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SUMMARYThe objective of this paper is to propose an FFT technique symmetrical for time and frequency, in which the symmetrization is done by introducing generating functions. By the symmetrical treatment, it becomes possible to derive several complementary relations in the time and frequency domains. Based on the idea of the symmetrical FFT technique, the phase problem of seismic waves is discussed not only in the frequency domain but also in the time domain. Furthermore, the deconvolution technique to evaluate the minimum-phase-shift and all-pass functions of seismic waves, which is not discussed sufficiently in earthquake engineering, is developed in the two domains. Numerical examples to present these basic ideas are also illustrated in the symmetrical framework.

This paper aims to describe the changes in the dynamic characteristics of two existing buildings in Miyagi Pref., Japan. One is a reinforced-concrete(RC) structure and the other is steel one. In this study, we found that the natural frequency of the RC structure is more strongly correlated with temperature in comparison with the steel structure. The temperature dependence of the natural frequencies is included in record indicating the amplitude dependence of the building's dynamic characteristics, and corrections with temperature data can deliver more accurate estimations of a building's structural soundness.