Computational simulations for analyzing progressive collapse resistance of structures following initial damage require specific attention to structural modeling of floor systems. In collapse analysis of RC structures, it is shown that the degrees of freedom of nonlinear beam, joist, and slab sections must include flexural and axial deformations. It is also shown that ignoring torsional cracking of beams can lead to a significant overestimation of the progressive collapse resistance of structures. Evaluating the response of a seven-story RC structure following 15 simulated single column removal scenarios, it is shown that a top floor column removal is more likely to cause structural collapse than failure on a lower floor. This is in part due to the lack of Vierendeel frame action after a top floor column removal. For the simulated scenarios in which the structure resists progressive collapse without experiencing large vertical displacements, the resistance is primarily provided by Vierendeel frame action and axial compressive force-moment interaction of beams. The importance of the floor system in-plane action in axial-flexural response of beams is discussed. The effect of accounting for the elevation difference between the centerlines of floor slabs and beam elements within the building model is studied.