## 1 Introduction
It was demonstrated that applying open hoop FRP strips, thus avoiding confrontation with breaking the slab, leads to limited shear upgrade because these open hoop FRP stirrups suffer from premature debonding, thus being completely neutralized [35; 36; 37]. This is presented and discussed in Sections 2-4. In Figure 4 an RC T-beam is shown schematically provided with external FRP reinforcement in order to increase its flexural and shear capacity. The positive bending moment capacity increase, as shown in Figure 4, is enhanced by FRP strips bonded at the bottom side of this T-beam with an FRP strip of one or multiple layers (indicated with red color) having as width the width of the bottom side of this T-beam. For negative bending moment capacity increase, the FRP strip should be bonded alternatively at the top side of this T-beam. In this case, this becomes relatively easy because the FRP strip width can be much wider than that bonded at the bottom side. This externally bonded CFRP strip will function in the same way as the internal longitudinal steel reinforcement developing tensile axial forces. The shear capacity is similarly enhanced by the transverse shear FRP open hoop strips (indicated with blue color) bonded externally; they will also develop axial forces resisting in this way the shear force demand after the formation of the diagonal shear cracks through the concrete volume. They will function in the same way as steel shear reinforcement placed internally in the form of steel stirrups. For either flexural or shear retrofitting utilizing externally bonded FRP strips, it is critical to investigate the capacity of the relevant bond surfaces which will be called to transfer the axial forces that develop in these FRP strips in each case. When the level of these axial tensile forces exceeds the corresponding bond capacity the debonding mode of failure appears rendering the relevant FRP reinforcement completely ineffective. This represents a serious limitation in applying such external FRP retrofitting either for flexural or shear upgrading. One effective way towards this objective has been to provide various practical schemes of anchoring that combined with the FRP strips can transfer the desired level of axial force beyond the limit posed by the relevant bonding surface as indicated in Figure 4. This has been the focus of the research reported here. In order to confront the unsatisfactory performance due to the debonding mode of failure various anchoring schemes have been devised [44; 45; 46; 47; 48; 49; 50; 51; 52; 53; 54; 55; 56; 57]. [PERSON] et al. [44] reported on the performance of RC shear deficient T-beams strengthened with carbon fiber reinforced polymers (CFRP) systems with and without mechanical anchoring in several different configurations tested under cyclic loading conditions. [PERSON] et al. [45; 46; 47; 48; 49; 50; 51; 52; 53], as well as [PERSON] et al. [54], used either CFRP or SFRP for shear strengthening. The authors of this work have devised and tested such anchoring schemes [48] which combined with externally applied  
Figure 4: Force transfer mechanisms for externally bonded FRP strips either for flexural or shear retrofit. FRP strips can provide the required substantial shear upgrade of RC T-beams, deficient in shear, as is presented in what follows. Moreover, a number of alternative anchoring devices to be used in shear strengthening schemes together with externally applied FRP strips are also presented and discussed. All these anchoring schemes together with external FRP strips can form equivalent closed hoop stirrups which can provide the required upgrade in shear strength for such deficient RC T-beams. In the following sections, the force transfer mechanism that is mobilized for open hoop CFRP strips with or without anchoring devices, used as transverse shear reinforcement, is presented and discussed. This is carried out initially utilizing a novel experimental set-up employing small-length \"unit T-beam\" specimens hosting such CFRP strips (Sections 2 and 3).