# A Comparative Analysis of International Standards on Curved Surface Isolators for Buildings
## 2 Case Study Building and Seismic Action
Figure 1: Two distinct perspectives of the hospital building in San José, Costa Rica, selected for the case study are presented: (**a**) a three-dimensional view and (**b**) a front elevation. These illustrations highlight the structural components, including beams, columns, and slabs, which function as diaphragm elements. The country has developed its own seismic code, known as the Costa Rican Seismic Code (CSCR-10 Rev. 2014--CFIA, 2010) [64], which has been in effect since 1974. Chapter 5 of the CSCR-10 outlines the procedure for calculating the seismic coefficient (\(C\)), which defines the horizontal seismic demand and corresponds to the spectral design acceleration for given levels of ductility and damping. The seismic coefficient is computed using the following equation [64]:  
\[C=\frac{I.a_{\text{ef}}.FED}{SR} \tag{1}\]  
where:  
* \(a_{\text{ef}}\) represents the effective peak ground acceleration at the base of the structure, expressed as a fraction of gravitational acceleration (\(g\)). This value is obtained from Table 2.3 of the CSCR-10 [64], based on the seismic zone and the site conditions. The concept of effective peak acceleration originates from ACT 3-06 (1981) [65] and represents the spectral acceleration values within the period range of 0.1 to 0.5 s, where maximum spectral accelerations typically occur. It is determined by averaging the spectral acceleration ordinates at 5% damping and dividing by a factor of 2.5;
* \(I\) is the importance factor, which is specified in Table 4.1 of CSCR-10 [64] based on the function and occupancy of the structure. This parameter ensures that essential facilities, such as hospitals, are designed to withstand higher seismic demands in accordance with the performance objectives stated in Section 4.1.b of the code [64];
* \(FED\) is the dynamic spectral factor, which defines the shape of the acceleration spectrum based on site conditions, seismic zones, and the assigned global ductility level;
* \(SR\) represents the overstrength factor, which accounts for the difference between the actual and nominal seismic resistance capacity of the structure. According to CSCR-10 [64], the overstrength factor reflects an inherent increase in structural capacity. Instead of directly comparing the actual resistance to the seismic demand, the code evaluates the nominal capacity of the structure against the demand reduced by the factor \(SR\). This approach justifies the presence of \(SR\) in the denominator of Equation (1). To provide a comprehensive summary of the key assumptions and parameters used in defining seismic actions for this study, Table 1 presents a concise overview of the selected values and their corresponding criteria. Moving from the seismic coefficient (\(C\) in Equation (1)), the response spectrum from the Costa Rican Seismic Code (CSCR-10) [64] is represented on a logarithmic scale in Figure 2. While the formulation and description of the response spectrum in CSCR-10 differ from those presented in ASCE/SEI 7-22 [58] and Eurocode 8 [57], the fundamental concept remains the same. However, significant differences exist in how these standards define the elastic response spectrum, particularly in terms of reference return periods and the anchoring of spectral ordinates used for the computation of the design spectrum. As discussed in [1; 2; 66], these variations stem primarily from the different approaches adopted by each standard in defining seismic hazard levels. \begin{table}
\begin{tabular}{l c} \hline \hline
**Parameter** & **Assumed Value** \\ \hline Effective peak ground acceleration \(a_{\text{ef}}\) & 0.36 g \\ Importance factor \(I\) & 1.25 \\ Dynamic spectral factor \(FED\) & Table 2.7 in CSCR-10 [64] \\ Overstrength factor \(SR\) & 1.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Assumptions for seismic parameters based on site-specific conditions in Costa Rica, used for developing the input spectra required for the design of the isolation system.