Fire-Resistance Behavior of a Newly Developed Cold-Formed Steel Composite Floor

摘要

The fire resistance of cold-formed steel (CFS) structures is receiving increasing concern in fire safety design. With the purpose of improving both fire performance and construction efficiency, a new CFS joist-autoclaved lightweight concrete (ALC) composite floor was developed, and a detailed fire experiment on five full-scale floor assemblies was performed. The results showed that the fire resistance of the floor assembly with a double layer of gypsum plasterboard ceiling and a load level of 2.0 kN= m(2) was extended from 75 to 83 min by the use of 35-mm thick rock wool insulation that was laid firmly between adjacent steel joists during construction; heat transfer to the compression flange of the steel joists was delayed significantly under fire conditions. The fire resistance of floor assemblies increased with decreasing load levels, but such behavior might become insignificant once the steel joists were directly exposed to fire as the ceiling finish fell off. It also was determined that the fire performance of Bolivian magnesium board was considerably better than that of gypsum plasterboard, extending fire resistance approximately 30 min in the tests. All assemblies experienced local compression failure of the top flange and the adjacent lip and web at the midspan of joists, and showed the fire resistance ratings beyond 60 min. The CFS composite floor with a ceiling configuration of only a single layer of Bolivian magnesium board demonstrated substantial competitive advantage in cost and efficiency, and was recommended for potential applications in midrise CFS structures. (C) 2017 American Society of Civil Engineers.