A new approach of selecting real input ground motions for seismic design: The most unfavourable real seismic design ground motions

This paper presents a new way of selecting real input ground motions for seismic design and analysis of structures based on a comprehensive method for estimating the damage potential of ground motions, which takes into consideration of various ground motion parameters and structural seismic damage criteria in terms of strength, deformation, hysteretic energy and dual damage of Park & Ang damage index. The proposed comprehensive method fully involves the effects of the intensity, frequency content and duration of ground motions and the dynamic characteristics of structures. Then, the concept of the most unfavourable real seismic design ground motion is introduced. Based on the concept, the most unfavourable real seismic design ground motions for rock, stiff soil, medium soil and soft soil site conditions are selected in terms of three typical period ranges of structures. The selected real strong motion records are suitable for seismic analysis of important structures whose failure or collapse will be avoided at a higher level of confidence during the strong earthquake, as they can cause the greatest damage to structures and thereby result in the highest damage potential from an extended real ground motion database for a given site. In addition, this paper also presents the real input design ground motions with medium damage potential, which can be used for the seismic analysis of structures located at the area with low and moderate seismicity. The most unfavourable real seismic design ground motions are verified by analysing the seismic response of structures. It is concluded that the most unfavourable real seismic design ground motion approach can select the real ground motions that can result in the highest damage potential for a given structure and site condition, and the real ground motions can be mainly used for structures whose failure or collapse will be avoided at a higher level of confidence during the strong earthquake. Copyright © 2007 John Wiley & Sons, Ltd.     

Analysis of the weightiness of site effects on reinforced concrete (RC) building seismic behaviour: The Adra town example (SE Spain)

The damage distribution in Adra town (south‐eastern Spain) during the 1993 and 1994 Adra earthquakes (5.0 magnitude), that reached a maximum intensity degree of VII (European Macroseismic Scale (EMS scale)), was concentrated mainly in the south‐east zone of the town and the most relevant damage occurred in reinforced concrete (RC) buildings with four or five storeys. In order to evaluate the influence of ground condition on RC building behaviour, geological, geomorphological and geophysical surveys were carried out, and a detailed map of ground surface structure was obtained. Short‐period microtremor observations were performed in 160 sites on a 100m × 100m dimension grid and Nakamura's method was applied in order to determine a distribution map of soil predominant periods. Shorter predominant periods (0.1–0.3 s) were found in mountainous and neighbouring zones and larger periods (greater than 0.5 s) in thicker Holocene alluvial fans. A relationship T = (0.049 ± 0.001)N, where T is the natural period of swaying motion and N is the number of storeys, has been empirically obtained by using microtremor measurements at the top of 38 RC buildings (ranging from 2 to 9 storeys). 1‐D simulation of strong motion on different soil conditions and for several typical RC buildings were computed, using the acceleration record in Adra town of the 1993 earthquake. It is noteworthy that all the aforementioned results show the influence of site effects in the degree and distribution of observed building damage. Copyright © 2007 John Wiley & Sons, Ltd.     

Stability and accuracy analysis of outer loop dynamics in real‐time pseudodynamic testing of SDOF systems

Real‐time pseudodynamic (PSD) testing is an experimental technique for evaluating the dynamic behaviour of a complex structure. During the test, when the targeted command displacements are not achieved by the test structure, or a delay in the measured restoring forces from the test structure exists, the reliability of the testing method is impaired. The stability and accuracy of real‐time PSD testing in the presence of amplitude error and a time delay in the restoring force is presented. Systems consisting of an elastic single degree of freedom (SDOF) structure with load‐rate independent and dependent restoring forces are considered. Bode plots are used to assess the effects of amplitude error and a time delay on the steady‐state accuracy of the system. A method called the pseudodelay technique is used to derive the exact solution to the delay differential equation for the critical time delay that causes instability of the system. The solution is expressed in terms of the test structure parameters (mass, damping, stiffness). An error in the restoring force amplitude is shown to degrade the accuracy of a real‐time PSD test but not destabilize the system, while a time delay can lead to instability. Example calculations are performed for determining the critical time delay, and numerical simulations with both a constant delay and variable delay in the restoring force are shown to agree well with the stability limit for the system based on the critical time delay solution. The simulation models are also used to investigate the effects of a time delay in the PSD test of an inelastic SDOF system. The effect of energy dissipation in an inelastic structure increases the limit for the critical time delay, due to the energy removed from the system by the energy dissipation. Copyright © 2007 John Wiley & Sons, Ltd.     

Prediction of the median IDA curve by employing a limited number of ground motion records

A methodology has been proposed which can be used to reduce the number of ground motion records needed for the reliable prediction of the median seismic response of structures by means of incremental dynamic analysis (IDA). This methodology is presently limited to predictions of the median IDA curve only. The reduction in the number of ground motion records needed to predict the median IDA curve is achieved by introducing a precedence list of ground motion records. The determination of such a list is an optimization problem, which is solved in the paper by means of (1) a genetic algorithm and (2) a proposed simple procedure. The seismic response of a simple, computationally non‐demanding structural model has been used as input data for the optimization problem. The presented example is a three‐storey‐reinforced concrete building, subjected to two sets of ground motion records, one a free‐field set and the other a near‐field set. It is shown that the median IDA curves can be predicted with acceptable accuracy by employing only four ground motion records instead of the 24 or 30 records, which are the total number of ground motion records for the free‐field and near‐field sets, respectively. Copyright © 2007 John Wiley & Sons, Ltd.     

非定常不稳定液固两相流动中旋涡对颗粒运动影响的数值研究

构建起双向耦合的液固两相流动旋涡动力学模型与数值方法;应用离散涡方法,计算非定常不稳定水流场;采用Lagrange方法模拟颗粒运动,颗粒对流体的反作用通过修正涡泡运动速度来实现。利用所建模型,计算了两种St数的泥沙粒子在圆柱绕流场中的运动。结果证明了液固两相流动中颗粒运动与旋涡存在着明确的相关结构:(1)当水沙混合物中的泥沙颗粒碰上旋涡时,泥沙颗粒被卷入旋涡中,被卷入旋涡中的泥沙颗粒在运动过程中始终分布于旋涡区;(2)均匀水沙混合物绕圆柱流动,由于流体流过圆柱时产生剧烈分离流动,使得在尾迹流内中等St数 (St～o (1))的泥沙颗粒从均匀水沙混合物中分离出来而往旋涡区聚集。     

Linear drift and periodic variations observed in long time series of polar motion

 Two long time series were analysed: the C01 series of the International Earth Rotation Service and the pole series obtained by re-analysis of the classical astronomical observations using the HIPPARCOS reference frame. The linear drift of the pole was determined to be 3.31 ± 0.05 milliarcseconds/year towards 76.1 ± 0.80° west longitude. For the least-squares fit the a priori correlations between simultaneous pole coordinates x _p , y _p were taken into account, and the weighting function was calculated by estimating empirical variance components. The decadal variations of the pole path were investigated by Fourier and wavelet analysis. Using sliding windows, the periods and amplitudes of the Chandler wobble and annual wobble were determined. Typical periods in the variable Chandler wobble and annual wobble parameters were obtained from wavelet analyses. Received: 21 January 2000 / Accepted: 28 August 2000     

由APRGP97～APRGP99的GPS联测资料确定的亚太地区地壳形变

使用伪无基准（pseudo nonfiducial）算法、利用GIPSY软件，归算了APRGP97、APRGP98 和APRGP99的GPS资料．对大多数站所得解的站座标的精度:南北分量是1～2mm，东西分量是2～5mm，垂直分量是5～10mm；并初步获得亚太地区84个站在ITRF97中的运动速度，其水平方向的精度约为1～4mm/a．基于ITRF97速度场建立一个新的现今全球板块运动模型ITRF97VEL，由此获得这些站相对于该模型的现今形变速度，并对这些站相对欧亚板块的运动情况作了初步分析．      

吐鲁番一场罕见降雪天气个例分析

对“2000·2”罕见降雪天气过程分析表明,低层强烈的辐合上升运动和低空急流的突然增强是产生降雪的关键.     

神经网络半主动TLCD对偏心结构的减震控制

本文采用在结构水平双向设置TLCD半主动控制装置的方法，对偏心结构在多维地震作用下的振动控制问题进行研究。首先利用多层前向神经网络，对偏心结构在双向地震输入下的两个平动方向的反应进行预测，然后在建立起半主动控制策略的基础上，利用神经网络根据控制准则调整TLCD的开孔率，实现以结构的半主动控制，数值结构表明，这种方法能对结构的平动反应和扭转反应都能起到的较好的减震效果。     

双侧破裂模型对地震动空间相关性影响的定量研究

本在震源为双侧线状断层破裂模型的假定下，根据震源理论和波谱随空间坐标的展开式，得到了场地两点地震动Fourier谱的表达式Ab(f)=Aa(f)exp(a1δ0 a2δθ，中提出了将双侧破裂模型分解为两个单侧破裂模型计算双侧破裂模型a1和a2的数值方法，以一次地震（M＝6）为例，分析了双侧破裂模型对地震动空间相关性的影响，计算了 a1和a2的实部和虚部以及孔径随震中距，方位角和频率变化的三维图像。