Role of Transient Creep in Fire Induced Progressive Collapse of Steel Framed Buildings

Fire in steel framed buildings can affect the stability of structural system at local, member or system level and in extreme cases may lead to progressive collapse. At stages close to instability (or failure), steel members experience a considerable amount of temperature induced transient creep strain, which can affect the deformations (at member and system levels), and in turn, the stability of the structure. This paper examines the influence of temperature induced transient creep on the fire response of steel framed building including potential collapse. A three-dimensional finite element model is developed in ABAQUS to trace the temperature induced transient creep effects in steel framed structures subjected to fire exposure. The transient creep strain that develops under fire conditions is explicitly accounted for in the fire resistance analysis, in addition to temperature dependent material properties and nonlinearity. The developed model is applied to predict the behavior of a 10-storey braced frame steel building under fire exposure. The effect of temperature induced transient creep strains on overall response of the structure, as well as failure pattern is quantified at both member and system levels. Results from the fire resistance analysis indicate that transient creep strains become significant when the temperature within the cross-section of the member increases beyond 600oC. Further, the results also show that neglecting an explicit treatment of transient creep in the model formulation can lead to unrealistic prediction of failure paths and global failure times in steel framed buildings exposed to fire.

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