Restrained Fire Resistance Ratings in Structural Steel Buildings

Unique to North America is a dual classification for fire resistance of supporting members in floor and roof system in buildings, depending on whether these members are restrained or unrestrained at their ends. When this dual classification was first introduced in 1970, the ASTM E-5 Fire Test Committee clearly recognized that architects, engineers and building code administrators not familiar with the nuances of structural fire testing would have difficulty in properly applying restrained and unrestrained fire ratings in the design of real buildings. As a result, general guidance was added to ASTM E119 Standard Fire Test in the form of Appendix X3, reproduced in its entirety herein as Appendix A, with the permission of ASTM. The purpose of this paper is to eliminate the confusion that has persisted in some regions of the USA concerning the proper application of restrained and unrestrained fire resistance ratings for steel beam floor and roof assemblies. The ASTM E119 Standard Fire Test and fire test procedures are discussed. Current building code requirements are summarized and results of extensive fire research and analysis of steel beam and concrete floor constructions are reviewed. Recent studies that provide greater understanding of how steel beam and concrete floor systems endure the effects of uncontrolled fire events in real buildings are briefly referenced. The information in this paper will enable architects and engineers to satisfy code provisions requiring justification where fire resistance for steel beam floor and roof systems are based on restrained assembly ratings.