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Behavior of Unrestrained and Restrained Steel Columns Surrounded by Localized Fire

Published

Author(s)

Chao Zhang, John L. Gross, Therese P. McAllister, Guo-Qiang Li

Abstract

Real fires start from localized burning, and will not develop to flashover if in an open space or in large open-plan compartments. Temperatures of gas and exposed steel columns in localized fires are not uniform. Current structural fire design methods are based on uniform heating and, therefore, uniform temperature conditions, and do not account for the temperature gradient in real fires. This paper is one of two independent papers on the behavior of steel columns subjected to localized fire. In this paper, the buckling behavior of steel columns surrounded by a fire source is investigated. A simple approach is presented to calculate the temperature of steel columns surrounded by localized fire. Coupled thermal-mechanical simulations were conducted. Both unrestrained, axially restrained, and rotationally restrained steel columns of various load ratios and dimensions subjected to different heating conditions were considered. The study finds that the temperature distribution within steel columns surrounded by localized fire is highly non-uniform both transversely and longitudinally, and the temperatures near the burning surface are much higher than those far from the burning surface. The steel columns surrounded by localized fire fail by local buckling, whilst the columns subjected to the standard ISO834 fire and uniform steel temperatures fail by global buckling. The failure (or buckling) temperatures are higher for localized fire than for both the standard ISO834 fire and uniform steel temperature condition. Structural fire design for steel columns based on the standard ISO834 fire or uniform steel temperatures may be very conservative if the potential real fires are localized fires that surround the columns.
Citation
Journal of Constructional Steel Research

Keywords

Steel columns, localized fires, Local and global buckling, Temperature gradient, Axial and rotational restraints, Coupled thermal-mechanical simulation

Citation

Zhang, C. , Gross, J. , McAllister, T. and Li, G. (2014), Behavior of Unrestrained and Restrained Steel Columns Surrounded by Localized Fire, Journal of Constructional Steel Research (Accessed April 14, 2024)
Created December 12, 2014, Updated October 18, 2017