## 7 Conclusions and Discussion  
Two beams (DB1, DB2) extracted from an old RC structure, were strengthened for shear by an EB-CFRP reinforcement and for bending by new bottom longitudinal rebars to be tested in the lab until failure. The case at hand is the only one with \"real\" old RC beams built with modest-quality concrete and transverse steel rebar distributed randomly along the beam, as in the case of many existing beams. Experimental tests on materials showed a wide scatter of the concrete compressive strength values and the concrete of the beam DB1 was, on average, of better quality with respect to the one of the beam DB2 even if the two beams were located very close in the structure. Furthermore, the concrete compressive strength at the beam top part was greater than the one at the bottom part along each beam; this is probably due to cracking of the beam region in tension and to concrete segregation. The experimental initial beam stiffness was up to 4-5 times smaller than the theoretical one calculated considering the uncracked gross section. This is expected because the beams were extracted from a building subjected to loads and therefore the beam sections were already cracked. Consequently, the \"real\" beam capacity in terms of strength and deformation should be closely considered by designers because the CFRP reinforcement can modestly restore the beam stiffness by up to 12-14%. From the experimental tests, the brittle failure mechanism of each beam was characterized by the propagation of concrete diagonal cracks and by the delamination of CFRP reinforcement as soon as the CFRP-concrete bond interface started to crack. The experimental transverse steel reinforcement, CFRP reinforcement and concrete contributions to the shear resistance were calculated based on the experimental measurements when the maximum shear was recorded on the beams. After the CFRP reinforcement failure, the sum of the experimental transverse steel reinforcement and concrete contributions are similar to the residual shear value recorded on each beam. This means that the aggregate interlock, the dowel effects of the longitudinal rebars and the other \"concrete\" resisting mechanisms gave a contribution to the shear resistance of the retrofitted beam. However, this concrete contribution is uncertain because it is obtained starting from the retrofitted beam maximum shear and from the experimental steel and CFRP reinforcement contributions that are uncertain. The evaluation of the steel contribution is uncertain because:  
1. The stirrup spacing was irregular;
2. The plastic force distribution was reduced by the CFRP reinforcement and so some stirrups could give a smaller contribution;
3. The CFRP reinforcement limited the crack width and so the stress in the stirrups could be smaller than the yield stress depending on the actual steel strain;
4. The scatter of the steel yield and of the maximum steel stresses were wide (SS2.2). For the tested beams, the experimental strain measured on the CFRP strips were about 0.3% (SS4.3.3) and so the stirrups more probably yielded because the steel yield strain is 0.2%. The evaluation of the CFRP contribution is also uncertain because:  
1. The number of the strips, that gave a contribution at the same time, is uncertain;
2. The actual strain of the CFRP fabric could be greater than the one measured locally where strain gauges were placed (Figure 9). For that reason, the retrofitted beam shear strength evaluated without considering the concrete contribution by the modern design code seems safer. Finally, the concrete contribution predicted by Eurocode 2 [70] without considering the new bottom longitudinal rebars, is similar to the experimental one for each beam. This means that the new bottom rebars, which had insufficient anchorages, did not give a contribution to the beam shear resistance. However, the new bottom rebars avoided flexural failure according the test design target. For that reason, retrofitting construction details should be closely considered by designers.