Study on elastic response of structures to near-fault ground motions through record decomposition

Accelerograms recorded near active faults have some important characteristics that make them different from those recorded in far-fault regions. High-frequency components in acceleration records and long-period velocity pulses are among notable specifications of such ground motions. In this paper, a moving average filtering with appropriate cut-off frequency has been used to decompose the near-fault ground motions into two components having different frequency contents: first, Pulse-Type Record (PTR) that possesses long-period pulses; second, the relatively high-frequency BackGround Record (BGR), which does not include large velocity pulses. Comparing the results with those extracted through wavelet analysis shows that moving average filter is an appropriate and efficient tool for near-fault records decomposition. The method is applied to decompose a suite of 91 selected near-fault records and the elastic response of structures is examined through their response to the decomposed parts. The results emphasizes that in contrast with ordinary far-fault earthquake records, response spectra of near-fault ground motions typically have two distinct local peaks, which are representatives of the high- and low-frequency components, i.e., BGR and PTR, respectively. Moreover, a threshold period is identified below which the response of structures is dominated by BGR while PTR controls the response of structures with periods longer than this period.     

地震力对高架桥梁轨道车辆影响之动态模型

将轨道车辆系统仿真成由车厢、转向架及轮轴所组成。车厢与转向架间有次悬吊系统,转向架与轮轴间则有主悬吊系统。数学模型之推导将考虑车辆横向、垂向、翻滚(roll)及摇摆(yaw)方向之运动,将车辆仿真成三维具16个自由度之系统。本研究将探讨行驶高架桥梁之轨道车辆受地震激振时,建立轨道车辆与高架桥相互耦合之动态数学模型。     

中小震近场地震动估计中地震动衰减关系的适用性分析

核工程场地设计基准地震动确定中涉及弥散地震的地震动估计，这导致中小震近场地震动估计成为被关注的研究课题。本文基于一些中小震近场地震动记录资料，分析和探讨了国内外多种地震动衰减关系对中小震近场地震动估计的适用性问题，并结合我国几个核工程地震问题研究工作的实践对中小震近场地震动衰减关系确定的思路和原则提出了建议。     

我国地形变观测预报地震的现状及对地震预测问题的思考

本文展示了我国地形变观测的状况,讨论了以地形变观测预报地震的基本思路及应用情况,探讨了地震预测面临的困难及地形变观测须解决的技术问题。最后,作者认为,地震预报目前或今后很长一段时间都将是以观测为主的试验性科学,物理统计分析方法是研究地震孕育动力学过程或进行预测的最具有潜力的途径之一。     

基于T-S模糊神经网络的采空塌陷危险性判别

采空区地面塌陷的危险性判别受地质因素、采矿因素等多重因素的影响,各因素往往影响程度不同且部分因素之间又相互联系。为了能够较准确地对采空塌陷危险性进行评估,引入了T-S模糊神经网络模型。以北京西山地区采空塌陷为例,根据塌陷特点,分别选取了地质构造复杂程度、覆盖层类型、第四系覆盖层厚度、覆岩强度、煤层倾角、采深采厚比、采空区埋深、采空区空间叠置层数8项影响因素作为评价指标,并建立了分级标准。将单因素评价指标均匀线性插值作为训练样本,建立了T-S模糊神经网络判别模型。利用训练好的神经网络模型对选取的8处采空区进行评估,结果分别为:Ⅰ、Ⅱ、Ⅲ、Ⅱ、Ⅲ、Ⅱ、Ⅲ、Ⅱ,结果与实际情况吻合。研究表明,利用T-S模糊神经网络研究采空塌陷危险性是可行的。     

软土地区双线区间盾构隧道施工对周边地表以及建筑物沉降的影响

研究盾构隧道施工对周围地面以及建筑物沉降造成的影响,是软土地区盾构隧道安全施工和正常运营的基础课题。为了分析宁波轨道交通5号线同德路站—石碶站区间双线盾构隧道施工对周边地表和建筑物的影响,本文在建立盾构隧道动态施工过程三维有限元模型的基础上,基于地表以及建筑物沉降数值模拟结果与现场监测值的对比,分析了隧道开挖对隧道周围地表沉降与建筑物沉降的影响。结果表明,掘进完成时,开挖方向沉降槽往上行线隧道方向偏移、呈现倒梯形形态,横断面影响区域为距离双线隧道轴线中心小于3倍隧道直径;上行线在下行线开挖后并不会增加地表沉降,但增大了沉降槽宽度;下行线到达前产生的沉降占最终累计沉降的67%;当盾构掘进面刚到达建筑物时、建筑物的倾斜方向与盾构掘进方向一致,当盾构掘进面离开建筑物时、建筑物将沿着盾构掘进的反方向倾斜;建筑物两侧沉降值较中部沉降值降低了83%;双线贯通后建筑物沉降呈“U”形分布,最大沉降量发生在远离隧道一侧距建筑物中心0.5 m处。     

基坑开挖对涉支护结构下穿盾构隧道变形的三维模拟与影响规律研究

依托某大厦基坑支护工程项目,研究深厚软土地层中基坑开挖对涉支护结构下穿盾构隧道变形的影响规律。采用三维有限元数值模拟分析隧道顶部支护桩的长度对支护结构变形和隧道隆起的影响,并将数值模拟结果与现场监测结果进行对比。结果表明：深厚软土地层中基坑开挖对下穿盾构隧道产生了较大的隆起变形;因下穿隧道的影响,隧道顶部支护桩嵌固深度的减小对支护结构的变形和下穿隧道的隆起会产生重要影响,当支护桩底与隧道顶的竖向间距S＞4 m或支护桩边缘与隧道边缘的水平间距S1＞4 m 时,支护桩的踢脚位移和下穿隧道的隆起变形迅速增加。研究成果可为类似工程提供应用参考和理论支撑。     

Centrifuge modeling of PGD response of buried pipe

A new centrifuge based method for determining the response of continuous buried pipe to PGD is presented. The physical characteristics of the RPI‘s 100 g-ton geotechnical centrifuge and the current lifeline experiment split-box are described: The split-box contains the model pipeline and surrounding soil and is manufactured such that half can be offset, in flight, simulating PGD. In addition, governing similitude relations which allow one to determine the physical characteristics, (diameter, wall thickness and material modulus of elasticity) of the model pipeline are presented. Finally, recorded strains induced in two buried pipes with prototype diameters of 0.63 m and 0.95 m (24 and 36 inch) subject to 0.6 and 2.0 meters (2 and 6 feet) of full scale fault offsets and presented and compared to corresponding FE results.     

Measurement of six degree-of-freedom ground motion by using eight accelerometers

A new integrated measuring system with eight force-balance accelerometers is proposed to obtain a direct measurement of six degree-of freedom （DOF） ground motions, including three rotational and three actual translational acceleration components without gyroscopes. In the proposed measuring system, the relationship between the output from eight force-balance accelerometer and the six DOF motion of the measuring system under an earthquake are described by differential equations. These equations are derived from the positions and directions of the eight force-balance accelerometers in the measuring system. The third-order Runge-Kutta algorithm is used to guarantee the accuracy of the numerical calculation. All the algorithms used to compute the six DOF components of the ground motion are implemented in a real-time in Digital Signal Processor （DSP）. The distortion of the measured results caused by position and direction errors of the accelerometers in the measuring system are reduced by multiplying a compensation coefficient C to the output and subtracting static zero drift from the measured results, respectively.     

Study on comparison between absolute and relative input energy spectra and effects of ductility factor

Introduction Estimation of an attenuation relationship for strong ground motion parameters has been an interesting research subject in the field of engineering seismology and has played a very important role in seismic safety evaluation, seismic zoning, seismic hazard evaluation of major constructions, etc. At present, the generally used parameters include peak acceleration, peak velocity and elastic response spectrum. Such parameters mentioned above are essentially independent of the duration…