Abstract
Recent earthquakes have exposed the vulnerability of existing buildings; this is demonstrated by damage incurred after moderate-to-high magnitude earthquakes. This stresses the need to exploit available data from different sources to develop reliable seismic risk components. As far as it regards empirical fragility assessment, accurate estimation of ground-shaking at the location of buildings of interest is as crucial as the accurate evaluation of observed damage for these buildings. This implies that explicit consideration of the uncertainties in the prediction of ground shaking leads to more robust empirical fragility curves. In such context, the simulation-based methods can be employed to provide fragility estimates that integrate over the space of plausible ground-shaking fields. These ground-shaking fields are generated according to the joint probability distribution of ground-shaking at the location of the buildings of interest considering the spatial correlation structure in the ground motion prediction residuals and updated based on the registered ground shaking data and observed damage. As an alternative to the embedded coefficients in the ground motion prediction equations accounting for subsoil categories, stratigraphic coefficients can be applied directly to the ground motion fields at the engineering bedrock level. Empirical fragility curves obtained using the observed damage in the aftermath of Amatrice Earthquake for residential masonry buildings show that explicit consideration of the uncertainty in the prediction of ground-shaking significantly affects the results.
Highlights
Accurate assessment of seismic risk for buildings at a territorial scale depends to a large extent on the availability of reliable and accurate fragility curves
The empirical fragility curves and the corresponding plus/minus one standard deviation interval for each class of masonry buildings defined in Sect. 3.1.2 (MBC1–4) and for the different damage grades defined in Sect. 3.1.1 (EMS-98, damage; Grade 2 (D2)–damage; Grade 5 (D5)) have been calculated following the procedure described in Sects. 2.3 and 2.4 and plotted in Figs. 7 and 8 based on Copernicus EMS and visual survey (Sect. 3.1.1), respectively
The consideration of ShakeMap for estimation of ground shaking shows significant discrepancies between the fragility curves obtained based on Copernicus and visual survey for MBC1 (D2 to damage; Grade 4 (D4)), MBC2 (D2 to damage; Grade 3 (D3)), MBC4(D2)
Summary
Accurate assessment of seismic risk for buildings at a territorial scale depends to a large extent on the availability of reliable and accurate fragility curves. The main advantage is that, being based on observed damage, the empirical fragility curves are—potentially—able to provide a realistic picture of post-earthquake damage. They can consider the possible soil-structure interactions, the cumulative damage due to aftershocks (or back-toback seismic events), the degradation in structural behaviour due to aging, and the effect of flexible diaphragm and secondary members (e.g., infills); just to name a few. The use of an established and standardized damage scale, in which different damage data should be converted, is one essential requirement for the derivation of empirical fragility curves. The European Macroseismic Scale (EMS-98, Grünthal 1998) is an example of a standard damage scale, very often used to report the empirical fragility curves in Europe
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