Numerical Simulation of the Partial Seismic Collapse of a 1960s RC Building

This study focuses on the partial seismic collapse of a building during the earthquake of L'Aquila (Italy) on April 6, 2009. Designed in the early 1960s, the seven-story building has a reinforced concrete frame structure. In elevation, above a first basement and a ground floor, three wings rise. The collapse affected the north wing, where all the columns at ground story and three columns, located at the interface with the other wings, failed on the full height. In the same area, subjected to strong distortions, a third collapse mechanism involved (at stories 1-4) a beam supporting a nonstructural wall inserted in recent renovation works. Previous investigations explained why the collapse was confined to the north wing, providing (and based on) the knowledge of the building to the date of the earthquake in terms of geometry, material properties, acting loads, and seismic input to the site. This study aims to simulate the structural response during the earthquake to investigate the sequence of the different mechanisms and their possible interdependence. Nonlinear dynamic analyses on OpenSees adopt a refined three-dimensional finite element model with beam-columns fiber elements and the components of the ground motion at site. Results up to the collapse onset (1) satisfactorily simulate the identified collapse mechanisms; (2) clarify the interaction and the likely sequence among the different mechanisms; and (3) highlight the negative role of the nonstructural wall in the collapse. Conclusions provide comprehension of the past design procedures and of the possible flaws affecting the structures of the time.