拟合加密控制点反应谱的地震动时程合成

在传统地震动反应谱频域拟合方法的基础上,提出了拟合加密控制点目标反应谱的地震动合成方法,并在此基础上利用实际算例与传统方法进行了对比.本文方法在每次迭代调整过程中均考虑了对地震动加速度强度包络函数的模拟,并且对调整后的地震动进行了基线校正,从而确保最终合成的地震动时程既能以一定精度拟合加密目标反应谱,又能满足目标包络函数的要求,同时保证积分所得位移曲线不产生基线漂移.数值算例分析结果表明,本文方法与传统非加密控制点目标谱拟合方法相比,在地震动时程曲线合成、反应谱拟合精度以及收敛速度等方面均具有一定的优势.      

拟合多阻尼比目标反应谱的高精度地震动调整方法

基于地震动调整效果的衡量指标比较了时域合成法和时频分析法的优缺点,在推导阿里亚斯强度与绝对加速度反应谱定量关系的基础上,将时域叠加小波函数法和时频小波分析调整法相结合,提出了一种能保留地震动强非平稳特性、对真实地震动相位差谱改动较少、能同时拟合多阻尼比目标反应谱的高精度地震动调整方法,并通过拟合美国规范D-V-A联合谱的算例证明了该方法的精度和通用性。     

人造地震动反应谱的非线性拟合

为了进一步提高人造地震动时程对目标反应谱的拟合精度和效率,本文提出了一种人造地震动反应谱非线性拟合方法.在人造地震动反应谱非线性拟合过程中,认为Fouricr幅值谱与反应谱调整项之间满足非线性(幂指数)关系.通过比例拉伸和折叠等数值技巧以促使模拟加速度向目标加速度逼近.算例分析结果表明,人造地震动反应谱非线性拟合方法具...     

基于数值模拟的设定地震场地谱时程拟合方法

本文将确定性数值模拟方法与地震动预测方程相结合,提出了一种重大水电工程场址设定地震的地震动时程生成方法。该方法基于场址设定地震,首先采用地震动预测方程确定场址的场地相关反应谱;其次建立包含震源和场址的场地模型,通过确定性数值模拟方法生成场址地震动时程;最后对生成的场址地震动时程进行调整,使其反应谱与设计谱相一致,用于工程抗震分析。这一方法生成的地震动时程既考虑了震源机制、传播路径以及局部场地效应等物理背景,又与场地相关的设计地震反应谱保持一致,为重大工程抗震分析与评价提供了一种新的思路。     

旋转地震合成及其在大跨度悬索桥中的应用

为探究旋转地震动在大跨度悬索桥中的应用,首先,从线弹性理论和功率谱角度基于随机振动理论提出了6维地震动加速度功率谱模型;其次,基于MATLAB编制旋转地震动人工地震合成程序,从反应谱角度对合成地震动进行了正确性验证和拟合精度迭代调整;最后,分析了旋转地震动与地震动入射角对桥梁结构地震响应的影响。研究表明：人工合成的地震动平动分量反应谱与实测地震动的平动分量反应谱吻合度较高;六维地震动的主梁跨中竖向位移越是三维平动地震动的3倍,而主缆轴力峰值接近2.25E+05kN,约是三维平动地震动的1.3倍;旋转地震动和地震动入射角将会加大桥梁结构的位移响应和内力响应,且会减小塔底截面和桩最不利截面的安全性。     

考虑相位谱的人造地震动反应谱拟合

本文在回顾了地震动模拟理论及反应谱拟合技术的发展后,提出了一个新的加速度时程曲线的拟合方法,以改进现有反应谱拟合精度和原则。此法不同于常规方法之处有二:(一)在对幅值谱修正时,考虑了傅氏谱各分量对最大反应贡献的正负;(二)对于仅用幅值谱修正不能满足要求的顽固点,提出了相位修正的方法。这一力法使拟合技术更为合理而有效。     

基于小波函数的地震动反应谱与峰值位移拟合方法

采用数值方法合成地震动时,除对反应谱拟合外,对峰值位移的拟合和天然地震动非平稳特性的模拟也具有重要的意义和工程应用前景.本文基于小波函数的拟合方法,提出了一种能够同时合成目标反应谱和峰值位移的地震动加速度时程.数值算例表明:该方法具有较快的收敛速度,可用较少的迭代运算实现对目标反应谱和目标峰值位移的较高精度拟合;相较于...     

基于等效群速度的非平稳地震动拟合方法研究

基于地震动能量传播速度为群速度这一概念,回顾了相位微分和窄带滤波两种频率相依波包时延计算方法及其在非平稳地震动相位拟合中的应用,归纳给出了一种非平稳地震动生成方法,通过模拟2条典型的海底与陆地地震动验证了方法的有效性,并将该方法应用于区域非平稳地震动场模拟中。结果表明:利用该方法所得模拟地震动记录平均加速度反应谱与原记录加速度反应谱有较高的一致性,而且能很好地再现地震的非平稳特性。     

考虑脉冲参数随机性的近断层地震动降维建模

根据50组近断层脉冲型强震动记录,采用连续小波变换提取最强速度脉冲分量,建立最强速度脉冲峰值时刻的统计模型。对近断层地震动加速度高频分量的演变功率谱模型参数进行识别,并利用谱表示-随机函数方法实现了降维模拟,进而积分得到速度高频分量。对脉冲参数进行随机化处理,并采用改进Gabor小波模型随机模拟速度低频分量。将速度高频分量与低频分量叠加得到近断层地震动速度时程。数值算例表明,近断层地震动加速度代表性时程集合的幅值谱和反应谱均与实测记录拟合一致,验证了降维模拟方法的工程适用性。近断层脉冲型地震动的降维模拟与概率密度演化理论相结合,可实现工程结构的随机地震反应与抗震可靠性精细化分析。     

汶川地震黄土地区地震动特征分析

汶川地震黄土地区强地震动加速度峰值（PGA）较小,然而震害却较为严重,局部场地震害和地震动放大效应显著。选取四川、甘肃及宁夏境内的部分强震动记录,探讨传播距离和场地条件对地震动的影响规律,重点研究黄土地区地震动幅值、频谱、持时特征以及对建筑结构的潜在影响,从地震动特征角度分析该地区震害相对较重的原因。结果表明:汶川地震黄土地区地震动速度峰值较大,地震动中频分量和中长周期成分较为突出;黄土地区自振周期为0.3~1s以及3~4s（尤其是此周期内30~40层）的结构物地震反应将显著放大;设计地震分组为第三组的Ⅲ类黄土场地,加速度反应谱拟合曲线在周期1~3.5s谱值明显高于规范设计谱;黄土场地地表地震动拥有更长持时。     

Wavelet-based generation of spectrum-compatible time-histories

This paper deals with the well-known problem of generating spectrum-compatible synthetic accelerograms for the linear and non-linear time-history analyses of structural systems. A wavelet-based procedure has been used to decompose a recorded accelerogram into a desired number of time-histories with non-overlapping frequency contents, and then each of the time-histories has been suitably scaled for matching of the response spectrum of the revised accelerogram with a specified design spectrum. The key idea behind this iterative procedure is to modify a recorded accelerogram such that the temporal variations in its frequency content are retained in the synthesized accelerogram. The proposed procedure has been illustrated by modifying five recorded accelerograms of widely different characteristics such that those are compatible with the same USNRC design spectrum.     

Generation of accelerograms compatible with design specifications using information theory

This paper deals with the generation of seismic accelerograms which are compatible with a given response spectrum and other design specifications. The time sampling of the stochastic accelerogram yields a time series represented by a random vector in high dimension. The probability density function of this random vector is constructed using the maximum entropy (MaxEnt) principle under constraints defined by the available information (design specifications). In this paper, an adapted algorithm is proposed to identify the Lagrange multipliers introduced in the MaxEnt principle to take into account the constraints. This algorithm is based on (1) the minimization of an appropriate convex functional and (2) the construction of the probability distribution defined as the invariant measure of an Itô stochastic differential equation in order to estimate the integrals in high dimension of the problem. The constraints related to a seismic accelerogram are developed explicitly. This methodology is validated through an application for which the available information is related to the variance of each component of the random vector representing the accelerogram, statistics on the response spectrum, on the peak ground acceleration, on the cumulative absolute velocity and on the end-values for the velocity and for the displacement.     

Simulation and generation of spectrum-compatible ground motions based on wavelet packet method

This paper deals with the problem of generating spectrum-compatible artificial accelerograms for seismic dynamic analysis of engineering projects. A wavelet-packet-based, two-step procedure for the issue is proposed. The first step is to generate acceleration time history that could account for temporal and frequency non-stationarities of recorded ground motions. The second step is to decompose it into a desired number of wavelet packet vectors with high frequency resolution and non-overlapping frequency contents. Then each wavelet packet vector is scaled suitably and iteratively for the response spectrum of the simulated accelerogram to fit a specified design spectrum. The advantages of this procedure are that it can simulate user-specified acceleration time history with only 6 input parameters and the adjusted accelerogram has similar characteristics to the recorded one. The proposed procedure has been illustrated by simulating and modifying acceleration time history that are compatible with two different design spectrums for nuclear power plants. In addition, iterative efficiency of the method is investigated by simulating and adjusting acceleration time history for 100 successive times. The maximum relative error of the 76 period control points can reach 6% or below. Results show that the proposed method is effective and practical to generate and find spectrum-compatible ground motions with both stochastic and deterministic aspects.     

Wavelet‐based simulation of spectrum‐compatible aftershock accelerograms

In damage‐based seismic design it is desirable to account for the ability of aftershocks to cause further damage to an already damaged structure due to the main shock. Availability of recorded or simulated aftershock accelerograms is a critical component in the non‐linear time‐history analyses required for this purpose, and simulation of realistic accelerograms is therefore going to be the need of the profession for a long time to come. This paper attempts wavelet‐based simulation of aftershock accelerograms for two scenarios. In the first scenario, recorded main shock and aftershock accelerograms are available along with the pseudo‐spectral acceleration (PSA) spectrum of the anticipated main shock motion, and an accelerogram has been simulated for the anticipated aftershock motion such that it incorporates temporal features of the recorded aftershock accelerogram. In the second scenario, a recorded main shock accelerogram is available along with the PSA spectrum of the anticipated main shock motion and PSA spectrum and strong motion duration of the anticipated aftershock motion. Here, the accelerogram for the anticipated aftershock motion has been simulated assuming that temporal features of the main shock accelerogram are replicated in the aftershock accelerograms at the same site. The proposed algorithms have been illustrated with the help of the main shock and aftershock accelerograms recorded for the 1999 Chi–Chi earthquake. It has been shown that the proposed algorithm for the second scenario leads to useful results even when the main shock and aftershock accelerograms do not share the same temporal features, as long as strong motion duration of the anticipated aftershock motion is properly estimated. Copyright © 2008 John Wiley & Sons, Ltd.     

A brief theory and computing of seismic ground rotations for structural analyses

The seismic ground rotations are important with respect to spatial structural models, which are sensitive to the wave propagation. The rotational ground motion can lead to significant increasing of structural response, instability and unusual damages of buildings. Currently, the seismic analyses often take into account the rocking and torsion motions separately using artificial accelerograms. We present an exact analytical method, proposed by Nazarov [15] for computing of three rotational accelerograms simultaneously from given translational records. The method is based on spectral representation in the form of Fourier amplitude spectra of seismic waves, corresponding to the given three-component translational accelerogram. The composition, directions and properties of seismic waves are previously determined in the form of a generalized wave model of ground motion. It is supposed that seismic ground motion can be composed by superposition of P, SV, SH- and surface waves. As an example, the dynamic response analysis of 25-story building is presented. Here recorded (low-frequency) and artificial (high-frequency) accelerograms were used; each of them includes three translational and three rotational components. In this structural analysis, we have clarified primarily conditions under which rotational ground motion should be taken into account. Next, we have calculated three rotational components of seismic ground motion. Then they were taken as additional seismic loads components for further seismic analysis of the building. Note, soil–structure interaction (SSI) is not considered in this study. For computing, we use the special software for structural analyses and accelerogram processing (FEA Software STARK ES and Odyssey software, Eurosoft Co., Russia). It was developed and is used in engineering practice in the Central Research Institute of Building Constructions (TsNIISK, Moscow, Russia).     

Numerical simulation of ground acceleration spectra and accelerograms for engineering application

A numerical approach to the earthquake ground motion analysis is proposed for regions where no accelerograms are available. Using Haskell matrix techniques, the response spectra of a layered substratum for SV waves were calculated and then multiplied by the spectra corresponding to Brune's type pulses. The ground acceleration spectra were obtained for different angles of pulse incidence at the substratum base. The spectrum shape depends upon the substratum response and the pulse shape, while its level was related to the maximum ground acceleration corresponding to the expected maximum intensity. Transformation of the ground spectra into the time domain produced numerical accelerograms for horizontal and vertical components and for different angles of pulse incidence. Finally, a standard statistical procedure was applied to obtain the design response spectra used in engineering applications.     

The use of optimization to construct critical accelerograms for given structures and sites

In this paper a methodology has been presented for constructing the most critical accelerogram from among a be class of candidate accelerograms for a given site and structure. This most critical accelerogram could be used to assess seismic resistance of a structure with a high level of confidence. Specifically, the method superimposes accelerograms recorded at similar sites to create the candidate accelerograms, then uses optimization and approximation techniques find the most critical accelerogram. The most critical accelerogram is defined as the one which maximizes damage is structure, as computed by non-linear dynamic structural analysis, as well as satisfies constraints on ground parameters to ensure credibility. The damage has been defined as cumulative inelastic energy dissipation or sure of interstorey drifts. The method is applied to ten examples in the paper.     

Simulation of artificial earthquakes

A procedure is developed for the simulation of artificial earthquake accelerograms, The time variation of amplitude and frequency content is preserved in the simulation procedure. Sixteen artificial earthquake accelerograms are simulated and compared with a target accelerogram. The time variation of amplitude and frequency content for 26 historical earthquake accelerograms is characterized.     

强震加速度记录的数据处理方法

本文用数值积分法,对RDZ1-12-66型自动触发电流计记录式强震仪的幅频响应失真进行校正。并采用高通数字滤波的方法,修正加速度图的零线.为此编制了计算机程序,绘制了修正后的加速度、速度和位移时程曲线.计算了修正前后加速度图的傅氏谱。同时,对这些结果加以讨论。 修正后的加速度图,精确地表示了仪器基本频带在0.09HZ和25HZ之间的绝对地面加速度。      

New method of generating spectrum compatible accelerograms using neural networks

A new method is proposed for generating artificial earthquake accelerograms from response spectra. This method uses the learning capabilities of neural networks to developed the knowledge of the inverse mapping from the response spectra to earthquake accelerogram. In the proposed method the neural networks learn the inverse mapping directly from the actual recorded earthquake accelerograms and their response spectra. A two-stage approach is used. In the first stage, a replicator neural network is used as a data compression tool. The replicator neural network compresses the vector of the discrete Fourier spectra of the accelerograms to vectors of much smaller dimension. In the second stage, a multi-layer feed-forward neural network learns to relate the response spectrum to the compressed Fourier spectrum. A simple example is presented, in which only 30 accelerograms are used to train the two-stage neural networks. This example demonstrates how the method works and shows its potential. © 1998 John Wiley & Sons, Ltd.