Fire is one of the extreme loading events that a building may experience during its service life and can induce severe consequences on the safety of its occupants, first responders, and the structure. Recent fire incidents have clearly shown that steel framed buildings are vulnerable to progressive collapse under severe fire conditions, if not duly considered in the design. The progressive collapse in steel framed buildings initiates with the onset of temperature-induced instabilities at a local or global level, which in turn can lead to the partial or complete collapse of the structure. Despite fire being a severe hazard, the current practice does not have specific recommendations or guidance to evaluate the fire-induced progressive collapse in critical buildings. This is unlike other loading events such as blasts, earthquakes, etc. Further, the current fire design philosophy of steel structures is primarily based on a member (or section) level behavior and does not account for several critical factors, including some of the temperature-induced instabilities. To overcome some of the knowledge gaps, a series of advanced simulations are carried out for tracing the fire-induced collapse in steel framed buildings. To establish the connection between evacuation strategies (times) and structural stability under fire, a set of evacuation simulations is undertaken to evaluate the effect of varying egress parameters on the emergency evacuation process in a high-rise building. In addition, the influence of incorporating situational awareness during an emergency evacuation is quantified. These evacuation strategies and times are to be considered, together with the fire-induced progressive collapse timelines, for achieving the required fire safety in critical buildings. Furthermore, for facilitating complete evacuation and efficient firefighting operations, stability of the structure is to be maintained and any chance of fire-induced collapse is to be minimized. Evaluating progressive collapse under fire conditions is highly complex and requires advanced analysis. For this purpose, a comprehensive finite element-based model is developed in ABAQUS to trace the overall response of a steel framed building under fire exposure, including the onset of instabilities leading to the progressive collapse. The developed model specifically accounts for high-temperature material properties and creep effects, geometric nonlinearity, altering load paths, connections, fire spread, local buckling effects, and realistic failure limit states. The model is validated by comparing the thermal and structural response predictions against the published test data at the member level (steel columns) and system level (steel framed structures). The validated model is applied to carry out a set of parametric studies on a ten-story braced framed building to quantify the influence of various fire, material, and structural parameters on the onset of fire-induced collapse in steel framed buildings. Results from the parametric studies indicate that the severity of the fire scenario, including the location and extent of burning, fire spread, varying load paths, and temperature-induced local instabilities have a significant influence on the onset of fire-induced progressive collapse. Moreover, accounting for the full effects of high-temperature creep in the fire-induced progressive collapse analysis is needed to obtain realistic failure times under severe to very intense fire exposure. Results from the parametric studies are used to propose guidelines for mitigating fire-induced collapse in critical buildings. Specific recommendations are provided for the treatment of high-temperature creep and local instabilities in the fire resistance analysis of steel structures. The proposed approach for advanced analysis, together with the design recommendations, can be utilized to minimize the onset of fire-induced collapse in critical steel framed buildings.
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