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

由于高周期地震波具有很大的加速度，作为地震严重破坏调查结果的影响，我们开始研制一种能够测量比标准地震仪更高周期波的宽量程地震仪。我们采用压电式压电式元件作为传感器，成功地完成了周期幅度高达500 Hz、采样间隔2 kHz的定向三分量地震仪。由于前者过于敏感而无法维护，因此考虑到损伤情况，选择了垂直分量作为测量对象。2004-2005年，安装在筑波的地震仪记录了2004年10月6日、23日和2005年2月16日的中等规模地震的加速度，证实了地震中50-500赫兹的高周期波。安装在同一地点的SMAC型地震仪记录的地震波一直持续到50赫兹，加速度约为高周波的3倍。可以在高频范围内检验地震仪的性能。另一方面，由于不能获得预期的大的加速度，所以我们在30厘米的距离上进行了一系列的钢块跌落试验。从15厘米的高度坠落的5公斤和10公斤的积木产生的加速度约为300加仑。通过一系列的加载试验，证实了延性钢管混凝土等结构构件对地震中的加速度过大是有效的。

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.