Selection and modification of ground motion records using Newmark-Hall spectrum as target spectrum for long-period structures

Input ground motions have significant impacts on the uncertainty of structural responses in time-history analysis.In this study,records were selected and scaled for the evaluation of mean structural responses according to the target spectrum.The Newmark-Hall spectrum is closely related to seismic response of short,medium and long-period structures,so it was taken as the target spectrum here.The nonlinear time-history analyses of 9-story and 20-story steel moment-resisting frame structures were carried out as examples.They represent medium and long-period buildings,respectively.Three target spectra with risk of 50%,10%and 2%probabilities for exceedance in 50 years were calculated by the average Newmark-Hall spectrum method for three ground motion sets developed in the SAC Steel Project.The predicted structural mean responses of these Newmark-Hall spectra were compared with those calculated by the average spectral acceleration method for the same record set.It is found that both methods have similar accuracy for estimating the structural mean response.However,the method proposed herein is more effective in reducing the variability of the structural responses.Also,the proposed method is more advantageous for the time-history analysis of long-period structures or structures with more severe nonlinear responses under strong seismic excitations.

Time-frequency response spectrum of rotational ground motion and its application

The rotational seismic motions are estimated from one station records of the 1999 Jiji （Chi-Chi）, Taiwan, earthquake based on the theory of elastic plane wave propagation. The time-frequency response spectrum （TFRS） of the rotational motions is calculated and its characteristics are analyzed, then the TFRS is applied to analyze the damage mechanism of one twelve-storey frame concrete structure. The results show that one of the ground motion components can not reflect the characteristics of the seismic motions completely; the characteristics of each component, especially rotational motions, need to be studied. The damage line of the structure and TFRS of ground motion are important for seismic design, only the TFRS of input seismic wave is suitable, the structure design is reliable.

Artificial ground motion compatible with specified ground shaking peaks and target response spectrum

This article describes a hybrid simulation method to generate artificial ground motion time histories that are compatible with specified peak seismic acceleration, velocity and displacement as well as the target response spectrum of absolute acceleration. First, based on traditional methods that match the target spectrum in the frequency domain, an initial acceleration time history was synthesized to satisfy the specified peak acceleration, target spectral acceleration and intensity envelope. Second, by using the inversion formula of the seismic input to a linear single-degree-of-freedom system and by superimposing a series of narrow-band time histories in the time domain, the initial time history is further modified to allow its peak velocity and displacement to approach the targets and improve its matching precision with the target spectrum. Numerical examples are provided to demonstrate that the proposed method achieves good agreement with the target values.

Generating ground motion by two new techniques of adding harmonic wave in the time domain and approximating to response spectrum as a whole

In this paper,two new methods are introduced to fit response spectrum in generating earthquake acceleration time history.The first method is Adding Harmonic Wave in Time Domain(AHWTD).In this method, a control point of response spectrum is adjusted by adding a harmonic time history to the adjusted one.Three features of the method are that it has small cross interference,small amount of computation and it can give consideration to the amplitude envelope.The second one is Approximating Response Spectrum as a Whole(ARSW).This method has following feature. When adjust a time history that is decided by amplitude spectrum A k and phase spectrum φ k(k =0, 1, 2, …, n ), the mean square root of every relative error E j(j= 1, 2, …, M ) between response spectrum and object spectrum V r=∑Mj=1E 2 j/M is used to decide adjusting direction of any amplitude spectrum A k . Because E j and V r are functions of A k and φ k , the problem of fitting response spectrum in generating earthquake acceleration time history can be changed to a problem of finding minimum point of V r . Restricted by Nyquist frequency, AHWTD is not suitable for high frequencies of response spectrum. Restricted by frequency distribution of FFT, the density of control points in the low frequency part can′t be too dense for ARSW. But two methods can replenish each other and get such a good fitting effect that we can fit the given peak ground acceleration and peak ground velocity well at the same time.

Artificial ground motion compatible with specified peak velocity and target spectrum

In this paper, a method, which synthesizes the artificial ground motion compatible with the specified peak velocity as well as the target acceleration response spectrum, was proposed. In this method, firstly, an initial acceleration time history α8^（0） （t）, which satisfies the prescribed peak ground acceleration, the target spectral acceleration ST（ω, ζ）,and the specified intensity envelope, is generated by the traditional method that generates the requency domain; secondly,α8^（0） （t）is further modulated by superimposing narrow-band time histories upon it in the time domain to make its peak velocity, approach the target peak ground velocity, and at the same time to improve its fitting precision to the target spectrum. Numerical examples show that this algorithm boasts high calculation precisions.

Instantaneous spectrum estimation of earthquake ground motions based on unscented Kalman filter method

Representing earthquake ground： motion as time varying ARMA model, the instantaneous spectrum can only be determined by the time varying coefficients of the corresponding ARMA model. In this paper, unscented Kalman filter is applied to estimate the time varying coefficients. The comparison between the estimation results of unscented Kalman filter and Kalman filter methods shows that unscented Kalman filter can more precisely represent the distribution of the spectral peaks in time-frequency plane than Kalman filter, and its time and frequency resolution is finer which ensures its better ability to track the local properties of earthquake ground motions and to identify the systems with nonlinearity or abruptness. Moreover, the estimation results of ARMA models with different orders indicate that the theoretical frequency resolving power of ARMA model which was usually ignored in former studies has great effect on the estimation precision of instantaneous spectrum and it should be taken as one of the key factors in order selection of ARMA model.

Pulse-like ground motion observed during the 6 February 2023 M_(W)7.8 Pazarcık Earthquake(Kahramanmaraş,SE Türkiye)

In this study,we analyzed 100 three-component strong ground motion records observed within 200 km of the causative fault of the 6 February 2023 M_(W)7.8 Pazarcık(Kahramanmaraş)Earthquake in SE Türkiye.The wavelet method was utilized to identify and analyze the characteristics of pulse-like ground motions in the near-fault region,while considering the uncertainty of the pulse orientation during the analysis.Our investigation focused on the effects of the focal mechanism and rupture process on the spatial distribution,pulse orientation,and maximum pulse direction of the observed pulse-like ground motion.We also analyzed the amplitude and period of the observed ground pulses and the effect of long-period amplification on the ground motion response spectra.Our results indicated the following:(1)A total of 21 typical ground velocity pulses were observed during this earthquake,exhibiting complex characteristics due to the influence of the strike-slip mechanism and rupture directivity.Most ground pulses(17 out of 21)were recorded within 20 km of the fault,in a wide range of orientations,including normal and parallel to the fault direction.The waveforms exhibited unidirectional features,indicating the effects of left-lateral fault slip.Distinct pulses observed more than 20 km from the fault were mainly oriented normal to the fault.The waveforms were bidirectional with double-or multi-round trips as a result of rupture directivity.(2)The amplitudes of the observed pulses ranged from 30.5 to 220.0 cm/s,with the largest peak velocity of 220.0 cm/s observed at Station 3138.The pulse periods ranged from 2.3 to 14.5 s,with the longest pulse period of 14.5 s observed at Station 3116.The amplitude and period of the pulses observed during this earthquake were comparable to those of similar-magnitude global earthquakes.The amplitude of the pulses decreased significantly with increasing fault distance,whereas the pulse period was not significantly affected by the fault distance.(3)Compared with non-pulse records,the velocity pulse records had a pronounced amplification effect on the acceleration response spectra near the pulse period,with factors ranging from 2.1 to 5.8.The larger velocity pulses also significantly amplified the velocity response spectra,particularly over the long periods.This significant amplification effect of the pulses on the response spectra leads to empirical models underestimating the long-period earthquake ground motion.

Texture Feature Extraction Method for Ground Nephogram Based on Contourlet and the Power Spectrum Analysis Algorithm

It is important to extract texture feature from the ground-base cloud image for cloud type automatic detection.In this paper,a new method is presented to capture the contour edge,texture and geometric structure of cloud images by using Contourlet and the power spectrum analysis algorithm.More abundant texture information is extracted.Cloud images can be obtained a multiscale and multidirection decomposition.The coefficient matrix from Contourlet transform of ground nephogram is calculated.The energy,mean and variance characteristics calculated from coefficient matrix are composed of the feature information.The frequency information of the data series from the feature vector values is obtained by the power spectrum analysis.Then Support Vector Machines(SVM)classifier is used to classify according to the frequency information of the trend graph of data series.It is shown that altocumulus and stratus with different texture frequencies can be effectively recognized and further subdivided the types of clouds.

An extended multiple-support response spectrum method incorporating fluid-structure interaction for seismic analysis of deep-water bridges

The effects of ground motion spatial variability(GMSV)or fluid-structure interaction(FSI)on the seismic responses of deep-water bridges have been extensively examined.However,there are few studies on the seismic performance of bridges considering GMSV and FSI effects simultaneously.In this study,the original multiple-support response spectrum(MSRS)method is extended to consider FSI effect for seismic analysis of deep-water bridges.The solution of hydrodynamic pressure on a pier is obtained using the radiation wave theory,and the FSI-MSRS formulation is derived according to the random vibration theory.The influence of FSI effect on the related coefficients is analyzed.A five-span steel-concrete continuous beam bridge is adopted to conduct the numerical simulations.Different load conditions are designed to investigate the variation of the bridge responses when considering the GMSV and FSI effects.The results indicate that the incoherence effect and wave passage effect decrease the bridge responses with a maximum percentage of 86%,while the FSI effect increases the responses with a maximum percentage of 26%.The GMSV and FSI effects should be included in the seismic design of deep-water bridges.

基于持时-条件谱双准则选取地震动的RC框架结构地震损伤分析

采用持时-条件谱双准则选择地震动记录,以损伤指数为性能指标对结构进行地震损伤分析。首先,根据选择的性能目标,确定不同水准地震加速度反应谱S_(a)(T_(1),5%),通过概率地震危险解聚分析确定不同水准S_(a)(T_(1),5%)对应的设计震级和设计震中距,结合地震动重要持时预测模型,通过调节持时预测模型标准差系数的范围,构建满足重要持时要求的待选地震动记录库。其次,建立地震动条件谱,从待选地震动记录库中选择地震动,并验证持时-条件谱双准则选择地震动记录方法的有效性。最后,以选择地震动为输入对一钢筋混凝土框架结构进行增量动力分析,结合考虑构件重要性系数的变形-滞回耗能双参数损伤模型,以损伤指数为性能指标分析结构的地震损伤。研究表明,与仅利用条件谱作为目标谱选择地震动相比,基于持时-条件谱双准则的地震动选取方法对结构变形和滞回耗能响应的离散性均可控且效果良好;对结构进行地震损伤分析发现,滞回耗能引起损伤的占比随S_(a)(T_(1),5%)的增大明显增大,同时滞回耗能可使结构的损伤模式发生改变,在地震损伤分析中不可忽略。

GPR信号去噪的变分模态分解

为了进一步提高探地雷达(ground penetrating radar,GPR)数据的信噪比,压制由随机扰动引起的随机绕射能量,将二维变分模态分解(two-dimensional variational mode decomposition,2D-VMD)引入二维GPR数据的噪声压制处理中。首先,对GPR数据进行2D-VMD处理,并分析各阶本征模态函数(intrinsic mode function,IMF)分量及其对应的频率-波数域谱来确定雷达剖面中的各回波类型。然后,计算IMF分量与原始数据的互相关系数来确定信号模态和噪声模态,并对信号模态进行重构得到降噪后的数据。理论数据和实测数据测试表明,相比于传统的1D-VMD法,2D-VMD滤波后的含噪正演记录峰值信噪比由6.44 dB增加到7.72 dB;经2D-VMD降噪处理后的雷达剖面在保留有效信号的基础上,可以有效压制随机扰动带来的噪声,并且得到的雷达剖面同相轴连续性更好。

城市功能区夜间光环境差异性分析

由于城市环境的复杂性,城市内的各功能区在环境、需求等方面存在着显著差异。夜间光环境在城市环境中占据重要地位,其特征对城市空间的规划、设计和管理至关重要。深入研究不同功能区夜间光环境的特点有助于全面了解城市在夜晚的特征与需求,为提升城市整体质量和可持续性提供了重要的参考依据。本研究针对六个具有代表性的城市功能区展开了夜间光环境的实地测量。通过绘制各功能区的夜间照明分布图,并对不同参数和多视角的照明数据进行了综合分析比较,揭示了这些功能区在夜间照明方面的显著差异。通过深入研究夜间照明特征,不仅为城市规划和设计提供了具体的数据支持,也为夜间照明管理策略的制定提供了理论依据。

基于监测台网加速度信号分析的上海周边区域地震影响评价

2021年11月至2023年8月期间,上海市周边区域共发生了5次有感地震,分别为江苏盐城市大丰区海域5.0级、江苏常州市天宁区4.2级、黄海海域4.8级、上海市青浦区3.1级和山东德州市平原县5.5级地震,同济大学监测台网的4个测站捕获了这5次地震的场地和典型结构加速度信号,分析了各次地震作用下场地和典型结构的加速度信号的峰值及持时,探讨了各次地震信号的反应谱特征,对照设计反应谱曲线的第一特征段和第二特征段,对这5次周边区域地震对上海市的影响进行评价。

2022年四川泸定 M_(s)6.8地震强震动特性研究

北京时间2022年9月5日12时52分,四川省甘孜州泸定县发生M_(s)6.8级地震。国家强震动台网获得了133组三分量加速度记录,在对记录进行初步筛选和滤波后,研究了PGA和PGV衰减关系、竖向地震动特点、地震动速度脉冲,对比分析了反应谱和设计谱,着重对石棉挖角台站附近震害与地震动的相关性进行了分析,结论如下:1)三种台站强震动记录的PGA和PGV拟合曲线都比较相近,PGA、PGV拟合曲线与霍俊荣的预测模型较为接近;2)竖向地震动偏大,约38.2%的强震动记录V/H大于2/3,可能是屋顶塌落、柱子扭转和天花板坠落等震害现象出现的主要原因;3)识别出具有速度脉冲特性的记录11条,该类记录对长周期结构影响较大;4)所选记录反应谱大多超过了罕遇地震设计谱水平段,具有速度脉冲特性的051SMW台站周围房屋破坏较严重,人员伤亡较重。

考虑场址危险一致性的中国完备条件目标谱与记录选取

即使所处地区的宏观抗震设防烈度相同,不同城市的地震地质构造与活动性背景仍然存在差异。为使地震动输入与所在场址的地震危险性水平保持一致,该研究衔接我国第五代地震区划图的概率地震危险性分析结果,给出了完备条件目标谱的构建方法。采用与第五代地震区划图相同的三级潜源分布和地震动预测方程,进行目标场址的危险性分析与设定地震解耦,衔接三维(震级-经纬度)设定地震解耦结果,给出了考虑所有潜源走向与位置相对贡献的“完备”条件谱。以北京近郊某城市作为算例,结果表明,完备条件谱的均值介于使用长轴和短轴衰减关系的粗略条件谱之间,条件标准差高于粗略条件谱。研究给出的完备条件谱适用于我国区划图的长短轴类型衰减关系,可以很好体现潜源的空间分布特征与背景地震危险性差异。基于我国强震动记录数据库拟合的加速度反应谱相关系数得到的条件谱要略高于基于国外数据库的计算结果。为了实现加速度反应谱均值和标准差的高效匹配,该研究采取多元高斯分布的协方差矩阵近似替换完备条件谱高斯混合分布的协方差矩阵,结合贪心优化算法,选取得到满足目标完备条件谱分布的强震动记录数据集。研究结果系统给出了我国条件目标谱进行记录选取的构建思路与选波方案,可为后续全概率结构性态分析提供依据。

某深埋输水隧洞放射性环境地质调查与评价

为探究某深埋输水隧洞穿越地层的放射性环境质量,采用原位测试和样品分析等手段,研究隧洞施工期的不利因素。结果表明:隧洞地表沿线的放射性元素含量在背景值变化范围内,未发现放射性异常现象。隧洞穿越的7个钻孔内γ总量和地温测井的结果表明:孔内核素放射性水平较低,基本处于豁免水平,但地温存在异常区域,施工期务必引起重视。钻孔目的层的岩心放射性核素活度浓度低,属于豁免范围内,孔内地下水放射性水平低,满足Ⅲ类地下水要求。辐射防护的计算结果显示,隧洞段地表沿线γ有效剂量当量为0.15 mSv/年,符合国家要求。隧洞段内照射指数和等效镭浓度符合约束值,ZK16钻孔的目的层外照射指数略高于标准值。因此,地下隧洞在施工期需着重关注洞内放射性水平,在辐射异常地段加强岩石采样与分析工作,以保证施工安全。

弹性滑板支座不同摩擦系数对楼层反应谱的影响

采用课题组建立的楼层反应谱Benchmark模型,研究弹性滑板支座不同摩擦系数对楼层反应谱的影响.使用ETABS软件建立隔震结构有限元模型,在底层柱底和基础之间布置弹性滑板支座,为了使楼层反应谱具有实用性和代表性,输入FEMA P695中推荐的22条远场地震动,分别对4个摩擦系数的基础隔震结构进行非线性时程分析,研究弹性滑板支座摩擦系数对楼层反应谱的影响,且与铅芯橡胶支座隔震结构楼层反应谱进行比较.结果表明:摩擦系数影响楼层反应谱的谱值,但不改变楼层反应谱峰值出现的周期,不影响楼层反应谱的频谱特征;在周期0~6 s内,文中4种摩擦系数的弹性滑板支座结构的楼层反应谱谱值均小于铅芯橡胶支座的谱值,说明该结构弹性滑板支座的隔震性能优于铅芯橡胶支座.

融合卫星姿态的星地信道建模及硬件模拟

针对传统星地信道模型及其硬件模拟方法没有考虑卫星姿态对信道特性影响的问题,本文基于几何地理随机模型(Geometry-based Stochastic Model,GBSM)框架,提出了一种融合卫星姿态的星地信道模型。该模型通过构建四个独立的坐标系并引入姿态修正矩阵,来描述卫星姿态变化对星地信道特性造成的影响。在此基础上,本文基于现场可编程门阵列(Field Programmable Gate Array,FPGA),设计并研制了一种星地信道硬件模拟器。硬件模拟器采用差分迭代的算法来生成信道衰落因子,可以极大提高硬件模拟的实时性,确保生成的衰落数据与实际场景相匹配。同时,还采用了并行处理架构,可以支持最大640 MHz带宽的星地信道模拟。为了将衰落数据与并行架构相匹配,引入了并行内插算法,可以将串行的衰落数据内插成同速率的多路并行衰落数据。此外,为了能够精准控制硬件装置输出信号的功率,设计了基于预训练的功率校正方法。通过内部校正源信号预先训练出整个模拟过程给信号带来的增益再进行功率补偿,从而保证输出信号的功率可以被精准控制。最后,在典型场景下开展仿真模拟,导出硬件模拟器的输出结果并分析其统计特性,结果表明实测输出的概率密度函数(Probability Density Function,PDF)和多普勒功率谱密度(Doppler Power Spectral Density,DPSD)与理论值吻合,证明本文设计的硬件模拟器可以准确地复现实际场景下卫星姿态发生变化的星地信道。本文提出的融合卫星姿态的星地信道模型以及研制的硬件模拟器很好地解决了传统模型以及硬件模拟方法的局限性,在卫星通信系统的优化、评估和验证环节具有极大的潜在价值。

基于谱压缩的大斜视TOPS BP图像自聚焦算法

在机动平台大斜视TOPS模式SAR成像时,通过使用地平面直角坐标系BP成像算法,能够在短时间内获取地距平面无畸变的宽幅SAR图像,但实际应用中如何对BP图像快速完成运动误差补偿与旁瓣抑制仍是一个难点。针对此问题,提出了一种改进的谱压缩方法,基于此能够快速实现机动平台大斜视TOPS模式地平面BP图像自聚焦等后续操作。首先,考虑到传统BP谱压缩方法仅适用于聚束成像模式,结合大斜视TOPS SAR虚拟旋转中心理论与波数谱分析,推导出了改进的精确谱压缩函数,能够通过全孔径压缩获得无模糊的地平面TOPS模式BP图像频谱。在此基础上,利用相位梯度自聚焦(PGA)能够快速完成全孔径运动误差估计与补偿。此外,基于提出的改进谱压缩方法得到的无模糊对齐BP图像频谱,可以在方位频域统一加窗实现图像旁瓣抑制。最后,通过仿真数据处理验证了所提算法的有效性。

基于Matlab的地震动参数综合确定

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