PSI - Issue 44

Gianmarco de Felice et al. / Procedia Structural Integrity 44 (2023) 2122–2127 G. de Felice / Structural Integrity Procedia 00 (2022) 000 – 000

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1. Introduction Most of historical buildings worldwide are made of masonry. A considerable amount of these constructions were designed through geometrical and empirical rules, which are suitable for static loads but not always sufficient to provide an adequate safety level towards earthquake actions, as dramatically shown by recent seismic events, Penna et al. (2019), Sorrentino et al. (2017). As for the peculiar case of churches, the significance of assessing their earthquake vulnerability is crucial, under several point of view. First of all, the protection of human life: indeed these constructions usually host a large number of people whose safety needs to be guaranteed when the seismic event occurs. Then, the artistic, cultural and historical standpoint: churches needs preservation since they gather – and are themselves – assets of inestimable value. And then again, the economic viewpoint related to tourism: damages to the structure may induce massive losses to the locality sheltering the monument, whose economic power is often represented by the tourism industry. The vulnerability of historic masonry churches to seismic action mainly lies in their incapability to behave as a whole structure (they do not display a global response under earthquake), whose box-type behaviour is prevented by (ii) the irregular and often complex geometry of the construction, whose development is predominant in the longitudinal direction, (iii) the absence of diaphragms in the transversal direction, and (iv) the lack of suitable connections between orthogonal walls. For this reason, masonry churches often fail by the overturning of a detaching part of the structure, Lagomarsino and Podestà (2004). On the basis of the above, the standard procedure adopted in Italy for assessing the seismic capacity of churches relies on the investigation of pre-established local mechanisms of collapse, by means of capacity curves derived by the application of the limit analysis kinematic theorem, Heyman (1966). Italian guidelines for the evaluation and the reduction of the seismic risk of the cultural heritage recommend the study of 28 frequent collapse mechanisms defined a priori, LG MBAC (2011). Even though these mechanisms are usually based on extensive data from previous post seismic surveys, their a priori determination needs to be enhanced by a precise representation of the geometry and masonry morphology (arrangement and shape of blocks), with particular regard to the interlocking/toothing between orthogonal walls – de Felice et al. (2022) – and the number of walls headers, de Felice (2011). The Distinct Element Method (DEM) which considers the real discontinuous nature of masonry, modelled as an assemblage of discrete units (blocks) separated by zero-thickness interfaces (joints), allows to account for all these features – Cundall (1971), Lemos (2007), Tondelli et al. (2016), Mordanova and de Felice (2020) – as well as for sliding and disaggregation phenomena, Meriggi et al. (2019). The more precisely geometry, masonry morphology and interlocking are represented, the more accurate the result of DEM analysis is. Within this framework, the present work aims at presenting an integrated approach for the investigation of the seismic behaviour of masonry churches, ranging from photogrammetric survey to seismic structural analysis, the latter performed through an automatic DEM pushover procedure. This methodology is applied to the case study of the Romanesque church of St. Maria Maggiore in Tuscania. 2. The case study: the church of St. Maria Maggiore in Tuscania St. Maria Maggiore (Fig. 1a) is a Romanesque church located in Tuscania, a small village in the north-west of Lazio region, in Italy. The church, dated back to the IX century AD and started out with a Latin cross plan, has undergone several transformations over the years, the most recent of which are due to damages induced by a 5.2 moment magnitude earthquake that occurred in Tuscania in 1971. At present, the church, about 33m long and 20m wide, is made of three naves with wooden roof and a presbytery (Fig. 1b). The naves, separated by arcades, consist of a central nave – 15m ridge height and 13m eaves height – with trusses and two lateral naves, both with the upper support at a height of 8m and the inferior one at 6m (Fig. 1c). The presbytery is provided with three apses, one central and two smaller on each side, and is slightly elevated with respect to the rest of the plan. Due to the large free span of walls in the longitudinal direction (SE-NW) and the lack of bracing elements (such as steel ties), the plan is evidently vulnerable in the transversal direction (SW-NE).