GNGTS 2019 - Atti del 38° Convegno Nazionale

GNGTS 2019 S essione 2.2 429 VULNERABILITY OF UNREINFORCED MASONRY CHURCHES DAMAGED BY THE 2016-2017 CENTRAL ITALY SEISMIC SEQUENCE A. Marotta, D. Liberatore, L. Sorrentino Sapienza Università di Roma, Dipartimento di Ingegneria Strutturale e Geotecnica, Roma, Italy Religious buildings constitute an important part of the cultural heritage of a country, for both spiritual and cultural reasons. The seismic sequence that struck Central Italy in 2016- 2017 highlighted once again the high vulnerability of unreinforced masonry churches, causing invaluable losses to the national heritage. It is widely known that churches frequently exhibit a seismic vulnerability higher than ordinary buildings (D’Ayala 2000), because of their architectural and structural characteristics such as open plan, large wall height-to-thickness and length-to-thickness ratios, and the use of thrusting horizontal structural elements for vaults and roofs (Sorrentino et al., 2014). As known, unreinforced masonry (URM) buildings, and particularly churches, tend to respond to earthquakes with local mechanisms rather than with a global behaviour (Giuffré 1988; Doglioni et al., 1994; Lagomarsino et al., 2004). Accordingly, in order to correlate the damage associated to each collapse mechanism against ground motion intensity and churches’ specific characteristics, the observed behaviour of a sample of 158 Central Italy URM churches is herein analysed by means of statistical procedures accounting for 28 possible local collapse mechanisms, as currently adopted in Italy for post-earthquake assessment of churches (Calderini and Lagomarsino 2010; Da Porto et al., 2012), according to DPCM (2011). Among the church sample assessed in the stricken regions, 32 are located in Latium, 41 in Umbria, 73 in Marche and 12 in Abruzzi regions. Local values of MCS intensity (Azzaro et al., 2016; Galli et al., 2016) are attributed to each church location using a triangulation-based linear 2-D interpolation when macroseismic intensity was not available for the settlement of interest. The majority of churches, during either the August 24 or October 30 main shocks, experienced a macroseismic intensity equal to V (20%), VII-VIII (15%) and VIII-IX (13%). The assessment of the damage occurred to the Central Italy churches was carried out by assigning six levels of damage, ranging between 0 (no damage) and 5 (total collapse), to each possible collapse mechanism following the qualitative expert judgment approach of the European Macroseismic Scale (Grünthal 1998). As showed in Marotta et al. (2017), the seismic vulnerability of URM churches is strongly influenced by structural details whose presence can improve the seismic performance, such as connections between walls and to horizontal structures, buttresses, tie rods, top beams, lateral restraint, lintels, braced roof pitch, or aggravate the seismic performance, such as poor masonry quality, asymmetry conditions, thrusting elements, large slenderness, large openings, heterogeneous materials, vertical-stacked-bond vaults, lunettes. For this reason, the presence and effectiveness of the aforementioned fifteen different vulnerability modifiers (Tab. 1) have been also investigated, and their effect on the damage of each mechanism has been addressed, following the approach in Marotta et al. (2018). Table 1 - List of the vulnerability modifiers used in the multi-linear regression models. Ref. no. Description Ref. no. Description Ref. no. Description x 2 Tie rods x 7 Large openings x 12 Slenderness x 3 Lateral restraint x 8 Top beam x 13 Asymmetry conditions x 4 Buttresses x 9 Heterogeneous materials x 14 Poor masonry quality x 5 Lintels x 10 Connections x 15 Vertical-stacked- bond vaults x 6 Thrusting elements x 11 Braced roof pitch x 16 Lunettes