Operational Basis Earthquake and Design Basis Earthquake: Normal and Abnormal Relations

Authors:  
Rubric:     Theoretical and experimental studies   
Key words: seismic analysis, Fourier spectra, response spectra, synthesis of the time-histories
Annotation:
The authors study the unexpected effect occurred in the practical design: the in-structure response spectrum for OBE proved to exceed the response spectrum for DBE at certain frequencies. It turns out that the reason is in the «abnormal» relation between Fourier spectra for the OBE and DBE time-histories. Such behavior was the result of the independent syntheses of the OBE and DBE time-histories matching target response spectra. «Normal» behavior of the response spectra does not guarantee «normal» behavior of the amplitude Fourier spectra throughout the whole frequency range, if phase Fourier spectra are independent. The «abnormal» effect under consideration is nonphysical. The authors give some recommendations to avoid it in the future analyses.