Analyses Of The Impact Of Loss Of Spray-applied Fire Protection On The Fire Resistance Of Steel Columns

Abstract

The loss of fire protection material is generally acknowledged to reduce the fire resistance of protected steel structural members, but the magnitude of the reduction is unknown. Two analyses are applied to assess the heat transfer to a steel column and investigate the proportional decrease in the fire resistance when relatively minor portions of spray-applied fire protection material are removed. One method is an elementary, lumped heat capacity analysis (LHC). The second method involves the application of a three-dimensional, finite element model. In both cases, the column is assumed to be subjected to the standard ASTM E119 fire resistance test. The predicted temperature distributions within the member over time are used in conjunction with the thermal endpoint criteria specified in ASTM E119. The LHC analysis of the temperature rise of the entire column shows the area of missing protection to be of little consequence in determining the average temperature of the entire column. The column temperatures calculated using the LHC approach are primarily dependent on the original fire resistance of the column for the small areas of missing protection examined. In contrast, the area of the missing protection and the size of the column are found to have an appreciable effect upon the thermal response of the column regardless of the protection thickness using the finite element analysis.