Investigating the effectiveness of a CRM system: full scale reverse cyclic tests on a two-storey rubblestone masonry building

The research work aims at investigating the effectiveness of a minimally invasive strengthening technique used to repair a full scale two-storey building, consisting of 350 mm thick two-leaf rubblestone masonry walls, a timber floor, and a timber roof with clay tiles. The strengthening technique consists in applying on the external façade of the building a single layer of a Composite Reinforced Mortar (CRM) System, which consists in a mortar coating containing a Glass Fiber Reinforced Polymer (GFRP) mesh; artificial diatons connecting both wythes of the walls were also applied. The reverse cyclic load was applied to each of the two longitudinal walls of the building by means of a servo-controlled hydraulic jack pinned to a vertical steel beam. This beam allowed splitting the total lateral force into two forces, acting at first story and roof levels; these forces were calculated proportional to the product of the floor mass with the floor level. The first cyclic test was carried out on the Unreinforced Masonry (URM) building up to attaining a damage level quite close to that corresponding to the ultimate limit state of the structure. Then, the building was repaired (RM) with the proposed technique and tested again, up to reaching a near-collapse condition. The experiments proved the effectiveness of the proposed strengthening method showing a resistance increment of 240%, a larger displacement capacity (150%) and a significant increase of the total dissipated energy. The importance of the artificial diatons to prevent the separation of the masonry leaves in strengthened walls was also clearly highlighted.