Seismic retrofitting of unreinforced load bearing brick walls in historic buildings using fiber-reinforced polymer strings

Most of the historical buildings and monuments in the world are unreinforced masonry (URM) type and they are vulnerable to seismic actions. Considering the seismic activities in the regions where historical masonry structures are located, their structural assessment and rehabilitation or retrofitting if necessary against seismic forces are needed in order to preserve them for future generations. International organizations such as UNESCO (United Nations educational, Scientific and Cultural Organization) and ICOMOS (International Council on Monuments and Sites) try to increase the awareness in need for preserving these world-heritage structures. However, historical masonry structures still need retrofitting techniques that are much different than that of buildings that were built using conventional construction practice since the architectural features of the historic buildings must remain unchanged after the retrofitting process. Therefore, conventional methods have been used in retrofitting works are not suitable for such purposes. In this study, the use of carbon fiber-reinforced polymer (CFRP) strings placed in mortar joints for strengthening of URM structures was investigated. Nearly full-scaled four URM brick wall specimens with aspect ratio of 1.00 were tested under varying axial load and cyclic lateral loading. Two of the specimens were tested as control specimens while other two specimens were retrofitted with horizontally-oriented CFRP strings. Also, one of the tested control specimens were repaired and retrofitted and re-tested in order to see the effect of this retrofitting technique after substantial damage occurred. Test results showed that energy dissipation capacity of the wall specimens were enhanced with the proposed technique. In addition, the crack openings due to shear effects were minimized while keeping the historic and aesthetical view of the structures intact, since they were directly placed inside the mortar joints and debonding of strings were prevented. However, no significant increase in the lateral load carrying capacity of the specimens was observed.