## 1 Introduction  
In seismic countries as Italy, many reinforced concrete (RC) buildings were built from the beginning of the 20 th century. The existing buildings designed by old design codes can be very vulnerable to the medium-high seismic hazard of Italy [1; 2; 3; 4]. Furthermore, Italy has extremely high exposure due to population density and its artistic, historical, and monumental heritage. During recent years, old artistic, industrial or civil RC buildings have increasingly been protected as historic symbols through carefully planned interventions [5; 6]. The conversion of these buildings, their rehabilitation, and their reuse for modern activities may assure their protection and represent a solution for the increasing need for new structures, assuring modest social, economic, and environmental impacts. For that reason, the attention of the construction industry increasingly moves from new constructions to maintenance, repair and/or retrofitting and rehabilitation of existing structures [7; 8; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23; 24; 25; 26; 27; 28]. In this context, this paper focuses on the study of retrofitting solutions to improve the load-carrying capacity of existing old RC beams by Externally Bonded Fiber-Reinforced Polymer (EB-FRP) reinforcement much used in construction. In particular, many researchers have extensively studied and tested the shear strengthening of RC beams by EB-FRP reinforcement [29; 30; 31; 32; 33; 34; 35; 36; 37; 38; 39; 40; 41; 42; 43] but the behavior of these beams is still much discussed in the literature [29; 31; 44; 45; 46]. The main discussion issues are regarding: the shear interaction between the different contributions for the shear strength [47; 48; 49], the influence of the beam size [50] of the shear span-to-depth ratio [30] and the contribution of the shear FRP reinforcement to the beam resistance in proportion to the FRP thickness [51]. Regarding the first issue, the experimental results have shown that not all steel stirrups crossed by shear cracks yield [32; 38; 39; 40; 45; 46; 52; 53; 54; 55], and so the steel shear reinforcement contribution may not be fully mobilized [48] especially in the case of FRP reinforcement debonding. For that reason, the shear strength value predicted by well-known models may be not safe [44; 48; 49]. Furthermore, many research efforts are still necessary for resolving some critical issues about FRP reinforcement such as: the brittle failure mode of retrofitted RC members due to sudden failure or debonding of the FRP reinforcement [56]; the effects of wet-dry cycles and freeze-thaw conditions on the FRP fabric that produce deterioration of the FRP mechanical properties; the reduction of the strength of the FRP reinforcement due to improper installation procedures, the lack of proper bond strength models and the need for efficient anchorage systems when it is not possible to provide a correct anchorage length or in the case of inevitable strip debonding [57]. These research studies were usually performed on beams purposely built in the lab to be retrofitted and tested, that did not present material deterioration phenomena (corrosion of rebar, concrete carbonatation or surface peeling) [58; 59], poor concrete quality, improper reinforcement detail and uncertainties about steel and concrete mechanical characteristics and rebar configuration typical of \"real\" old RC structures [60; 61]. For that reason, the experimental tests are necessary to evaluate the shear strength, the failure mode, and the strain of the FRP reinforcement for \"real\" beams. The present paper investigates the shear strength of two \"real\" retrofitted beams extracted by an old RC structure built with poor-quality concrete in Rome in 1929. The two beams were removed during retrofitting of the building (Figure 1) and brought to 'the Proof testing and Research in Structures and Materials Laboratory (PRiSMa)' of the Roma Tre University (Rome, Italy) (SS2).