Effect of Fire Exposure on Structural Response and Fireproofing Requirements of Structural Steel Frame Assemblies

Fire endurance ratings of structural steel frame assemblies are based on limiting temperature rise and on preventing structural collapse during a specified fire. Currently, a single standard fire, ASTM Method for Fire Tests of Building Construction and Materials E 119-83, is specified as the fire exposure. Thermal and structural responses can be determined either by a standard test or by calculations using computer programs such as FIRES-T3 and FASBUS II. Use of analytical methods in predicting thermal and structural responses of steel frame assemblies, with or without fireproofing, permits evaluation of the effect of different fire exposures. In this paper, a general approach for the evaluation of structural responses and fireproofing requirements of steel assemblies under different fire exposures is described and the results of three case studies are presented.

Data required for and procedures used in evaluating the response to fire, as well as the response acceptance criteria for the desired level of fire protection, are discussed. Two fire exposures, short duration high intensity (SDHI) and long duration low intensity (LDLI), are described. These fire exposures together with the ASTM E 119 standard fire, are used in the evaluation of fire responses of a typical steel deck floor assembly specimen. Response of this assembly with different thicknesses of fireproofing is determined analytically, and the results are summarized.