Structural identification in the frequency domain from earthquake records

A method has been developed to identify the parameters of the lower modes of a linear, time-invariant model of a structure from its recorded earthquake response. The identification is performed by selecting the parameters to obtain a least squares fit over a specified frequency band between the unsmoothed, complex-valued finite Fourier transform of the recorded acceleration response and the corresponding transform calculated from the response of the model. By including the effects of the initial and final conditions in the analysis, only a portion of the recorded excitation and response acceleration histories need be considered. The method is demonstrated first by an application to generated test data, and then to measured earthquake response.     

Dynamic equivalent soil characteristics identification using earthquake records

Techniques for soil property estimation can be categorized into two main groups, in-situ and laboratory methods. Previous investigations indicated that strong ground motions record provides a very useful tool to estimating the in-situ characteristics of soil. The main objective of the present work is to utilize the particle swarm optimization algorithm(PSOA) integrated with linear site response method to obtain the equivalent soil profile characteristics from the available surface and bedrock earthquake motion records. To demonstrate the numerical efficiency and the validity of this approach, the procedure is validated against an available case. Then this procedure is utilized to identify the soil properties profiles of the site by using strong ground motions data recorded during the Bam earthquake of December 26, 2003. The magnitude and PGA of Bam earthquake were MW 6.6 and 0.8 g respectively.     

Stiffness‐damping simultaneous identification using limited earthquake records

A new method of stiffness‐damping simultaneous identification of building structures is proposed using limited earthquake records. It is shown that when horizontal accelerations are recorded at the floors just above and below a specific storey in a shear building model, the storey stiffness and the damping ratio can be identified uniquely. The viscous damping coefficient and the linear hysteretic damping ratio can also be identified simultaneously in a numerical model structure. The accuracy of the present identification method is investigated through the actual limited earthquake records in a base‐isolated building. It is further shown that an advanced identification technique for mechanical properties of a Maxwell‐type model can be developed by combining the present method with a perturbation technique. Copyright © 2000 John Wiley & Sons, Ltd.     

System identification of the Vincent Thomas suspension bridge using earthquake records

The Vincent Thomas Bridge in the Los Angeles metropolitan area, is a critical artery for commercial traffic flow in and out of the Los Angeles Harbor, and is at risk in the seismically active Southern California region, particularly because it straddles the Palos Verdes fault zone. A combination of linear and non‐linear system identification techniques is employed to obtain a complete reduced‐order, multi‐input–multi‐output (MIMO) dynamic model of the Vincent Thomas Bridge based on the dynamic response of the structure to the 1987 Whittier and 1994 Northridge earthquakes. Starting with the available acceleration measurements (which consists of 15 accelerometers on the bridge structure and 10 accelerometers at various locations on its base), an efficient least‐squares‐based time‐domain identification procedure is applied to the data set to develop a reduced‐order, equivalent linear, multi‐degree‐of‐freedom model. Although not the main focus of this study, the linear system identification method is also combined with a non‐parametric identification technique, to generate a reduced‐order non‐linear mathematical model suitable for use in subsequent studies to predict, with good fidelity, the total response of the bridge under arbitrary dynamic environments. Results of this study yield measurements of the equivalent linear modal properties (frequencies, mode shapes and non‐proportional damping) as well as quantitative measures of the extent and nature of non‐linear interaction forces arising from strong ground shaking. It is shown that, for the particular subset of observations used in the identification procedure, the apparent non‐linearities in the system restoring forces are quite significant, and they contribute substantially to the improved fidelity of the model. Also shown is the potential of the identification technique under discussion to detect slight changes in the structure's influence coefficients, which may be indicators of damage and degradation in the structure being monitored. Difficulties associated with accurately estimating damping for lightly damped long‐span structures from their earthquake response are discussed. The technical issues raised in this paper indicate the need for added spatial resolution in sensor instrumentation to obtain identified mathematical models of structural systems with the broadest range of validity. Copyright © 2003 John Wiley & Sons, Ltd.     

Parameter identification of torsionally coupled shear buildings from earthquake response records

This paper presents an efficient procedure to determine the natural frequencies, modal damping ratios and mode shapes for torsionally coupled shear buildings using earthquake response records. It is shown that the responses recorded at the top and first floor levels are sufficient to identify the dominant modal properties of a multistoried torsionally coupled shear building with uniform mass and constant eccentricity even when the input excitation is not known. The procedure applies eigenrealization algorithm to generate the state‐space model of the structure using the cross‐correlations among the measured responses. The dynamic characteristics of the structure are determined from the state‐space realization matrices. Since the mode shapes are obtained only at the instrumented floor (top and first floors) levels, a new mode shape interpolation technique has been proposed to estimate the mode shape coefficients at the remaining floor levels. The application of the procedure has been demonstrated through a numerical experiment on an eight‐storied torsionally coupled shear building subjected to earthquake base excitation. The results show that the proposed parameter identification technique is capable of identifying dominant modal parameters and responses even with significant noise contamination of the response records. Copyright © 2008 John Wiley & Sons, Ltd.     

Simulating earthquake evacuation using human behavior models

In classical earthquake risk assessment, the human behavior is actually not taken into account in risk assessment. Agent‐based modeling is a simulation technique that has been applied recently in several fields, such as emergency evacuation. The paper is proposing a methodology that includes in agent‐based models the human behavior, considering the anxiety effects generated by the crowd and their influence on the evacuation delays. The proposed model is able to take into account the interdependency between the earthquake evacuation process, and the corresponding damage of structural and non‐structural components that is expressed in term of fragility curves. The software REPAST HPC has been used to implement the model, and as a case study, the earthquake evacuation by a mall located in Oakland has been used. The human behavior model has been calibrated through a survey using a miscellaneous sample from different countries. The model can be used to test future scenarios and help local authorities in situations where the human behavior plays a key role. Copyright © 2017 John Wiley & Sons, Ltd.     

Exploring the feasibility of earthquake early warning using records of the 2008 Wenchuan earthquake and its aftershocks

Earthquake early warning system (EEWS) is one of the effective ways to mitigate earthquake damage and can provide few seconds to tens of seconds of advanced warning time of impending ground motions, allowing for mitigation measures to be taken in the short term. After the devastating Ms8.0 Wenchuan earthquake, hundreds of M4-6 earthquakes occurred with depth range of 2–24 km. We explore a practical approach to earthquake early warning in Wenchuan area by determining a ground-motion period parameter τ_c and a high-pass filtered vertical displacement amplitude parameter Pd from the initial 3 s of the P waveforms of these aftershocks with M≥4.0. The empirical relationships both between τ_c and M, and between Pd and peak ground velocity PGV for the Wenchuan area are presented. The τ_c result shows that it is systematically greater for slow earthquakes, leading to a possible false alarm. The moment rate function is used to handle the fact that the Pd parameter alone miss the M=8.0 mainshock. These two relationships can be used to detect the occurrence of a major earthquake and provide onsite warning in the area around the station where onset of strong ground motions is expected within seconds after the arrival of the P wave. The robustness of onsite early warning can be increased by using multistation data when the station density is high or by combing τ_c and Pd as a single indicator.     

Structural identification of Egnatia Odos bridges based on ambient and earthquake induced vibrations

The dynamic characteristics of two representative R/C bridges on Egnatia Odos motorway in Greece are estimated based on low amplitude ambient and earthquake-induced vibrations. The present work outlines the instrumentation details, algorithms for computing modal characteristics (modal frequencies, damping ratios and modeshapes), modal-based finite element model (FEM) updating methods for estimating structural parameters, and numerical results for the modal and structural dynamic characteristics of the two bridges based on ambient and earthquake induced vibrations. Transverse, bending and longitudinal modes are reliably identified and stiffness-related properties of the piers, deck and elastomeric bearings of the FEMs of the two bridges are estimated. Results provide qualitative and quantitative information on the dynamic behavior of the bridge systems and their components under low-amplitude vibrations. Modeling assumptions are discussed based on the differences in the characteristics identified from ambient and earthquake vibration measurements. The sources of the differences observed between the identified modal and structural characteristics of the bridges and those predicted by FEMs used for design are investigated and properly justified.     

Classification and rating of strong-motion earthquake records

Ninety-two strong-motion earthquake records from the California region, U.S.A., have been statistically studied using principal component analysis in terms of twelve important standardized strong-motion characteristics. The first two principal components account for about 57 per cent of the total variance. Based on these two components the earthquake records are classified into nine groups in a two-dimensional principal component plane. Also a unidimensional engineering rating scale is proposed. The procedure can be used as an objective approach for classifying and rating future earthquakes.     

Neural network estimation of duration of strong ground motion using Japanese earthquake records

The duration of strong motion has a significant influence on the severity of ground shaking. In this work, a combination of average values of four geophysical properties of site (Standard Penetration Test (SPT) blow count, primary wave velocity, shear wave velocity, and density of soil) including hypocentral distance of less than 50 km and magnitudes more than 5.0 from Japanese ground motion records were used for development of neural network model, to estimate duration of strong ground motion. Since majority of strong motion databases provide only average shear wave velocity for site characterization, an attempt has also been made to train the neural network with magnitude, hypocentral distance and average shear wave velocity as three input variables. Results obtained from this study show that the duration of strong motion is mostly dependent on average shear wave velocity rather than other geophysical properties of site.     

Seismic response evaluation of Meloland Road Overpass using 1979 imperial Valley earthquake records

During the 1979 Imperial Valley earthquake, an array of 26 strong-motion accelerometers produced records for the Meloland Road Overpass, a two-span reinforced concrete bridge structure located only 0.5 km away from the causative fault for this earthquake event. This paper describes the application of a new system identification methodology to the array of strong-motion measurements, in order to assess seismic response characteristics of this bridge. Results of this application show that (1) linear models provide an excellent fit to the measured motions of the bridge, despite the fact that it was subjected to very strong shaking; (2) the transverse response of the structure is controlled by its abutment motions, with no significant dynamic amplification in the deck; and (3) the vertical response of the bridge deck at the midlength of its spans is dominated by a single vertical translational mode whereas, above the central pier, the deck's vertical response is most affected by the vertical motions of the pier base and by torsion of the deck. Also, systematic estimates of modal damping ratios and qualitative assessments of states of stress developed in the bridge during the earthquake are provided.     

鲁甸地震强震动记录与地震动衰减模型的对比研究

利用2014年鲁甸M_S6.5地震断层距小于300 km的32个自由场地观测台站的地震动加速度记录,分析了地震动峰值加速度(PGA)和峰值速度(PGV)的空间分布特征,并对已有地震动衰减模型中的NGA-West2四个模型和1个中国川藏区模型进行了比较分析.研究表明,地震动PGA和PGV衰减最快的方向与断层主破裂方向一致.在整个断层距(R_rup)范围内大多数台站的地震动PGA、PGV和加速度反应谱值(Sa(T=0.1、5.0 s))均位于NGA-West2四个模型预测曲线的±1倍标准差之外.PGA、PGV和Sa(T=5.0 s)的事件内残差均值在-1.43~-0.74之间.Sa(T=0.01~5.0 s)事件内残差均值在整个距离范围内均表现出系统性偏负.NGA-West2四个模型的PGA事件内残差的空间分布特征相似,其最大正值和最大负值分布区域的震源-场地方位角约为-90°和90°,与主破裂断层方向垂直,所处地势较为平坦且台站场地V_S30相对较大.NGA-West2四个模型总体上会较大地高估鲁甸地震整个断层距范围内各个周期尤其是短周期(T < 1.0 s)的地震动加速度反应谱值.考虑本地区实际地震资料的中国川藏区地震动衰减模型也会在一定程度上高估鲁甸地震大多数台站的地震动加速度反应谱值,但是相对于NGA-West2四个模型,其预测值更接近鲁甸地震的实际观测值.

     

Evaluating nonlinear effective stress site response analyses using records from the Canterbury earthquake sequence

A widely used one-dimensional nonlinear effective stress site response analysis program is used to model the response of potentially liquefiable soils during strong shaking. Ground motion records from six events of the 2010–2011 Canterbury earthquake sequence and the extensive site investigation data that have been obtained for the Christchurch area provide the basis for the analyses. The results of the analyses depend significantly on the input motions and soil profile characterization, so these important aspects are examined. Deconvolved Riccarton Gravel input motions were generated, because recorded rock or firm layer motions were not available. Nonlinear effective stress seismic site response analyses are shown to capture key aspects of the observed soil response through the comparison of acceleration response spectra of calculated surface motions to those of recorded surface motions; however, equivalent-linear and total stress nonlinear analyses capture these aspects as well. Biases in the computed motions compared to recorded motions were realized for some cases but they can be attributed primarily to the uncertainty in the development of the input motions used in the analyses.     

地震记录处理的一种新方法

介绍了M icrosoftV isual C (VC )和M atlab相结合开发地震记录处理软件的一种新方法。VC 和M atlab相结合开发地震记录处理软件,减轻了编程人员的工作量,提高了软件的开发效率和处理能力,为此类软件的开发提供了一种方便灵活的实现方法。通过一简单地震记录处理程序的三种不同实现途径,详细讲述了VC 和M atlab的编译环境。三种不同实现途径分别是:(1)VC 中直接调用M atlab C 数学图形函数库生成独立可执行程序;(2)VC 调用M程序生成的C/C 代码生成独立可执行程序;(3)VC 调用M文件转换成的DLL(动态链接库)生成可执行程序。文章还对三种实现途径进行了优缺点的比较,为开发人员在具体开发时提供参考。     

Sliding and overturning potential of Christchurch 2011 earthquake records

The 22 February 2011 M_w 6.3 earthquake produced a number of unique accelerograms in the city of Christchurch and the port of Lyttelton. Four of these records are analyzed in this paper. The two are from the Christchurch Catholic Cathedral College and Christchurch Hospital stations in the center of the city, which were placed on top of loose sandy soils that suffered softening due to liquefaction; one is from the Lyttelton station, Lyttelton Port Company, on a rock outcrop; and one is from the station at the Heathcote Valley Primary School, on stiff colluvial silts and sands near the edge of a steep and stiff sedimentary basin. The (elastic) response spectra are discussed and related to some salient characteristics of the motions. Symmetric and asymmetric sliding of a block resting through Coulomb friction on horizontal or inclined planes and rocking–overturning of rigid blocks, when excited at their base by these records, offer a strong indication of their ‘destructiveness potential’. The corresponding sliding and overturning spectra of the 2011 records are compared with those of some historic accelerograms to get an understanding of the severity of ground shaking that caused 170 deaths and heavy geotechnical and structural damage in the city of Christchurch. The possible role played by the unusually large vertical accelerations is also explored. Copyright © 2012 John Wiley & Sons, Ltd.     

Probabilistic representation and transmission of earthquake ground motion records

A relatively simple and straightforward procedure is given for representing analytically defined or data-based covariance kernels of arbitrary random processes in a compact form that allows its convenient use in later analytical random vibration response studies. The method is based on the spectral decomposition of the random process by the orthogonal Karhunen-Loeve expansion and the subsequent use of least-squares approaches to develop an approximating analytical fit for the data-based eigenvectors of the underlying random process. The resulting compact analytical representation of the random process is then used to derive a closed-form solution for the non-stationary response of a damped SDOF harmonic oscillator. The utility of the method for representing the excitation and calculating the mean-square response is illustrated by the use of an ensemble of acceleration records from the 1971 San Fernando earthquake.     

Relationship between earthquake and volcanic eruption inferred from historical records

Introduction From the records of Wudalianchi volcanic group eruption in 1720~1721 obtained from the Man ethnic group files of Heilongjiang General Yamen in Qing Dynasty (WU, 1998; CHEN, WU, 2003), we have discovered the eruption time, state, material and scale of Laoheishan and Hu-oshaoshan volcanoes, as well as numerous seismic records. These historical materials are discov-ered for the first time although the study on Wudalianchi volcanic group has a long history. These earthquakes co…     

类新西兰地震波形分析方法

对泰安地震台记录的2010年9月4日新西兰地震波形,进行震相、震源深度等地震参数辨析和分析,以具有代表性的2009年7月15日新西兰南岛西海岸远海地震波形和2010年4月5日墨西哥地震波形分析为辅,提出震中距大于83°、小于105°的类新西兰地震分析方法.根据两个辅震的波形特性,结合中国地震台网中心定位结果,对震级误差...