Investigation On The Temperature Field And Structural Behaviors Of Non-uniformly Heated Steel Columns In A Fire

Temperature gradient will occur when a steel column is heated non-uniformly in a fire. Current codes for structural fire design provide the design equations to calculate the temperature evolution of steel columns in a fire. However, the design equations are based on the assumption that the temperature distribution is uniform across the section.The temperature field of steel columns across the section with three sides and two adjacent sides exposed to ISO834 standard fire were analyzed respectively through finite element method. The columns were protected by sprayed fire retardant coatings. For the analyzed 3-sided heated column, thermal gradient exists along the depth of the H-section. But for the column exposed to fire from two adjacent sides, thermal gradient exists both along the width and depth of the H-section. The design equation in EN 1993-1-2 based on the element factor approach was modified through parametric analysis. And simplified temperature distribution profiles were proposed according to the finite element simulation results.Effects of different temperature distribution profiles on structural behaviors of steel column exposed to fire from three sides were investigated through finite element method. Studied behaviors included thermal bowing and reverse thermal bowing of the column, axial stress distribution across the section and critical temperature of the column. Parametric study showed that the linear A distribution was accurate enough in predicting critical temperature of the non-uniformly heated steel column. So it can be used to represent the non-uniform temperature distribution of the column.Critical temperature of steel columns exposed to fire from three sides and two adjacent sides were obtained through the structural analysis model. Temperature results from the heat transfer analysis and simplified linear temperature distribution profile were taken as input data. The 3-sided heated steel column may fail by flexural buckling or flexural-torsional buckling. And the column exposed to fire from two adjacent sides fail by flexural-torsional buckling.EN 1993-1-2 could provide a slightly conservative estimate of the critical temperature of 3-sided heated steel column. But for the 2-adjacent-sided heated column, was proposed to modify the calculation results of EN 1993-1-2. The equation to calculate this correction factor with respect to different slenderness ratio and load ratio was given.