Observations of earthquake motions and their simulative analyses of a PWR-type nuclear power station

The authors have been measuring earthquake motions at the Ikata Nuclear Power Station in Japan. So far we have observed two significant earthquakes: The Bungo Channel Earthquake (1977, M=4.2, Δ=21 km) and the Suoh-Nada Earthquake (1979, M=6.1, Δ=55 km). This report describes the observed and simulated results of these earthquake motions. Conclusions: 1) Analytical resonant frequencies of the model coincided with the observed ones when the elastic modulus of concrete was assumed as 3.4-4.0x105 kg/cm2 and that of steel as 2.1x106 kg/cm2. Considering that the strain level of the structures was small, these values seem to be appropriate. 2) Damping factors obtained by the 1/√2 method from the Fourier spectra of the observed motions are 3.0-3.5% for the concrete structures and 2.0% for the C/V. 3) Using the above mentioned damping factors, time history analyses were done. The results agreed well with the observed ones, and so the lumped mass model adopted in aseismic designs could be justified. (orig./HP)