A cloud method for generating percentile engineering demand parameter versus intensity measure (EDP-IM) curves ofa structure subjected to a set of synthetic ground motions is presented.To this end,an ensemble of synthetic ground motions based on available real ones is generated.This is done by using attenuation relationships,duration and suitable Gutenberg-Richter relations attributed to the considered seismic hazard at a given site by estimating a suitable distribution of magnitude and site to source distance.The study aims to clarify the significance of the duration and frequency content on the seismic performance of structures,which were not considered in developing percentile incremental dynamic analysis (IDA) curves.The collapse probabilities of two steel moment-resisting frames with different ductility levels generated by IDA and the proposed cloud method are compared at different intensity levels.When compared with conventional IDA,the suggested cloud analysis (SCA) methodology with the same run number of dynamic analyses was able to develop response hazard curves that were more consistent with site-specific seismic hazards.Eliminating the need to find many real records by generating synthetic records consistent with site-specific seismic hazards from a few available recorded ground motions is another advantage of using this scheme over the IDA method..