Recording-based identification of site liquefaction

Reconnaissance reports and pertinent research on seismic hazards show that liquefaction is one of the key sources of damage to geotechnical and structural engineering systems. Therefore, identifying site liquefaction conditions plays an important role in seismic hazard mitigation. One of the widely used approaches for detecting liquefaction is based on the time-frequency analysis of ground motion recordings, in which short-time Fourier transform is typically used. It is known that recordings at a site with liquefaction are the result of nonlinear responses of seismic waves propagating in the liquefied layers underneath the site. Moreover, Fourier transform is not effective in characterizing such dynamic features as time-dependent frequency of the recordings rooted in nonlinear responses. Therefore, the aforementioned approach may not be intrinsically effective in detecting liquefaction. An alternative to the Fourier-based approach is presented in this study, which proposes time-frequency analysis of earthquake ground motion recordings with the aid of the Hilbert-Huang transform （HHT）, and offers justification for the HHT in addressing the liquefaction features shown in the recordings. The paper then defines the predominant instantaneous frequency （PIF） and introduces the PiF-related motion features to identify liquefaction conditions at a given site. Analysis of 29 recorded data sets at different site conditions shows that the proposed approach is effective in detecting site liquefaction in comparison with other methods.     

Hilbert spectrum and intrinsic oscillation mode of dynamic response of a bilinear SDOF system： influence of harmonic excitation amplitude

Under harmonic wave excitation, the dynamic response of a bilinear SDOF system can be expressed by the Hilbert spectrum. The Hilbert spectrum can be formulated by (1) the inter-wave combination mechanism between the steady response and the transient response when the system behaves linearly, or (2) the intra-wave modulation mechanism embedded in one intrinsic mode function (IMF) component when the system behaves nonlinearly. The temporal variation of the instantaneous frequency of the IMF component is consistent with the system nonlinear behavior of yielding and unloading. As a thorough study of this fundamental structural dynamics problem, this article investigates the influence of the amplitude of the harmonic wave excitation on the Hilbert spectrum and the intrinsic oscillatory mode of the dynamic response of a bilinear SDOF system.     

非线性振动输入反演的时频域法

本文是文献〔2〕的继续。该文献中作者们提出在频域反演求输入的方法,误差一般在10％左右,主要来自所采用的等效线性化方法。为了减小这一误差,本文采用一种时域频域的混合法,在时域中进行正演计算,在频域中进行反演计算,假设传递函数在一轮迭代之内是不变的。从计算结果来看,误差大为减小。     

地震断层作用下埋地管线壳有限元分析的等效边界方法

壳有限元方法是目前较先进的分析地震活动断层作用下埋地管线反应的方法 ,但是由于受断层错动影响的管道一般较长 ,因此该方法需要较大的计算资源 .本文提出一种等效边界方法 ,可以克服现有壳有限元方法的缺点 .埋地管线在地震断层作用下的大变形反应往往只发生在断层附近 ,而离断层较远处管段的变形反应相对较小 .本文从理论上得出一个等效边界 ,以非线性弹簧的形式应用到壳单元分析模型的两端 ,替代模型以外管段的影响 .这样只需对感兴趣的发生大变形的管段进行壳单元建模型 ,从而解决了现有的壳有限元方法需要大量计算机时和资源的缺点 .与现有的壳模型固定边界方法进行比较 ,验证了等效边界方法的合理性和有效性 .     

地震危险性估计中不确定性的概率分析

本文首先介绍了地震危险性估计中存在的随机、知识不完备(模型)、模糊这三类不确定因素以及当前对这三类因素处理的几种方法;然后提出了作者自己的见解,即这三类看来性质不同的不确定因素,归根到底,都来自知识不完备,或为了简化而不求完备;接着说明了这三类因素的不确定性都可以用概率密度表示,随机因素用客观概率,后两类用主观概率;最后指出,在地震危险性分析中,这三类因素可以统一按Bayesian方法综合处理,从而避免了过去采用的超越概率曲线的分位数曲线这种概率的概率的困难。     

The relation between the response spectrum and the phase diference spectrum

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Synthesized Poisson and renewal model and its application in seismic hazard analysis

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地震带与地震统计区关系探究

总结和分析了中国地震带划分的研究历史、目的和用途、划分原则、表现形式以及基本特点,指出地震带是以地震活动性区域划分研究为目的,它不同于概率地震危险性方法中的地震统计区的概念．文中对地震统计区概念及其演化历史进行了分析和论述,认为地震统计区与地震带在统计意义、物理内涵、层次性、划分规模的要求、对空间重叠的排斥性以及划分目的和用途等方面,均存在较大差异．现行工作中将两者不加区分地使用是不合适的, 一方面造成地震统计区未形成自身的适应概率地震危险性分析方法的划分理论,另一方面也造成以地震活动特征和地震孕育发生环境、机制研究为目的的地震带划分研究的停滞不前．文中最后指出,地震统计区划分是以地震带划分研究为基础,它产生并服务于考虑地震活动时空不均匀性的概率地震危险性分析方法,应将其与地震带概念加以明确区分,并加强其划分原则、理论和方法的研究．     

Identification of acceleration pulses in near-fault ground motion using the EMD method

In this paper, response spectral characteristics of one-, two-, and three-lobe sinusoidal acceleration pulses are investigated, and some of their basic properties are derived. Furthermore, the empirical mode decomposition （EMD） method is utilized as an adaptive filter to decompose the near-fault pulse-like ground motions, which were recorded during the September 20, 1999, Chi-Chi earthquake. These ground motions contain distinct velocity pulses, and were decomposed into high-frequency （HF） and low-frequency （LF） components, from which the corresponding HF acceleration pulse （if existing） and LF acceleration pulse could be easily identified and detected. Finally, the identified acceleration pulses are modeled by simplified sinusoidal approximations, whose dynamic behaviors are compared to those of the original acceleration pulses as well as to those of the original HF and LF acceleration components in the context of elastic response spectra. It was demonstrated that it is just the acceleration pulses contained in the near-fault pulse-like ground motion that fundamentally dominate the special impulsive dynamic behaviors of such motion in an engineering sense. The motion thus has a greater potential to cause severe damage than the far-field ground motions, i.e. they impose high base shear demands on engineering structures as well as placing very high deformation demands on long-period structures.     

关于地震危险性估计中不确定性的统一分析

本文首先全面回顾了国内外现有地震危险性估计中的不确定性分析方法, 指出了其中存在的问题。同时, 通过分析认为, 不确定性可以分为随机、模糊及知识不完备三类, 它们均与知识不完备性相关, 因而可以进行统一分析。由此, 基于随机标值点过程理论, 给出了地震危险性估计的一般表达式;基于全概率理论, 给出了地震危险性估计中不确定性的统一分析表达式;最后, 探讨了本文提出的地震危险性估计中不确定性分析方法与国内外主要不确定性分析方法的关系。分析表明, 它们只是本文的特例。