Experimental study on seismic performance of unreinforced masonry walls retrofitted with low-strength engineered cementitious composites

Engineered cementitious composites have recently been investigated for seismic retrofitting on unreinforced masonry walls due to their ductile strain hardening behavior. It has been found in literature that the normal-strength engineered cementitious composite can significantly increase the strength of the wall under cyclic in-plane lateral loadings. At the same time, the improvement of the deformation capacity is limited, possibly due to the incompatibility between the masonry wall and the composite in terms of strength and stiffness. To achieve better compatibility, one possible solution is to use low-strength engineered cementitious composites as the retrofitting material. Through an experimental study, this paper investigates the performance of the unreinforced masonry wall retrofitted with the low-strength engineered cementitious composite. Six unreinforced masonry wall specimens with aspect ratios of 0.55 and 0.7 were tested at one-third scale under cyclic in-plane lateral loadings. Two specimens were built without retrofitting as reference cases. The other four were retrofitted by directly troweling the composite on each face of the wall without anchoring to the foundation. The low-strength composite was designed with two compressive strengths, 10 MPa and 25 MPa respectively. From the test results, it was found that the low-strength composite can change the failure mode of the wall, effectively enhance its deformation and ductility capacities, and improve its energy dissipation. The overall deformation and ductility capacities can be increased by 50% ~ 100% depending on the strength of the composites. Additionally, an analytical procedure was proposed to estimate the lateral force capacity of the retrofitted wall based on a section analysis.