# Retrofit of Existing Reinforced Concrete (RC) Buildings: Steel vs. RC Exoskeletons
## 2 Case Study Building  
The examined case study system is an RC building located in the Municipality of Reggio Calabria (RC), Italy, near the Mediterranean University of Reggio Calabria (Figure 1). The system consists of a residential building with a multi-story RC frame structure and brick infill, built in the early 1970s, as documented by calculation reports found in accessible historical archives.  
The building structure was originally designed in accordance with the Technical Standards of Royal Decree N. 2229 of 16 November 1939, which presents \"Standards for the execution of simple and reinforced concrete structures\" [26; 27]. The structural solution is typical of buildings constructed in the 1970s, and resistant only to gravity loads. The case study system has a typical L-shaped plan layout, with maximum dimensions of 28.0 m \(\times\) 22.0 m (Figure 2).  
Figure 1: Localization and general view of the case study RC building in Reggio Calabria (Italy).  
Figure 2: Typical horizontal section of the 1 st floor (scanned archive drawings).  
The system is also characterized by seven moment-resisting frames arranged along the X-direction and six moment-resisting frames arranged along the Y-direction. These assembled frames comprise the 3D-resistant structure. In the elevation, the building consists of six floors; the first story level has a total height of 3.6 m, while the inter-floor height of the other five floors is reduced to 3.4 m.  
Knowledge of the basic structural characteristics of the building components was obtained by a campaign of diagnostic investigations, including non-destructive (pacometric and rebound hammer tests) and destructive (compressive tests on cores and tension tests on steel) experiments. In accordance with NTC2018 [28], the level of the building regarding geometry, structural details and material properties is to be considered equal to level 2 (LC2).  
The foundations are superficial and consist of orthogonal RC beams. All the RC beams and columns for the 3D system, as shown in Figure 2, have a rectangular cross-section, with dimensions summarized in Figure 3.  
The concrete resistance class originally used in the construction of the building was \(\mathrm{R_{bk}}\) 250. For the mechanical characterization of concrete, a number of 26 cores were extracted from selected structural elements. To this end, two cores were taken for beams and columns at the level of each floor, with the addition of two cores for the foundation beams. Based on major information and the details herein summarized, it was possible to obtain the previously amended knowledge level LC2 for structural analysis. An average strength value of 15 MPa, as obtained from the material characterization tests, was in fact used in the current numerical simulations. The steel shear reinforcement for RC beams consisted of \(\upphi\)6 transverse stirrup smooth rebars with 150 mm spacing, while the transverse stirrups of RC columns were realized with \(\upphi\)6 members, with spacing between 200 mm and 300 mm. The type of used steel was \(\mathrm{Aq50}\), with a minimum yield strength of 270 MPa. In the present numerical analyses, according to [PERSON] [29], a reference value of 372 MPa was taken into account.