Post-Fire Residual Stress Predictions in Steel I-Sections

Fire has been recognized as a significant cause of structural failures in recent decades, and increasingly sophisticated experimental and analytical tools are being developed to better predict the responses of structures to natural fires. Structures are also known to collapse several hours after the fires were extinguished, indicating that although they survived the fire, they could not withstand the post-fire stresses. These post-fire stresses may arise due to system behavioural changes that happen in the cooling phase of a fire or due to additional locked-in stresses due to the rapid heating and cooling of structural members. Residual stresses play a primary role in the design strength equations of steel beams and columns, even at ambient temperatures. However, there needs to be more understanding of how the distribution and magnitude of these residual stresses change after the event of a fire and its impact on the residual strength of structures. Limited data in the literature indicate a reduction in the residual stresses after exposure to high temperatures, but the studies were limited to all-side exposure (uniform temperature) and natural air cooling. The present work uses finite element simulations to predict the residual stresses in compact steel I-sections for both air and water cooling after the event of a fire.