This paper presents a qualitative assessment of the influence of the composite floor system and shear-tab connections on the stability behavior of a typical mid-rise (10-story) steel building subjected to corner compartment fires. A ten-story steel building with composite floor systems was designed following the design practices in the US. The building had an interior core of reinforced concrete (RC) shear walls to resist the lateral loads. Effects of gravity loads and fire conditions were simulated using the finite element method and numerical analysis techniques. The concrete material model used in the numerical simulations was benchmarked using experimental data from concrete slab thermal tests. The results from the numerical investigations indicated that at elevated temperatures, the composite beam undergoes elongation, sagging and rotation at the beam ends. This results in additional rotation and compression demands on the connections at the ends. The shear-tab connections provided significant negative moment resistance at the beam ends at elevated temperatures. This negative moment resistance at the shear-tab connections increased the flexural capacity of the composite beam by effectively redistributing the moment demands due to the applied gravity loads.