Collapse behaviour of FRP reinforced masonry arches: a parametric enquire

Masonry arch systems and vaulted structures constitute a structural typology widely spread in the historical building heritage. These constructions often require to be repaired, strengthened or reinforced in order to have their structural safe enhanced. Furthermore the maintenance of their architectural aspects is often necessary. The use of composite sheets placed at the surface of the structures usually allows to satisfy both requirements. Many experimental investigations showed the effectiveness of the technique in improving the strength of the structures and, in addition, the well known properties of the FRP sheets make the intervention fast, reversible and very well adaptable to different shapes with a strong concern to the architecture of the system. The application of FRP sheets modifies the collapse behavior of the system without any reinforcement. Indeed the collapse of the reinforced arches can be shifted by the classical mechanism towards a local failure at some critical sections due to one of the following type of failure: masonry crushing, the tensile failure of the composite fibres, the bond failure at the masonry-FRP interface and slip at a mortar bed orthogonal to the arch axis. If the FRP sheets are not bonded below the springing sections, the structure can overturn around the right (left) corner of the right (left) restrained section. This failure mode, which is never activated in the unstrengthened structure, must be always considered if the FRP reinforced structure is subjected to horizontal loads. The problem of evaluating analytically the failure load of a strengthened arch has been addressed, with some simplifying assumptions, in different papers. In particular some of the authors have already developed and presented a simple method for calculating the failure load of a single arch completely reinforced at intrados and/or extrados and subjected to vertical and horizontal loading. As a result a method to evaluate the interaction failure locus in the plane of the horizontal and vertical load has been defined. In this paper the above-mentioned model is applied and extended to different geometries and load conditions of masonry arches. In particular a parametric enquire will be carried out by varying the geometrical characteristics of the bare structure, the thickness and location of the FRP sheets, the load condition. These aspects need to be carefully analysed since they influence the ultimate behaviour of the arch. In fact the collapse mode can be different if the composite is applied at the intrados or at the extrados, if the strengthening is partial or complete or if the thickness and the diameter of the arch vary. The results of the paper will be summarized in non-dimensional design curve reporting the failure loads and the expected type of failure for each geometry, mechanical ratio of FRP fibers, FRP arrangement and load condition.