Non-linear dynamic analyses of an RC frame building collapsed during L'AQUILA 2009 earthquake

This study focuses on the partial seismic collapse of a building during the earthquake of L'Aquila (Italy) on April 6th 2009. Designed in the early ‘60s, the 7-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 three separate collapse mechanisms were identified. All the columns at ground story failed with a weak-story mechanism in North-South direction. Three columns, located near the interface with the other wings, failed on the full height. In the same area, subjected to strong distortions due to the difference in vertical displacements following the weak-story mechanism, at stories 1-4 a third collapse mechanism involved a beam supporting a non-structural wall inserted in recent renovation works. Previous investigations carried out with both pushover and nonlinear dynamic analyses explained why the collapse was confined to the North wing, the collapse sequence and the role of the non-structural wall. Based on nonlinear dynamic analyses on a refined 3D FE model, this study focuses on the role of the East and West wings that survived the earthquake. The subdivision of the base shear among the three wings at the collapse onset confirms that only few elements in the East and West wings contributed to resist horizontal forces in the North-South direction where the weak story mechanism took place.