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This paper presents a comparison of two compartment fire experiments performed on the 9.1 m × 6.1 m composite floors using a full-scale two-story steel gravity frame to study the influence of slab reinforcement on the overall structural integrity. The floor specimens were designed to achieve a 2-h fire rating but had dissimilar slab reinforcement. The Test #1 specimen had steel wire reinforcement of 60 mm2/m width as the minimum permitted in the United States practice whereas the Test #2 specimen was reinforced with deformed steel bars (230 mm2/m) determined by incorporating tensile membrane action. The Test #1 specimen exhibited mid-panel slab integrity failure before reaching the specified fire rating period. However, the Test #2 specimen exhibited much smaller concrete cracks until it was heated up to 131 min and retained the post-fire residual strength at least two times greater than the design demand at ambient temperature. This unique large-scale testing demonstrated that the appropriate slab reinforcement scheme can delay the vertical deflection of the heated composite floor and maintain the structural integrity at large vertical displacements over a longer duration of fire exposure. • The influence of slab reinforcement on the structural integrity of steel-concrete composite floors under fire was evaluated. • Compartment fire experiments were conducted on the composite floor assemblies located in a full-scale two-story steel gravity frame. • Slab reinforcement of larger area and ductility can maintain the structural integrity of the slab for longer period of fire. • The enhanced slab reinforcement significantly delayed the increase in the vertical displacement of the composite floor. [ABSTRACT FROM AUTHOR]