# Seismic Upgrade of an Existing Reinforced Concrete Building Using Steel Plate Shear Walls (SPSW)
## 1 Introduction  
The majority of reinforced concrete (r/c) buildings in Greece, for residential, office, and other purposes, were constructed before 1985, and their seismic design was performed on the basis of the 1959 Greek Seismic Code [1]. These r/c buildings normally do not possess the desirable characteristics that modern seismic codes envisage through the application of certain design criteria. Consequently, these r/c buildings are considered susceptible to seismic damages or failures and necessitate an in-depth evaluation in order to assess the feasibility of their possible seismic retrofit and upgrade. The methods used in seismic retrofit and upgrade of existing r/c buildings in Greece and elsewhere are described in detail in [2] and commonly involve r/c and FRP (fiber-reinforced polymer) jacketing, r/c shear walls, strengthening of infill panels and steel braces, as well as the mature technologies of base isolation and added damping devices. Despite the versatility and diversity of the seismic retrofit options offered by steel elements, it seems that their use has been restricted to steel braces, usually positioned in a concentric (diagonal or cross-diagonal) manner with respect to a r/c frame, whereas steel jackets and plates have been almost totally substituted by FRP materials [2]. It is true that modern seismic codes, e.g., [3], do not promote specific steel elements for the seismic retrofit and upgrade of existing r/c buildings. The reason is that extensive numerical and experimental data that certify the benefits behind the use of many novel steel elements in seismic retrofits and upgrades of existing r/c buildings became available after the initiation of such codes. The most representative example of such steel elements is the buckling-restrained brace [4; 5; 6; 7; 8], even though other steel systems have also evolved or seem to have potential [9; 10; 11; 12]. A steel element of special interest for the seismic retrofit and upgrade of existing r/c buildings is the Steel Plate Shear Wall (SPSW). The use of SPSW in steel structures as a lateral force-resisting system enjoys popularity in several countries, e.g., Japan, Mexico, Canada, and the U.S.A., and detailed design criteria are available in ANSI/AASC 341-22 [13] and CSA S16-19 [14] design standards. With respect to the application of SPSW in the seismic retrofit of existing r/c buildings, to the best of the authors' knowledge, one can consult [15; 16; 17]. Among the various numerical and experimental works dealing with the seismic retrofit and upgrade of r/c buildings with SPSW, one can name those in [18; 19; 20; 21; 22; 23]. A key issue with respect to the anticipated seismic performance of a retrofitted SPSW r/c building is the interaction achieved between the steel and the existing r/c system, i.e., the actual forces transferred between the two materials. A typical SPSW system, shown in Figure 1, consists of a thin steel web-plate with a common thickness ranging from 5 to 25 mm, two boundary columns, and horizontal boundary beams [17]. The boundary columns are called vertical boundary elements (VBE), and the beams are called horizontal boundary elements (HBE). With respect to terminology, in steel structures, the term SPSW is used if standard steel sections are employed as HBEs and VBEs. However, when referring to a r/c frame, two configurations can be accomplished: (i) in the first one, a metal sheet or plate is inserted between the existent r/c beams and columns that essentially play the role of the HBEs and the VBEs; (ii) in the second one, the steel plate is inserted between added steel columns (HBEs), implying that the resulting SPSW does not occupy the entire bay span of the r/c frame. Taking into account the relevant literature for both configurations (i) and (ii) studied in the following, it is decided for reasons of uniformity to keep the term SPSW. Figure 1: Elements of a typical SPSW for a 3-story. The strength of the connection of the SPSW with the surrounding members has to be greater than the strength of the SPSW itself.