Study on measurement for impact waves in the earthquake and seismic design methods

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Since the high-cycle seismic waves with very large acceleration have influence as the results of investigation on severe damage by earthquakes, we started to develop a wide-range seismograph able to measure higher cycle waves than the standard seismograph. We used piezo register type piezo electric elements for the sensor and succeeded to complete an aimed three-component seismograph with extent of cycle up to 500Hz and sampling interval of 2kHz. Because the first one was too sensitive to maintain, the vertical component was selected for the object of measurement considering the situation of damage. Consequently, the seismograph became stable and was installed in some buildings at Tsukuba City.In 2004 to 2005, the seismographs installed at Tsukuba recorded accelerations of middle sized earthquakes on 6 and 23 October, 2004 and on 16 February, 2005 and proved the high cycle waves of 50-500Hz in earthquake. The seismograph of SMAC type installed at the same place recorded waves until 50 Hz and the values of acceleration was about three times of the high cycle waves. The performance of seismographs may be examined in the range of high frequency. On other hand, fabricate of a seismograph able to record the higher cycle waves than 500Hz is easily possible.Since we could not gain the large accelerations expected, we performed a series of dropping tests of steel blocks at a distance of 30 cm. The blocks of 5 and 10 kg fallen from a height of 15 cm generated the accelerations of about 300 gal. These values are large enough to suggest the existence of excessive acceleration with the high frequency.We confirmed trough a series of loading tests that the structural members such ductile as a reinforced concrete filled tube (RCFT) are effective for these excessive acceleration in the earthquakes.