Mass Participation in Non-classical Mass Isolated Systems

Application of new techniques in seismic design of structures is usually accompanied withthe use of large capacity energy dissipation devices in the system. In such cases, theassumption of classical (proportional) damping is not usually valid and non-classicalfeatures prevail in the system. Non-classical behavior is a known subject in dynamics ofstructures and the required mathematical basis to address different aspects of such systems is readily available in the literature. In the context of system characteristics, however, the role and the significance of each mode in total response of these structure, subjected to earthquake excitation, has not yet been properly communicated among the researchers. This study offers an intuitive adaptation for mass participation factor of non-classical systems to signify the modal contribution role of non-classical mass isolated buildings. The proposed factor is useful in determining the importance of isolated modes of such systems and speculating on the general behavior of these structures. A spectrum analysis technique for non-classical systems is also projected in this study. Reliability of the definition for mass participation factor in this study is verified through some numerical examples. A supplementary conclusion suggests limiting the use of classical analytical tools in analysis of mass isolated systems to the structures with low damping ratios.