# A Comparative Analysis of International Standards on Curved Surface Isolators for Buildings
## 2 Case Study Building and Seismic Action  
This study examines a case involving a ten-story hospital building situated in San Jose, Costa Rica, designated as an essential facility. This designation highlights the hospital's critical function in ensuring continuous medical services, particularly during and after seismic events. The structural analysis of the hospital was performed using ETABS (v.21) [60], a widely recognized structural analysis software. The hospital, covering a total area of approximately 4150 m\({}^{2}\), is designed as a reinforced concrete frame structure. The building has a total height of 35 m, with plan dimensions of 46.35 m in the \(X\)-direction and 93.72 m in the Y-direction. The building employs a dual system consisting of reinforced concrete columns and beams forming moment-resisting frames, with reinforced concrete slabs acting as rigid diaphragms to ensure effective in-plane distribution of lateral forces. The columns are predominantly rectangular and symmetrically reinforced, measuring 600 mm \(\times\) 600 mm at the lower levels (basement to 3 rd floor) and reducing to 500 mm \(\times\) 500 mm from the 4 th to the 10 th floor. Longitudinal reinforcement consists of 12 to 16 bars of \(\phi\)25 mm (Grade 500 MPa), arranged to provide balanced capacity under biaxial bending. Transverse reinforcement is provided in the form of closed stirrups and seismic hoops with \(\phi\)10 mm diameter spaced at 100 mm centers near potential plastic hinge regions and 200 mm in the remaining regions, ensuring confinement as per ductility requirements. Beams span between columns and are generally 400 mm wide and 700 mm deep. They are reinforced with four to five top and three to four bottom bars of \(\phi\)20 mm in typical spans, depending on the moment envelope. Stirrups of \(\phi\)10 mm are spaced at 100 mm near supports and at 150-200 mm in midspan regions. Additional top bars are provided over intermediate supports to resist negative moments and maintain continuous reinforcement. All longitudinal bars are anchored with standard hooks or mechanical couplers, and lap splices are avoided in high-moment zones. The floor system is composed of 200 mm thick precast, prestressed hollow-core slabs with a cast-in-place topping of 60 mm reinforced with a light mesh (\(\phi\)8 mm @ 150 mm in both directions). The slabs act as horizontal diaphragms and are mechanically connected to primary beams using cast-in-place concrete keys and shear connectors. Vertical elements are monolithically connected to the foundation, which is a 1.2 m thick reinforced concrete mat foundation designed to distribute loads evenly over variable subsoil conditions. The seismic weight at the level of the isolation interface is estimated to be approximately 746,673.25 kN. Figure 1 illustrates a three-dimensional representation of the hospital structure, modeled from the foundation to the roof level. The isolation system is incorporated at the first story, where the interface between the superstructure and the isolation units is defined. Seismic action, also referred to as seismic hazard, is typically characterized using the acceleration response spectrum. While various seismic codes and regulations prescribe different methodologies for deriving this spectrum, the underlying principle remains consistent. For this case study, the seismic action was defined based on Costa Rica's specific seismic conditions, despite the fact that international standards such as ASCE/SEI7-22 [58] and EN 1998-1:2004 [57] also provide methodologies for estimating seismic action. Costa Rica is situated in Central America along the Pacific Ring of Fire and experiences significant seismic activity due to the subduction interactions between the Caribbean, Cocos, Nazca, and North American tectonic plates [61]. As a result, the region is prone to both shallow and intermediate-depth seismic events [62], with earthquakes ranging in magnitude from 5.5 to 8.0 (\(M_{w}\)) originating from interplate and intraplate sources [63].