STRENGTHENING WITH FRP BARS OF URM WALLS SUBJECT TO OUT-OF-PLANE LOADS

Abstract

For the retrofitting of the civil infrastructure, an alternative to Fiber Reinforced Polymer (FRP) externally-bonded laminates is the use of near surface mounted (NSM) FRP bars. This technique consists of placing a bar in a groove cut into the surface of the member being strengthened. The FRP bar may be embedded in an epoxy- or cementitious-based paste, which transfers stresses between the substrate and the bar. The successful use of NSM FRP bars in the strengthening of concrete members has been extended to unreinforced masonry (URM) walls, one of the building components most prone to failure during a seismic event. This paper presents the results of an experimental program on the flexural behaviour of URM walls strengthened with (NSM) FRP bars. A total of fifteen URM walls reinforced with NSM FRP bars were tested. The specimens were strengthened with different amounts of reinforcement to observe their improved performance and the mode of failure. The influence of the bar shape (i.e. circular vs. rectangular), dimension of the groove and type of embedding material (i.e. epoxy or cementitious-based paste), were studied. Two types of FRP fabrics, glass (GFRP) and carbon (CFRP), were used as externally bonded reinforcement to provide the benchmark. Strength and pseudo-ductility of URM walls were significantly increased by strengthening with FRP bars. Based on experimental evidence and on the data found in the literature, the paper provides criteria that can be used in the development of design guidelines.