# A Comparative Analysis of International Standards on Curved Surface Isolators for Buildings
## 5 Conclusions  
This research presents a comprehensive comparative analysis between two internationally recognized seismic design codes, Eurocode 8 (EN 15129) and ASCE/SEI 7-22, specifically focusing on their application to seismically isolated structures. The study objectively evaluates each code's approach to base isolation design, highlighting both its strengths and limitations. The findings provide valuable insights into how different engineering assumptions influence seismic performance predictions and the subsequent design choices for base-isolated buildings. One of the most critical differences identified in this study pertains to re-centering capability, a fundamental requirement in seismic isolation design. The European standard (EN 15129) adopts an energy-based approach, where the re-centering capability is inherently linked to the level of friction. This implies that as friction increases, the system must store more elastic energy to ensure successful re-centering. In contrast, the ASCE/SEI 7-22 standard determines re-centering solely based on the isolator's radius, without considering the influence of frictional resistance. This divergence raises significant concerns, particularly in high-friction scenarios where the ASCE model may overestimate the ability of an isolator to return to its original position. While a frictionless system would re-center automatically, the presence of friction can make re-centering difficult or even impossible, a factor that ASCE/SEI 7-22 does not fully account for in its framework. Additionally, the comparison revealed a systematic difference of approximately \(\pm\)12% in the values of the damping reduction factor (\(\eta\)) and its inverse (\(1/B_{M}\)) between the two codes. This difference is directly related to the higher displacements and accelerations observed when applying the ASCE/SEI 7-22 methodology. Such discrepancies emphasize the sensitivity of seismic response predictions to the assumptions embedded within each standard. The ASCE code, by yielding higher displacement and acceleration estimates, tends to lean toward a more conservative design philosophy. However, this conservatism may lead to increased structural costs or suboptimal design choices in cases where excessive displacement predictions result in over-designed systems that may not reflect the actual seismic demands on the structure. Beyond numerical differences, this study highlights the fundamental philosophical distinctions between the two codes. Eurocode 8 integrates friction into its design approach, recognizing its effect on system behavior, while ASCE/SEI 7-22 assumes an idealized restoring force mechanism. These contrasting methodologies underscore the need for engineers to critically assess which framework best aligns with the specific site conditions, structural characteristics, and isolation system used in a given project. From a practical perspective, the findings of this study emphasize that choosing between EN 15129 and ASCE/SEI 7-22 should not be based solely on regulatory compliance but rather on a thorough understanding of the fundamental principles underlying each approach. Designers must carefully consider whether the ASCE/SEI 7-22's higher displacement and acceleration estimates, coupled with its neglect of friction in re-centering calculations, align with the practical realities of seismic isolation system performance. Conversely, the Eurocode approach, while more explicit in its treatment of friction and damping, may still require careful validation through advanced nonlinear analyses to ensure its applicability to specific seismic isolation configurations. About possible future research directions, while this study has provided valuable insights into the differences between ASCE/SEI 7-22 and EN 15129, further research is necessary to:  
1. Validate these findings through full-scale experimental testing of isolated structures designed according to each standard, providing empirical data on re-centering behavior and displacement demands;
2.