PSI - Issue 44

Romina Sisti et al. / Procedia Structural Integrity 44 (2023) 1848–1855 Romina Sisti et al./ Structural Integrity Procedia 00 (2022) 000–000

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4. Triumphal Arch The macro-element triumphal arch, as highlighted by Fig.1, is one of the most problematic even for cases that are apparently clearly explained in the user manual. The macro-element presents in the majority inconsistencies linked to the difference of judgement between the two surveys (23%), but also maintains high percentages of discrepancies between the forms and subsequent revision (12%) and conceptual ambiguity (13%). Several cases were identified in which, although the triumphal arch, defined as a wall panel with an arched opening separating the nave and the apse (Fig. 4a), is present, it was not reported in any of the two forms. In particular, in churches with small apses, the arch opening is small compared to the size of the entire panel and the triumphal arch is often not identified, perhaps because it is far from the architectural idea of this element (example in Fig. 4b). To prevent this problem in future inspections, it is suggested to improve the definition of the macro-element as well as the choice of examples collected in the manual. In very simple churches it is not uncommon to find several wall panels with arched openings supporting the roof (colored elements in Fig. 4c, example in Fig. 4d). Some compilers report damage of these elements in the M13 mechanism related to the triumphal arch, rather than through the transverse response mechanism of the nave M5. It is considered appropriate to include an example in the manual in order to clarify this point. As far as more complex churches are concerned, the majority of errors are concentrated in vaulted churches, where it is not possible to inspect the attic and therefore it is not possible to know whether the arch is actually a wall (as defined in the manual), or a simple thickening of the arches forming the vaults of the nave.

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Fig. 4. a) Diagram of the macro-element triumphal arch according to the definition proposed by the manual of A-DC form. b) Church of San Lorenzo, Giano dell’Umbria (PG). c) Diagram of wall panels with arched openings supporting the roof which are often incorrectly evaluated as triumphal arches. d) Church of Madonna di Loreto, Avendita, Cascia (PG). 5. Apse There is no specific collapse mechanism in the A-DC form to describe damage to the back wall of a church without an apse, and neither does the user manual specify how to deal with this case. This lack generates a variety of solutions by the technicians. In particular, some describe the damage of the back wall only in the notes. However, in this way the damage reported by an important macro-element is not considered in the calculation of the global damage index of the church, leading to an underestimation of the damage. Other technicians use the mechanisms of the apse to describe the damage to the back wall. The latter solution is very common and, if it were possible to specify whether the damage is related to the apse or to the back wall, it can also be considered effective, since the overturning (M16) and the in-plane response (M17) mechanisms of the apse would remain unused when there is no apse. Thus, the issue could be overcome by providing a standard guideline on how consider this, probably with the use of M16 and M17 with the possibility to specify which is the microelement involved. 6. Transept The transept is the element with the highest level of inconsistencies, exceeding 50% of the total number of churches with an assumed or presumed presence of the element. The inconsistencies that emerged were largely related to the discrepancy between the forms (33%), and between the two forms and the subsequent analysis of the photos and documentation available (12%), with, however, a good percentage (15%) related to ambiguities. A frequently encountered problem is of a conceptual nature: when the transept, although clearly distinguishable both architecturally and functionally, assumes, at floor level, the same dimension as the nave (i.e. the outer perimeter of the church remains rectangular and does not assume the classic cross shape), the mechanisms associated with it are not always recognized as possible (Fig. 5a). The difficulty of identification could be linked to the definition of transept in the manual, which clearly refers to a Latin cross plan.