Modified Cloud Analysis: Non-Linear Dynamic Analysis With Unscaled Records

One of the most efficient non-linear dynamic analysis procedures for analytic fragility evaluation is based on simple regression of structural response versus seismic intensity for a set of registered records. this procedure, also known as the cloud method (jalayer, 2003), has many advantages such as simplicity, use of un-scaled records, and relatively small computational effort. this method suffers draw-backs such as modeling of record-to-record variability with constantstandard deviation. nevertheless, the simplicity of the formulation makes it a quick and efficient analysis procedure for fragility assessment or safety-checking in the context of the sac-fema formulation (cornell et al., 2002). record selection is quite critical for cloud analysis as the results are often sensitive to the suite of ground motion records selected. the criteria for record selection for use in cloud analysis can be summarized as (jalayer et al., 2015 and 2017): 1. the records should span a wide range of the intensity measure (in order to reduce the error in the estimation of theregression slope)2. a significant proportion of the records should lead to the exceedance of the limit state (in order to avoid extrapolationin the zone of interest)3. the number of ground motion records from the same event should be limited (in order to avoid data set with highcorrelation)4. the soil type and the predominant focal mechanism (s) for the site should be kept in mind.