Pattern of nonstationary frequency properties of earthquake strong ground motions and response of structures

Through an evolutionary spectral analysis, nonstationary frequency properties included in real earthquake strong ground motions are determined, and are grouped into five patterns through observation upon spectral diagrams. Inelastic responses of structures subjected to intense motions are evaluated, and the evidence is realized that nonstationary frequency properties generate responses with the condition that the resultant equivalent periods of structural response coincide with the dominant periods of motion within the duration of motion. Found is the conclusion that motions having nonstationary frequency properties can generate excessively large responses under certain conditions fulfilled. (author)