PSI - Issue 44

Michele Mirra et al. / Procedia Structural Integrity 44 (2023) 1856–1863 Michele Mirra et al. / Structural Integrity Procedia 00 (2022) 000 – 000

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Fig. 5. (a) Numerical model of the church; rocking mechanisms of the façade after the kinematic analyses of the as-built configuration (b); equivalent-frame model of retrofitted configuration (c) and governing capacity curve from the pushover analyses (X) on it (d).

The seismic action for the location of Ceto was prescribed, considering soil type A, topographic amplification factor of 1.2 (accounting for the sloping ground), importance class III, given the historical relevance of the building. This corresponded to a PGA of 0.08g for the no-collapse requirement. After having specified these properties, the as-built configuration of the church was firstly analyzed. Since prior to the retrofitting, the building did not feature any effective connections between roof and masonry wall, the development of an effective box behaviour was considered unlikely. Thus, the vulnerability of the construction was evaluated by analyzing local collapse mechanisms, in agreement with the Italian guidelines for seismic assessment of churches (DPCM 09-02-2011). From these investigations, the aforementioned ratio ζ E,1 was determined. For the retrofitted configuration, with a roof well connected to the walls and able to act as a stiff diaphragm, local mechanisms can be prevented, also given the compactness of the church. Thus, after a modal analysis, a series of 16 pushover analyses were conducted on the whole building in both plan directions, and from the most vulnerable combination of seismic actions, the aforementioned ratio ζ E,2 was derived. For these pushover analyses, the control node was taken as the center of mass of the building, on top of the vault. In order to conservatively prevent the possible overestimation of the displacement capacity of the building, each analysis was stopped as soon as the first pier experienced a drop in in-plane capacity larger than 20% of its strength. During an earthquake, because of the beneficial redistribution effect provided by the roof, it is expected the building could globally retrieve a larger displacement capacity; in these analyses, the objective was to quantify as conservatively as possible the improvement in seismic capacity after retrofitting the church. 5. Results from the analyses 5.1. Evaluation of seismic improvement Because of the low PGA intensity of the site, as well as the regularity and compactness of the church, the as-built configuration showed sufficient capacity to withstand the expected seismic action for several of the most common local collapse mechanisms (e.g. overturning of gables or of nave walls). However, the front façade showed a strong vulnerability (Fig. 5b), leading to ζ E,1 = 0.23 only (PGA at collapse of ≈ 0.02g). It should be noticed that this value can be considered as very conservative, since from the conducted inspections the façade appeared to be well connected to the rest of the structure. Yet, without a roof acting as diaphragm and proper joints, able to redistribute seismic actions among other structural components, similar failure mechanisms could still take place in the event of an earthquake. With regard to the retrofitted configuration, the modal analysis highlighted a regular dynamic response for both plan directions X and Y, with periods of 0.47 and 0.35 s, respectively. This is coherent with the regularity and symmetry of the church, as well as the proper distribution and arrangement of all masonry piers and buttresses. From