Axial Compression Performance of Stiffened Square SRC Columns After Fire Exposure

Literature Overview

This paper by Li Xuefeng, Wang Huifeng, and Liu Zhenhui, published in the Journal of Shenyang Jianzhu University (Natural Science Edition) in 2021 (Volume 37, Issue 4), investigates the axial compression performance of stiffened square steel tube concrete (SRC) columns after fire exposure. The research is supported by the National Natural Science Foundation of China (Project 52078310). The study employs finite element analysis using ABAQUS, with model validation based on existing experimental literature, followed by parametric analysis of fire duration, stiffener rib thickness, and steel yield strength effects on post-fire bearing capacity.

Fire Exposure and Post-Fire Performance

The study applies the ISO 834 standard fire curve for thermal exposure, which is the internationally recognized standard fire test regime used in structural fire engineering. The results show that post-fire bearing capacity is significantly reduced compared to ambient temperature conditions, which is expected due to the degradation of both steel and concrete material properties at elevated temperatures.

The observation that stiffener rib thickness and steel yield strength have relatively minor influence on post-fire capacity is notable. This suggests that the primary degradation mechanism is thermal, and that geometric and material strengthening measures provide limited benefit once significant fire exposure has occurred. The fire duration remains the dominant factor controlling residual structural capacity.

Load Sharing Mechanism and Stiffener Effectiveness

The load sharing analysis reveals that the concrete load-sharing ratio follows a non-monotonic pattern, first increasing and then decreasing during the loading process, with a maximum value of 40.11%. This behavior reflects the progressive interaction between the steel tube and concrete core: initially, the steel tube carries most of the load, but as deformation increases, the concrete core becomes more engaged through confinement and arching effects. The eventual decrease indicates concrete crushing and loss of confinement effectiveness.

The presence of stiffener ribs effectively enhances the bearing capacity of SRC columns, and the study concludes that even after fire exposure, stiffened SRC columns retain sufficient safety reserve. This is a critical finding for fire-resistant structural design, as it demonstrates that stiffened configurations provide inherent fire resistance beyond what unstiffened columns can achieve. The stiffeners prevent premature local buckling of the steel tube, maintaining the composite action between steel and concrete for longer durations.

Study Insights and Reflections

The research provides important guidance for the design of fire-resistant SRC columns. The finding that stiffener ribs maintain effectiveness even after fire exposure supports their use in critical structural elements where post-fire integrity is essential for occupant evacuation and firefighting operations. The load sharing analysis provides insight into the progressive degradation mechanism, which can inform the development of performance-based fire design criteria.

Engineers should note that the relatively minor influence of stiffener thickness and steel strength on post-fire capacity implies that optimizing these parameters for ambient temperature performance may not translate to improved fire performance. Instead, fire protection strategies such as intumescent coatings, fire-resistant concrete mixes, or thermal insulation should be prioritized for fire-critical applications.

This study advances the understanding of post-fire behavior of stiffened SRC columns and provides a basis for developing design guidelines that ensure adequate residual capacity after fire exposure. The combination of validated numerical modeling and parametric analysis offers a reliable framework for evaluating fire performance of these structural systems.