采用板式橡胶支座的连续斜梁桥横向抗震行为研究          下载免费PDF全文

姚凯  徐略勤  李建中  龚恋 《地震工程学报》2018,40(2):265-272

为了提高采用板式橡胶支座的斜梁桥横向抗震能力,揭示其在不同设计参数下的横向抗震行为,考虑板式橡胶支座的滑移、钢筋混凝土挡块的滞回力学性能、桥台-背土效应等非线性因素,采用OpenSEES建立某连续斜梁桥的三维分析模型,提出支座位移评价指标、主梁平面转角指标、墩柱曲率延性指标和抗剪指标,研究不同挡块强度和间隙组合下桥梁的横向抗震性能。研究表明:同时增大挡块强度和间隙,总体上会降低支座的横向变形,但会增加其纵向变形;挡块强度越高,主梁的横向位移有所下降,但平面转角越大,对两侧桥台处的支座抗剪越不利;挡块强度越高,间隙越小,墩柱越有可能进入弹塑性状态。在本文桥例中,当挡块强度取40%支反力,间隙取0.08m时,所有抗震指标都可满足规范要求。  相似文献   

薄互层弹性波反演面临的困境   总被引：2，自引：0，他引：2       下载免费PDF全文

王赟  杨春  芦俊 《地球物理学报》2018,61(3):1118-1135

对于薄互层地震传播特征的研究我们已有了充分的认识,这是一种完全不同于现有的基于厚层单阻抗差界面地震反射理论的、具有频率依赖性的调谐反射.因而也使得对具有N层结构的弹性介质薄互层反演时,现有有限带宽的基于空间-频率域采样的地震观测难以规避多解性问题.长波长假设下的薄互层VTI近似似乎可以为我们提供一种待反演弹性参数只有5个的可行性方案,使得我们可以将薄互层背景下任一目标薄层的反演看作VTI厚层介质背景下单薄层的反演.但是,我们首先面临薄互层VTI近似的误差和适用性条件等问题;其次,既使对于单薄层厚度的反演,目前地震领域也未能提供一种通用有效的解决方案,实际地震勘探中薄层厚度的预测依然是一个悬而未决的难题.因此在此基础上再进行单薄层的物性参数、裂缝隙和流体的预测则更叠加了难以预知的多解性.显然单纯P波已难以应对,弹性波的介入成为必然;而且单薄层含裂缝与流体的预测更需要横波分裂和双相介质理论的支撑.可以预见的是,除了纵、横波速度,薄互层反射系数的频率依赖性是我们试图给出相对可靠的、单薄层物性精细刻画必须使用的一种重要地震属性.  相似文献   

Early‐stage aeolian protodunes: Bedform development and sand transport dynamics          下载免费PDF全文

Matthew C. Baddock  Joanna M. Nield  Giles F.S. Wiggs 《地球表面变化过程与地形》2018,43(1):339-346

Early‐stage aeolian bedforms, or protodunes, are elemental in the continuum of dune development and act as essential precursors to mature dunes. Despite this, we know very little about the processes and feedback mechanisms that shape these nascent bedforms. Whilst theory and conceptual models have offered some explanation for protodune existence and development, until now, we have lacked the technical capability to measure such small bedforms in aeolian settings. Here, we employ terrestrial laser scanning to measure morphological change at the high frequency and spatial resolution required to gain new insights into protodune behaviour. On a 0.06 m high protodune, we observe vertical growth of the crest by 0.005 m in two hours. Our direct measurements of sand transport on the protodune account for such growth, with a reduction in time‐averaged sediment flux of 18% observed over the crestal region. Detailed measurements of form also establish key points of morphological change on the protodune. The position on the stoss slope where erosion switches to deposition is found at a point 0.07 m upwind of the crest. This finding supports recent models that explain vertical dune growth through an upwind shift of this switching point. Observations also show characteristic changes in the asymmetric cross‐section of the protodune. Flow‐form feedbacks result in a steepening of the lee slope and a decline in lower stoss slope steepness (by 3°), constituting a reshaping of protodune form towards more mature dune morphology. The approaches and findings applied here, (a) demonstrate an ability to quantify processes at requisite spatial and temporal scales for monitoring early‐stage dune evolution, (b) highlight the crucial role of form‐flow feedbacks in enabling early‐stage bedform growth, alluding to a fluctuation in feedbacks that require better representation in dune models, and (c) provide a new stimulus for advancing understanding of aeolian bedforms. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

Flow structure in large bedrock-channels: The example of macroturbulent rapids,lower Mekong River,Southeast Asia     

Paul A. Carling  He Qing Huang  Teng Su  Duncan Hornby 《地球表面变化过程与地形》2019,44(4):843-860

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Seismoelectric numerical simulation in 2D vertical transverse isotropic poroelastic medium     

Munirdin Tohti  Yibo Wang  Evert Slob  Yikang Zheng  Xu Chang  Yi Yao 《Geophysical Prospecting》2020,68(6):1927-1943

Seismoelectric coupling in an electric isotropic and elastic anisotropic medium is developed using a primary–secondary formulation. The anisotropy is of vertical transverse isotropic type and concerns only the poroelastic parameters. Based on our finite difference time domain algorithm, we solve the seismoelectric response to an explosive source. The seismic wavefields are computed as the primary field. The electric field is then obtained as a secondary field by solving the Poisson equation for the electric potential. To test our numerical algorithm, we compared our seismoelectric numerical results with analytical results obtained from Pride's equation. The comparison shows that the numerical solution gives a good approximation to the analytical solution. We then simulate the seismoelectric wavefields in different models. Simulated results show that four types of seismic waves are generated in anisotropic poroelastic medium. These are the fast and slow longitudinal waves and two separable transverse waves. All of these seismic waves generate coseismic electric fields in a homogenous anisotropic poroelastic medium. The tortuosity has an effect on the propagation of the slow longitudinal wave. The snapshot of the slow longitudinal wave has an oval shape when the tortuosity is anisotropic, whereas it has a circular shape when the tortuosity is isotropic. In terms of the Thomsen parameters, the radiation anisotropy of the fast longitudinal wave is more sensitive to the value of ε, while the radiation anisotropy of the transverse wave is more sensitive to the value of δ.  相似文献   

楔形挡块对中小跨径梁桥横向抗震性能的影响          下载免费PDF全文

赵竞  项长生  周宇  刘桂山 《地震工程学报》2020,42(1):22-31

在地震作用下中小跨径梁桥横向易出现落梁以及桥墩破坏。为了防止桥梁出现上述震害,提出以楔形挡块作为限位装置来提升桥梁的横向抗震性能。以一座3×20 m连续混凝土梁桥为例,通过OpenSees软件来建立有限元模型,在考虑板式橡胶支座的摩擦滑移效应、钢筋混凝土桥墩的非线性等力学效应的情况下,对其进行动力时程分析。引入主梁位移响应、桥墩顶部最大位移响应等作为指标,用柔性挡块、刚性挡块两种工况来与楔形挡块进行对比分析,并且分析楔形挡块不同角度对位移响应的影响。结果表明:楔形挡块角度设置合适时能够有效约束梁体位移响应,并且不显著提高桥墩顶部的位移响应。  相似文献   

Analyses of iron oxide assemblages within Namib dune sediments using high field remanence measurements (9 T) and Mössbauer analysis     

John Walden  Kevin H. White  Susan H. Kilcoyne  Phillip M. Bentley 《第四纪科学杂志》2000,15(2):185-195

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Dunefield Activity and Interactions with Climatic Variability in the Southwest Kalahari Desert     

J. E. Bullard  D. S. G. Thomas  I. Livingstone  G. S. F. Wiggs 《地球表面变化过程与地形》1997,22(2):165-174

An analysis is undertaken of the temporal variability of climatic parameters that influence dunefield aeolian activity. Data from seven meteorological stations in the southwestern Kalahari Desert are used, spanning the period 1960–1992. Erosivity is considered through analysis of wind data, and erodibility through analysis of precipitation and potential evapotranspiration, which together influence dune surface plant growth. The data are integrated using Lancaster's ‘mobility’ index which provides a measure of potential dune surface sand transport. This is renamed ‘potential dune surface activity index’, to reflect the actual characteristic that is measured. The subsequent analysis indicates that dunefield activity is episodic and temporally variable, that both erosivity and erodibility vary through time, and that present levels of activity cannot be characterized by a single simple state. © 1997 by John Wiley & Sons, Ltd.  相似文献   

Crescentic dunes at Schiermonnikoog,The Netherlands     

Patrick A. Hesp  Sebastiaan M. Arens 《地球表面变化过程与地形》1997,22(8):785-788

This paper describes the appearance and maintenance of crescentic dunes in high wind speed conditions on a frozen beach at Schiermonnikoog, The Netherlands. The dunes were cresentic forms with horns. They were barchanoidal in plan view, but had reverse morphologies to typical barchans: the highest and steepest slopes were upwind and led to long low slopes downwind. Slipfaces were absent. It is hypothesized that such crescentic dunes may be a stable aerodynamic form under high to very high (c. 15–20 m s⁻¹) flow conditions. © 1997 by John Wiley & Sons, Ltd.  相似文献   

Evolution of anisotropy with saturation and its implications for the elastoplastic responses of clay rocks     

Sabrina C.Y. Ip  Ronaldo I. Borja 《国际地质力学数值与分析法杂志》2022,46(1):23-46

Many clay rocks have distinct bedding planes. Experimental studies have shown that their mechanical properties evolve with the degree of saturation (DOS), often with higher stiffness and strength after drying. For transversely isotropic rocks, the effects of saturation can differ between the bed-normal (BN) and bed-parallel (BP) directions, which gives rise to saturation-dependent stiffness and strength anisotropy. Accurate prediction of the mechanical behavior of clay rocks under partially saturated conditions requires numerical models that can capture the evolving elastic and plastic anisotropy with DOS. In this study, we present an anisotropy framework for coupled solid deformation-fluid flow in unsaturated elastoplastic media. We incorporate saturation-dependent strength anisotropy into an anisotropic modified Cam-Clay (MCC) model and consider the evolving anisotropy in both the elastic and plastic responses. The model was calibrated using experimental data from triaxial tests to demonstrate its capability in capturing strength anisotropy at various levels of saturation. Through numerical simulations, we demonstrate the role of evolving stiffness and strength anisotropy in the mechanical behavior of clay rocks. Plane strain simulations of triaxial compression tests were also conducted to demonstrate the impacts of material anisotropy and DOS on the mechanical and fluid flow responses.  相似文献