## 3 Cyclic Behaviour of a RC One-Bay, One-Story Frame Retrofitted with an RC Infill Panel
### Unit T-Beams with Open Hoop CFRP Strips Employing Specific Mechanical Anchoring Devices
For comparison purposes, an equivalent shear strain for the whole infilled frame is also plotted based on the measured horizontal displacement of the top beam of each tested specimen, which is identical to the drift value for this single-story frame (H-top). From Figure 14a, it can be deduced that for specimen UC-IP 1 the maximum applied load (127 kN) results in equivalent shear strain (drift) of approximately 1.5%. This is mainly due to the formation of the plastic hinges at the columns and beam and the separation of the infill panel from the surrounding frame, due to the absence of any ties, whereas the shear strain of the infill panel itself is almost zero. As already discussed, during this test the concrete of the infill panel was crashed locally at its four corners without the development of any diagonal tension cracking within the panel itself. This explains the zero shear strain in Figure 14a deduced from the instrumentation readings of the displacement transducers located within the infill panel away from the corners. It was underlined that this limit state is rather undesirable because this localized damage limits the horizontal load-bearing capacity of such a retrofitting scheme. This local damage at the corners of the RC infill may also inflict damage on the joints of the RC frame. Figure 14c demonstrates that the presence of net reinforcement in the RC-IP3 leads this panel to sustain larger shear strain values within itself and for larger horizontal load (408 kN) than the case in which the infill panel was unreinforced (Figure 14b, UC-IP2, applied horizontal load 338 kN). The displacement response in terms of sliding and separation between the infill panels and the two columns (E-East, and W-West) of the surrounding RC frame close to the region of the column-to-beam joints is also monitored. This response versus the applied load is depicted in Figure 15a-c for specimens UC-IP1, UC-IP2, and RC-IP3, respectively. The absence of any steel ties results in large sliding and separation displacement response at this interface (Figure 15a). The presence of steel ties (Figure 11) combined with a reinforced concrete infill panel (RC-IP3, Figure 15c) results in small separation displacement response, while allowing for considerable sliding displacements for relatively large horizontal load values (408 kN). In this way, the steel ties contribute to the accumulation of plastic energy through dowed action, which is an additional beneficial effect toward seismic resistance. The effect of the presence of the steel is also seen for the unreinforced concrete specimen but to a lesser extent (UC-IP2, Figure 15b). The absence of met reinforcement leads to the premature failure of the unreinforced panel (Figure 13b). Figure 15: _Cont._  
In Figure 16, the top horizontal load versus the equivalent shear strain of the infilled frame is shown for all three tested specimens with concrete infill panels in the form of envelope curves. As can be seen in this figure (see also Table 3), the steel ties result in a substantial increase of the in-plane horizontal load-bearing capacity. However, the lack of reinforcement of the infill concrete panel in this case results in its premature failure limiting this specimen in sustaining this load-bearing capacity for relatively low equivalent shear strain values (0.8%); this limitation is resolved by providing the infilled concrete panel with partial reinforcement. In this case (RC-IP 3), the maximum horizontal load-bearing capacity attains an even higher value (408 kN) than for UC-IP 2 (338 kN); moreover, this horizontal load-bearing capacity is sustained for equivalent strain (drift) values of nearly 4%. The specific limitations of the UC-IP 1, in terms of both load-bearing capacity and deformability, have been noted. Figure 15: (**a**) Horizontal load cyclic response versus sliding at the contact surface of the concrete infill panel and surrounding frame for specimen UC-IP 1.