共查询到19条相似文献，搜索用时 171 毫秒
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不同地区黄土阻尼比变化特性试验研究 总被引：5，自引：0，他引：5
通过兰州、洛川、杨凌地区黄土在不同条件下的动扭剪三轴试验,研究了黄土阻尼比滞回圈形状变化的基本特性以及黄土阻尼比在不同固结压力、不同含水率条件下的变化规律。结果表明,黄土阻尼比滞回圈形状受动剪应变、含水率影响较明显;黄土阻尼比受一般的固结作用的影响并不大,但受含水率的影响较明显。根据含水率的不同,按照半对数坐标中的直线方程,分别给出了兰州、洛川、杨凌地区黄土阻尼比在不同固结压力下的拟合结果,并对拟合结果进行了对比分析;在此基础上,进一步对该三个地区黄土的阻尼比进行了汇总拟合,为西北相近地区黄土在中、大应变条件下的阻尼比取值提供了参考。 相似文献
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索网屋盖结构阻尼特性试验研究 总被引：3，自引：0，他引：3
为研究悬索结构阻尼特性进行了２．２５×３．００ｍ索网模型试验，探索了阻尼比幅度、阻尼比变化对地震动力内力、动力位移影响规律系列问题。综合试验与理论研究结果，对悬索结构抗震设计给出有效的结论。 相似文献
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窗函数对地基阻尼比测试的影响 总被引：1，自引：0，他引：1
根据某块体基础的实测数据,讨论了常见平滑方法对时域对数衰减法和频域点峰法竖向阻尼比测试的影响。结果表明,无论采用时域方法还是频域方法,分别对测试曲线进行相邻三点的滑动平均、汉宁窗、哈明窗平滑,阻尼比计算数值差别很小。平滑次数对时域阻尼比结果有影响,平滑次数越多,时域阻尼比有减少的趋势,而频域阻尼比有增大的趋势。滑动平均方法和平滑次数的合理选取,应通过理论和试验方法的研究进一步确定。 相似文献
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钢筋混凝土建筑非线性阻尼性能及阻尼比表达式研究 总被引：4，自引：0，他引：4
阻尼比是反映结构耗能能力的参数，它对结构的振动反应有重要的影响。目前结构设计阶段通常取阻尼比为常数，这不能真实反映建筑物的阻尼机理，与阻尼比的实测结果也有很大的差距。通过对建筑物阻尼机理、建筑材料、建筑物和建筑模型阻尼性能试验数据的分析，本文对混凝土强度、纵向配筋率、结构形式和结构变形大小等建筑阻尼性能的主要影响因素进行了分析。在此基础上，本文提出了钢筋混凝土结构非线性阻尼比的统一表达式。 相似文献
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对岷县地震台、庆阳黄土塬2~12m深度土层的粉土、粉质黏土样品,利用室内动三轴试验和扫描电镜试验,测定阻尼比和微观结构特征,研究了粉土、粉质黏土的阻尼比随深度的变化及应力应变关系,采用灰色关联度方法,分析了黄土竖向（沉积方向）和横向（垂直于沉积方向）的微观结构参数对阻尼比影响的主次关系及其权重。研究结果表明:小应变下,粉土和粉质黏土阻尼比随着深度的增加而减小;粉土和粉质黏土的微观参数与阻尼比有一定的关联性,粉土竖向的微观参数对阻尼比的影响较为敏感;粉质黏土横向的微观参数对阻尼比的影响更加敏感;影响权重方面,粉质黏土的平均形状系数影响权重最大,对阻尼比的影响最大;粉土的平均形状系数、分形维数和概率熵影响权重最大,对阻尼比影响最敏感。平均面积无论在关联度还是影响权重方面对阻尼比影响最小,该结论粉土与粉质黏土保持一致。 相似文献
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研究屈曲约束支撑半刚性连接框架弹塑性位移计算方法,为这种结构抗震设计提供依据.推导了屈曲约束支撑半刚性连接框架结构侧移刚度计算方法,通过计算屈曲约束支撑和半刚性连接在罕遇地震作用下的有效阻尼比,修正弹性设计反应谱,再利用修正后的设计反应谱进行结构弹塑性层间位移简化计算.通过与弹塑性时程分析对提出的计算方法进行验证.基于有效阻尼比的思想给出的弹塑性位移的简化计算方法可进行屈曲约束支撑半刚性连接框架罕遇地震下的抗震设计. 相似文献
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桥梁高阻尼橡胶支座力学性能试验研究 总被引：11，自引：3，他引：8
目前高阻尼橡胶支座在国内桥梁工程建设中使用尚处于起步阶段。本文对高阻尼橡胶支座的力学性能进行了系统的试验研究,研究了该支座的竖向刚度、水平刚度、阻尼比及水平剪切大变形等。该支座的推广应用,将使桥梁结构在地震(中震、大震)时降低地震作用力,对整体结构能进行限位,有效地控制桥梁结构的地震反应,达到桥梁结构隔震减震的目的,弥补我国桥梁结构中现在所用支座之不足,同时可降低成本,节省使用空间,便于施工。 相似文献
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针对广西上林县原状红黏土开展一系列循环加载动三轴试验,分析天然含水率、围压与固结应力比等对红黏土动力特性,包话动应力-动应变关系、动弹性模量以及阻尼比等的影响来研究循环荷载作用下红黏土的动力特性。试验结果表明:广西原状红黏土动应力-动应变关系曲线接近双曲线;由于初始剪应力的影响,达到相同的动应变,在均压固结下所需的动应力比在偏压固结下所需动应力要小;动弹性模量随着动应变的增加而减小,且减小幅度随应变增加逐渐减小,初始应力状态对动弹性模量的影响最为显著;固结应力比、围压、含水率和振动次数等对阻尼比均有影响,综合反映在阻尼比随动应变增加而减小,阻尼比离散性较大,取值范围在0.05~0.20之间。利用Konder双曲线模型对试验数据进行拟合,得到相关参数,可为广西地区原状红黏土动力特性设计和数值计算提供一定的理论和参数支持。 相似文献
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等效阻尼比对基于位移的抗震设计的影响分析 总被引：3，自引：0，他引：3
等效阻尼比是基于位移抗震设计中确定等效周期的一个关键参数。通过对不同研究者提出的等效阻尼比模型进行比较研究,重点讨论了滞回模型、延性系数和等效周期对等效阻尼比的影响。结果表明,不同等效阻尼比模型的总体变化趋势是一致的;滞回模型对等效阻尼比有很大影响,Ramberg-Osgood模型的等效阻尼比是Flagshaped模型的2.56倍;等效阻尼比随着延性系数的增大而增大,尤其在μ=2～4范围内变化幅度最大;短周期与中长周期等效阻尼比相差2倍多,故等效周期小于1 s时,必须考虑其对等效阻尼比的影响。 相似文献
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J. X. ZHAO 《地震工程与结构动力学》1997,26(1):93-113
For the one-dimensional analysis of soft-soil layers on an elastic half-space, a general form of analytical solution is developed for converting radiation damping due to energy leaking back to the half-space into equivalent modal damping, allowing the modal analysis technique to be extended to a site where radiation damping has to be accounted for. Closed-form solutions for equivalent modal damping ratios and effective modal participation factors are developed for a single layer with a shear wave velocity distribution varying from constant to linearly increasing with depth. Compact and recursive forms of solutions for equivalent modal damping ratios are developed for a system with an arbitrary number of homogeneous layers on an elastic half-space. Comparisons with numerical solutions show that the modal solutions are accurate. The nominal frequency of a site, i.e. the inverse of four times the total shear wave travel time through the layers, is an important parameter for estimating the high mode frequencies. A parameter study shows that for the same impedance ratio of the bottom layer to the elastic half-space, a system of soil layers with an increasing soil rigidity with depth has, in general, larger peak modal amplifications at the ground surface than does a single homogeneous layer on an elastic half-space, while a system with a decreasing soil rigidity with depth has smaller modal peak amplifications. © 1997 by John Wiley & Sons, Ltd. 相似文献
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It is widely known that the seismic response characteristics of a soil site depends heavily on several key dynamic properties
of the soil stratum, such as predominant frequency and damping ratio. A widely used method for estimating the predominant
frequency of a soil site by using microtremor records, proposed by Nakamura, is investigated to determine its effectiveness
in estimating the damping ratio. The authors conducted some microtremor measurements of soil sites in Hong Kong and found
that Nakamura’s method might also be used to estimate the damping ratio of a soil site. Damping ratio data from several typical
soil sites were obtained from both Nakamura’s ratio curves using the half power point method and resonant column tests. Regression
analysis indicates that there is a strong correlation between the damping ratios derived from these two different approaches.
Supported by: Research project (PolyU 5076/97E), of the Department of Civil and Structural Engineering, The Hong Kong Polytechnic University 相似文献
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Grigori Muravskii 《地震工程与结构动力学》2000,29(4):399-418
The paper presents a study of time-harmonic surface waves in a linearly inhomogeneous half-space. The study is based on the solution of that problem for an arbitrary (from 0 to 1/2) value of Poisson's ratio. Vertical vibrations due to a vertical harmonic force, which at large distances from the force represent Rayleigh-type waves, and transverse horizontal vibrations due to a horizontal force, which at large distances form waves of Love's type, are considered in detail. Material damping is taken into consideration. Inhomogeneity significantly affects relationships connecting wave characteristics and the frequency of vibration, and it is shown in the paper how this fact can be used for determining material properties (surface shear modulus, degree of inhomogeneity, damping ratio) with the help of experimental results concerning wave propagation over the surface of the half-space. It is shown that for forced waves the relationship between the wave phase angle and distance can significantly differ from a straight line, i.e. the wave number varies with distance. Therefore, it is desirable to relate experimental and theoretical results to such parts of wave propagation line, which correspond to same phase angle intervals. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
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The Seismic Cone Penetration Test (SCPT) is used to determine the variation with depth of the shear (and longitudinal) wave velocity at various sites in Belgium. The cross correlation technique together with a posteriori increase of the sampling frequency proves to be a reliable method to determine wave velocities by the SCPT. Additionally, the Spectral Ratio Slope (SRS) method is applied to Fourier transforms of the measured response to determine the variation of the material damping ratio with depth. This method is applied to synthetic signals computed for three different soil profiles with known characteristics and to the horizontal acceleration time histories that have been measured during SCPT on two sites. The influence of some signal processing techniques commonly applied in the SRS method is studied. A remarkable influence of the window length, applied on the predicted signals, on the computed material damping ratio is found, especially its scattering. It is therefore concluded that the use of a window function should be avoided wherever possible. On one of the two test sites, results of Resonant Column Tests and Free Torsion Pendulum Tests on undisturbed soil samples have been used to evaluate the values of the shear wave velocity and the material damping ratio as obtained in the in situ test. 相似文献
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Correction factors for SSI effects predicted by simplified models: 2D versus 3D rectangular embedded foundations 
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下载免费PDF全文 The effects of soil‐structure interaction (SSI) are often studied using two‐dimensional (2D) or axisymmetric three‐dimensional (3D) models to avoid the high cost of the more realistic, fully 3D models, which require 2 to 3 orders of magnitude more computer time and storage. This paper analyzes the error and presents correction factors for system frequency, system damping, and peak amplitude of structural response computed using impedances for linear in‐plane 2D models with rectangular foundations, embedded in uniform or layered half‐space. They are computed by comparison with results for 3D rectangular foundations with the same vertical cross‐section and different aspect ratios. The structure is represented by a single degree‐of‐freedom oscillator. Correction factors are presented for a range of the model parameters. The results show that in‐plane 2D approximations overestimate the SSI effects, exaggerating the frequency shift, the radiation damping, and the reduction of the peak amplitude. The errors are larger for stiffer, taller, and heavier structures, deeper foundations, and deeper soil layer. For example, for a stiff structure like Millikan library (NS response; length‐to‐width ratio ≈ 1), the error is 6.5% in system frequency, 44% in system damping, and 140% in peak amplitude. The antiplane 2D approximation has an opposite effect on system frequency and the same effect on system damping and peak relative response. Linear response analysis of a case study shows that the NEHRP‐2015 provisions for reduction of base shear force due to SSI may be unsafe for some structures. The presented correction factor diagrams can be used in practical design and other applications. 相似文献
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Many laminar shear boxes have recently been developed into sliding-frame containers that can reproduce 1D ground-response boundary conditions. The measured responses of such large specimens can be utilized to back-calculate soil properties. This study investigates how the boundary effect in large specimens affects the identified soil properties through shaking table tests on a soil-filled large laminar box conducted at the National Center for Research on Earthquake Engineering in Taiwan. The tested soil-box system is unique because only 80% of the container is filled with soil. This system can be regarded as a two-layer system: an empty top and soil-filled bottom. The dynamic properties of this two-layer system are identified through various approaches, including theoretical solutions of wave propagation, free vibration, and nonparametric stress–strain analyzes. Therefore, the coupling effect of the box and soil can be evaluated. Results show that, compared with the two-layer system considering the influence of the box, the conventional approach with a single-layer system slightly underestimates shear wave velocity but obtains the same damping ratio of the soil layer. In addition, the identified modulus reduction and damping curves in the two-layer system are consistent with those obtained in a laboratory test on a small specimen. Furthermore, based on detailed acceleration measurements along different depths of soil, a piecewise profile of shear wave velocity is built. The identified shear wave velocity increases with depth, which is not uniform and differs from the constant velocity typically assumed for the specimen. 相似文献
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Cones can be used to model soil in a unified strength-of-materials approach. For the vertical and rocking motions involving predominantly compressional-extensional deformation, the corresponding dilatational wave velocity tends to infinity for Poisson's ratio approaching 1/2. Based on the rigorous solution for the dynamic stiffness of a rigid disk for all frequencies, whereby the partition of the power among P-, S- and Rayleigh waves is also discussed, two special features are necessary for the vertical and rocking motions for nearly incompressible soil with Poisson's ratio between 1/3 and 1/2: (1) The appropriate wave velocity is selected as twice the shear wave velocity and not as the dilatational wave velocity; (2) A trapped mass which increases linearly with Poisson's ratio is introduced. The trapped mass can be assigned to the base mat, allowing the cone model to be constructed in the same way for all Poisson's ratios. The realization of cone models for surface foundations on a homogeneous half-space and on a layer on a flexible half-space and for embedded and pile foundations is addressed. 相似文献
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