Experimental investigation on local aspects of the FRP strengthening of masonry arches

The paper presents a contribution to the experimental study of two local failure mechanisms observed during the testing of masonry arches, and barrel vaults, reinforced by means of externally applied fibre Reinforced Polymers (EB FRP).In particular, the first campaign is related to the detachment of the intrados reinforcement, prone to stresses normal to the surface, from the support. The investigation consists in performing three types of mechanical test on the same clay element, namely a three-point bending on the intact brick, a compressive test or a splitting tensile test on one of the two portion produced by the flexural failure, and two pull-off tests on the remaining clay piece, after the application of a layer of FRP textiles on both the wider surfaces. Based on the results, the possible relations between the pull-off strength and each of the other parameters (?flexural, compressive and splitting tensile strength) were investigated, taking into account the variation of the clay substrate, the type of fibres (carbon, CFRP, or glass, GFRP) and the presence, or not, of a layer of primer.The second campaign is related to the sliding on a mortar joint due to excessive shear force, the primary failure mechanism experimentally observed in the case of extrados reinforcement. This experimental activity, aimed at investigating a possible contribution of the reinforcement to the resistance of the joint, is based on the "V-shape Peel Test", which consists in pulling down the middle part of a strip of composite applied on the clay substrate - two solid bricks juxtaposed along their longitudinal axis - acting orthogonally to the strip's plane, so as the reinforcement, during the detachment, assumes a typical "V" shape. The purpose of this test, of which the first results related to fourteen trials are reported, was to reproduce and isolate the behaviour of the reinforcement connected to the above mentioned failure mechanism.