# A Comparative Analysis of International Standards on Curved Surface Isolators for Buildings
## 1 Introduction
This shift significantly reduces seismic design forces, especially in structures with shorter natural periods. In contrast, structures with inherently longer periods experience a comparatively smaller effect. This flexibility is particularly advantageous for safeguarding non-structural components, such as mechanical systems [47; 48; 49; 50; 51] and precision instruments [52; 53], which are highly susceptible to seismic accelerations. 2. Controlled inelastic deformation: although seismic isolation increases overall structural displacements, it ensures that inelastic deformations occur primarily within the isolation system itself, preserving the integrity of the main structural and nonstructural components [47; 48; 49; 50; 51; 52; 53]. As a result, the primary structure remains within the elastic range even during strong ground motions, reducing the likelihood of significant damage and minimizing post-earthquake repair costs. 3. Energy dissipation and improved damping: seismic isolation systems not only provide flexibility but also enhance energy dissipation, which is crucial for mitigating seismic forces. Some isolation devices exhibit inherent damping characteristics due to their material properties, while hybrid systems integrate additional damping mechanisms at the isolation interface to further attenuate seismic energy. By increasing damping, these systems help limit displacement demands on isolators and enhance the overall resilience and safety of the structure. A wide range of isolation technologies is available in the market, each designed to fulfill the essential requirements of vertical load-bearing capacity, lateral flexibility, and energy dissipation efficiency [54]. The selection of an appropriate isolation device depends on several factors, including cost, availability, and the specific technical requirements dictated by the building's location, function, and design constraints. This research focuses specifically on FPIs, a widely utilized class of seismic isolation devices. Furthermore, this study presents a comparative analysis of international design standards governing the application of FPIs, using a case study of a hospital located in San Jose, Costa Rica. Given the varying seismic environments worldwide, different countries have established their own regulatory frameworks to ensure the effective implementation of seismic base isolation systems. In Europe, standards such as EN 15129:2018 [55], EN 1337-2:2004 [56], and the Eurocodes (EN 1998-1:2004--Eurocode 8, EC8) [57] provide specific guidelines for the design, testing, and application of FPIs. Likewise, in the United States, similar standards exist, including the Minimum Design Loads and Associated Criteria for Buildings and Other Structures (ASCE/SEI 7-22) [58] and the AASHTO Guide Specification for Seismic Isolation Design (AASHTO-GSID-14) [59]. While seismic isolation is widely used, its implementation is governed by national and international standards, each offering different approaches to design, analysis, and safety verification. Notably, ASCE/SEI 7-22, adopted in the United States, and Eurocode 8 (EN 1998-1 and EN 15129), adopted across Europe, present substantial methodological differences in how isolation systems are modeled, how damping and displacement demands are calculated, and how re-centering capability is ensured. These discrepancies can lead to significantly different design outcomes, even for the same structure. Despite the widespread adoption of both standards, comparative studies examining their implications on isolated system performance remain limited, particularly in the context of friction pendulum isolators. Understanding and systematically comparing these regulatory frameworks is crucial for ensuring the efficient and reliable design of FPIs, particularly when adapting isolation strategies to different seismic hazard levels and construction practices.