Numerical Simulation of Seismic Collapse of a RC Frame Building: a Case Study

The paper investigates the partial collapse (during the April 6, 2009 earthquake of L’Aquila, Italy), of a seven-story reinforced concrete building designed in 1965. The three-wing building underwent a partial collapse in one of them. Within the affected wing, two collapse mechanisms developed, one in a horizontal plane and the other in vertical direction. The former was a soft/weak story mechanism at the ground floor, the latter involved the failure of three columns (and of the supported beams) at all the levels from the ground floor to the roof. Casualties are all due to this second mechanism, as nobody was trapped in the soft-story collapse. The three columns were located at the interface with the remaining building, in the zone undergoing a severe distortion because of the dramatic difference in vertical displacements due to the soft–story mechanism. At levels from 1 to 4, one of the columns was supporting a beam that was in turn carrying, on half of its span, a non-structural wall added during a refurbishment work. The beam failed in shear, approximately at midspan, at the end cross-section of the wall. A previous study, based on linear analyses only, showed that the lack of flexural strength of ground story columns was the main cause of the collapse. Through non-linear static analyses, the paper investigates the collapse sequence and the role played by the non-structural wall (and by the related shear failure of beams). A refined numerical model of the structure, including the reinforcement layout, has been developed to find the reasons for the disproportionate effects that the partial softstory collapse had. The results clarify the role of the added wall and of the lack of beam shear strength on the collapse of the three columns.