人造地震动反应谱拟合的窄带时程叠加法

提出了一种在时域内叠加窄带时程的方法以提高人造地震动时程对目标反应谱的拟合精度。该方法首先利用传统的在频域内调整傅立叶幅值谱的方法合成以给定峰值加速度、反应谱和强度包线为目标的初始加速度时程;然后基于线性单自由度体系的地震输入反演公式,利用在时域内叠加窄带时程的方法继续调整该初始时程以进一步提高其对目标反应谱的拟合精度。算例分析结果表明,该算法所得到的人造地震动时程对目标谱具有较高的拟合精度。     

苏通桥对非一致地震地面运动的反应和人工波质量的讨论

台湾集集地震SMART-II密集台阵的,带有GPS国际标准时间校准的7群非一致地震地面加速度记录,和2群以杂交法针对苏通桥桥位断层和地质构造产生的非一致地震人工地面加速度时程历史作为输入,分析了世界最大跨斜拉桥——苏通桥——对非一致地震地面运动的变形和内力反应。每群地震输入由两个或三个台站的三分量加速度记录组成。还考虑顺桥向与波传播方向、断层走向间不同夹角、大桥是否跨越断层的情况下非一致地震地面运动的反应,并与由每群台站记录中含最大水平地面峰值加速度的记录构成的一致地震地面运动的反应做了比较。比较表明:尽管相应的一致地震输入是由一群台站记录中含最大水平地面峰值加速度的记录组成,苏通桥的半数非一致地震反应仍比相应的一致地震反应大,个别情况的非一致反应甚至比一致反应大得多。因此,苏通桥这样的特大桥的抗震设计应当考虑非一致地震的影响。还提出桥梁设计者应根据桥的动力特性对地震安全性评价提出所需的地震动参数。还检查了有关部门对苏通桥抗震设计提供的人工加速度波的反应谱和互相关系数,结果表明桥梁设计者应当在多方面检查所提供的人工波的质量。     

近断层速度脉冲对钢筋混凝土框架结构地震反应的影响

在加速度反应谱一致的前提下,研究了近断层速度脉冲的工程特性。首先,构造两组加速度反应谱一致的地震动时程:第一组时程为实际强震观测记录且含有明显的速度脉冲;第二组时程为以第一组时程的反应谱为目标谱合成的模拟地震动时程,在合成过程中,利用窄带时程叠加法,通过控制峰值速度可以使得这些时程不再含有速度脉冲。其次,通过分析钢筋混凝土框架结构在这两组输入地震动作用下动力响应的差异,研究了在加速度反应谱一致的前提下,速度脉冲对结构地震反应、尤其是弹塑性地震反应的影响。分析结果表明:对于层剪力、层间位移、各层最大位移等结构动力响应参数,当结构地震反应进入弹塑性阶段后,与不含速度脉冲地震动作用下的反应相比,在含有速度脉冲的地震动作用下,结构的反应有较大幅度的增大,尽管这两组输入地震动的加速度反应谱相同;在这种情况下,加速度反应谱将不能充分地体现出速度脉冲对结构地震反应的影响。     

面波产生的地震动转动分量的试验验证

迄今为止,地面运动转动分量主要是通过弹性波动理论方法间接由平动分量获得,但并未得到证实。首次运用面波试验验证了这种求取转动分量的方法的合理性。重锤击落地面,在半无限空间弹性介质的地表附近,可产生面波(瑞利波和乐夫波),合理布置拾振器位置,测得产生面波的时程,利用两点差原理可以测得地面近似转动分量;将实测转动分量和用理论方法求得的转动分量的时程曲线以及傅立叶谱进行对比,由两种方法得到的转动分量加速度时程在振动持续时间内的开始阶段、强震阶段和衰减阶段基本一致;Fourier谱峰值、峰值点个数、峰值出现的位置以及谱曲线的形状走向是接近的。     

基于数字滤波技术拟合规范反应谱的地震动研究EI北大核心CSCD

在重要结构的抗震设计与分析中,常需要输入拟合设计反应谱的地震动时程。该研究提出一种基于数字滤波技术调整天然地震动记录拟合规范反应谱的方法,以设计谱频率控制点为中心确定频带数目与范围,针对各个频带利用无限冲激响应数字滤波器对强震动记录时程开展带通滤波,并以滤波所得频带分量为基函数重构地震动时程;以重构时程为种子时程,引入影响矩阵方法开展迭代计算逐步调整频带分量的幅值向量,直至时程反应谱与目标谱的拟合精度满足要求为止。选取3个不同类型设计谱为目标谱分别开展拟合计算,结果表明:该方法分解并重构的地震动时程与天然强震动记录在时域和频域的重合度均较高;可与不同设计谱实现高精度拟合,时程反应谱迭代收敛性好,且能较好地保留时程非平稳性,可为工程结构抗震设计与分析提供合适的地震输入。     

拟合核电厂多维设计反应谱及相关峰值的地震动调整方法

依据核电厂结构的特殊性,提出了一种以核电厂多维设计用伪加速度反应谱及峰值加速度(PGA)、峰值速度(PGV)、峰值位移(PGD)为目标的实际地震动调整方法。该方法首先应用二阶基数B－样条小波函数模拟实际多维地震动场,然后基于离散小波变换的快速算法,将实际地震动加速度时程应用二阶基数B－样条小波函数进行分解;一方面探寻对各向分量的PGA、PGV及PGD影响最大的小波分量,另一方面通过对小波系数进行初步调整以改进时域叠加小波函数的收敛性;最后通过循环调整实现对多维目标反应谱及PGA、PGV、PGD的同时拟合。选取了四组代表不同设计地震分组的三维实际地震记录分析了该方法的可行性,结果表明该方法不仅较好的保留了原地震动的局部时频特性,且能满足核电厂抗震设计规范的精度要求。     

斜拱面非对称钢箱系杆拱桥的抗震分析

天津大沽桥主跨103米,采用全钢斜拱斜系杆面无顶部水平支撑的结构形式,结构复杂,振型多是空间的,自振频率密集。我国新版桥梁抗震设计规范正在编制,目前我国缺少对这种桥抗震设计的明确规定。参考国内外相关规范,采用两阶段抗震设计,确定了表达两阶段水平和竖向地震作用的反应谱,选择和产生合格的三分量地震地面加速度时程历史;计算了拱圈的几何刚度和斜吊杆的割线刚度对地震反应的影响;用有效振型参与质量分别确定了对顺桥向和横桥向地震作用的振型组合所必须的振型数,和非弹性时程积分的合理步长,表明用前57阶振型进行振型组合,以及0.02秒的积分步长能给出可靠的结果。对大沽桥弹性反应分析,反应谱振型叠加法必须使用CQC组合,还应考虑对三向地震作用的反应的组合。利用作者开发的程序BER2002进行三分量地面运动同时输入下的非弹性时程积分。分别考虑水平主波沿顺桥向和横桥向的反应,取大者。分析表明,大沽桥的设计方案有良好的抗震性能。     

时程分析考虑高阶振型影响的多频段地震波选择方法研究

针对结构抗震时程分析输入地震波选择问题,以加速度反应谱（或设计谱）为目标谱,在反应谱平台段和结构基本周期附近误差双控指标中,引入了由归一化振型参与系数确定的前几阶振型的权重系数,提出了考虑多频段加权匹配的时程分析输入地震波选择方法,以充分考虑高阶振型的影响。以美国SAC Steel Project提出的9层和20层抗弯钢框架Benchmark结构为实例,为方便将建议选波方法与较多地震波输入时程分析结果进行比较,以简单地震信息初选的小型地震波数据库中的20条地震波的均值（放大系数）谱作为目标谱,以这20条地震波时程分析得到的结构最大基底剪力和层间位移角均值为目标反应,前者考虑弹性状态,后者对应弹塑性情况。将按该文方法选出的3条波输入下结构反应均值与目标反应进行了比较分析,初步证实了建议选波方法的可行性。将该文方法与ASCE 7-05地震波输入要求方法对比,在弹塑性反应状态下,两者对结构最大层间位移角沿楼层分布规律的估计以及薄弱层位置的判断均与目标反应较为一致。ASCE 7-05方法输入下结构反应均大于目标反应,偏于安全。而按该文方法输入存在高估和低估结构反应的情况,建议附加"在0.2T₁~1.5T₁（T₁为结构基本周期）区间内,3条地震波的平均谱应在目标谱上方"这一限制条件,以防止低估结构反应的情况发生。     

考虑非比例阻尼的基础隔震结构非线性反应谱研究

对于基础隔震结构而言,其上部结构和隔震层的阻尼特性截然不同,往往呈现出明显的非比例阻尼特性。因此,有必要建立一种考虑非比例阻尼的隔震结构实用计算方法以便于推广和应用。通过用双自由度振动体系模拟基础隔震结构,在建立运动方程时考虑其非比例阻尼效应。通过对该简化模型进行动力时程分析,得到其在近场及远场地震记录作用下考虑非比例阻尼与瑞利阻尼的反应谱,并通过曲线拟合得到了非比例阻尼反应谱和瑞利阻尼反应谱的谱比值与结构自振周期之间的关系式。然后对某实际隔震工程进行地震响应分析,验证所提公式的合理性。     

结构时程分析中强震记录选取研究综述

该文论述了近年来国内外在结构抗震时程分析中输入强震记录选取的各种方法,对评判指标的选取及样本容量的确定进行了分类梳理和评述。震级、震中距、场地等地震信息常作为选波的第一评判指标,而目标谱及其他地震动强度指标则作为第二评判指标。地震动强度指标已总结出数十种,它们与结构反应的相关性及其在选波研究中的优越性认识不一。以反应谱为目标进行匹配、缩放及选择的方法（目标谱选波法）,成为目前最主流的方法。目标谱的种类较多,最广泛采用的是规范设计谱,工程应用比较方便;条件均值谱方法精度较高,但如何将条件均值谱与我国规范接轨,仍需深入研究。结构反应均值估计中,反映强震记录反应谱与目标谱匹配程度的误差指标及缩放方法的取用,应力求能够选出谱形匹配较优的强震记录。随着基于性能抗震理念的深入及地震危险性概率分析方法的逐渐完善,结构反应的估计也从均值发展到概率分布,其所需的样本容量及所采用的评判指标研究仍需进一步深入。     

设计谱长周期段取值与能量特征研究

基于由随机振动理论得到的功率谱密度与加速度反应谱之间的关系,以及由傅里叶幅值谱精确计算输入能量反应谱方法,提出了建立与设计加速度反应谱匹配的输入能量谱方法。计算了与《建筑抗震设计规范》(GB50011-2010)设计反应谱匹配的输入能量谱,通过与实际强震记录输入能量谱特征对比,对设计反应谱长周期段输入能量特征进行了分析。结果表明,由于规范设计谱长周期段取值比较保守,在长周期段输入能量随着周期变长逐渐增加,与实际地震动记录输入能量谱长周期特征明显不同。根据实际强震记录输入能量谱特征,给出了设计反应谱长周期直线下降段的取值建议。     

Non-stationary stochastic vector processes: seismic ground motion applications

A spectral-representation-based simulation algorithm is used in this paper to generate sample functions of a non-stationary, multi-variate stochastic process with evolutionary power, according to its prescribed non-stationary cross-spectral density matrix. If the components of the vector process correspond to different locations in space, then the process is also non-homogeneous in space (in addition to being non-stationary in time). The ensemble cross-correlation matrix of the generated sample functions is identical to the corresponding target. For the important application of earthquake ground motion simulation, an iterative scheme is introduced to generate seismic ground motion time histories at several locations on the ground surface that are compatible with prescribed response spectra, correlated according to a given coherence function, include the wave propagation effect, and have a specified duration of strong ground motion. Three examples involving simulation of earthquake ground motion are presented in order to demonstrate the capabilities of the proposed methodologies. In the first two examples, acceleration time histories at three points on the ground surface are generated according to a prescribed cross-spectral density matrix, while in the third example, the acceleration time histories are generated to be compatible with prescribed response spectra.     

A hybrid neural network method for simulating spatial variation in earthquake ground motion

Different excitations for supports should be considered for the analysis of long-span structures. The excitation of each support has time delay and spatial variation relative to other support excitations. The present study aims to propose a new method for simulating accelerograms for various distances considering spatial variation of earthquake records. The accelerograms are simulated based on response or design spectra using the learning capabilities of neural networks. In this method, the response spectrum, and the distance parameter (distance from fault rupture) are the input, and the corresponding accelerograms are the output of the network. There are three stages involved in this study. In the first stage, a replicator neural network is used as a data compressor to increase capability of the simulation. In the second stage, a radial basis function neural network is employed to generate a compressed accelerogram for a certain distance and a response spectrum. In the third stage, the compressed acceleration data is decompressed to resemble real earthquake records. Recorded accelerograms of the strong motion array in Taiwan are used to train the artificial neural network. The obtained results show the robustness of the applied method in producing spatially varying accelerograms. Finally, compatible accelerograms of the design spectrum, suggested in the Taiwan building seismic design code, are simulated for different distances with the proposed method.     

地铁引起建筑物振动评价研究

因为不能直接量测地铁环境中拟建建筑物的振动,介绍基于理论计算分析对地铁运行引起建筑物振动的评价方法。由于地铁隧道底面振动记录资料缺乏,量测困难;列车-轨道-地基系统的模拟不尽完善。针对上海地铁隧道正上方某拟建建筑物的振动问题,建立上部结构的刚性地基有限元模型,输入场地实测地面振动加速度激励,计算结构振动在时域内的响应。利用傅里叶变换,对结构时域内的响应进行频域分析,根据国家标准对地铁引起建筑物的振动做出评价,从而为地铁环境中建筑物防振设计提供依据。     

Intelligent Seismic Acceleration Signal Processing for Damage Classification in Buildings

Three new pattern recognition methods, based on fuzzy logic techniques that are suitable for seismic acceleration signal classification, are proposed in this paper. The classification of unknown signals is carried out according to the structural or architectural damage that is produced by the seismic signals. A set of 400 natural accelerograms, which have been recorded in various regions with well-known strong seismic activity, has been used for evaluation of the proposed methods. The seismic accelerograms are first treated as graphs; the similarity between them is exploited in order to perform the classification. In the second approach, a set of parameters are derived from each signal through computer analysis. These describe effectively the intensity measure of the seismic excitation, and they are used instead of the accelerograms. Similarity between them is appropriately utilized. Finally, a method that depends purely on fuzzification of the accelerograms parameters is also described. Classification results are presented for each method, and correct classification rates up to approximately 85% are recorded. The contribution of this paper to seismic signal classification lies in the methodology that allows for classification of seismic signals according to the damage in buildings. This process depends strongly on the structural parameters of the specific building, and therefore, given a building and a seismic signal, each signal can be classified into one of the four well-defined and scientifically approved damage classes. Consequently, the proposed paper contributes an effective method for engineers to test the response of a building to seismic signals, produced by earthquakes.     

Empirical formula for strength reduction factor based on artificial ground accelerations compatible with design spectra in Taiwan

In the seismic design of structural systems, an elastic design spectrum is reduced to an inelastic one by the strength reduction factor, which depends on the ductility capacity. All 1062 artificial ground accelerograms compatible with the design spectra provided in the Taiwan seismic design code are generated in order to acquire an empirical formula for predicting the strength reduction factor based on the ductility capacity and the natural vibration period. For a given ductility capacity, the variation of the mean strength reduction factor on the natural vibration period is minimal despite the differences in epicentral distances, site conditions, and return periods. Such a variation tends to be trilinear, where the two points of transition locate exactly at both ends of the platform in the target response spectra. On the basis of the mean strength reduction factors, an empirical formula is proposed. This empirical formula generally overestimates the strength reduction factors in the long-period region for a large ductility capacity, but offers conservative estimates elsewhere.