## 1 Introduction  
In seismic regions such as Italy, the evaluation of the capacity and fragility of structural and infrastructural systems subjected to seismic events [1; 2; 3; 4; 5; 6; 7; 8; 9], and implementing proper survey programs to monitor the evolution of their capabilities [10; 11] are important for preventing severe seismic damage being observed in recent seismic events [12] by means of retrofitting interventions [13; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23; 24; 25; 26; 27; 28; 29; 30; 31]. Repair strategies to restore or improve the seismic capacity of reinforced concrete (RC) components, usually seriously damaged after a strong earthquake [32; 33; 34; 35; 36; 37; 38; 39; 40; 41; 42; 43; 44], may significantly reduce the economic, social, and environmental impacts with respect to reconstruction. Repairs should be performed simply and quickly on construction sites to assure that the strategy is appropriate also in case of bridges that are strategic for the emergency response. In the literature, the repair of RC components is usually performed in case of modest damage (local concrete spalling or modest deformation of the steel reinforcement) when the deformed rebar can be straightened, and the cover can be restored by simple mortar patches. Finally, an external fiber reinforced polymer (FRP) is applied to improve the shear strength and the ductility of the component [33]. However, serious damage, which includes high deformation of longitudinal rebar in tension or in compression, steel reinforcement rupture, and concrete core crashing in compression, may arise: (1) In the plastic hinge region of the RC components designed by capacity design criteria after a strong earthquake; (2) in the most stressed zones of the RC components not properly designed or built for the seismic action after a moderate earthquake; and (3) along the RC component when the corrosion of the steel reinforcement is severe. Damaged rebar substitution is problematic because anchoring new rebar in the existing foundation is difficult, and new rebar may congest the existing steel reinforcement and complicate the concrete pouring to restore the removed concrete parts. The substitution of the damaged rebar segments only in the plastic hinge using new rebar segments may minimize these problems. The new segments can be connected to the existing anchorages and to the rebar part outside the plastic hinge region, and the use of rebar segments can limit the congestion of the steel reinforcement. The protection of the rebar connections then become one of the most important design targets. A review of the literature provided few solutions for the local substitution of the broken rebar. Therefore, new research efforts are necessary. These research studies presented different solutions to connect new rebar to the existing rebar. The rebar substitution performed by [PERSON] et al. [35] used special dog-bone bars connected by welding to the existing rebar and guaranteed plastic deformation along the plastic hinge only. This dog bone was a special piece built in the laboratory, so the proposed connection with the original rebar can be problematic on actual construction sites. [PERSON] et al. [36] successfully tested a local rebar substitution using stainless steel rebar to improve the durability of the intervention. A new rebar connection system using asymmetric lateral welding showed possible failure in the case of high levels of rebar deformation. [PERSON] et al. [37] locally substituted the damaged rebar parts with identical rebar segments connected by different connection systems by welding. This resulting solution was effective, but the column core was entirely removed to ensure adequate proper work space, and the use of steel segment rebar with the same size and mechanical characteristics of the existing rebar may not guarantee plasticization in the plastic hinge only--away from the original anchorages of the rebar--because the strength of the new steel segments may be statistically higher than that of the original rebar.