## 3 Analyzed Irregular Building and Characterization of Retrofitting Intervention
### Geometrical Configuration of the Structure  
The existing RC-framed building considered for the study is located in central Italy in a region with a very relevant seismicity. In particular, according to the current Italian design code [3], the region is subjected to PGA (peak-ground-acceleration) that is superior to 0.25 g and associated with an exceedance probability of \(10^{-1}\) in 50 years concerning the life safety limit state. In the next section, the main geometrical features of the building are reported, focusing on the RC-framed structure and masonry infills. The building has been realized since the 1960s according to an Italian design code that, at the time, was related to seismic design for a small part of the specifications. For instance, the structure has been realized without appropriate seismic conception and detailing. The structure, built during the 1960s, is constituted by a cast in situ RC structure that consists of orthogonal frames dislocated along \(X\) (i.e., longitudinal) and \(Y\) (i.e., transverse) directions. The foundations are stiff, inverted, continuous RC beams along the direction of the RC frames. The in-plane sizes of the building are 59.8 m in the \(X\) direction and 12.2 m in the \(Y\) direction. Figure 3 illustrates, schematically, the column disposition with the related frames identified as \(X\)1, \(X\)2 in the \(X\) direction and \(Y\)1, \(Y\)2, \(Y\)3 along the \(Y\) direction. With reference to the elevation, the maximum height of the building is equal to 15.9 m measured from the foundation level. The RC structure presents 5 stories, including the roof level. The details of the geometry of the different RC frames that constitute the structure are reported in Figures 4 and 5. Concerning the boundary conditions, around the structure for a height of 3.5 m measured from the foundation level, there is a soil embankment that is able to limit displacements in the X and Y directions of story 1. This is a relevant aspect of  
Figure 2: Micro-model with shell **(a)** and macro-model with single-strut **(b)** using SAP2000 for partially in-filled masonry panels. the seismic behavior of the structure, and it is accounted for during the definition of the numerical model. Different types of members (i.e., columns and beams) are present, as illustrated in Figure 6. The reinforcement arrangement (both for shear and bending) concerning each member is summarized in Table 1. Data from inspections denote that the clear concrete cover (on average) is equal to 3 cm for all structural members. The horizontal floors are built using a lightened \"latero-concrete\" technical solution with RC joists and a top slab. The RC joists are 16 cm high with a base of 10 cm with 0.5 m as center-to-center distance in the transverse direction. They are oriented along the longitudinal direction (X), that is, according to the short beam floor pattern. The top slab is 4 cm thick and connects the joists realizing the floor, and, for modeling purposes, it can be considered sufficient to realize a rigid floor able to transfer horizontal actions to the longitudinal and transverse RC frames [3]. The only external masonry infills have been considered to be able to contribute to the overall seismic response of the building. In particular, the masonry infills have a total thickness equal to 34 cm and are realized with the following stratigraphy: external facing in exposed brick (8 cm); air cavity (13 cm); internal facing in perforated bricks (12 cm); and internal cement plaster (1 cm). The disposition of the partially infilled and totally infilled masonry panels within the external RC frames of the structure is reported in Figure 7. It can be noted that the geometry of the external infills in the longitudinal direction is particularly unfavorable due to the presence of many partial infill panels. Figure 4: Details of the RC frames that constitute the structure, including cross-sections of main members in X direction. Reprinted/adapted with permission from [26]. Dimensions in centimeters.