PSI - Issue 44

A. Sandoli et al. / Procedia Structural Integrity 44 (2023) 1332–1339 A. Sandoli / Structural Integrity Procedia 00 (2022) 000 – 000

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an earthquake. Italy is recognized as one of the Nations mainly exposed to seismic risk within the Mediterranean basin area due to a combination of high seismic vulnerability of building stock and seismic hazard (Dolce et al., 2021). For this reason, several methodologies for assessing seismic vulnerability - based on empirical, mechanical, expert-judgement or hybrid methodologies - have been developed by researchers over the years, whose final scope consists of defining fragility curves and likelihood damage scenarios (Calvi et al., 2006). Empirical methods, which derive fragility curves and damage scenarios based on data coming from post earthquake surveys, are most used. In Italy, one of the first works was developed by Braga et al. (1982) based on damaging data coming from 1980 Irpinia-Basilicata earthquake, followed by several others developed in the aftermath of 2009 L’Aquila and 2016-17 Central Italy earthquakes (Del Gaudio et al., 2019; Brando et al., 2017). Mechanical approaches define fragility curves by post-processing the results of nonlinear static or dynamic analyses conducted on building prototypes, real or simulated, through the Monte Carlo method (Donà et al., 2020). Expert judgement methods, instead, derive the seismic fragility based on the experience of a team of experts that estimate the damage level of the building classes (ATC-85). It is worth mentioning that, in the face of a significant number of data, the main disadvantage of empirical and expert-judgement methods is the representativeness of data coming from post-earthquake inspections because related to the knowledge level of the detector. On the other side, mechanical-based approaches treat results often based on a not consistent number of buildings and are affected by uncertainties related to material properties or modelling assumptions (Sandoli and Calderoni 2018). In this framework, hybrid methodologies, which combine two of the abovementioned approaches, represent a useful tool that overcomes some disadvantages related to each approach. Kappos et al. 2006 presented a hybrid-based approach to develop fragility curves for Greece ’s building stock combining statistical data with nonlinear analysis results. Lagomarsino and Giovinazzi 2006 and Lagomrasino et al. 2020 developed expert-judgement procedures combined with empirical-based and mechanical approaches. Instead, hybrid typological fragility curves valid for the Italian building stock and obtained by combining expert-judgement with mechanical methods have been presented in Sandoli et al. 2021. This paper presents and critically discusses the results of a hybrid-based fragility model to derive urban-scale fragility curves. The methodology - which combines expert-judgement with mechanical approach - has been applied to the case study of Balvano, a little town of about 1700 inhabitants in the province of Potenza (Basilicata Region, Southern Italy). The histogram of Fig. 1a shows that several earthquakes hit Balvano during the past centuries and that one of the most severe events was the 1980 Irpinia-Basilicata earthquake (M=6.90). Over the histogram, the Mercalli-Cancani-Sieberg macroseismic intensities felt in Balvano as a consequence of the earthquakes (provided by the National Institute of Geology and Volcanology, INGV) and the peak-ground associated accelerations are indicated. 1980 earthquake had epicenter placed between the towns of Teora and Conza della Campania (both in Campania Region), 30 km away from Balvano (Fig. 1b). After this earthquake, Balvano was subjected to a consistent reconstruction process which has changed the town’s urban planning in its current configuration.

b)

Epicenter

CONZA DELLA CAMPANIA

TEORA

a)

10 12

0,00 0,10 0,20 0,30 0,40 0,50 0,60

MCS intensity PGA/g

0 2 4 6 8

a g /g

I MCS

1466

1561

1561

1694

1826

1857

1910

1923

1966

1980

1982

1982

1989

1990

1991

1996

2002

2002

2004

2004

2006

year

BALVANO

BALVANO

Fig. 1. (a) History of earthquake felt in Balvano (source INGV); (b) Distance from epicentre to Balvano