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

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. Introduction ASTM E119 documents the standard test to assess the fire resistance of structural members in North America [1]. The temperature endpoint criteria for steel columns are: an average temperature of 538°C and 649 °C at a single point [1]. One method of protecting steel columns is through the use of an insulating, spray-applied fire protection material. Several such materials are identified as part of listed steel column assembly designs included in the Fire Resistance Directory [2]. The intent of this study is to compare the results from two separate analysis methods, one relatively simple and one relative complex, to provide an estimate of the impact of missing fire protection material on the temperature rise experienced by a steel column exposed to the conditions associated with the ASTM E119 standard test. One method, referred to as the LHC analysis, uses an algebraic equation that is reiterated to determine the temperature rise of the column [3]. The second analysis method uses a finite element model, FIRES-T3, to conduct the analysis [4]. Assessing the impact of the local temperature rise on the structural performance of the column is beyond the scope of this paper. However, such is needed to conduct a more comprehensive analysis of the impact of the missing protection, rather than applying the endpoint temperature criteria from ASTM E119. 1 Copyright © International Association for Fire Safety Science