Cyclic behavior of masonry walls retrofitted with post-installed twisted bars or bonded rebars

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.