Pullout strength of NSM CFRP strips bonded to vintage clay brick masonry

The frequently observed inadequate seismic performance of unreinforced masonry (URM) buildings necessitates the development of cost effective minimally-invasive seismic improvement techniques for this type of construction. One promising solution is use of the near surface mounted (NSM) technique to incorporate fibre reinforced polymers (FRP) strips as longitudinal reinforcement. In particular, the NSM technique provides several advantages over externally bonded (EB) FRP as a seismic improvement technique including significantly higher axial strain at debonding, minimal negative impact upon the aesthetics of the structure, reduced installation time, and superior protection from fire and the environment, thus providing a cost effective and minimally-invasive option for seismically strengthening URM buildings. An experimental program consisting of 39 pull tests was conducted using NSM carbon (C)FRP strips bonded to vintage solid clay brick masonry, to provide data with which to validate the accuracy of existing predictive FRP-to-masonry bond models. Based on experimental findings, a variation of an existing analytical FRP-to-masonry bond model is proposed and the effects of geometric variation of the NSM groove and the reinforcing CFRP strip are discussed.