Experimental Investigation of Fatigue Shear Behavior of RC Beams Strengthened with FRP Bars Using Embedded Through-Section Technique

This study presents the results of an experimental investigation of fatigue shear behavior in reinforced concrete (RC) beams strengthened with fiber-reinforced polymer (FRP) bars using the embedded through-section (ETS) technique. Thirteen ETS-FRP-strengthened beams were tested under two scenarios of medium-cycle fatigue (MCF) and high-cycle fatigue (HCF). The design variables were the number of stirrups, the FRP type, and the FRP size, and their effect on the fatigue characteristics of ETS-retrofitted RC beams was examined. The displacement and strain in flexural and shear reinforcement in the ETS-strengthened beams increased during the initial cycles and tended to stabilize during the rest of the fatigue process. Under MCF and HCF conditions, the fatigue stress ranges for longitudinal steel with ETS-FRP-strengthened beams satisfy the limits mandated in the American Association of State Highway and Transportation Officials code. Similar to previous studies, the maximum strain of 2,000 µɛ in the ETS-FRP strengthening systems can be considered the strain limit for the fatigue design of ETS-FRP-retrofitted beams. The use of glass FRP bars with a narrow spacing substantially extended the fatigue life of ETS-strengthened beams (to more than 3,000,000 cycles) compared with unstrengthened beams and beams retrofitted with carbon FRP bars. Conversely, a large number of stirrups reduced the contribution of ETS-FRP strengthening. The strength of the retrofitted beams increased with increasing FRP elastic modulus and bar diameter. Failure of ETS-FRP-strengthened beams under fatigue tests and static tests occurred in a safe and ductile manner because no rupture of the steel stirrups or the FRP bars occurred, and no early FRP debonding was observed.