The behavior of concrete-filled steel columns against fire in the entire structure

Concrete-filled columns, if properly designed, can withstand fire for a duration of 2 hours or more. The Iranian National Building Code, Part 10, provides guidelines for calculating the fire resistance time of individual CFT columns. However, the evaluation of fire performance for CFT columns should consider the overall structure and factors such as beam moments and column effective length. The absence of specific methods to assess the fire performance of CFT columns in real structures limits their application in common projects. This study introduces a systematic approach to evaluate the fire performance of CFT columns in a structure. For this purpose, 10-story buildings in Tehran were designed with different lateral load-resisting systems: 1- special moment frame, 2- special shear wall, and 3- dual system. The buildings were designed with varying story heights ranging from 3 to 4 meters and two types of concrete aggregates: 1- carbonate and 2- silica. The results indicate that, for a story height of 3.2 meters and using silica aggregate, approximately 7%, 19%, and 48% of the columns in the dual system, shear wall system, and moment frame system respectively, failed during the fire. The analysis revealed that an increase in story heights had a significant impact on the fire behavior of moment frames, while it had no notable effect on other systems. Sensitivity analyses demonstrated that a reduction factor of 0.1 for the rotational stiffness of the columns in structural analysis is appropriate, as it considers moment redistribution and ensures model convergence.