Progressive Collapse Response of Reinforced Concrete Frame Structures with Masonry Infills

The paper investigates the role of masonry infills on the progressive collapse response of reinforced concrete frame structures. A wide parametric investigation is carried out to assess the influence of frame aspect ratio, seismic detailing, and lateral constraint degree for the cases of bare and infilled frames. Numerical pushdown tests simulating a column-loss scenario are carried out on reference two-bay frames extracted from different 5-story frame buildings. Infill-frame systems are modeled by means of a refined nonlinear finite-element modeling approach experimentally validated. Bearing capacity under the column-loss scenario is compared with the expected dynamic load demand, highlighting most influencing parameters and determining capacity/demand ratios by means of an energetic approach. Results show a significant increase in strength and stiffness of infilled frames to vertical collapse with respect to bare frames, accompanied by substantial modification of damage framework, resisting mechanism, and overall safety margins. The adaptability of the common equivalent-strut modeling approach as a simple assessment method is finally tested, comparing results from refined finite-element models and simplified fiber section models.