Site-specific seismic design of damage tolerant structural systems using a novel concept

Designing more seismic load-tolerant structures is one of the major challenges of the world communities. It is due to the inability of the profession to predict future design earthquake time histories at a site compounded by the failure to appropriately incorporate uncertainties in other design variables and structural behavior just before failure. A site-specific method is proposed to generate a suite of ground excitation time histories and a novel risk estimation is developed considering major sources of nonlinearity and uncertainty. For wider application and acceptance, the risk evaluation procedure essentially consists of few deterministic time domain finite element analyses. The procedure is verified and showcased by estimating risks associated with three buildings designed by professional experts in the Los Angeles area satisfying the post-Northridge design criteria for the overall lateral deflection and inter-story drift. The accuracy of the estimated risk is verified using the Monte Carlo simulation technique. In all cases, the probabilities of collapse are found to satisfy the current code requirements. The spread in the reliability indexes for each building for both limit states cannot be overlooked, indicating the significance of the frequency contents of the time histories. The inter-story drift is found to be more critical than the overall lateral displacement. The reliability indexes for both limit states are similar only for few cases. The authors believe that they proposed an alternative to the classical random vibration and simulation approaches. The proposed site-specific seismic safety assessment procedure can be used by practicing engineers for routine applications.     

Improving hydrodynamic modeling of river networks by incorporating data assimilation using a particle filter

Numerical modeling is a well-recognized method for studying the hydrodynamic processes in river networks.Multi-source measurements also offer abundant information on the patterns and mechanisms within the processes.Therefore,improving hydrodynamic modeling of river networks through the use of data assimilation techniques has become a hot research topic in recent years.The particle filter(PF)is a commonly used data assimilation method and has been proven to be applicable to various nonlinear and non-Gaussian models.In the current study,an improved numerical hydrodynamic model for large-scale river networks is established by incorporating the advanced PF algorithm.Furthermore,the PF method based on the Gaussian likelihood function(GLF)and the method based on the Cauchy likelihood function(CLF)are compared for a complex river network scenario.The feasibility of the PF-based methods was evaluated through application to the Yangtze-Dongting River-lake Network(YDRN)by assimilating water stage data collected at six hydrometric stations during the entire hydrodynamic process in 2003.Additionally,the parameters used in the likelihood function,which affect the assimilation performance,also were explored in the current study.The study results found that the accuracy of the model-derived water stage data was improved when the PF-based methods are utilized,with improvement not only at the data assimilation(calibration)sites but also at three hydrometric stations not used in the data assimilation(i.e.,verification sites).The highest average Nash-Sutcliffe Efficiency result for the six assimilation sites were 0.98 while the lowest summed root-mean-square-error result was 1.801 m.The comparison results also indicated that the CLF-based PF outperformed the GLF-based PF when high-accuracy observed data are available.Specifically,the CLF can effectively resolve the filtering failure problem and the dispersion problem of PFs,and further improve the accuracy of the filtering results for a river network scenario.In summary,the CLF-based PF method along with high-accuracy observation data shows promise to provide reliable reference and technical support for hydrodynamic modeling of large-scale river networks.     

唐山震后建设与抗震结构体系

1976年唐山大地震至今已30年,唐山的震后建设先后经历了抗灾建设、恢复建设和发展建设三个阶段。三个不同的建设阶段所采用的抗震结构体系有所不同,也反映了我国抗震理论和实践的进步与发展。本文总结了三个不同建设时期唐山市建筑工程采用的主要抗震结构体系,并对唐山市建筑抗震结构体系的发展提出了建议。     

Estimation of design flood using EWT and ENE metrics and uncertainty analysis under non-stationary conditions

Concepts of Expected Waiting Time (EWT) and Expected Number of Exceedances (ENE) have been presented in much literature for estimating the Design Flood (DF) under non-stationary conditions. The parameters of the EWT and ENE are generally no less than four, which inevitably leads to the uncertainty of the DF estimation. In this paper, the Bayesian method is proposed to analyze the impact of parameter estimation uncertainty on the EWT- and ENE-based estimation of the DF and Corresponding Design Reliability (CDR). In addition, a comparison analysis between the EWT and ENE is conducted in terms of the DF and CDR with or without a consideration being given to the impact of parameter uncertainty. In the case of giving no consideration to the impact of parameter uncertainty, the experiment results indicate that the EWT-based estimations are less than that of ENE in terms of DF and CDR in the case of a decreasing trend. While in the case of an increasing trend, the EWT-based estimations are bigger than that of ENE. In the case of considering the impact of parameter uncertainty, results in the case study show that the distribution of the EWT-based estimations of DF and CDR are left shifted compared to that of the ENE. Overall, the EWT-based estimations are significantly different from that of ENE in terms of DF and CDR. Therefore, it is necessary and open for further discussions about which metric will be optimal between the EWT and ENE for estimating the DF under non-stationarity.     

Analysis of dispersed multi-mode signals of the SASW method using the multiple filter/crosscorrelation technique

Spectral analysis of surface waves (SASW) is a nondestructive in-situ testing method used for determining the thickness and elastic properties of pavement and soil sites using the dispersion characteristics of surface waves. In previous studies, it has been demonstrated that for some sites errors may arise in experimental dispersion curves when the usual SASW test and data analysis procedures are followed, in particular the phase unwrapping procedure and source-to-near-receiver spacing distance. These errors occur due to the participation of more than one surface wave mode in SASW signals. In this study, the multiple filter/crosscorrelation technique often used in earthquake seismology for the analysis of multi-mode earthquake records is presented and applied for calculating phase velocities from SASW signals. It is demonstrated that this technique produces results that are generally more accurate than those produced by the usual phase unwrapping procedure.     

利用模板匹配技术识别大岗山水库库区爆破事件

采用匹配定位方法,利用大岗山水库库区及附近(29.2°—29.9°N,101.9°—102.5°E)5次已知爆破事件对2014年3月1日至2015年12月31日内连续波形进行模板检测与定位,经过人工复核后共获取23次疑爆事件,这些事件与模板事件间有较高的相关性,相关系数达0.7734,匹配后疑爆事件数为模板数的4.6倍...     

Propagation of partially coherent non-stationary random waves in a viscoelastic layered half-space

This paper presents a highly accurate method based on the precise integration method (PIM) and on the pseudo excitation method (PEM). The method computes the propagation behaviour of partially coherent non-stationary random waves in a viscoelastic, transversely isotropic solid, which consists of a multi-layered soil resting on a homogeneous semi-infinite space. The excitation source is a local rupture between two layers, which causes a partially coherent non-stationary random field. The analysis of non-stationary random wave propagation is transformed into that for deterministic waves by using PEM. The resulting governing equations in the frequency-wavenumber domain are linear ordinary differential equations, which are solved very precisely by using PIM. The evolutionary power spectral densities of the ground level responses are investigated and some typical earthquake phenomena are explained.     

Criteria for assessing dynamic collapse of elastoplastic structural systems

Criteria are presented for assessing the propensity for dynamic collapse of elastoplastic structural systems. To detect the onset of dynamic collapse, three key concepts are introduced. First, the equations of motion are linearized and time shifted relative to a reference time in a dynamic process. Second, we study the free vibration of the system after the reference time. Third, we use a modal decomposition of the response. We suggest that dynamic collapse is likely if (1) there exist negative eigenvalues of the Hessian of the total potential energy and (2) the direction of motion is consistent with the loading direction of the elastoplastic material. The direction of motion is determined by using the gradient of total potential energy and the eigenmodes corresponding to the negative eigenvalues. The fidelity of the present criteria is demonstrated through numerical examples for which the non‐linear equations of motion can be integrated exactly. With the present approach, it becomes apparent that p‐delta effects, the tangent stiffness, the internal resistance, and the direction of unloading all play key roles in the dynamic collapse of structures. Copyright © 2000 John Wiley & Sons, Ltd.     

A test problem for structural systems with discontinuities

The direct integration method for structural systems having force and/or stiffness discontinuities is known to present considerable numerical difficulties. A non-linear one-degree-of-freedom test problem having these characteristics is developed and its exact oscillation period determined. The effects on amplitude and phase of small perturbations of the switching point, such as are caused by fixed-step integration, have been studied. Artificial energy changes introduced at discontinuities by fixed-step explicit and implicit methods are investigated. For a number of commonly used algorithms orders of convergence in fixed-step integration of the test problem degrade from design value before, toO(h) after, the first discontinuity traversal.O(h) convergence is maintained for any number of discontinuity traversals thereafter, but design order can be recovered by locating the switching point sufficiently precisely.     

Water pollution control by filter

The effect of the water soluble oil dispersant Corexit 9527 was tested on larvae from several species of sea urchins and marine fishes. Severe effects in fertilization and development were registered often resulting in pathological larvae and rapid cytolysis. The combination of Corexit 9527 with oil was found to be even more dangerous to the embryo than Corexit or oil alone.     

In situ bioremediation of trichloroethylene-contaminated water by a resting-cell methanotrophic microbial filter

Abstract

An in situ microbial filter technology is being tested and developed for remediating migrating subsurface plumes contaminated with low concentrations of trichloroethylene (TCE). The current focus is the establishment of a replenishable bioactive zone (catalytic filter) along expanding plume boundaries by the injection of a representative methanotrophic bacterium, Methylosinus trichosporium OB3b. This microbial filter strategy has been successfully demonstrated using emplaced, attached resting cells (no methane additions) in a 1.1 m flow-through test bed loaded with water-saturated sand. Two separate 24 h pulses of TCE (109 ppb and 85 ppb), one week apart, were pumped through the system at a flow velocity of 15 mm h^?1; no TCE (< 0.5 ppb) was detected on the downstream side of the microbial filter. Subsequent excavation of the wet sand confirmed the existence of a TCE-bioactive zone 21 days after it had been created. An enhanced longevity of the cellular, soluble-form methane monooxygenase produced by this methanotroph is a result of the laboratory bioreactor culturing conditions. Additional experiments with cells in sealed vials and emplaced in the 1.1 m test bed yielded a high resting-cell finite TCE biotransformation capacity of about 0.25 mg per mg of bacteria; this is suitable for a planned sand-filled trench field demonstration at a Lawrence Livermore National Laboratory site.     

Time-domain identification of dynamic properties of layered soil by using extended Kalman filter and recorded seismic data

A novel time-domain identification technique is developed for the seismic response analysis of soil-structure interaction. A two-degree-of-freedom (2DOF) model with eight lumped parameters is adopted to model the frequency-dependent behavior of soils. For layered soil, the equivalent eight parameters of the 2DOF model arc identified by the extended Kalman filter (EKF) method using recorded seismic data. The polynomial approximations for derivation of state estimators are applied in the EKF procedure. A realistic identification example is given for the layered-soil of a building site in Anchorage, Alaska in the United States. Results of the example demonstrate the feasibility and practicality of the proposed identification technique. The 2DOF soil model and the identification technique can be used for nonlinear response analysis of soil-structure interaction in the time-domain for layered of complex soil conditions. The identified parameters can be stored in a database for use in other similar soil conditions. If a universal database that covers information related to most soil conditions is developed in the future, engineers could conveniently perform time history analyses of soil-structural interaction.     

日本结构控制的工程应用

提出了包括基础隔震系统、质量阻尼系统和其他阻尼器的结构振动控制系统,阐述了结构控制系统在日本的实际工程应用,同时还介绍了于2000年11月召开的第二届日本结构控制学术会议的情况.     

ARX结构模态参数识别方法对比(Ⅱ)——基于地震观测记录的对比

结构参数识别是结构抗震安全性能鉴定和健康诊断的基础,利用地震观测记录来识别结构模态参数,是地震工程领域备受关注的研究课题之一。本文利用实际结构的地震观测记录,对一维、多维和整体ARX模型三种模态参数识别方法进行了对比分析。结果表明：整体ARX模型对多自由度结构的模态参数识别较为稳定且精度较高;实际应用中多维ARX模型有时会导致丢失模态和虚假模态现象。     

ARX结构模态参数识别方法对比(I)——基于理论地震反应时程的对比

结构参数识别是结构抗震安全性能鉴定和健康诊断的基础。利用地震观测记录来识别结构模态参数,是地震工程领域备受关注的研究课题之一。本文利用三层平面框架结构的理论地震反应时程,对一维、多维和整体ARX模型三种模态参数识别方法进行了对比分析。结果表明：整体ARX模型的识别结果较为稳定且精度较高,更适合于进行多自由度结构参数识别。     

Efficient simulation of spatially correlated non-stationary ground motions by wavelet-packet algorithm and spectral representation method

Although the classical spectral representation method(SRM)has been widely used in the generation of spatially varying ground motions,there are still challenges in efficient simulation of the non-stationary stochastic vector process in practice.The first problem is the inherent limitation and inflexibility of the deterministic time/frequency modulation function.Another difficulty is the estimation of evolutionary power spectral density(EPSD)with quite a few samples.To tackle these problems,the wavelet packet transform(WPT)algorithm is utilized to build a time-varying spectrum of seed recording which describes the energy distribution in the time-frequency domain.The time-varying spectrum is proven to preserve the time and frequency marginal property as theoretical EPSD will do for the stationary process.For the simulation of spatially varying ground motions,the auto-EPSD for all locations is directly estimated using the time-varying spectrum of seed recording rather than matching predefined EPSD models.Then the constructed spectral matrix is incorporated in SRM to simulate spatially varying non-stationary ground motions using efficient Cholesky decomposition techniques.In addition to a good match with the target coherency model,two numerical examples indicate that the generated time histories retain the physical properties of the prescribed seed recording,including waveform,temporal/spectral non-stationarity,normalized energy build-up,and significant duration.     

Solution of viscously damped linear systems using a set of load-dependent vectors

This paper considers a solution method for viscously damped linear structural systems which are subjected to transient loading. The equations of motion of such systems are written in a first-order form. A solution subspace is generated using the damped dynamic matrix and the static deflection from the first-order form of the equations of motion. Two convenient bases, Lanczos vectors and Ritz vectors, are constructed from this subspace. An approximate solution is then obtained by superposition of the Lanczos vectors or the Ritz vectors. In contrast to the traditional mode superposition method using complex eigenvectors, the Lanczos vectors or the Ritz vectors are less expensive to generate than the complex eigenvectors, yet yield comparable accuracy. In addition, there is no need for a static correction since the static deflection is already contained in our solution subspace. Numerical examples are presented to show the potential of using the Ritz vectors to compute responses of damped dynamic systems.     

基于神经网络和滤波技术的贮仓结构参数识别

利用神经网络和Kalman滤波技术,提出了一种直接识别结构物理参数的方法,用Kalman滤波技术训练网络。在贮仓振动台实验的基础上,用贮仓在动载作用下的位移、速度作为网络的输入,激振加速度和响应加速度作为网络的输出。仿真计算表明,本文方法是可行的。