Structural upgrade of deficient Unreinforced Masonry structures using Ultra High Performance Fibre Reinforced Concrete

The structural upgrade of substandard Unreinforced Masonry (URM) is an urgent need worldwide and especially in earthquake prone areas and in low and middle income countries. The majority of the existing URM buildings in these areas have not been designed to resist seismic action, and in many cases, substandard materials have been used, therefore the structural strengthening of these structures is essential. The strengthening of existing low strength masonry is a quite challenging task since the effectiveness of the external application of high strength materials (e.g. Fibre Reinforced Polymers) is limited due to the poor connection between the new materials and the existing substrate which leads to de-bonding and premature failure of the strengthened structures. In this study, a novel strengthening technique has been examined using Ultra High Performance Fibre Reinforcement Concrete (UHPFRC) layers in addition to partial replacement of the existing mortar with UHPFRC. Experimental investigation has been conducted on brick walls constructed using low strength bricks. UHPFFRC layers with various thicknesses with and without UHPFRC at the joints have been applied to the URM walls and flexural out-of-plane tests have been conducted. The experimental results demonstrate that the proposed technique can considerably improve the ultimate load and the ductility of the URM walls. Also, the proposed technique offers improved UHPFRC-to-URM interface conditions.