The lack of effective connection between masonry walls is one of the most common reasons leading to the activation of out-of-plane failure mechanisms in masonry buildings during earthquakes. Thus, retrofitting interventions aimed at improving the box-like behavior of masonry structures are of primary importance. The paper presents the results of an experimental program aimed at investigating the effectiveness of two different fastening solutions to improve the joint connection of masonry walls in existing unreinforced masonry buildings. A full scale C-shaped clay brick masonry specimen was built featuring purposely weakened wall intersections. Vertical prestress was applied on top of the specimen to represent the weights of upper floors. The specimen was first tested in the unreinforced configuration under monotonic out-of-plane displacement, until a main crack was detected. Then, its corner connections were repaired using twisted bars, and tested under cyclic out-of-plane displacement. Lastly, the twisted bars were removed and replaced with bonded bars, and the specimen was tested again under cyclic out-of-plane displacement. The test results showed that both retrofitting solutions were able to recover the full capacity of the unreinforced wall, with higher displacement and dissipation capacity for the twisted bars solution, and higher resistance for bonded bars. The latter seems to be the most effective solution, especially in terms of monolithic behavior achieved; however, the large displacements associated to twisted bars could be a great advantage in case of earthquake actions.

The damage observed after the recent earthquakes showed that the most common failures for masonry buildings involve out-of-plane mechanisms associated to the ineffective connection between walls. For this reason, retrofitting techniques aiming to achieve a box-like behavior are of great interest. This paper presents the results of an experimental study conducted to investigate two different retrofitting solutions used to improve the structural connection between orthogonal walls: a mechanical connection by means of twisted bars and a fastening solution with rebars and injection mortar. Two full-scale T-shaped masonry specimens were realized in solid clay brick, with a “weak” connection between the front and the back wall. The specimens were tested in unreinforced and strengthened configurations, considering different retrofitting layouts. An out-of-plane load was applied on the front wall, together with a vertical prestress to simulate the gravity load coming from the floors and walls above. Each specimen was tested in three consecutive runs: a monotonic one on the unreinforced masonry, a first cyclic run with the wall intersection reinforced with twisted bars, and a second cyclic run on the wall retrofitted with rebars and injection mortar, after the removal of the twisted bars. The twisted bar solution resulted in a significant increase of the dissipative capacity of the wall despite the number of adopted bars, while, in the case of rebars and adhesive, a higher resistance was achieved together with a perfect box-like behavior.