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削山造地后形成的黄土高填方场地对地震动参数特性影响较大。以实际工程项目为研究对象,构造不同填土高度的计算剖面,采用一维等效线性化方法计算土层地震动参数,分析基岩地震动输入参数和填土高度对场地地表放大效应的影响。研究表明:场地地震放大系数随填土层的高度增加呈递减趋势。在多遇地震动和基本地震动作用下,场地地震放大系数递减速度比罕遇地震动和极罕遇地震动作用下要大。当填土高度达到一定程度后放大效应趋于平稳;填土高度的变化,会改变地表加速度反应谱的形状。填土高度越大,地表反应谱长周期的频谱成分越显著,反应谱曲线向后移,反应谱峰值点均明显向长周期移动,并出现多个峰值点,反应谱特征周期值变大;下伏基岩的刚度越大,地表峰值加速度的放大效应越大。地表加速度反应谱特征值相比变小。当填土高度增大到一定程度时,下伏基岩的种类对地表地震动特性影响则不明显。该研究成果对高填方场地的地震安全评价和结构抗震设计提供参考。 相似文献
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《世界地震工程》2014,(4)
随机数是人工合成基岩地震动输入的必备参数,对地表地震动参数有一定影响。以某实际化工工程场地剖面及其基岩加速度反应谱为基础,调整随机数,人工合成不同的基岩加速度时程,以此为输入,计算场地地表地震动参数,并对比不同随机数下地表加速度反应。对比结果表明,相同的场地和基岩反应谱输入,不同随机数对应得到的地表反应谱高频部分(0.2s)影响显著,而对地表反应谱周期部分(0.2s)影响不大,其中峰值加速度差别最为显著,输入地震动强度越大差别越大,大震输入下可达到60gal,有可能影响烈度判断结果。基岩人造地震动随机数主要影响峰值加速度和地表反应谱高频部分,基本不影响反应谱长周期部分。 相似文献
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为研究土洞对岩溶场地地表地震动参数的影响,选取广西桂林市某岩溶场地,分析土洞的存在对地表地震动峰值和频谱的影响。依据场地地震反应分析理论,建立包含土洞与不包含土洞的有限元模型并进行地震反应分析,应用计算结果中1-3层土体表面中心点的地震动,作为原始信号输入,进行FFT(离散傅氏变换的快速算法)转换,得到场地各层土体表面中心点的频谱分析图。分析结果表明:(1)土洞的存在对地表峰值速度和峰值位移影响相对较小,对峰值加速度影响较大,且越上层土体地震动参数受土洞影响越大;(2)包含土洞的加速度频域分布峰值大于不包含土洞的岩溶场地,并且包含土洞与不包含土洞岩溶场地主要(卓越)频率分布在0-5Hz范围,分布较集中,峰值加速度对应的频率在2.5Hz附近。 相似文献
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通过日本KiK-net台网数据库的各种地震记录,研究了土体的非线性行为对场地响应的影响。这个台网由不少于688个地表—井下仪器构成,从这个台网还获得了直到井孔深度的剪切波和压缩波速度剖面的特征。为了通过计算每个场地的地表与井下频谱比来表征土体的线性行为,我们挑选了井下台站地震动峰值加速度（PGA）〈10cm/s2的事件。使用强震动事件（PGA〉50cm/s2）计算的场地响应曲线相对线性表征的变化被认为是由非线性土体行为造成的。为了描述每个事件土体非线性行为对场地响应的影响,我们提出了场地响应曲线相对线性估计的变化（放大或衰减）百分比（PNL ev,非线性百分比）和有关的位移频率（Sh ev）。这些参数被用于估计非线性场地响应显著区别于相应线性场地响应的概率。我们发现,不管何种场地,这个概率即使对低输入地震动峰值加速度（井下传感器的值不小于30cm/s2）也是重要的。这表明,在中强地震动场地响应评估中必须考虑非线性土体行为。此外,对记录了至少两个强震事件（井下PGA〉50cm/s2）的KiK-net台网数据库的54个场地,我们定义了每个场地的表征土体非线性行为对场地响应影响的另外4个参数：（1）地震动峰值加速度阈值（PGA th）,定义为PNL ev高于10%的地震动峰值加速度值;（2）地震动峰值加速度为50cm/s2的特定场地的PNL（PNL site）;（3）地震动峰值加速度为50cm/s2的卓越频率的特定场地移位（Sh site）;（4）在非线性和线性场地响应之间观测到衰减的频率（fNL）。我们观察到在fNL之下的频率,非线性土体行为可增强放大作用。我们发现fNL介于场地响应基频率和卓越共振频率之间,近地表具有V S反差的场地触发低地震动峰值加速度输入阈值的非线性行为。这些结果表明,非线性行为多发生在地表土层中。此外,通过研究地表的地 相似文献
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以天津滨海某软弱场地为例,在不同强度不同相位的地震动时程输入下,用等效线性化技术考虑土的动力非线性特性,计算水平成层场地的地震反应,研究天津地区厚层淤泥质粉质黏土的动剪模量比和阻尼比与剪应变幅值的关系曲线的变异性对深软场地地表峰值加速度及其反应谱的影响。结果表明:(1)在阻尼比较均值加减一倍标准差对地表地震动参数变化影响不大;(2)在动剪模量比均值增加或减1倍标准差,对2%超越概率水平下地表峰值加速度影响显著,对应地表峰值加速度可能增加或减小20%~30%,其地表反应谱谱型也有变高变瘦或变矮变胖的趋势;(3)在动剪切模量均值减1倍标准差时,对10%超越概率水平下的地表峰值加速度的影响比较显著,减小幅度在15%左右,反应谱也存在变矮变胖的趋势;在动剪切模量均值加1倍标准差时,对10%超越概率水平下的地表地震动参数影响不明显;(4)在动剪切模量或阻尼比均值加减1倍标准差时,对63%的地表地震动参数影响均不明显。 相似文献
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为研究高层RC框架结构罕遇地震下的易损性,设计了一个7度区典型11层RC框架结构。采用IDA方法进行时程分析,以地震动峰值地面加速度和结构第一自振周期对应的谱加速度为地震动强度指标,最大层间位移角为结构损伤指标,分别得到了单一地震动强度和双地震动强度参数下的IDA曲线和失效概率,绘制了双地震动强度参数下易损性曲面,并对单一地震动强度和双地震动强度参数下的易损性分析结果进行了对比。结果表明:罕遇地震下,采用双地震动强度参数结构失效概率明显低于采用单一地震动强度参数结构失效概率;对高层RC框架结构,采用双地震动强度参数进行易损性分析反映的地震动信息更全面;采用双地震动强度参数得到的结构失效概率公式更能真实量化不同强度地震作用下结构的失效概率。 相似文献
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《国际地震动态》2018,(10)
随着综合国力迅速提升,我国进行了大规模的公路网络建设,兴建了数以万计的公路桥梁,为整个经济社会的可持续发展提供了有力支撑。然而,国内外历次大地震中有大量公路桥梁发生破坏,这极大地降低了公路交通的通行能力,严重阻碍应急救援工作和城市日常生活。我国是遭受地震灾害最多的国家之一,因此,在我国开展公路桥梁地震易损性研究具有重要的现实意义。本文在对汶川地震公路桥梁调查数据深度挖掘整理和全面归纳总结之基础上,采用多种方法比较系统地研究了当代公路桥梁的地震易损性,还开展了基于公路桥梁震害评定地震烈度的研究,旨在更好地服务于公路桥梁的震害预测和损失评估、震后可恢复性研究、交通系统的地震风险分析,以及应急救灾决策的制定和完善抗震设计理论等工作,从而达到减轻桥梁震害和提高救援效率之目的。论文主要完成了以下工作:(1)针对低烈度区公路桥梁调查数据不完备、遗漏大量基本完好桥梁的实际情况,按照烈度区面积与调查桥梁数量相近的原则对低烈度区的调查数据进行了补充估计,利用常见的几种经验分布函数拟合了破坏概率直方图,对公路桥梁的易损性矩阵进行了改进,还分析了地震地质灾害的影响。(2)合理地估计了桥址处的PGA数值,基于补充后的调查数据建立了一系列"桥梁-破坏等级-桥址处PGA"样本对,采用最大似然估计法确定了易损性函数中的待定参数,给出了汶川地震公路桥梁的经验易损性曲线,比较分析了拱桥与梁桥之间的易损性差异,并探讨了桥梁规模对易损性的影响。(3)基于SAP2000建立了9种工况下的连续梁桥有限元分析模型,选取36条典型地震动记录为输入,考虑支座和桥墩的非线性行为,进行了桥梁非线性时程分析,在此基础上首先建立了支座和桥墩两种构件的易损性曲线,随后利用一阶界限法合成了整座连续梁桥的易损性曲线,并讨论了不同支承方式对地震易损性的影响,同时验证了桥梁规模对地震易损性的影响规律。(4)通过统计整理近2 000座公路桥梁的详实震害资料,分别得到了拱桥和梁桥的主要震害类型,探讨了它们的发生概率与不同地震烈度的对应关系,分析了关键构件的破坏程度随地震烈度的变化规律。最后,以桥梁破坏等级和典型震害的形式分别提出了评定地震烈度的建议指标,并进行了对比分析和验证。 相似文献
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研究基岩输入时程随机数对场地峰值加速度的影响,对核电厂设计地震动参数的合理确定具有重要意义。本文选取了某重要核电站场地具有代表性的3个钻孔,建立了场地计算模型。根据确定性方法、概率性方法得到的基岩反应谱及其包络谱,基于不同随机数,分别合成了400条基岩输入时程。采用LSSRLI-1程序进行了场地地震反应,根据4800个计算结果,研究了不同随机数对地表峰值加速度的影响,给出了自然对数下峰值加速度标准差的估计,揭示了峰值加速度的分布规律,提出了对核电厂设计地震动参数合理确定的建议。 相似文献
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以美国西部地区某斜交公路连续刚构桥为研究对象，研究其不等高墩易损性差异以及斜交角的改变对桥墩地震易损性的影响。考虑桥梁结构参数和地震动的不确定性，选取100条地震动，沿纵桥向输入，生成"结构-地震动"样本库，以地震动峰值加速度（PGA）为强度指标（IM），利用OpenSees软件对结构进行非线性时程分析得到桥墩动力响应，而后以桥墩曲率延性比衡量桥梁破坏状态，在确定桥墩损伤指标的基础上，采用可靠度理论得到各桥墩的地震易损性曲线，判断桥墩的损伤模式、损伤特点。在此基础上，改变桥梁斜交角度进行易损性分析，得到斜交角变化对桥墩地震易损性的影响。研究表明：该桥最矮墩发生损伤的概率大于其他桥墩，桥墩最先进入塑性的是墩顶和墩底区域；不同斜交角对桥墩的地震响应影响显著，各墩损伤破坏排序与斜交桥结构构造特点有关，同一排架墩的两侧墩柱易损性呈现与角度变化趋势相反的排列，损伤越严重，趋势越明显；对于此不等高的斜交刚构桥，最矮墩为其抗震薄弱环节，斜交角越大，越应该关注钝角处矮墩的损伤情况，并提高其设计标准，在进行斜交刚构桥抗震设计中应予以重视。 相似文献
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Fragility curves are found to be useful tools for predicting the extent of probable damage. They show the probability of highway structure damage as a function of strong motion parameters, and they allow the estimation of a level of damage probability for a known ground motion index. In this study, an analytical approach was adopted to develop the fragility curves for highway bridges based on numerical simulation. Four typical RC bridge piers and two RC bridge structures were considered, of which one was a non‐isolated system and the other was an isolated system, and they were designed according to the seismic design code in Japan. From a total of 250 strong motion records, selected from Japan, the United States, and Taiwan, non‐linear time history analyses were performed, and the damage indices for the bridge structures were obtained. Using the damage indices and ground motion parameters, fragility curves for the four bridge piers and the two bridge structures were constructed assuming a lognormal distribution. It was found that there was a significant effect on the fragility curves due to the variation of structural parameters. The relationship between the fragility curve parameters and the over‐strength ratio of the structures was also obtained by performing a linear regression analysis. It was observed that the fragility curve parameters showed a strong correlation with the over‐strength ratio of the structures. Based on the observed correlation between the fragility curve parameters and the over‐strength ratio of the structures, a simplified method was developed to construct the fragility curves for highway bridges using 30 non‐isolated bridge models. The simplified method may be a very useful tool to construct the fragility curves for non‐isolated highway bridges in Japan, which fall within the same group and have similar characteristics. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
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Masanobu Shinozuka 《地震工程与结构动力学》2012,41(14):2111-2124
This study examines the effect of the angle of seismic incidence θ on the fragility curves of bridges. Although currently, fragility curves of bridges are usually expressed only as a function of intensity measure of ground motion (IM) such as peak ground acceleration, peak ground velocity, or Sa(ω1), in this study they are expressed as a function of IM with θ as a parameter. Lognormal distribution function is used for this purpose with fragility parameters, median cm and standard deviation ζ to be estimated for each value of θ chosen from 0 < θ < 360°. A nonlinear 3D finite element dynamic analysis is performed, and key response values are calculated as demand on the bridge under a set of acceleration time histories with different IM values representing the seismic hazard in Los Angeles area. This method is applied to typical straight reinforced concrete bridges located in California. The results are validated with existing empirical damage data from the 1994 Northridge earthquake. Even though the sample bridges are regular and symmetric with respect to the longitudinal axis, the results indicate that the weakest direction is neither longitudinal nor transverse. Therefore, if the angle of seismic incidence is not considered, the damageability of a bridge can be underestimated depending on the incidence angle of seismic wave. Because a regional highway transportation network is composed of hundreds or even thousands of bridges, its vulnerability can also be underestimated. Hence, it is prudent to use fragility curves taking the incident angle of seismic waves into consideration as developed here when the seismic performance of a highway network is to be analyzed. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
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The influence of vertical ground motions on the seismic response of highway bridges is not very well understood. Recent studies suggest that vertical ground motions can substantially increase force and moment demands on bridge columns and girders and cannot be overlooked in seismic design of bridge structures. For an evaluation of vertical ground motion effects on the response of single‐bent two‐span highway bridges, a systematic study combining the critical engineering demand parameters (EDPs) and ground motion intensity measures (IMs) is required. Results of a parametric study examining a range of highway bridge configurations subjected to selected sets of horizontal and vertical ground motions are used to determine the structural parameters that are significantly amplified by the vertical excitations. The amplification in these parameters is modeled using simple equations that are functions of horizontal and vertical spectral accelerations at the corresponding horizontal and vertical fundamental periods of the bridge. This paper describes the derivation of seismic demand models developed for typical highway overcrossings by incorporating critical EDPs and combined effects of horizontal and vertical ground motion IMs depending on the type of the parameter and the period of the structure. These models may be used individually as risk‐based design tools to determine the probability of exceeding the critical levels of EDP for pre‐determined levels of ground shaking or may be included explicitly in probabilistic seismic risk assessments. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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Fragility curves express the probability of structural damage due to earthquakes as a function of ground motion indices, e.g., PGA, PGV. Based on the actual damage data of highway bridges from the 1995 Hyogoken‐Nanbu (Kobe) earthquake, a set of empirical fragility curves was constructed. However, the type of structure, structural performance (static and dynamic) and variation of input ground motion were not considered to construct the empirical fragility curves. In this study, an analytical approach was adopted to construct fragility curves for highway bridge piers of specific bridges. A typical bridge structure was considered and its piers were designed according to the seismic design codes in Japan. Using the strong motion records from Japan and the United States, non‐linear dynamic response analyses were performed, and the damage indices for the bridge piers were obtained. Using the damage indices and ground motion indices, fragility curves for the bridge piers were constructed assuming a lognormal distribution. The analytical fragility curves were compared with the empirical ones. The proposed approach may be used in constructing the fragility curves for highway bridge structures. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
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针对非规则人字形桥梁在地震作用下灾变严重的问题,以一座非规则人字形桥梁为研究对象,建立其空间分析模型,研究综合考虑支座摩擦滑移、结构碰撞对非规则人字形桥梁地震响应的影响。结果表明:邻梁间的碰撞作用可使得桥梁墩顶位移及内力相比不考虑时有所减小,但同时也使梁体产生了较大的加速度脉冲效应;当考虑支座摩擦滑移和结构碰撞时,固定墩墩顶位移和邻梁相对位移峰值有一定程度增大,然而对梁体加速度脉冲效应结果影响并无统一规律;纵向地震波作用下,非规则人字形桥梁不仅存在顺桥向的碰撞,横桥向的碰撞响应也不容忽视。非规则人字形桥梁进行抗震设计计算时应选取符合实际情况的计算模型,考虑支座摩擦滑移及结构间的碰撞。 相似文献
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This paper presents the first of a series of case studies on the seismic design of long span bridges （cable-stayed bridges, suspension bridges and arch bridges） under a cooperative research project on seismic behavior and design of highway bridges between the State Key Laboratory for Disaster Reduction in Civil Engineering, Tongji University and the Multidisciplinary Center for Earthquake Engineering Research, University at Buffalo. The objective of this series of case studies is to examine the differences and similarities on the seismic design practice of long span bridges in China and the U.S., to identify research needs and to develop design guidelines beneficial to bridge engineers in both countries. Unlike short to medium span bridges, long span bridges are not included in most seismic design specifications, mainly because they are location dependent and structurally unique. In this paper, an available model of a steel tied half through arch bridge with a main span of 550m in China is discussed. Analysis is focused on comparisons of the seismic responses due to different ground motions. Seismic design criteria and seismic performance requirements for long span bridges in both countries were first introduced and compared, and then three near field earthquake records with large vertical components were selected as the excitations to examine the seismic behavior and seismic vulnerability of the bridge. Results show that （1） the selected near field ground motions cause larger responses to key components （critical sections） of the bridge （such as arch rib ends） with a maximum increase of more than twice those caused by the site specific ground motions; （2） piers, longitudinal girders and arch crowns are more vulnerable to vertical motions, especially their axial forces; and （3） large vertical components of near field ground motions may not significantly affect the bridge＇s internal forces provided that their peak acceleration spectra ordinates only appear at periods of less than 0.2s. However, they may have more influence on the longitudinal displacements of sliding bearings due to their large displacement spectra ordinates at the fundamental period of the bridge. 相似文献
18.
Seismic pounding between adjacent frames in multiple-frame bridges and girder ends in multi-span simply supported bridges has been commonly observed in several recent earthquakes. The consequences of pounding include damage to piers, abutments, shear keys, bearings and restrainers, and possible collapse of deck spans. This paper investigates pounding in bridges from an analytical perspective. A simplified nonlinear model of a multiple-frame bridge is developed including the effects of inelastic frame action and nonlinear hinge behavior, to study the seismic response to longitudinal ground motion. Pounding is implemented using the contact force-based Kelvin model, as well as the momentum-based stereomechanical approach, Parameter studies are conducted to determine the effects of frame period ratio, column hysteretic behavior, energy dissipation during impact and near source ground motions on the pounding response of the bridge. The results indicate that pounding is most critical for highly out-of-phase frames and is not significant for frame period ratios greater than 0.7. Impact models without energy dissipation overestimate the displacement and acceleration amplifications due to impact, especially for elastic behavior of the frames. Representation of stiffness degradation in bridge columns is essential in capturing the accurate response of pounding frames subjected to far field ground motion. Finally, it is shown that strength degradation and pounding can result in significant damage to the stiffer frames of the bridge when subjected to large acceleration pulses from near field ground motion records. 相似文献
19.
Laminated elastomeric bearings have been widely used for small-to-medium-span highway bridges in China, in which concrete shear keys are set transversely to prohibit large girder displacement. To evaluate bridge seismic responses more accurately, proper analytical models of bearings and shear keys should be developed. Based on a series of cyclic loading experiments and analyses, rational analytical models of laminated elastomeric bearings and shear keys, which can consider mechanical degradation, were developed. The effect of the mechanical degradation was investigated by examining the seismic response of a small-to-medium-span bridge in the transverse direction under a wide range of peak ground accelerations (PGA). The damage mechanism for small-to-medium-span highway bridges was determined, which can explain the seismic damage investigation during earthquakes in recent years. The experimental results show that the mechanical properties of laminated elastomeric bearings will degrade due to friction sliding, but the degree of decrease is dependent upon the influencing parameters. It can be concluded that the mechanical degradation of laminated elastomeric bearings and shear keys play an important role in the seismic response of bridges. The degradation of mechanical properties of laminated elastomeric bearings and shear keys should be included to evaluate more precise bridge seismic performance. 相似文献