The Study on the Influence and Application of Foundation Pier Height on Strong Motion Records
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摘要: 强震动观测的加速度仪通常是固定安装在一定高度的混凝土基墩上,不能完全反映理想自由场地的地震动.为研究基墩高度对于强震动记录的影响,设计了3种高度不同、截面尺寸相同的基墩,通过地震模拟振动台实验,以基岩记录作为地震动输入,分析基墩高度对于强震动记录的时频特性影响,并结合数值模拟进行了验证,同时对泸定地震51SMM台站记录通过滤波修订到标准基墩.研究结果表明:不同高度基墩,对于水平向PGA、PGV、PGD影响整体随着高度增大而增大,对于垂直地震动,PGA与PGV幅值均缩小;与其他频带相比,0.5~7 Hz范围内的傅里叶幅值谱,0.6 m和1.2 m高的基墩影响较小,2.0 m高的基墩影响最大;高度较小基墩对反应谱影响较小.通过以上实验表明滤波修订不同高度的基墩效果较好,在代码为51SMM强震动台站记录中得到较好应用,同时应避免采用高度超过1.2 m的基墩用于强震动观测.Abstract: The accelerometer for strong motion observation is usually fixed on the concrete pier at a certain height, and the ground motion of ideal free field cannot be reflected completely. In order to study the influence of pier height on the strong motion records, three piers with different heights and the same cross-sectional dimension are designed, and the effect of the pier height on the time-frequency characteristics of the strong motion records is analyzed through seismic simulation shaking table tests, bedrock records are selected as the ground motion input, and numerical simulations are applied to verify the research results, at the same time, the strong motion records of station 51SMM in Luding earthquake is modified to standard pier by filtering. It shows that the effect of the piers on the horizontal PGA, PGV and PGD increases with the increasing height, while the PGA and PGV amplitudes decrease for the vertical ground motion. Fourier amplitude spectrum in the range of 0.5-7 Hz shows that 0.6 m and 1.2 m high piers have less influence than other frequency bands, while 2.0 m high piers have the greatest influence. The experiments above show the filtering effect is better for modifying the pier with different heights, and it is better used in strong motion records of station coded by 51SMM.The piers with the height exceeding 1.2m should be avoided for strong motion observations.
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表 1 加速度峰值
Table 1. PGA
方向 基墩高度(m) 0.6 1.2 2.0 东西 748.0(881.7) 825.0(897.5) 1 830.0(1 280.3) 南北 731.0(737.3) 1 030.0(763.4) 1 960.0(1 350.7) 垂直 510.0(561.8) 542.0(564.6) 331.0(568.7) 注:括号外为试验数据,括号内为模拟数据,单位:gal 表 2 振动台试验不同高度基墩速度峰值比(%)
Table 2. The ratios of PGV for different height pier(%)
方向 基墩高度(m) 0.6 1.2 2.0 东西 87.2 75.9 197.2 南北 103.6 102.7 225.9 垂直 95.6 98.2 58.8 表 3 振动台试验不同高度基墩位移峰值比(%)
Table 3. The ratios of PGD for different height pier(%)
方向 基墩高度(m) 0.6 1.2 2.0 东西 125.0 125.0 200.0 南北 116.7 166.7 233.3 垂直 100.0 100.0 60.0 表 4 校正记录和标准基墩记录傅里叶幅值谱的相关性(EW)
Table 4. Correlation of Fourier Amplitude Spectrum between Correction Record and Standard Base Pier Record(EW)
序号 高通截止频率 低通截止频率 PGA
(cm/s2)相关系数 ① 0.01 25 -542.4 0.96 ② 0.01 30 -618.3 0.97 ③ 0.01 32 -667.6 0.97 ④ 0.01 35 -738.2 0.97 ⑤ 0.01 36 -758.1 0.97 ⑥ 0.01 40 -819.7 0.96 ⑦ 0.05 30 -618.3 0.97 ⑧ 0.10 30 -617.8 0.97 -
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