All FRP structures represent by now a solid reality in the field of structural engineering. In fact, almost all potential applications have already been investigated through in-depth studies, except for seismic performance. The research aims to make a contribution to improving the current knowledge level on the item with reference to an all FRP multi-story building with respect to structures built with traditional materials. The analysis is carried out considering an equivalent (with the same cross sections) steel structure. This research is also in view of future potential comparison with respect to an optimized steel structure (with transformed strengths and deformations). The present study is realized by comparison between modal analysis and participating masses, fundamental period and elastic spectrum response in the case of FRP and steel materials. The investigation starts from a well known all FRP spatial structure build in Italy (L’Aquila), after 2009 earthquake emergency, and already analyzed inside the European TC 250 WG 4 in view of the next Eurocode dedicated to all FRP structures.