汶川地震中强震动台基墩引起的记录异常分析
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摘要
自由场地上的强震动记录是研究地震动衰减规律、制定抗震设计规范等的基础数据,因此,强震动记录是否可靠至关重要,将直接影响相关的统计分析结果.在汶川地震中,宜宾高场强震动台记录了一组3分量加速度记录,其中东西向峰值加速度为101.2cm/s2,南北向峰值加速度为122.1cm/s2,垂直向峰值加速度为94.4cm/s2.加速度时程图示结果表明记录曲线呈现明显的不对称,尤其是垂直向更甚.此外,较之附近其它强震动台峰值加速度明显偏大.本文针对这一异常记录进行了分析,并通过现场实验、振动台实验和数值模拟分析了异常产生的机理.结果表明,记录异常是由仪器墩的放大作用和碰撞效应引起的.放大作用起因于仪器墩高宽比过大,而运动中的仪器墩底部接触碰撞使地震动记录呈现显著的不对称,即"瀑布"现象.
The strong motion accelerograms on the free-field are basic data used for the study of the attenuation law of ground motion,and the formulation of aseismic design code.Therefore,the reliability of strong motion accelerograms is very important,or the improper data would lead to unreliable statistic results.In the Wenchuan Ms8.0 earthquake,May 12th 2008,a set of three-component accelegrams was recorded at strong motion station Yibin Gaochang,and the peak acceleration of east-west(EW),north-south(NS) and up-down(UD) component was 101.2cm/s2,122.1cm/s2 and 94.4cm/s2 respectively.As shown in acceleration histories,the record curves appear obviously asymmetric,especially in the UD component.Moreover,compared with the accelerograms from nearby strong motion stations,its peak acceleration was obviously larger.The cause of anomaly was analyzed,and the mechanism of anomaly was discussed by in-situ test,shaking table experiments and numerical stimulation.The results showed that the anomaly of accelerograms was caused by the effects of amplification and impact of instrument pier.The effect of amplification was resulted from larger aspect ratio of the instrument pier,and the obvious asymmetry,namely the waterfall phenomenon,was caused by the bottom contact-impact of the instrument pier in motion with surrounding rock.
The strong motion accelerograms on the free-field are basic data used for the study of the attenuation law of ground motion,and the formulation of aseismic design code.Therefore,the reliability of strong motion accelerograms is very important,or the improper data would lead to unreliable statistic results.In the Wenchuan Ms8.0 earthquake,May 12th 2008,a set of three-component accelegrams was recorded at strong motion station Yibin Gaochang,and the peak acceleration of east-west(EW),north-south(NS) and up-down(UD) component was 101.2cm/s2,122.1cm/s2 and 94.4cm/s2 respectively.As shown in acceleration histories,the record curves appear obviously asymmetric,especially in the UD component.Moreover,compared with the accelerograms from nearby strong motion stations,its peak acceleration was obviously larger.The cause of anomaly was analyzed,and the mechanism of anomaly was discussed by in-situ test,shaking table experiments and numerical stimulation.The results showed that the anomaly of accelerograms was caused by the effects of amplification and impact of instrument pier.The effect of amplification was resulted from larger aspect ratio of the instrument pier,and the obvious asymmetry,namely the waterfall phenomenon,was caused by the bottom contact-impact of the instrument pier in motion with surrounding rock.
引文
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