistance becomes the dominant load-carrying mechanism. This transition is critical because the catenary mechanism can provide significant additional load capacity, but it requires adequate ductility in the beam connections and sufficient reinforcement to develop the tensile forces.

Influence of Infill Walls on Collapse Resistance

The most significant finding of this study is that masonry infill walls substantially improve the progressive collapse resistance of SRC composite frames. The infill walls act as diagonal struts under lateral displacement, providing additional compressive resistance that reduces the demand on the structural frame. This diagonal strut action is particularly effective during the beam mechanism stage, where the infill wall shares the load redistribution burden with the beams. The study quantifies this improvement by comparing the collapse load and displacement response of frames with and without infill walls, showing that the presence of infill walls can increase the ultimate collapse load by a significant margin.

Comparison of Collapse Resistance with and without Infill Walls

The mechanism of infill wall action is primarily through the formation of diagonal compression struts across the wall panel. As the frame deforms laterally due to column removal, the infill wall develops diagonal cracks and forms a truss-like load path that transfers forces to the surrounding frame elements. This additional load path provides redundancy and helps prevent the collapse from propagating. However, the study also notes that the infill wall action is most effective during the early stages of collapse (beam mechanism stage), and as the collapse progresses into the catenary mechanism stage, the contribution of the infill wall diminishes as the wall panels may have already failed or separated from the frame.

Engineering Practice and Design Recommendations

From a structural engineering practice standpoint, this study provides clear evidence that infill walls should not be neglected in progressive collapse design of SRC composite frames. Traditional design approaches often treat infill walls as non-structural elements, but this study demonstrates that they contribute significantly to the collapse resistance. The design implication is that progressive collapse assessment should include the infill wall contribution, particularly during the beam mechanism stage where the infill wall provides the most benefit. In my engineering experience, many progressive collapse assessments conducted in practice have ignored infill walls, leading to overly conservative structural requirements or, conversely, to inadequate collapse resistance if the infill walls are later removed during renovation.

FMEA Analysis of Progressive Collapse in SRC Frames with Infill Walls

Key Questions and Reflections

A key question that emerges from this study is the long-term reliability of the infill wall contribution to collapse resistance. Infill walls are susceptible to deterioration over time due to environmental exposure, and their contribution may diminish as the wall material degrades. Additionally, the assumption of full composite action between the infill wall and the frame requires proper tie-in details, which may not always be present in existing structures. Another consideration is the effect of partial infill walls, where only some of the bays have infill walls. The load redistribution pattern in such cases may be asymmetric, and the collapse mechanism could be more complex. The study provides valuable insight, but practical design should consider the variability and uncertainty in infill wall properties and their long-term performance.

Study Insights and Conclusions

This paper provides important evidence that masonry infill walls significantly enhance the progressive collapse resistance of steel tube concrete composite frames, particularly during the beam mechanism stage through diagonal strut action. The numerical modeling approach using ABAQUS/Explicit is validated and provides a reliable tool for assessing collapse resistance. From a steel pipe manufacturing perspective, the study reinforces the importance of producing high-quality steel tubes for SRC frames, as the structural performance of the composite frame depends on the integrity and mechanical properties of the steel tube members. Engineers should adopt a performance-based approach to progressive collapse design, incorporating the contribution of infill walls while ensuring that the structural frame itself has adequate redundancy and ductility to resist collapse even if the infill walls are removed or deteriorate over time.