地震动瞬时能量谱与结构位移响应关系研究

本文通过HHT变换得到瞬时能量谱,并以HHT对地震动作用下的结构位移响应进行分析,发现长周期结构动力响应的显著特点:最大结构位移响应总是滞后于地震动激励的最大能量谱值时间.滞后的时间主要取决于结构的动力特性参数(特别是自振周期),也与地震动的类型有关.仿真计算的结果表明:长周期结构的破环与倒塌并不发生在地震动强度最大的时刻,而多数是在地震动末期,甚至在地震动完全消失之后.有益的结论为结构控制设计与安全提供科学依据.     

用位移反应谱研究长周期设计地震反应谱

利用美国太平洋地震工程研究中心NGA数据库,分析了滤波低频截止周期(Tc)对位移反应谱的影响。选择较小的Tc将严重抑制长周期位移反应谱幅值。本文选用可靠使用周期不小于10 s的强地面运动加速度记录,研究了位移反应谱的长周期特性。结果表明,位移反应谱峰点周期是长周期地震反应谱的关键控制参数,受场地条件和震级的影响相对较小,但与震中距基本呈线性增长关系,而动力放大系数最大值波动范围较小,设计中可视为常数。建议在现行抗震设计规范谱的基础上,在速度控制段与位移控制段之间增加一个过渡段,以体现位移反应谱的有峰特征,并给出了控制参数的建议值。     

强震动记录自适应基线校正方法:汶川地震应用

基线校正是强震动记录数据处理非常关键的环节之一。现有方法大都依赖主观经验,得到的永久位移值存在较大的不确定性,不能实现自动化处理。为此,提出一种自适应的强震动记录基线校正方法,以汶川地震中汶川卧龙台站(051WCW)获取的强震动记录为例叙述新方法的每个环节,并与已有方法进行比较,验证了新方法的计算准确性。最后,将新方法运用于汶川地震主震中,得到了37个强震动台站的永久位移场。通过与Wang等的研究结果比较,发现除3个台站由于数据不全无法比较外,新方法给出的24个台站的最大永久位移无论是数值还是对应方位角都与其一致。表明新方法具有一定的可靠性,同时通过对比也发现新方法存在一定的局限性,还有待进一步改进。     

土层时域分析中黏滞阻尼形式的比较

时域分析中采用粘滞阻尼反映小应变条件下土的阻尼特性,瑞雷阻尼则是常用的黏滞阻尼形式。本文基于有限差分方法,构建一组数值计算模型,以实际地震记录作为输入,以不同的土层条件作为分析对象,采用加速度、位移和反应谱指标评价了瑞雷阻尼形式对土层地震反应的影响,并将不同阻尼形式下的计算结果与响嘡台阵真实记录进行了对比分析。计算结果表明:阻尼形式对加速度反应和反应谱的影响显著,对位移反应影响有限,但位移幅值沿土层高度的变化规律较复杂;不同阻尼形式时反应谱短周期段的谱值差别明显,而对反应谱长周期段谱值影响有限;高频地震动激励,深软土层中不同阻尼形式的计算结果离散性大;在确定阻尼形式时要综和考虑土层特征和地震动频谱特性,只考虑土层卓越频率的阻尼形式会低估土层地震反应。对于长周期地震动输入,本文建议目标频率取土层第3阶频率,对于高频地震动,目标频率可取为反应谱峰值对应频率。     

平面不规则结构的实用多维反应谱计算方法

因地震动输入方向对平面不规则结构响应的影响显著,所以本文对该类的实用多维反应谱计算方法进行了研究。首先,基于多维加速度功率谱矩阵的研究成果,引入激励输入角度和相应参数,推导了能合理考虑激励输入方向的加速度功率谱和基于平稳随机振动求解响应的计算公式。然后再引入位移谱,利用其能合理考虑激励非平稳性的特点,提出了水平双向的实用反应谱法计算公式。最后,以平面为L形的空间钢结构为例,对不同输入角度时的节点位移公式计算值与多条地震波的时程响应值进行了比较,证明该计算方法是合理的,可供结构抗震设计与分析作参考。     

基于第四代地震区划的跨越发震断层永久位移概率分析方法

本文主要借鉴了Lee(2007)和Youngs(2003)提出的地表永久位移估计方法,联合中国第四代地震区划图的潜在震源区参数,给出了适合中国跨越发震断层永久位移概率分析方法。震害调查表明,近场的结构破坏不仅是地震动引起的,地震地表的破裂或永久位移引起的破坏也占很大比重。应用与概率估计地震动相似的方法,给出不同概率水准的地震地表永久位移,使之服务于穿越地震发震断层管线、桥梁工程的抗震设防,采取有效的抗御永久地表位移措施,减小地震灾害带来的损失。     

基于HHT变换瞬时能量谱的长周期结构地震反应分析

基于HHT变换得到瞬时能量谱,并以简谐地震反应为理论基础进行多自由度体系在地震动作用下的瞬态反应计算。通过对一个长周期(十五层)结构工程实例的地震瞬态反应计算分析,揭示长周期结构有别于短周期结构动力响应的独特特性:长周期结构位移响应的瞬时能量峰值的时间滞后于地震动能量峰值的时间,且主要受到瞬态振动的控制,并以低阶振型的控制为主,第一阶振型峰值位移滞后的时间最长,滞后的时间主要取决于结构的第一阶自振周期。研究结果表明,长周期结构在强烈地震动作用下,地震动强度出现的最大时刻并不总是对应于结构破环与倒塌的时间。     

长周期地震动对广州塔TMD减震控制性能的影响

研究长周期地震动对广州塔TMD体系的影响及结构响应的时频分布规律。对国内现行规范反应谱长周期段进行延长,选取7条地震动时程记录,并补充7条长周期地震动时程记录作为输入样本,研究不同周期的强震激励对超高耸结构TMD体系的影响。研究表明,长周期成分的地震激励显著增加了超高耸结构的响应,卓越周期在2.341 s至6.425 s的长周期地震动输入,比卓越周期低于1 s的短周期地震动输入,平均使结构桅杆顶的位移峰值与均方根值分别放大125.49%和91.63%;最优参数设计的TMD对短周期、长周期地震响应均起减震控制作用,对8度长周期大震下主塔顶和桅杆顶的位移峰值控制降幅分别达到28.61%和42.69%,对相应的位移时程响应均方根值的控制降幅分别达到32.56%和44.20%, TMD体系的减震控制性能对地震动卓越周期具有一定鲁棒性;对结构弱轴向的地震响应时程进行数值小波功率谱分析,结果表明:由于一般长周期地震动的卓越周期更接近广州塔结构弱轴向的二阶周期(2.888 s),不仅增加了一阶振型的响应,更显著加剧了以二阶振型为主的桅杆鞭梢效应, TMD对该效应一定程度上起了抑制作用;建议对周期大于6 s的超高耸结构TMD体系,在按规范反应谱选取地震动之外,应注意考虑长周期地震动的影响,以更全面评估结构性能。     

多点输入反应谱中耦合系数的研究

首先利用虚拟激励法推导了仅考虑行波效应下多点输入反应谱表达式,重点对多点输入反应谱中动位移耦合系数ρijpq及拟静位移耦合系数ρSpq的计算方法及其特性进行了研究。为了避免繁琐的积分运算,提出了一种"拟合+插值"的耦合系数计算方法,不但精度高,而且大大提高了计算效率。研究表明,ρijpq相对于地震波到达支座点的时差Δt具有明显的三角函数的关系;从总体趋势上看,ρijpq绝对值基本随ωj/ωi的增大而减少,这一点与一致输入时的振型耦联系数ρij相同。在仅考虑行波效应的情况下,可以认为,各支座点的拟静力位移完全相关,即ρSpq=1,结构拟静力位移谱与地震动的位移谱相同。     

双向地震动作用的拟等延性系数谱

首先建立了以强度折减系数表述的恢复力特性满足二维屈服面模型的理想弹塑性单质点系统(它在2个相互垂直的主轴方向上分别具有水平平动自由度)在双向地震动作用下的归一化运动方程。然后引入单向地震动作用下等延性系数的强度折减系数谱,给出了双向地震动作用的拟等延性系数谱(定义为系统分别承受双向和单向地震动作用,在同一主轴方向上的最大位移反应之比)最后通过硬土场地10组双向地震动记录拟等延性系数谱的统计平均结果,分析了结构周期、位移延性系数和阻尼等因素对谱值及结构双向地震反应的影响。结果表明,双向地震动作用与单向地震动作用相比主要增加结构较长周期方向的最大位移反应。若在基于位移的抗震设计中降低结构较短周期方向的设计位移延性系数,可在一定程度上降低双向地震动的不利影响。因定义的谱为比值形式,阻尼对其影响不大。     

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.     

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.     

考虑超随机特性的人工地震动合成

文中根据自相关函数随机噪声部分的2个重要性质提出了自相关函数随机噪声部分的迭代生成算法,并给出了以确定性自相关函数为目标函数,考虑随机噪声部分影响的人工合成地震动方法.本文的研究结果表明地震动加速度的平方和（SS）比峰值加速度（PGA）更好地量度了地震地面运动强度.文中用蒙特卡罗方法分析了自相关函数噪声项对人工合成地震动幅值和反应谱的影响：由于自相关函数的随机噪声项对地震动总功率或平方和的贡献为0,因此随机噪声项对合成地震动幅值的影响不大,但由于自相关函数随机噪声项明显改变了地震动功率谱在频域上的分布特征,使原本光滑的平均反应谱出现了明显的波动,从而在一定程度上提高了平均反应谱的峰值,使自相关函数噪声部分对平均反应谱也有一些影响.     

利用数字化速度记录实时仿真位移与加速度时程

根据地震仪的原理和作者提出的单自由度系统地震反应的递归公式,本文系统研究了利用数字化宽频带速度型记录仿真地面位移和地面加速度等问题,从时域上提出了一套实时计算公式,数值计算结果表明,本文所提方法速度快、精度高,可广泛应用于地震监测和地震动参数的实时计算。     

Correction of highly noisy strong motion records using a modified wavelet de-noising method

During the past earthquakes, many valuable acceleration time histories were recorded by analog and digital accelerometers. These records are important sources of information in the field of earthquake engineering and engineering seismology. However, a large number of these records are contaminated by noise and it is necessary to correct them for practical applications. On the other hand, only a few records can be corrected using conventional filtering because of mathematical limitations of the method. However, advances in the field of time–frequency analysis and wavelet transform theory provide useful non-linear and adaptive de-noising methods for removing of non-stationary and high-energy noise from the recorded signals. In this paper, the characteristics and capabilities of the modified non-linear adaptive wavelet de-noising method are examined for correction of highly noisy strong motion records. In the frequency domain, it is shown that this method can attenuate the noise in the whole frequency range of engineering interest while in the time domain it can detect and remove non-stationary noise. In addition, the displacement response spectra of these wavelet de-noised records are more stable than conventional filtered records with respect to different correction functions. It is found that a large number of noisy acceleration records that are usually discarded from sets of records used for estimating the ground motions can be corrected using this new method.     

Deterministic sliding block methods for estimating seismic displacements of earth structures

A review and quantitative comparison of existing deterministic sliding block methods for predicting permanent displacements of earth structures subjected to seismic loading is presented. The reviewed sliding block methods are divided into two main groups based on the characteristic earthquake parameters referenced in each method. One group uses the maximum horizontal ground acceleration and velocity, and the other uses the maximum horizontal ground acceleration and the predominant period of the acceleration spectrum. Displacement functions published by previous authors are reformulated to give common non-dimensionalized displacement functions of the critical acceleration ratio which are then used to compare the different methods for the estimate of permanent seismic displacement of soil structures. The results show that despite the fact that the different methods were formulated using a wide range of earthquake records and different characteristic seismic parameters, permanent displacement values predicted using these methods fall within a reasonably narrow band. Selected acceleration data from three recent earthquakes that occurred in California are used to evaluate and compare the accuracy of the reviewed displacement methods for practical applications.     

Ground motion models for the Molise region (Southern Italy)

The aim of this paper is to evaluate empirical attenuation relationships in order to validate peak values and pseudo-velocity spectra to calibrate shaking scenarios for the Molise area, which was struck by two earthquakes of M_w=5.7 (INGV-Harvard European-Mediterranean Regional Centroid-Moment tensor project) on October 31st and November 1st, 2002. Before the earthquake occurrence this region was classified as not hazardous, according to the former Italian seismic code. After the main-shocks, felt in many towns of the Molise and Puglia regions, a strong motion and a seismic temporary network were installed in the epicentral area and surrounding regions. This allowed the collection of a large data set, useful to characterize this area. The joint velocity-acceleration data set has been used to derive ground motion models for peak ground acceleration, peak ground velocity, and pseudo-velocity response spectra for both maximum horizontal and vertical components of the motion.The results obtained for the Molise area have been compared with the attenuation pattern of the Umbria-Marche region (central Italy) and the Italian territory. Remarkable differences have been observed leading to a discussion of the possible regional dependence of ground motion.     

Regional seismic slope failure probability matrices

A method for constructing seismic slope failure probability matrices is presented. The core of the method is a probabilistic sliding block model which allows for systematic incorporation of the uncertainties associated with both the ground excitation and the strength of the slope materials. The extent of damage to a slope is defined in terms of the magnitude of the earthquake-induced permanent displacement. The intensity of the ground shaking is characterized by a peak ground acceleration as well as an earthquake magnitude, and the possible scatter in the ground motion details is included through the use of an equivalent stationary motion model. After the effects of essential contributing factors are discussed, regional seismic slope failure probability matrices are presented for general applications.     

On the reliability of long‐period response spectral ordinates from digital accelerograms

Using records from co‐located broadband and digital strong motion (SM) instruments, it is first shown that the displacement waveforms obtained by double integration of the accelerogram need not be free of unrealistic baseline drift to yield reliable spectral ordinates up to at least 10 s. Secondly, to provide objective criteria for selecting reliable digital SM records for ground motion predictions at long periods, a set of synthetic accelerograms contaminated by random long‐period noise has been used, and the difference between the original accelerograms and the spurious ones in terms of response spectra has been quantified, by introducing a noise index that can be easily calculated based on the velocity waveform of the record. The results of this study suggest that high‐pass filtering the digital acceleration record from a cutoff period selected to suppress baseline drifts on the displacement waveform appears to be in most cases too conservative and unduly depletes reliable information on long‐period spectral ordinates. Copyright © 2007 John Wiley & Sons, Ltd.     

强震作用下桩-土-断层非线性动力相互作用特性

为研究强震区跨断层桥梁桩基非线性动力相互作用特性,依托海文大桥实体工程,利用MIDAS/GTS有限元软件,建立了桩-土-断层相互作用模型,分析0.20~0.60g地震动强度下断层上下盘桩基加速度响应、桩顶水平位移、桩身弯矩以及桩身剪力响应情况。结果表明:覆盖层土体对桩身加速度放大作用明显,且随着输入地震动强度的增大,放大作用逐渐减弱;覆盖层对地震波的滤波作用显著,随着输入地震动强度的增大,滤波作用逐渐减弱;上盘桩基达到桩顶峰值加速度的时刻滞后于下盘;随着输入地震动强度的增大,上、下盘桩的桩顶产生的永久位移和水平位移峰值逐渐变大,上盘桩顶产生的永久位移和桩顶峰值位移均大于下盘,产生显著的"上盘效应";不同强度地震动作用下,断层上、下盘桩基弯矩均在上部土层界面处达到峰值,剪力均在基岩面处达到峰值,下盘桩基弯矩和剪力峰值大于上盘桩基,呈现出显著的"下盘效应"。在桥梁桩基抗震设计时,应着重考虑断层上、下盘桩基的差异和不同强度地震作用对桩基承载特性的影响。