Composite Framed Buildings under Fire-Induced Progressive Collapse: Computational Analysis and Design Recommendations

Abstract

Empirical and scientific evidence suggests that buildings may be susceptible to fire-induced progressive collapse if they are not specifically designed to resist the effects of fire. Although prior studies have shed some light on the problem, there is still a lack of quantitative research on structural robustness in fire, leading to a gap in building codes related to fire-induced progressive collapse. This dissertation aims to address these issues by proposing a comprehensive method for quantifying structural robustness in fire, which integrates the existing standards on structural performance at room temperature and fire protection requirements. Additionally, a macro-element model for beam-to-column connections was developed to offer an accurate analysis at a reasonable computational cost. Test data from experimental studies on moment-resisting structures at room temperature and elevated temperatures were used to validate the appropriateness of the connection model. 2D and 3D macro-element models were developed to explore the robustness of composite steel structures against fire-induced progressive collapse. Sequentially coupled thermal-structural analysis using an explicit dynamic approach in ABAQUS was adopted for the analysis. The elements used in the 3D model include beam-column elements for the steel beams and columns, shell elements for the reinforced concrete slabs, and kinematic coupling constraints for the connections. The 3D model was validated against the experimental data of the Cardington Fire Test 3 and was employed to investigate 10-story composite buildings exposed to various fire scenarios. It was found that failure of the insulation materials determined the time limit of the structure in most cases. Although the buildings were sufficiently designed for progressive collapse at room temperature and one-hour rated fire protection was applied for all steel members, the buildings could only withstand less than an hour of fire. In other words, prescriptive design is insufficient to ensure the robustness in fire. Additionally, several design improvements were explored to study the effectiveness of different structural enhancement strategies. It was found that increasing fire protection applied to the columns or increasing the capacity of the columns was the most effective approach for the moment-resisting framed building considered in this study.