Output-only modal identification in unfavourable testing conditions and finite element model updating of a seismically damaged building

Knowledge of the dynamic behavior of complex buildings subjected to near-fault earthquakes may be enriched by valuable information obtained through rapid on-site dynamic testing to aid in the design of appropriate retrofitting interventions. Through a case study, the paper demonstrates the enhancement in comprehension of the structural behavior obtained by means of a two-day testing campaign conducted on a complex building of the Engineering Faculty, Edifice A, which was heavily damaged in the 2009 L’Aquila earthquake. The on-site testing was carried out with a network of thirteen accelerometers opportunely located to identify the dynamic characteristics of the structure by means of ambient noise induced vibration. Enhanced Frequency Domain Decomposition (EFDD) and Stochastic Subspace Identification (SSI) output only-procedures were both used to identify the main modal parameters of two substructures of the building. The modal model was used to update a finite element numerical model representing small amplitude vibrations of the damaged structures. The direct comparison of the identified modal models with finite element models, in which damaged member locations are determined by on-site visual observations, has permitted to identify a model representative of the structural behavior of the building in the immediate post-earthquake conditions.