Mechanical devices for manually prestressing FRP and their applications in structural strengthening
Fiber reinforced polymer (FRP) systems have demonstrated to be effective for the retrofitting of masonry walls and reinforced concrete (RC) members. Prestressing of the FRP can further improve the serviceability and capacity of the strengthened elements. This dissertation presents the development of one mechanical device to prestress glass FRP (GFRP) bars and another device to prestress carbon FRP (CFRP) sheets and their applications for the retrofit of unreinforced masonry (URM) walls and RC beams. For the GFRP bar system, the bars are installed in grooves of the URM walls with near surface mounted (NSM) technique and then post-tensioned with the hand-held device to partially close cracks and increase shear capacity of the walls. For the CFRP sheet system, the sheets are temporarily anchored to the device, and prestressing is achieved by applying an equal vertical uplift displacement at an equal distance away from the anchorage regions. For both devices, prestressing forces are applied manually without the need for hydraulic jacks. The URM walls were then tested under one in-plane diagonal compressive load, and the RC beams were tested under one four-point bending system. Increase of the shear capacity of the strengthened walls and the flexural capacity of the strengthened beams was observed. A theoretical analysis of the shear capacity of the tested URM walls was conducted. A theoretical model for calculating prestressing stresses of the CFRP sheet and the allowable prestressing level before the CFRP system fails was proposed. Flexural and premature failure of the RC beams strengthened with the prestressed CFRP sheets was investigated as well. The theoretical investigations and the experimental programs of the walls and the beams are presented in this dissertation.