Assessment of failure mode and seismic performance of damaged masonry structures retrofitted with grout-injected ferrocement overlay reinforcement (GFOR)

Abstract The vulnerability of unreinforced masonry (URM) structures under seismic action has promoted efforts to explore a wide variety of retrofitting and repairing methods. However, most studies have focused on the in-plane response of newly built walls; few have discussed the failure mode and seismic behavior of damaged walls before and after retrofitting. Hence, the present study was conducted to investigate the failure mode and seismic performance of damaged URM walls retrofitted with grout-injected ferrocement overlay reinforcement (GFOR). The main parameters in the experiments were the aspect ratio and the stiffness ratio of the spandrel to the pier. Two groups of URM specimens with different vertical loads were fabricated using identical clay brick units and cement mortar. The specimens in the first group had a length of 2450 mm, a height of 2550 mm, and a thickness of 240 mm, while those in the second group had a length of 3300 mm, a height of 1950 mm, and a thickness of 240 mm. Testing was performed with a gradual increase in the horizontal load and displacement reversals, combined with a constant vertical load. Subsequently, both sets of damaged URM walls with pier failure were retrofitted with GFOR; the retrofitted specimens were designated as ferrocement reinforced masonry (FRM) walls and were retested to their ultimate state under load conditions identical to those in the initial test. Finally, the results for the URM and FRM walls were compared in terms of the failure modes, force–displacement curves, and other experimental parameters. The findings indicate that the spandrel failure mode was more likely in the walls under larger vertical loads. The walls exhibited the spandrel failure mode had a greater lateral force and better energy dissipation. Both sets of damaged walls exhibited a more reasonable failure mode (from “pier before spandrel” to “spandrel before pier”) after the GFOR technique was adopted.