Rapid tools for assessing building heritage's seismic vulnerability: a preliminary reliability analysis

Earthquakes represent a relevant issue for Building Heritage safety, especially while referring to historic urban fabric scenarios. Mitigation strategies should limit damages and losses to the Heritage, as well as critical emergency conditions at the urban scale (e.g. earthquake-induced damages on outdoor spaces; occupants’ safety). The possibility to promote numerical analyses and focused retrofitting interventions on isolated buildings and building aggregates (e.g. urban blocks) is strictly connected to the (limited) availability of time and economic resources. Hence, a current key strategy is to detect high-vulnerability elements and then define related risk maps to evidence critical conditions in the urban fabric by using quick-to-be applied approaches, especially about data collection, to allow a quick but enough reliable application at urban scale. Anyway, even if aggregates represent the most common building layout in historic city centres, most of such methods are focused on single structural units, composing the building aggregate, often requiring substantial detail levels (i.e. data from indoor surveys), to estimate post-earthquake conditions (i.e.: Macroseismic Vulnerability Assessment Methods – MVAMs). On the contrary, the few building aggregate-based approaches are generally based on outdoor expeditious data collection methods. Since estimations at urban scale could take advantages of rapid tools by using the related simplified approaches, this research considers two activities. Firstly, a preliminary reliability test is performed to evaluate a novel quick remote data collection approach on two well-known MVAMs. Then, a formulation to assess the seismic vulnerability of the entire aggregate from the indexes of each single structural units (MVAMs-based) is studied. This changing of scale could facilitate risk maps definition, by also extending inspected areas and reducing not necessary details, as well as emergency plans and strategies to define possible unavailable/obstructed paths in historic centres could take advantages to this proposal. A comparison with results from another existing rapid aggregate vulnerability assessment method (SISMA) is employed as a first attempt to verify the reliability of this proposed approach. MVAMs with the extended formulation for aggregates and SISMA according to the remote approach are applied to a real-world sample composed by historic masonry buildings recently affected by earthquakes (i.e. Central Italy, 2016–2017). Results firstly confirm that the novel remote data collection-based for MVAMs do not provokes an underestimation of the building vulnerability, moreover the comparison between the aggregates MVAM-based vulnerability indexes and SISMA underlines the presence of a reliable correlation.