The intrados strengthening of masonry arches with FRCM. The three-centred arch

The reinforcement of masonry arches with the FRCM (Fiber Reinforced Cementitious Matrix) technique is an increasingly used solution to improve the structural strength of masonry arches and vaults[1] . In some cases where it is not possible to intervene on the extrados, such as for cultural heritage and monumental buildings where it is necessary to reduce the impact of the interventions by preserving the shape of the arches and vaults, reinforcement with FRCM is applied to the intrados [2]. In this case, the composite tensile strength compensates for the lack in the masonry apparatus of it by counteracting the opening of cracks and plastic hinges. This work focuses on the FRCM strengthening performed with PBO (Polyparafenilenbenzobisoxazole) textile applied on three-centred arches. This type of arches can present greater structural vulnerability due to its particular shape. The presence of different curvatures leads to a non-uniform distribution of stresses. In the central part of the arc with a higher radius, the vertical components of the actions are, in fact, more significant than the rest of the structure. This work aims to assess the effectiveness of FRCM with PBO textiles, strengthening by comparing the results of several numerical modelling with a load test performed on a three-centred arc. The load test has been performed on an arc of the historical complex of "Santa Maria delle Grazie" church sited in Barano on the isle of Ischia, where restoration works are still ongoing. Moreover, the historical site hosts an experimental campaign for structural monitoring with innovative techniques. In detail, the load test has been performed with traditional instruments, a fibre optic transducer [3] installed on the tested arc and acoustic sensors for acoustic emission monitoring.