Behavior of Composite Floor Assemblies Subject to Fire: Influence of Slab Reinforcement

Abstract

A series of fire experiments are being conducted on the 2‐story steel framed building with composite floors in the National Fire Research Laboratory. This paper presents a brief overview of experimental design and discusses some results of the first test conducted on 6.1 m by 9.1 m composite floor assembly exposed to a standard fire. The test floor slab was constructed with lightweight concrete cast on 7.7 cm deep formed steel deck units and welded wire fabric (60 mm/m2) as the minimum shrinkage reinforcement required in the U.S. practice. The structural steel beams and girders were sprayed with a cementitious fire resistive material for a 2‐hour restrained fire resistance rating. While the test floor assembly resisted mechanical loads (2.7 kN/m2) applied using hydraulic actuators, its underside was exposed to a natural gas‐fueled compartment fire that was equivalent to the standard gas temperature‐time relationship. The study revealed that the test floor assembly could withstand an imposed load at a large vertical deflection on the order of span / 16, but the concrete slab failed due to limited ductility and strength prior to 2 hours in a standard fire. Simple post‐test predictions were performed incorporating tensile membrane action in the floor slab to compare with the measured behavior. Limited comparisons discuss the contribution of steel decking and slab reinforcement to the load‐carrying capacity of a floor assembly in fire.

Experimental study on fire resistance of a full-scale composite floor assembly in a two-story steel framed building

“…More recently, the second fire experiment was conducted to study the influence of enhanced slab design (with an increased area of slab reinforcement), determined based on Choe et al (2021b), on the fire performance of composite floor systems, which will be discussed in the authors' future publications.…”

Steel Structures Research Update: Structural Fire Engineering

“…The reinforcement ruptured before any membrane action could be developed, leading to integrity failure of the floor slab prior to the specified rating period (Choe et al, 2020b). Slab reinforcement and fire performance of composite floor systems were explored further with the second test in 2021 (Choe et al, 2021).…”