Estimation of peak relative velocity and peak absolute acceleration of linear SDOF systems

In the seismic analysis and design of structures, the true velocity and absolute acceleration are usually approximated by their corresponding pseudo-values. This approach is simple and works well for structures with small damping (say, less than 15%). When the damping of a structure is enhanced for the purpose of response reduction, it may result in large analysis and design errors. Based on theory of random vibration and the established mechanism of seismic response spectra analysis, a method is developed (1) to predict the relative velocity spectra with any damping ratio level directly from the 5% standard pseudo-acceleration spectrum; and (2) to estimate the peak absolute acceleration. The accuracy of both is validated by using two selected ensembles of ground motion records.     

Correlation in spectral accelerations for earthquakes in Europe

The shape of a uniform hazard spectrum has been criticized to be unrealistic for a site where the spectral ordinates of the uniform hazard spectrum at different periods are governed by different scenario events and conservative for long‐return‐period earthquake shaking. The conditional mean spectrum considering epsilon (CMS‐ε) takes into account the correlation of spectral demands (represented by values of ε) at different periods, to address these issues. This paper proposes new prediction models for the correlation coefficient of ε(T₁) and ε(T₂), a key component for developing a CMS, using Pan‐European earthquake records from a European ground motion database. Epsilon (ε) for each record is computed using the 2005 Ambraseys ground‐motion prediction equation. The model can be used to develop CMS for European sites, and it can be incorporated in the European seismic standards. Copyright © 2012 John Wiley & Sons, Ltd.     

HORIZONTAL-TO-VERTICAL SPECTRUM RATIO OF EARTHQUAKE GROUND MOTION FOR SITE CHARACTERIZATION

Nakamura's method, which uses a horizontal-to-vertical Fourier spectrum ratio of microtremor, has become popular to determine the predominant period and amplification of a site. In this study, this method is extended for earthquake ground motion recordings using new strong motion data recorded by JMA-87-type accelerometers. From the analysis of these accelerograms, horizontal-to-vertical Fourier spectrum ratios of a site for different earthquakes are also found to be stable irrespective of magnitude, distance and depth. To establish this fact, attenuation relations of velocity response spectra for horizontal and vertical components are derived for three damping ratios (0, 2 and 5 per cent) using the JMA data. Then the horizontal-to-vertical ratios of the velocity response spectra are obtained. The results show that the horizontal and vertical velocity response spectra are dependent on magnitude, distance and depth, but that their ratios are almost independent of magnitude, distance and depth. However, since the current data set consists of mostly intermediate to far field data, this observation should be limited to records of these distance ranges. Introducing station coefficients, representing site amplification, to this relation yields the value comparable to the horizontal-to-vertical Fourier spectrum ratio at a specific site. The stability of the spectrum ratio is explained by the transfer function between the ground surface and stiff-soil outcrop due to S-wave propagation. These results suggest that site amplification characteristics can be evaluated by one-point two-component surface recordings of earthquake ground motion, in a similar manner as proposed by Nakamura for microtremor. © 1997 by John Wiley & Sons, Ltd.     

Simulation of non-stationary ground motion processes (II)

Introduction When doing Monte Carlo analysis of stochastic earthquake response of nonlinear structures, it is necessary to have a great number of ground motion processes with an identical statistical feature; In theoretical analysis of earthquake resistance of structures, to study the effect of one parameter, it is required to keep other parameters fixed, and it is often needed one set of ground motion proc-esses having an identical statistical feature; Similarly, while doing structural model…     

非平稳地震动过程模拟方法(Ⅱ)

在总结回顾具有同一统计特征非平稳地震动过程模拟的研究基础上, 提出了一个模拟产生与某个给定地震动记录具有同一统计特征[CD2]时变功率谱的非平稳地震动过程的方法. 方法具有如下一些特点: 模拟产生的样本过程在幅值上和频率上均是非平稳的, 幅值和频率的非平稳性均取决于目标时变功率谱; 任意一个样本过程的时变功率谱未必符合目标谱, 但在统计意义上却严格符合目标谱. 最后, 论文以Landers地震的一个加速度记录为例对方法进行了验证.      

Spectral Aerosol Transmittance in the Ultraviolet and Visible Spectra in Athens,Greece

This work investigates the spectral atmospheric transmittance due to aerosols in the urban environment of Athens during a period of one year. The spectral transmittance due to aerosols is derived using measurements of spectral direct-beam solar irradiance in the 310–575 nm spectral band. This derivation is accomplished by using a radiative transfer model for estimating the partial spectral atmospheric transmittance functions due to Rayleigh scattering, and absorption by ozone, nitrogen dioxide and water vapor. The seasonal and diurnal variation of the aerosol transmittance is investigated and the results are discussed with a view to air pollution sources, meteorological factors and topographic characteristics of the Athens basin.     

Consecutive combined response spectrum

Appropriate estimates of earthquake response spectrum are essential for design of new structures, or seismic safety evaluation of existing structures. This paper presents an alternative procedure to construct design spectrum from a combined normalized response spectrum(NRSC) which is obtained from pseudo-velocity spectrum with the ordinate scaled by different peak ground amplitudes(PGA, PGV, PGD) in different period regions. And a consecutive function f(T) used to normalize the ordinates is defined. Based on a comprehensive study of 220 strong ground motions recorded during recent eleven large worldwide earthquakes, the features of the NRSC are discussed and compared with the traditional normalized acceleration, velocity and displacement response spectra(NRSA, NRSV, NRSD). And the relationships between ground amplitudes are evaluated by using a weighted mean method instead of the arithmetic mean. Then the NRSC is used to define the design spectrum with given peak ground amplitudes. At last, the smooth spectrum is compared with those derived by the former approaches, and the accuracy of the proposed spectrum is tested through an analysis of the dispersion of ground motion response spectra.     

The relation between the response spectrum and the phase diference spectrum

ＴｈｅｒｅｌａｔｉｏｎｂｅｔｗｅｅｎｔｈｅｒｅｓｐｏｎｓｅｓｐｅｃｔｒｕｍａｎｄｔｈｅｐｈａｓｅｄｉｆｅｒｅｎｃｅｓｐｅｃｔｒｕｍＦＥＮＧ－ＸＩＮＺＨＡＯ（赵凤新）ａｎｄＹＵ－ＸＩＡＮＨＵ（胡聿贤）ＩｎｓｔｉｔｕｔｅｏｆＧｅｏｐｈｙｓｉｃｓ，Ｓｔａ...     

竖向地震动加速度反应谱特性

以33次地震中的地表地震动记录为数据基础,考虑场地条件、震级和距离的影响,分别对竖向地震动的加速度规准化反应谱和双规准化反应谱进行了研究。结果表明,规准反应谱明显受到场地条件、震级和震中距的影响,不同场地、距离和震级的平均规准反应谱之间差别显著;相比较而言,不依赖于场地、距离和震级的平均双规准反应谱之间却表现出良好的规律性和一致性。双规准反应谱的统一特性可以为竖向地震动设计谱的预测提供参考依据。     

汶川地震前后水位频谱特征分析

以频谱分析方法作为理论基础,采用周期图法计算汶川地震前后距震中500 km以内10口观测井水位（包括动水位与静水位）的功率谱,对比分析2009年无大震年份同时期的数据,研究结果表明：水位的频域特征受制于观测井的地质构造背景、观测方式和观测深度;水位的波动能量主要集中于大于4天与小于0.5天周期,震后水位波动能量则集中在大于8天的周期;动水位频谱更加丰富.另外,不同井水位的频域响应特征与该井观测层岩性有关,需进一步研究.     

Wavelet analysis of lightning return stroke

In this investigation, time series consisting of electric field waveforms of 15 positive return strokes and 10 negative return strokes were analyzed. The data came from a summer thunderstorm in March in a range of about 200 km around São José dos Campos, São Paulo. The electric field recording system consisted of a flat plate antenna with a decay time constant of 260 μs and a sample rate of 800,000 samples per second. The bandwidth observed was up to 100 kHz and the recording system was synchronized with GPS time and located at São José dos Campos. Wavelet analysis of the electric field waveforms was done in order to investigate the behavior of the return stroke spectrum in time. The return stroke was suggested to be divided into two portions: initial stage and overshoot (for far return stroke) and initial stage and ramp (for close return stroke). The return stroke power spectrum was observed to be distributed in a frequency range with the peak value also distributed in a fraction of this range. Power peaks for ramps are stronger than power peaks for initial stage and overshoot. Finally, it was observed how powerful the wavelet is in the analysis of lightning.     

Response spectrum to strong aftershocks of the Lancang-Gengma earthquake

Near-field records of two strong aftershocks with magnitudeM _S=6.7 andM _S=6.3 in the Lancang-Gengma earthquakes sequence, Yunnan Province, November 1988, are used to calculate the response spectrum. The instruments, site conditions and the methods for computing are also illustrated in this paper. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,13, 338–343, 1991. This project is supported by The Chinese Joint Seismological Science Foundation, SSB and the West Yunnan Earthquake Prediction Test Field, Yunnan Seismological Bureau.     

Bi-normalized response spectral characteristics of the 1999 Chi-Chi earthquake

To develop uniform and seismic environment-dependent design spectrum, common acceleration response spectral characteristics need to be identified. In this paper, a bi-normalized response spectrum (BNRS) is proposed, which is defined as a spectrum of peak response acceleration normalized with respect to peak acceleration of the excitation plotted vs. the natural period of the system normalized with respect to the spectrum predominant period, Tp. Based on a statistical analysis of records from the 1999 Chi-Chi earthquake, the conventionally normalized response spectrum(NRS) and the BNRS are examined to account for the effects of soil conditions, epicentral distance, hanging wall and damping. It is found that compared to the NRS, the BNRS is much less dependent on these factors. Finally, some simple relationships between the BNRS for a specified damping ratio and that for a damping ratio of 5%, and between the spectra predominant period and epicentral distance for different soil types are provided.     

Occurrence of negative epsilon in seismic hazard analysis deaggregation,and its impact on target spectra computation

This paper investigates circumstances behind the occurrence of negative ε (the normalized difference between the spectral acceleration of a recorded ground motion and the median response predicted by a ground motion prediction equation) in probabilistic seismic hazard deaggregation. Negative ε values are of engineering interest because of their impact on the conditional mean spectrum (CMS), which is a proposed alternative to the uniform hazard spectrum (UHS) as a target spectrum for ground motion selection. In the case where target ε values from deaggregation are positive, the CMS calculation produces relatively lower response spectra than the UHS. Positive target ε values occur almost universally in active seismic regions at long return periods of engineering interest, but the possibility of negative target ε values is important because in the case of negative target ε, some relationships between the CMS and UHS would reverse. This paper describes the calculation of target ε, performs parametric studies to determine when negative ε values occur in deaggregation, and investigates the potential impact on target spectrum calculation and ground motion selection. The case studies indicate that special seismicity models and certain ground motion prediction equations have the most significant effect on ε values and a combination of these characteristics in Eastern North America creates the most likely situation for negative target ε to occur. CMS results are nonintuitive when the target ε is negative, but it is not clear that this is a common practical concern because negative target ε occurs only in well‐constrained areas. Copyright © 2011 John Wiley & Sons, Ltd.     

古田地震水口水电站重力坝强震观测记录HHT分析

利用HHT变换研究2008年3月6日福建古田ML4.6地震中,水口水电站重力坝强震反应台阵获取的强震反应观测资料的时频特性及重力坝结构动力特性,得到如下结论:(1)强震记录能量集中在0～15Hz频段和10～15s时段;(2)重力坝顺河向主频为3.7Hz。分析结果对认识水库地震近场地震动特性和重力坝地震反应有一定的实际意义。     

RESPONSE SPECTRA FOR DIFFERENTIAL MOTION OF COLUMNS

The validity of the response spectrum concept for determining loads in structures excited by differential earthquake ground motion is examined. It is shown that the common definition of response spectrum for synchronous ground motion can be reconciled to remain valid in cases when the columns of extended structures experience different motions. Then, a relative displacement response spectrum for design of first-storey columns, SDC(T, δ, ζ, τ), is defined. In addition to natural period, T, and fraction of critical damping, ζ, this spectrum depends also on the ‘travel time’, τ (of the waves in the soil over distances about one half width, or length of the structure), and on a factor, δ, specifying the relative displacement of the first floor. It is shown how this spectrum can be determined using existing empirical scaling equations for relative displacement spectra SD(T, ζ) and for peak velocity and peak acceleration of strong ground motion. These new spectra are illustrated for a horizontal component of a record in the near field of the 1994 Northridge earthquake. The results show that differential motions are more important for short period (stiff) than for longer period (flexible) structures, and for structures founded on softer ground (small shear wave velocity). © 1997 by John Wiley & Sons, Ltd.     

Conditional spectrum‐based ground motion record selection using average spectral acceleration

The use of a seismic intensity measure (IM) is paramount in decoupling seismic hazard and structural response estimation when assessing the performance of structures. For this to be valid, the IM needs to be sufficient;that is, the engineering demand parameter (EDP) response should be independent of other ground motion characteristics when conditioned on the IM. Whenever non‐trivial dependence is found, such as in the case of the IM being the first‐mode spectral acceleration, ground motion selection must be employed to generate sets of ground motion records that are consistent vis‐à‐vis the hazard conditioned on the IM. Conditional spectrum record selection is such a method for choosing records that are consistent with the site‐dependent spectral shape conditioned on the first‐mode spectral acceleration. Based on a single structural period, however the result may be suboptimal, or insufficient, for EDPs influenced by different period values, for example, peak interstory drifts or peak floor accelerations at different floors, potentially requiring different record suites for each. Recently, the log‐average spectral acceleration over a period range, AvgSA, has emerged as an improved scalar IM for building response estimation whose hazard can be evaluated using existing ground motion prediction equations. Herein, we present a recasting of conditional spectrum record selection that is based on AvgSA over a period range as the conditioning IM. This procedure ensures increased efficiency and sufficiency in simultaneously estimating multiple EDPs by means of a single IM. Copyright © 2017 John Wiley & Sons, Ltd.     

福建数字地震台网台址背景噪声分析

在使用福建区数字地震台网选台过程中,用１２个台址得到的背景噪声数字记录,计算分析了其背景噪声地动速度均方根值（ＲＭＳ）,有效测量动态范围、噪声功率谱及功率谱密度。所得结果可作为供评价仪器性能,台址安静程度的参考。对利用仪器所提供的动态范围,根据区域台网周围地震环境和台网记录地震的目的及任务设置适当的增益量程是也是有用的 。     

A new model for spectral velocity ordinates at long periods

The estimation of peak linear response via elastic design (response) spectra continues to form the basis of earthquake‐resistant design of structural systems in various codes of practice all over the world. Many response spectrum‐based formulations of peak linear response require an additional input of the spectral velocity (SV) ordinates consistent with the specified seismic hazard. SV ordinates have been conventionally approximated by pseudo spectral velocity (PSV) ordinates, which are close to the SV ordinates only over the intermediate frequency range coinciding with the velocity‐sensitive region. At long periods, PSV ordinates underestimate the SV ordinates, and this study proposes a formulation of a correction factor (>1) that needs to be multiplied by the PSV ordinates in order to close the gap between the two sets of ordinates. A simple model is proposed in the form of a power function in oscillator period to estimate this factor in terms of two governing parameters which are in turn estimated from two single‐parameter scaling equations. The parameters considered for the scaling equations are (1) the period at which the PSV spectrum is maximized and (2) the rate of decay of the pseudo spectral acceleration (PSA) amplitudes at long periods. For a given damping ratio, four regression coefficients are determined for the scaling equations with the help of 205 ground motions recorded in western USA. A numerical study undertaken with the help of several design PSA spectra and ensembles of spectrum‐compatible ground motions illustrates the effectiveness of the proposed correction factor, together with the proposed scaling models, in comparison with the PSV approximation in a variety of design situations. Both the input parameters mentioned above can be easily obtained from the specified design spectrum, and thus the proposed model is convenient to use.     

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

ＧｅｎｅｒａｔｉｎｇｇｒｏｕｎｄｍｏｔｉｏｎｂｙｔｗｏｎｅｗｔｅｃｈｎｉｑｕｅｓｏｆａｄｄｉｎｇｈａｒｍｏｎｉｃｗａｖｅｉｎｔｈｅｔｉｍｅｄｏｍａｉｎａｎｄａｐｐｒｏｘｉｍａｔｉｎｇｔｏｒｅｓｐｏｎｓｅｓｐｅｃｔｒｕｍａｓａｗｈｏｌｅＣＨＡＮＧ...