# A Comparative Analysis of International Standards on Curved Surface Isolators for Buildings
## 1 Introduction  
Earthquakes remain one of the most destructive natural hazards, with the potential to cause widespread loss of life, property damage, and long-term disruption to critical infrastructure. In seismically active regions, the development of resilient structural systems is a priority for safeguarding both human life and the post-disaster functionality of essential facilities. Among modern seismic protection strategies, seismic isolation has emerged as a highly effective approach for decoupling structures from ground shaking. By inserting flexible, energy-dissipating devices between the foundation and superstructure, isolation systems significantly reduce the seismic demand on the structure [1, 2, 3, 4, 5]. The use of Friction Pendulum Isolators (FPIs) has proven to be particularly effective in seismic isolation due to their ability to support vertical loads while simultaneously allowing lateral flexibility inthe horizontal plane [6; 7]. These isolators provide substantial energy dissipation through friction and possess a self-centering capability, which helps restore the structure to its original position after a seismic event. The fundamental mechanism of FPIs relies on a concave sliding surface and an articulated slider, which work together to generate a controlled pendulum motion, reducing seismic forces transmitted to the superstructure [8; 9; 10; 11]. The effectiveness of seismic isolation has been unequivocally demonstrated through the outstanding performance of isolated structures in major earthquakes, such as the 1994 Northridge [12] and 1995 Hyogoken-Nanbu and Kobe events [12; 13]. Conversely, the severe damage observed in buildings, infrastructure, and industrial facilities during seismic events, including the 2009 L'Aquila [14; 15; 16; 17], 2012 Emilia [16; 17; 18; 19] and 2016 earthquakes in Italy [16; 19], the 1997/2000 Jabalpur [20; 21; 22] and 2001 Bluj earthquakes in India [23; 24; 25], and the 2013 and 2016 earthquakes in New Zealand [26; 27; 28], highlighted the vulnerabilities of conventional construction techniques. Post-earthquake assessments revealed recurring failure patterns across multiple seismic events [16], indicating that many structures, including those made of reinforced concrete [16; 29; 30; 31], precast elements [16; 32; 33], lightweight concrete/infill [34; 35; 36] and steel [16; 37; 38; 39], were originally designed using outdated seismic provisions that did not adequately address modern seismic demands. These observations have reinforced confidence in seismic isolation as a reliable protective strategy and validated analytical models predicting its performance. As a result, the adoption of isolation techniques has expanded, both for new constructions and retrofit applications [40; 41; 42]. Seismic isolation functions by incorporating flexible elements, such as elastomeric bearings, sliding interfaces, or rolling mechanisms, positioned between a structure's superstructure and its foundation [43; 44]. Often, these components are combined with damping devices to absorb and dissipate seismic energy, thereby lengthening the building's natural period and reducing resonance effects with high-frequency ground motions. Recent advancements in seismic isolation have further extended its application to more flexible structures, such as silos [45; 46], leading to reduced accelerations and displacements. This has allowed for the optimization of structural design, minimizing the dimensions of load-bearing elements, mitigating damage potential, and ensuring continued functionality post-earthquake, particularly for critical facilities housing essential services or sensitive equipment [47; 48; 49; 50; 51]. The core benefits of implementing seismic isolation in structural design, whether for new or existing buildings, can be summarized as follows:  
1. Enhanced flexibility and period shift: seismic isolation increases structural flexibility, effectively shifting the fundamental period of the building away from the high-energy frequency range of seismic ground motions.