Aseismic retrofitting of unreinforced masonry walls using FRP

Many of existing unreinforced masonry (URM) buildings are seismically vulnerable and require retrofitting. This paper investigates in-plane seismic behaviour of URM walls before and after retrofitting using fiber-reinforced polymers (FRP). Dynamic in-plane tests were carried out on five half-scale specimens with two different effective moment/shear ratios namely 0.7 and 1.4. The specimens were retrofitted on a single side using different types and structures of FRPs. The test specimens were subjected to a series of synthetic earthquake motions on a uni-axial earthquake simulator. The retrofitting technique improved the lateral strength and stiffness of the URM walls. Moreover, the fundamental frequency and the initial stiffness of each specimen remained approximately constant before and after retrofitting. During the test, the slender specimens failed in flexural. For specimens failed in flexural, the measured FRP axial strains showed that the strain distributions along the specimens' cross-sections are approximately linear even at failure. Hence, the flexural strengths of the specimens were calculated using linear elastic approach. The measured lateral resistances of slender specimens are approximately 130% of the calculated flexural strength. This difference attributed to the difference in the nominal ultimate strains of FRPs and the real values at failure. The measured axial strains in FRPs during this test were approximately 50% of its nominal values. In addition, the shear strengths of the squat specimens were calculated using two different models. The calculated shear strengths approximately range from 99 to 177% of the measured lateral resistances.