Effect of retrofitting on the structural factors for seismic assessment of unreinforced masonry structures: a review

When considering models for seismic assessment and retrofit design, designers need to account for any changes in the structural ductility factor and performance factor between an original unreinforced masonry structure and one which has been subsequently retrofitted. There are enough data available in the literature and the standards to suggest ductility and performance factors for existing unreinforced masonry walls or buildings. However, there is a lack of information regarding the above-mentioned factors for retrofitted structures or walls. Retrofitting unreinforced masonry buildings can improve the behaviour factors, displacement capacity, stiffness and performance of the structure. Retrofit strategies are aimed at improving the performance of the structure locally by considering the weak or brittle elements, and/or to improve the global behaviour of the building by focusing on the connections of the elements. In the present paper, the different retrofitting techniques for unreinforced masonry walls and unreinforced masonry buildings are considered. The structural factors for retrofitted walls and structures are calculated using experimental data extracted from the literature and are compared, together with a discussion, to the pre-retrofitting factors available in the literature and different standards. The implications for the relevant standards regarding the performance of retrofitted masonry structures are also discussed.