Identification of Minimum Unit of Analysis for seismic performance assessment of masonry buildings in aggregate

Abstract

Italy is characterized by high seismicity and the recent earthquakes (L’Aquila 2009, Emilia Romagna 2012, Centre of Italy, 2016) have highlighted the high vulnerability of the Italian real estate, mainly composed of historical and old masonry buildings. The greatest damages mostly occurred in the historical centres, where masonry buildings in aggregate are the prevalent structural typology. This circumstance has renewed the need of procedures for the seismic risk assessment and the unitary planning of strengthening interventions, according to a specific methodology appropriate for the masonry aggregates, in order to achieve safety standards. Indeed, the identification of a determined building (i.e., structural unit) as an independent structure can become difficult, since it is often in adjacency to others. These systems do not have an independent structural behaviour, given the reciprocal interactions with adjacent structures during a seismic event (namely, the “aggregate effect”), and their analysis is naturally affected by uncertainties. Hence, this research project aims at understanding how the “aggregate effect” should be modelled for a more accurate assessment of the global seismic performance of the masonry buildings in aggregate, reducing the uncertainties related to too extensive knowledge process. To this end, a new procedure, referred to as “target structural unit approach”, is proposed, aiming at identifying the optimal portion of the aggregate that best represents the “aggregate effect” for the investigated building, i.e. the Minimum Unit of Analysis. This procedure is based on a multi-level analysis of the seismic response of the target structural unit, investigating different modelling configurations in addition to the complete aggregate or the isolated building. The evaluation is preliminarily performed at global– and wall– level; then, the structural unit– level is introduced as additional verification level, with the aim to understand the variability of the seismic response of the case study building in function of different boundary conditions. A preliminary step of this study is a sensitivity analysis on prototype aggregates, for evaluating the influence of the main interaction factors. Then, the new procedure is defined and applied on the prototypes, for providing general schemes in function of the analysed case. Finally, it is validated on two case studies: an L aggregate in Faro (Portugal) and a row aggregate in Castelnuovo (L’Aquila).