Dynamic interaction of bridge–train system under non‐uniform seismic ground motion     

X. T. Du  Y. L. Xu  H. Xia 《地震工程与结构动力学》2012,41(1):139-157

The probability that an earthquake occurs when a train is running over a bridge in earthquake‐prone regions is much higher than before, for high‐speed railway lines are rapidly developed to connect major cities worldwide. This paper presents a finite element method‐based framework for dynamic analysis of coupled bridge–train systems under non‐uniform seismic ground motion, in which rail–wheel interactions and possible separations between wheels and rails are taken into consideration. The governing equations of motion of the coupled bridge–train system are established in an absolute coordinate system. Without considering the decomposition of seismic responses into pseudo‐static and inertia‐dynamic components, the equations of motion of the coupled system are formed in terms of displacement seismic ground motions. The mode superposition method is applied to the bridge structure to make the problem manageable while the Newmark‐β method with an iterative computation scheme is used to find the best solution for the problem concerned. Eight high‐speed trains running over a multi‐span steel truss‐arch bridge subject to earthquakes are taken as a case study. The results from the case study demonstrate that the spatial variation of seismic ground motion affects dynamic responses of the bridge–train system. The ignorance of pseudo‐static component when using acceleration seismic ground motions as input may underestimate seismic responses of the bridge–train system. The probability of separation between wheels and rails becomes higher with increasing train speed. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Seismic demand models for probabilistic risk analysis of near fault vertical ground motion effects on ordinary highway bridges     

Zeynep Gulerce  Emrah Erduran  Sashi K. Kunnath  Norman A. Abrahamson 《地震工程与结构动力学》2012,41(2):159-175

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   

Inelastic displacement demands in steel structures and their relationship with earthquake frequency content parameters     

C. Málaga‐Chuquitaype  A. Y. Elghazouli 《地震工程与结构动力学》2012,41(5):831-852

This paper deals with the estimation of peak inelastic displacements of SDOF systems, representative of typical steel structures, under constant relative strength scenarios. Mean inelastic deformation demands on bilinear systems (simulating moment resisting frames) are considered as the basis for comparative purposes. Additional SDOF models representing partially‐restrained and concentrically‐braced (CB) frames are introduced and employed to assess the influence of different force‐displacement relationships on peak inelastic displacement ratios. The studies presented in this paper illustrate that the ratio between the overall yield strength and the strength during pinching intervals is the main factor governing the inelastic deformations of partially‐restrained models and leading to significant differences when compared with predictions based on bilinear structures, especially in the short‐period range. It is also shown that the response of CB systems can differ significantly from other pinching models when subjected to low or moderate levels of seismic demand, highlighting the necessity of employing dedicated models for studying the response of CB structures. Particular attention is also given to the influence of a number of scalar parameters that characterise the frequency content of the ground motion on the estimated peak displacement ratios. The relative merits of using the average spectral period T_aver, mean period T_m, predominant period T_g, characteristic period T_c and smoothed spectral predominant period T_o of the earthquake ground motion, are assessed. This paper demonstrates that the predominant period, defined as the period at which the input energy is maximum throughout the period range, is the most suitable frequency content scalar parameter for reducing the variability in displacement estimations. Finally, noniterative equivalent linearisation expressions based on the secant period and equivalent damping ratios are presented and verified for the prediction of peak deformation demands in steel structures. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Nonlocal period parameters of frequency content characterization for near-fault ground motions     

Dixiong Yang  Wei Wang 《地震工程与结构动力学》2012,41(13):1793-1811

This paper focuses on the frequency property analysis of near-fault ground motions with and without distinct pulses, separately from the Chi-Chi and Northridge earthquakes. Ten scalar period parameters of ground motions, especially several nonlocal period parameters, are considered. Two new nonlocal parameters, namely the mean period of Hilbert marginal spectrum (T_mh) and the improved characteristic period (T_gi), are suggested. Moreover, comprehensive comparison and analysis indicate that T_mh, T_gi and T_avg (average spectral period) can distinguish the low-frequency components of near-fault ground motions; T_m (mean period of Fourier amplitude spectrum) and T_o (smoothed spectral predominant period) represent the moderate- and high-frequency components, respectively. The variance coefficient of predominant instantaneous frequency of Hilbert spectrum (H_cov) can be regarded as an alternative index to measure the non-stationary degree of near-fault ground motions. Finally, the velocity pulses and earthquake magnitude remarkably affect the frequency parameters of near-fault ground motions. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Efficient risk assessment of lifeline networks under spatially correlated ground motions using selective recursive decomposition algorithm     

Hyun-Woo Lim  Junho Song 《地震工程与结构动力学》2012,41(13):1861-1882

For effective hazard mitigation planning and prompt-but-prudent post-disaster responses, it is essential to evaluate the reliability of infrastructure networks accurately and efficiently. A nonsimulation-based algorithm, termed as a recursive decomposition algorithm (RDA), was recently proposed to identify disjoint cut sets and link sets and to compute the network reliability. This paper introduces a ‘selective’ RDA, which preferentially identifies critical disjoint cut sets and link sets to calculate the probabilities of network disconnection events with a significantly reduced number of identified sets. To this end, the original RDA is improved by replacing the shortest path algorithm with an algorithm that identifies the most reliable path, and by using a graph decomposition scheme based on the probabilities associated with the subgraphs. The critical sets identified by the algorithm are also used to compute conditional probability-based importance measures that quantify the relative importance of network components by their contributions to network disconnection events. This paper also introduces a risk assessment framework for lifeline networks based on the use of the selective RDA, which can consider both interevent and intraevent uncertainties of spatially correlated ground motions. The risk assessment framework and the selective RDA are demonstrated by a hypothetical network example, and the gas and water transmission networks of Shelby County in Tennessee, USA. The examples show that the proposed framework and the selective RDA greatly improve efficiency of risk assessment of complex lifeline networks, which are characterized by a large number of components, complex network topology, and statistical dependence between component failures. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

The response of braided planform configuration to flow variations,bed reworking and vegetation: the case of the Tagliamento River,Italy     

Matilde Welber  Walter Bertoldi  Marco Tubino 《地球表面变化过程与地形》2012,37(5):572-582

Morphological features of braided rivers (bars, channels and pools) experience major changes in area, shape and spatial distribution as a response to (i) the pulsation of discharge during a flood and (ii) the bed evolution induced by floods. In this work, at‐a‐station relationships between water level and planform configuration were investigated on the Tagliamento River, a large gravel‐bed braided river in northeast Italy, over a 2‐year study period comprising three bankfull events and several small‐to‐medium floods. The analysis was performed on two 1‐km‐long reaches, characterized by different riparian vegetation cover. Ground‐based images with an hourly temporal resolution were acquired using software‐controlled, digital cameras. Bars, channels, pools and vegetated patches were manually digitized on more than 100 rectified images. Sequences of constant‐level images spanning the study period were used to quantify the impact of floods on the stability of at‐a‐station relationships and on the turnover rate of water bodies. The analysis shows that wetted area increased almost linearly with water level in both reaches. The average number of branches per cross‐section peaked at intermediate flow levels, increasing from 2 at low flow up to 6–7. The number of branches displayed the largest fluctuations over time, with significant changes produced also by moderate floods. Turnover rates were high in both reaches, with more than 30% of wetted areas at low flow converting into bare gravel in less than 2 months. Vegetation colonization was found to limit the mobility of the low flow channels over time by concentrating the flow in fewer, deeper anabranches. The number of channels per cross‐section was 30–40% less in the vegetated reach and the proportion of low flow water bodies in the same position after 12 months increased from 3% to 14%. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

汶川地震强地面运动模拟   总被引：3，自引：0，他引：3       下载免费PDF全文

常莹  周红  俞言祥 《地震学报》2012,34(2):224-234

基于确定性震源模型的方法主要用于计算低频(11 Hz)地震动常用经验格林函数法或随机方法,对低频地震动模拟不够准确．本文在确定性震源模型方法基础上,尝试采用分解给定的震源模型的方法来模拟宽频带(0.1——10 Hz)强地面运动,即采用分级离散断层面和分解断层面破裂单元上升时间的方法,增加震源时间函数中的高频信号,从而避免了对地震记录丰富程度和准确性的依赖．文中模拟计算了汶川MS8.0地震在8个地震观测台的地震动,将模拟结果和观测记录进行了加速度时程曲线和傅里叶振幅谱的对比分析．对比结果显示,模拟估计的地震动峰值加速度和持续时间与观测记录的数据基本在plusmn;50%的精度范围内相同,傅里叶振幅谱显示模拟结果有得到10 Hz左右的高频成分. 四川盆地中的台站模拟结果高频衰减比观测记录要快,原因是模拟过程没有考虑场地效应.对强地震动模拟还是要综合考虑震源、传播路径和场地的影响．研究结果表明,此改变震源输入的确定性方法可应用于模拟近断层宽频强地面运动．   相似文献   

Characterization of hydraulic suitability of Chinese sturgeon (Acipenser sinensis) spawning habitat in the Yangtze River   总被引：1，自引：0，他引：1  

Yuankun Wang  Ziqiang Xia  Dong Wang 《水文研究》2012,26(23):3489-3498

Hydrodynamic flow fields affect the ecological processes such as the water diversity and the distribution of organisms. Understanding the hydrodynamic and ecological processes is critical for the restoration and protection of especially fragile ecological habitats in river systems. This study uses turbulent flow to characterize the ecological behaviour of Chinese Sturgeon (Acipenser sinensis) in the Yangtze River. The Delft3D‐Flow model, which is first validated with field‐measured data, is used to simulate the flow field within spawning habitats of Chinese Sturgeon, downstream of Gezhouba Dam. The model‐simulated turbulent kinetic energy (TKE) and its distribution pattern are then used to characterize the hydraulic environment of the fish's spawning habitat. For the spawning habitat, downstream of Gezhouba Dam, the lower limit of TKE for the Chinese Sturgeon egg mass field is 0.025 m²/s², which occurs at a velocity less than 1.7 m/s. Chinese Sturgeon prefers habitats with TKE range of 0.010 ~ 0.015 m²/s² for resting. This suggests that discharge regimes provide the basis for ecological regulation of the Three Gorges Reservoir and the scientific reference for river management. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

破坏性地震的应急通信需求与应用初探   总被引：1，自引：0，他引：1  

赵恒  白仙富  张方浩  苗云西  陈征山 《地震研究》2012,35(1):139-144

通过分析MS5～6、MS7～8及MS8以上地震案例造成的地面通信受损规律,剖析不同震级地震应急通信的主体通讯业务,针对目前地震行业的通信技术系统现状,探讨了地震应急通信开展方式。  相似文献   

震后城市地震动场快速评估方法——以福州盆地为例     

丁海平  卜超鹏  杨朝辉 《地震工程与工程振动》2012,32(1):11-15

震后灾情的快速获取是灾后应急的基础,传统的方法是根据现场调查结果决定应急方案。受灾程度的分布常以烈度分布图描述,而烈度又与加速度峰值密切相关。本文提出了一种震后地震动场分布快速评估的方法。该方法将主要依据灾区基岩台站的实时强震记录(无强震记录也行)和该地区的加速度衰减关系,再结合该地区各类场地的地震动放大因子,则可快速估计该地区地震动场分布,从而确定灾情,为政府的应急决策提供依据。  相似文献