Study on Site Specific Design Earthquake Ground Motion of Nuclear Power Plants in China

The main technical backgrounds and requirements are introduced with regard to earthquake ground motion design parameters in several domestic and American standards, codes and guides involved in the seismic analysis and design activities of nuclear power plants in China. Based on the research results from site seismic safety evaluation of domestic nuclear power plant projects in the last years, characteristics and differences of site specific design spectra are analyzed in comparison with standard response spectra, and the suitability of standard response spectra for domestic nuclear power plant projects is discussed.     

Levels of Probability of Exceedance for Current Code Spectra in China

Long-period acceleration spectra determined by seismic safety evaluation for project sites are generally lower than that given by relative code spectra. In this paper, we discuss the recurrence periods corresponding to the code spectra of different periods, by using ground motion attenuation laws for sites of types Ⅰand Ⅲ. We show the results that the longer the periods of code spectra are commonly the more conservative the seismic level is. As for the project examples in this paper, when the periods are longer than 3.7 or 5.2 seconds for sites of types Ⅰ or Ⅲ, the recurrence periods corresponding to the code spectra are longer than 5000 years. We suggest that some problems need to be further discussed, including the reliability of the present attenuation laws, the performance of those project structures that suffer long period seismic waves and have been designed according to the conservative codes, and the effects of ground motion parameters such as velocity and displacement on seismic design.     

Reproducing fling-step and forward directivity at near source site using of multi-objective particle swarm optimization and multi taper

This paper presents a technique to reproduce compatible seismogran3s involving permanent displacen3ent effects at sites close to the fault source. A multi-objective evolutionary algorithm is used to minimize the differences between the response spectra and multi-tapered power spectral delsilies corresponding to the recorded and simulated wavelbrms. The multi-taper method is used to reduce the spectral leakage that is inherent in the Fourier rams formed form ofwavelbrms, ieading to a reduction of variance in power spectral amplitudes, thus permitting the calibration of the two sets of data. The technique is implemented using the 1998-Fandoqa （lran） earthquake data and the results are compared with the actual observed data. Additionally, a comparison is made with a SAR interfcrometry study leading to fair agreement with the reported dislocation along the main fault. The simulation procedure and results are discussed and assessed concluding that, although the technique may be associated with uncertainties, it can still be used to reproduce wavelbnns at near source sites that include permanent dislocation, and can be used for seismic pertbrmance evaluation of structures in the region under study.     

Near-fault ground motion bi-normalized pseudo-velocity spectra and its applications

Ground motions with forward-directivity effect in the near-fault region are obviously different from ordinary far-field ground motions. Design spectral models for this kind of motions have been proposed by correlating sim-ple pulses with parameters attenuation relationships in a previous study of the authors. To further test the applica-bility of the established design spectral model, we analyze ground motion pseudo-velocity response spectra (PVS), normalized pseudo-velocity spectra (NPVS) and bi-normalized pseudo-velocity spectra (BNPVS) of 53 typical near-fault forward-directivity ground motions. It is found that BNPVS not only has more salient features to reflect the difference between soil and rock sites, but also has less scattering to reveal the nature of forward-directivity motions. And then, BNPVS is used for prediction of design spectra accounting for the influence of site conditions, and the constructed design spectra are compared with those spectra established previously. It is concluded that site condition can heavily affect ground motions, buildings on rock can be even more dangerous than those on soil sites, in particular for ordinary buildings with short to middle vibration periods. Finally, pulse models are also suggested for structural analyses in the near-fault region.     

云南ELF电磁观测资料的异常特征分析

Located in an earthquake-prone region,the geological structures in Yunnan Province are complex. Taking into account that Tonghai county is located in the intersection of Xiaojiang fault and Honghe fault, an ACF-4M ELF electromagnetic instrument was installed at the Tonghai seismic station,which has produced continuous reliable data. The author collected the data and information for the year 2009 and 2010,and performed analysis on the variation characteristics of both geomagnetic fields and electrical resistivity. The result shows that the 1Hz and 39Hz electromagnetic power spectra are 0. 2 to 1. 4 orders of magnitude higher than the normal values immediately before many earthquakes. The anomalies are represented by the abrupt changes of the electric and magnetic field power spectra in earthquake and aftershock sequences,and the amplitude of change is related to the size of earthquake magnitude and epicentral distance. The electrical resistivity also obviously changes. Therefore, further research on the anomalous characteristics of ELF electromagnetic data will be meaningful to the future use of this instrument in earthquake prediction.     

Statistical Characteristics of Strong Ground Motion Specified by Response Spectrum and Power Spectral Density Function

The statistical characteristics of strong ground motion specified by response spectrum and power spectral density function are studied using 190 strong-motion records of the Haicheng and Tangshan earthquakes in China and 138 earthquakes in the western United States.The response spectrum is normalized by the peak ground acceleration(i.e.,represented as spectral magnification factor),and the power spectral density function is described by the Kanai-Tajimi spectrum.The statistics and dependence of parameters are evaluated,and correlations between the spectral magnification factor or Kanai-Tajimi spectral parameters and the site condition,epicentral distance,or local magnitude are investigated.The statistical characteristics of spectra China and the U.S.A.are compared.Based on the results obtained the values of the statistics on spectral parameters for earthquake engineering applications in China are suggested.     

Anisotropy of the horizontal velocity fluctuation field in the large wavenumber region

Mesoscale atmospheric wind, temperature, and density fluctuations are described in terms of their power spectra. In the early 1980s, VanZandt[1] showed that the observed spectrum of the atmospheric fluctuations can result, as in the ocean, from an interna…     

Earthquake accelerogram simulation with statistical law of evolutionary power spectrum

By using the technique for evolutionary power spectrum proposed by Nakayama and with reference to the Kameda formula, an evolutionary spectrum prediction model for given earthquake magnitude and distance is established based on the 80 near-source acceleration records at rock surface with large magnitude from the ground motion database of western U.S.. Then a new iteration method is developed for generation of random accelerograms non-stationary both in amplitude and frequency which are compatible with target evolutionary spectrum. The phase spectra of those simulated accelerograms are also non-stationary in time and frequency domains since the interaction between amplitude and phase angle has been considered during the generation. Furthermore, the sign of the phase spectrum increment is identified to accelerate the iteration. With the proposed statistical model for predicting evolutionary power spectra and the new method for generating compatible time history, the artificial random earthquake accelerograms non-stationary both in amplitude and frequency for certain magnitude and distance can be provided.     

Effects of rotational components of earthquake on seismic response of arch concrete dams

The present study deals with dynamic analysis of arch concrete dams, taking rotational components of earthquakes into account. A modified methodology was used to evaluate the rotational components of the earthquake. The translational components of the earthquake have been used in to obtain the rotational components of the earthquake, based on the intersecting isotropic elastic wave propagation. Two rotational components of Taft, Tabas and San-Fernando earthquakes are evaluated based on the translational components of the earthquakes and considering frequency dependencies of incident angle and wave velocity. Finally, dynamic analyses of Morrow Point Dam are presented to evaluate the effects of combined translational and rotational components on the seismic response of the dam. Various conditions of reservoirs, including full and empty state, are considered in the analyses. Fluid–structure interaction was completely taken into account. It was realized that incorporating rotational components increased the maximum compressive and tensile stresses in both empty and full reservoir analyses. Distribution of maximum tensile stresses is very sensitive to the rotational components of the earthquake. Also, it can be concluded that the segregated effect of the rocking component on the response of concrete dams is more effective than the sole effect of the torsional component.     

Response spectra for nuclear structures on rock sites considering the near-fault directivity effect

Near-fault ground motions, potentially with large amplitude and typical velocity pulses, may significantly impact the performance of a wide range of structures. The current study is aimed at evaluating the safety implications of the near-fault effect on nuclear power plant facilities designed according to the Chinese code. To this end, a set of nearfault ground motions at rock sites with typical forward-directivity effect is examined with special emphasis on several key parameters and response spectra. Spectral comparison of the selected records with the Chinese and other code design spectra was conducted. The bi-normalized response spectra in terms of different corner periods are utilized to derive nuclear design spectra. It is concluded that nuclear design spectra on rock sites derived from typical rupture directivity records are significantly influenced both by the earthquake magnitude and the rupture distance. The nuclear design spectra specified in the code needs to be adjusted to reflect the near-fault directivity effect of large earthquakes.     

CHARACTERISTICS OF TORSIONAL GROUND MOTIONS

Due to the inherent difficulty in directly recording the rotational ground motions, torsional ground motions have to be estimated from the recorded spatially varying translational motions. In this paper, an empirical coherency function, which is based on the recorded motions at the SMART-1 array, is suggested to model the spatial variation of translational motions. Then, the torsional ground motion power spectral density function is derived. It depends on the translational motion power spectral density function and the coherency function. Both the empirical coherency function and the torsional motion power spectral density function are verified by the recorded motions at the SMART-1 array. The response spectra of the torsional motions are also estimated. Discussion on the relations between the torsional motion response spectrum and the corresponding translational motion response spectrum is made. Numerical results presented can be used to estimate the torsional ground motion power spectral density function and response spectrum.     

On the characteristics of ground motion rotational components using Chiba dense array data

An effort is made to examine the properties of rotational (torsional and rocking) ground motions using Chiba dense array data. The Chiba array system, located 30 km east of Tokyo, Japan, is composed of 15 boreholes with separation distances varying from 5 to 320 m. This provides a unique opportunity to examine the characteristics of rotational components. For this purpose, 17 events are considered and rotational ground motions are evaluated using spatial derivatives of translational ones. The effects of seismological parameters and separation distances between stations on properties of rotational motions are examined, showing a sudden increase in rotational motions for the earthquakes with large magnitude or PGA and decrease of these motions with increasing separation distance. While the duration of torsional motion is found to be larger than translational ones, there is no significant difference between durations of rocking and vertical motions. The effects of separation distance and earthquake magnitude on rotational response spectra are also investigated. The normalized rotational response spectra are found to be strongly affected by separation distance. The spectral ratios of rotational and translational motions are not linearly proportional to period as suggested by the previous studies. Finally, the torsional motion is predicted from translation ones for different separation distances at the site. The comparison of the predicted and the calculated torsional motions reveals a weak estimation in close separation distances (<30m) and satisfactory predictions in other cases. Copyright © 2007 John Wiley & Sons, Ltd.     

Apparent translational component for rotational ground motions

Even though the rotational ground motion may contribute significantly to the response of certain structures, their effects are generally ignored in seismic design, because of non-availability of appropriate instruments for direct recording of the rotational components. Like many others, a simplified framework was proposed by the authors elsewhere (Rodda and Basu in Int J Earthq Impact Eng 1(3):253–288, 2016) to extract the rotational motion as a temporal derivative of an apparent translational component (ATC) followed by scaling with an apparent velocity. ATC was defined such that its time derivative is closely correlated with the respective rotational motion. But the a priori knowledge of rotational motion is required in estimating the ATC for rocking component. An empirical procedure has been proposed here to bypass the requirement of rotational motion a priori. This paper also assesses the definition of ATC through examining the similitude between the time derivative of ATC and the respective rotational motion (benchmark) quantitatively. Similitude is assessed on smoothened response spectra (by Hamming window) of the time derivative of ATC and that of rotational motion. A new definition of spectral contrast angle (SCA) based on distance correlation has been proposed to assess the spectral similitude. To differentiate the similar from non-similar spectra, SCA corresponding to an acceptable degree of similarity is proposed by studying a large ensemble of ground motions from the PEER database. This similitude study is further extended using relative energy build up and energy spectra.     

Approximate formulas for rotational effects in earthquake engineering

The paper addresses the issue of researching into the engineering characteristics of rotational strong ground motion components and rotational effects in structural response. In this regard, at first, the acceleration response spectra of rotational components are estimated in terms of translational ones. Next, new methods in order to consider the effects of rotational components in seismic design codes are presented by determining the effective structural parameters in the rotational loading of structures due only to the earthquake rotational components. Numerical results show that according to the frequency content of rotational components, the contribution of the rocking components to the seismic excitation of short period structures can never be ignored. During strong earthquakes, these rotational motions may lead to the unexpected overturning or local structural damages for the low-rise multi-story buildings located on soft soil. The arrangement of lateral-load resisting system in the plan, period, and aspect ratio of the system can severely change the seismic loading of wide symmetric buildings under the earthquake torsional component.     

Changes of GPR spectra due to the presence of hydrocarbon contamination in the ground

The location of hydrocarbon contamination in the ground using the GPR method is based mainly on information taken from reflected signals. In the cases investigated in Polish contaminated sites, such signals were very seldom recorded. A long time after spillage, contamination takes the form of plumes with different size and distribution, which depends on geological and hydraulic properties of the ground. In this paper, it is shown that the set of hydrocarbon plumes should be described with a stochastic model, and such plumes may generate the scattered waves which cause changes in the power spectra. It has been observed that the power spectra of GPR signals over contaminated areas are quite different from such spectra over clear ones. These differences were discussed in this paper on the basis of theoretical analysis, numerical modelling and the results of GPR terrain surveys.     

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 。     

Torsional spectrum for earthquake motions

A computational scheme is presented to construct torsional spectra due to the rotational component of seismic ground motions. The rotational component of ground motion is estimated from the measured earthquake acceleration records. In contrast to previous studies, no differentiation of acceleration records is involved in the present scheme. The torsional spectrum of the 1940 El Centro earthquake is computed and compared with previous results. An average and a mean plus one standard deviation torsional spectrum is presented for design purposes. These spectra are results based on four historical records (1934 El Centre, 1940 El Centro, 1949 Olympia and 1952 Taft) normalized to the 1940 El Centro intensity.     

六分量弹性波场数值模拟与分析

地震波传播过程中,质点的振动不仅包括三个独立的平移部分,还包括三个独立的旋转部分.本文基于一阶速度-应力弹性波方程,采用分裂完全匹配层(SPML)的吸收边界条件,推导了时间导数二阶精度和空间导数高阶精度的交错网格有限差分格式的弹性波速度与应力各分量计算公式,模拟了各向同性介质中均匀模型和层状模型下的六分量波场,并对二维各向同性层状模型下的三个分量地震记录做高分辨率线性拉东变换得到各自的频散能谱.数值模拟分析结果表明:(1)旋转分量的能量要比平动分量弱的多;(2)在平动分量上,面波能量强,频率低,反射P波能量较强,反射S波能量稍弱;在旋转分量上,反射P波能量很弱,S波能量强;(3)与平动分量相比,旋转分量的频散能谱效果更好,能看到基阶和完整的高阶面波,即旋转分量能反映更多的地下介质信息.     

Conversion and comparability of data presentations on seismic background noise

Data on seismic background noise are collected, amongst others, for assessing the suitability of sites for temporary or permanent seismic recordings. Site quality requirements depend on the task of seismic observations and thus on their resolution, dynamic range, bandwidth and frequency range. Till now noise data are collected with a wide range of instruments, both analog and digital, of different bandwidth, resolution and transfer functions. Accordingly, noise appearence in seismic records, amplitude- and frequency-wise, differs and the various kinds of noise spectra derived therefrom vary too. They are not easily comparable amongst each other and with older presentations of noise spectra derived from analog records. Also, when having determined noise power density spectra from digital records it is not so obvious what this means in terms of noise ground motion amplitudes or noise appearance in records of different bandwidth and vice versa. The paper does not aim at serving as a guide to station site selection but rather to present and comment the relationships to be used for the conversion of power and amplitude spectra into different kinematic units and for calculating from the spectral representations of seismic noise the related frequency dependent RMS or average peak amplitudes of different bandwidth and vice versa. For the new global high (NHNM) and low-noise model (NLNM) given by Peterson (1993) in dB of acceleration power density the related velocity and displacement power spectral densities are presented both graphically and tabulated. Examples for the application of the conversion relationships and the effect of bandwidth on noise and signal amplitudes are given. For a selected data set from a site-selection noise survey in NW Iran the suitability of some potential sites is assessed by comparison with the NLNM.