Advanced FE nonlinear numerical modeling to predict historical masonry vaults failure: Assessment of risk collapse for a long span cloister vault heavily loaded at the crown by means of a general-purpose numerical protocol

A simple and rapid approach aimed at the failure prediction of historical masonry vaults exhibiting stability issues under gravity loads is presented and applied to a paradigmatic case study in Italy. The benchmark structure under examination is a cloister vault with a considerable span, over which a slender load-bearing wall was built over the keystone. The urgency of a stability assessment to prevent failure is evident. The geometrical characteristics and some material information are obtained through in situ surveys. To assess its stability, determine the risk of collapse and propose a sound strengthening on the already cracked structure, a general numerical protocol that comprises five different 2D finite element models is proposed, each with different assumptions. In all models, blocks are discretized using 4-noded elastic elements in plane-strain, and mortar joints are modeled employing (i) orthotropic shell elements coupled with (ii) fragile cutoff bars. Model 1 considers only the arch without spandrels, unlike Model 2, which comprises them. The backfill is included in Models 3 and 4 using a system of equivalent forces mimicking both soil self-weight and the horizontal passive pressure, whilst Model 5 −used for validation purposes- employs elastic perfectly plastic elements that obey a Mohr-Coulomb failure criterion. Model 3 and Model 4 differ only in the dimension of the buttresses, which are thickened in Model 4 to improve the stability of the vault. Additionally, in Model 3 the effect of a possible retrofitting intervention is studied, having an insight into the role played by Carbon Fiber Reinforced Polymer (CFRP) strips positioned at the intrados and modeled with elastic perfectly ductile cutoff bars connected to surface nodes, thus ensuring a perfect bond between substrate and reinforcement. After a thorough analysis of the results, which focuses on both global force–displacement curves and failure mechanisms triggered, a safety assessment of the cloister vault is provided.