## 1 Introduction
The design of isolated buildings according to the current seismic codes implicitly ensures the minimum level of safety by preventing the collapse of buildings. This could be achieved by requiring an acceptably low collapse probability of structures subjected to MCE ground motions, which is based on the evaluation of their collapse capacities. In parallel with this, FEMA P695 allows a more practical assessment methodology of the performance of structures [16; 17]. FEMA P695 established a consistent method for evaluating structures to ensure minimal structural safety to resist collapse and for calculating a collapse margin ratio (CMR) that can be utilized as a simple and intuitive indicator [17]. In this methodology, the CMR is computed as a ratio of the median collapse intensity to the representative intensity of an ensemble of MCE ground motion records. Using the FEMA P695 procedure, the seismic fragilities of isolated buildings were evaluated using an incremental dynamic analysis method [18]. [PERSON] et al. [19] investigated the effects of limiting the displacement demands of isolators by the use of moat walls with various clearances and behavior. Although several studies demonstrated that seismically isolated buildings have better performance than comparable typical non-isolated buildings [20; 21; 22], recent research studies focused on more rigorous evaluation of the seismic performance of isolated buildings designed according to the requirements prescribed in design codes. [PERSON] and [PERSON] [23] investigated the reliability of the ASCE/SEI (American Society of Civil Engineers/Structural Engineering Institute) provisions using the archetypical 6-story perimeter frame isolated buildings that were assumed to be located at California, U.S., and similar analytical research works were also carried out by [PERSON] and [PERSON] [24]. Nevertheless, related research studies on the collapse capacities of isolated buildings are still limited and only focused on the design requirements regarding seismic effects on them. In addition, it is questionable that an acceptably low probability of collapse can be achieved for isolated buildings at low-to-moderate seismicity regions even if they are designed by current seismic codes. Therefore, this paper aims to investigate the collapse capacities of isolated buildings built at low-to-moderate seismicity regions. The collapse capacity is mainly governed by system-level uncertainty, which is mainly influenced by the displacement and strength capacities of isolation systems determined by the prescribed design criteria. In order to clarify the relation between the collapse capacity of isolated structures and their possible uncertainty induced by design conditions, the study first starts with the design of prototype isolated buildings at both high and low-to-moderate seismicity regions. The prototype isolated buildings were designed to meet the requirements prescribed in the ASCE/SEI 7 [14]. Then, simplified numerical models were constructed for a larger number of nonlinear incremental dynamic analyses. The analysis results are presented in terms of their collapse capacities including possible uncertainties related to seismic demand and analytical modeling, and consequently, they are discussed to obtain rational collapse probabilities of such isolated buildings at low-to-moderate seismicity regions in comparison to isolated buildings at high seismicity regions of which seismic performance has been already guaranteed by many researchers. The important influential factors on the collapse probabilities of isolated buildings at low-to-moderate seismicity regions are identified, and recommendations are suggested to ensure their reliable target collapse capacity.