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1.
Influences of type of wave and angle of incidence on seismic bending moments in pile foundations 
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下载免费PDF全文 When analysing the seismic response of pile groups, a vertically‐incident wavefield is usually employed even though it does not necessarily correspond to the worst case scenario. This work aims to study the influences of both the type of seismic body wave and its angle of incidence on the dynamic response of pile foundations. To this end, the formulation of SV, SH and P obliquely‐incident waves is presented and implemented in a frequency‐domain boundary element‐finite element code for the dynamic analysis of pile foundations and piled structures. Results are presented in terms of bending moments at cap level of single piles and 3 × 3 pile groups, both in frequency and in time domains. It is found that, in general, the vertical incidence is not the most unfavourable situation. In particular, obliquely‐incident SV waves with angles of incidence smaller than the critical one, a situation in which the mechanism of propagation of the waves in the soil changes and surface waves appear, yield bending moments much larger than those obtained for vertically‐incident wavefields. It is also shown that the influence of pile‐to‐pile interaction on the kinematic bending moments becomes significant for non‐vertical incidence, especially for P and SV waves. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
2.
The influence of stochastic kinematic interaction (SKI) on structural response is investigated in this paper. The SKI is evaluated through a computational model based on the boundary element method (BEM) formulated in the frequency domain. The singular integrals required in the computation of BEM are evaluated in a closed form. It is assumed that the foundation input motion (FIM) is the result of the superposition of many plane, stationary, correlated stochastic SH‐, P‐ and SV‐waves travelling within a homogeneous viscoelastic soil at different angles. The results obtained indicate that the effect of SKI on the foundation response is qualitatively similar to that of wave passage. Both effects involve a reduction of translational components of the response at intermediate and high frequencies and creation of a rotational response component at intermediate frequencies, which decreases at high frequencies. While, it is found that the SKI decreases the maximum response of structures built on embedded rigid strip foundations excited by SH‐ and P‐waves, it increases the maximum response for SV‐waves, except when the natural frequency of the structure is less than 0.5 Hz and for short structures excited by shallowly incident SV‐waves. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
3.
弹性层状半空间中凸起地形对入射平面SH波的放大作用 总被引：7，自引：0，他引：7
对Wolf理论进行拓展,使之可解决凸起地形对波的散射问题,进而利用间接边界元法,求解了弹性层状半空间中凸起地形对入射平面SH波的放大作用问题。本文模型的显著特点之一是考虑了层状半空间的动力特性以及层状半空间和凸起地形的阻尼;特点之二是计算精度高。文中以基岩上单一土层中半圆凸起地形对入射平面SH波的放大作用为例进行了数值计算分析。研究表明,基岩上单一土层中凸起地形对入射平面SH波放大作用和均匀半空间中凸起地形有着本质的差别;土层动力特性不仅影响凸起地形地表位移的幅值,还会影响地表位移的频谱;阻尼会显著降低凸起地形对高频波的放大作用。 相似文献
4.
Amplitudes of surface particle velocities are calculated when time-harmonic seismic waves of uniform amplitude are incident upon an arbitrary stratified elastic soil layer from the underlying bedrock. Whereas previous workers have mainly treated normally incident S waves, we allow the waves to be of SV, P, or SH types and to have arbitrary angles of incidence. Following standard practice the problem is set up as a matrix differential system, but in such a way that incident SV and P waves may be treated together (the system for SH decoupling). Though complicated, the 4 × 4 SVP system has considerable structure which is elucidated in Appendices 1 and 2. These results, though not altogether new, are of independent interest, and are gathered together in concise form for reference. The theory for low- and for high-frequency approximations is given. The main results of the work are illustrated by two numerical examples: Model 1 where the soil layer is homogeneous; and Model 2 where the soil layer has a linear velocity profile. 相似文献
5.
Steady state scattering of incident P, SV, SH and Rayleigh waves by general non-axisymmetric three dimensional dipping layers is investigated by using an indirect boundary integral equation method. Material of the half-space and the layer is assumed to be linear, weakly anelastic, homogeneous and isotropic. Systematic comparisons between three dimensional and two dimensional models demonstrate that the validity of a two dimensional approximation for a given basin shape may be affected strongly by changes in azimuthal angle of incidence, type of incident wave and frequency. The discrepancies of two dimensional modelling appear to be much more pronounced for the case of an incident SH wave. Another important feature of the results is the existence of strong coupling between P/SV and SH modes, which has no correspondence in two dimensional models. Such off-azimuthal mode conversions are particularly strong for an incident SH wave. 相似文献
6.
Doriam Restrepo Juan David Gómez Juan Diego Jaramillo 《Pure and Applied Geophysics》2014,171(9):2185-2198
We present a closed-form frequency-wave number (ω – k) Green’s function for a layered, elastic half-space under SH wave propagation. It is shown that for every (ω – k) pair, the fundamental solution exhibits two distinctive features: (1) the original layered system can be reduced to a system composed by the uppermost superficial layer over an equivalent half-space; (2) the fundamental solution can be partitioned into three different fundamental solutions, each one carrying out a different physical interpretation, i.e., an equivalent half-space, source image impact, and dispersive wave effect, respectively. Such an interpretation allows the proper use of analytical and numerical integration schemes, and ensures the correct assessment of Cauchy principal value integrals. Our method is based upon a stiffness-matrix scheme, and as a first approach we assume that observation points and the impulsive SH line-source are spatially located within the uppermost superficial layer. We use a discrete wave number boundary element strategy to test the benefits of our fundamental solution. We benchmark our results against reported solutions for an infinitely long circular canyon subjected to oblique incident SH waves within a homogeneous half-space. Our results show an almost exact agreement with previous studies. We further shed light on the impact of horizontal strata by examining the dynamic response of the circular canyon to oblique incident SH waves under different layered half-space configurations and incident angles. Our results show that modifications in the layering structure manifest by larger peak ground responses, and stronger spatial variability due to interactions of the canyon geometry with trapped Love waves in combination with impedance contrast effects. 相似文献
7.
In this paper, antiplane response of an isosceles triangular hill to incident SH waves is studied based on the method of complex
function and by using moving coordinate system. The standing wave function, which can satisfy the governing equation and boundary
condition, is provided. Furthermore, numerical examples are presented; the influences of wave number and angle of the incident
waves and the angle of the hill's peak on ground motion are discussed. 相似文献
8.
In this paper, antiplane response of an isosceles triangular hill to incident SH waves is studied based on the method of complex function and by using moving coordinate system. The standing wave function, which can satisfy the governing equation and boundary condition, is provided. Furthermore, numerical examples are presented; the influences of wave number and angle of the incident waves and the angle of the hill‘s peak on ground motion are discussed. 相似文献
9.
In this paper we analyse the two-dimensional scattering and diffraction of plane SH waves by a semi-elliptical canyon. The exact series solution of the problem, for general angle of incidence of the plane SH waves, has been used to examine the dependence of surface amplifications inside and near the canyon. The nature of ground motion has been found to depend on two key parameters: (a) The angle of incidence. (b) The ratio of the canyon width to the wave length of incident SH waves. For short incident waves surface displacement amplitudes change rapidly from one point to another, while for the long waves and shallow canyons displacement amplitudes display only minor departure from the uniform half-space amplification of 2. For shallow canyons and long incident waves, the angle of incidence introduces only minor changes into the overall behaviour of surface amplitudes. For deep canyons and nearly grazing incidences, a prominent shadow zone is realized behind the canyon. 相似文献
10.
Seismic stability of slopes has been traditionally analyzed with vertically propagated earthquake waves. However, for rock slopes, the earthquake waves might approach the outcrop still with a evidently oblique direction. To investigate the impact of obliquely incident earthquake excitations, the input method for SV and P waves with arbitrary incident angles is conducted, respectively, by adopting the equivalent nodal force method together with a viscous-spring boundary. Then, the input method is introduced within the framework of ABAQUS software and verified by a numerical example. Both SV and P waves input are considered herein for a 2D jointed rock slope. For the jointed rock mass, the jointed material model in ABAQUS software is employed to simulate its behavior as a continuum. Results of the study show that the earthquake incident angles have significance on the seismic stability of jointed rock slopes. The larger the incident angle, the greater the risk of slope instability. Furthermore, the stability of the jointed rock slopes also is affected by wave types of earthquakes heavily. P waves induce weaker responses and SV waves are shown to be more critical. 相似文献
11.
弹性层状半空间中沉积谷地对入射平面SH波的放大作用 总被引：9，自引：3，他引：6
对Wolf理论进行拓展,使之可解决沉积谷地对波的散射问题,进而利用间接边界元法,求解了弹性层状半空间中沉积谷地对入射平面SH波的放大作用问题。通过自由场反应分析,求得假想边界上各点的位移和各单元的应力反应。施加虚拟均布荷载,求得位移和应力的格林函数。根据应力和位移连续边界条件确定虚拟分布荷载,将自由场反应和虚拟分布荷载产生的反应叠加起来,即得到问题的解答。最后,以基岩上单一土层中沉积谷地对入射平面SH波的放大作用为例进行了数值计算分析,结果表明,层状半空间中沉积谷地和均匀半空间中沉积谷地对波的放大作用存在显著差别。文中分析了造成差别的原因,并讨论了覆盖层厚度和刚度对放大作用的影响。 相似文献
12.
Propagation in the plane of mirror symmetry of a monoclinic medium, with displacement normal to the plane, is the most general circumstance in anisotropic media for which pure shear-wave propagation can occur at all angles. Because the pure shear mode is uncoupled from the other two modes, its slowness surface in the plane is an ellipse. When the mirror symmetry plane is vertical the pure shear waves in this plane are SH waves and the elliptical SH sheet of the slowness surface is, in general, tilted with respect to the vertical axis. Consider a half-space of such a monoclinic medium, called medium M, overlain by a half-space of isotropic medium I with plane SH waves incident on medium M propagating in the vertical symmetry plane of M. Contrary to the appearance of a lack of symmetry about the vertical axis due to the tilt of the SH-wave slowness ellipse, the reflection and transmission coefficients are symmetrical functions of the angle of incidence, and further, there exists an isotropic medium E with uniquely determined density and shear speed which gives exactly the same reflection and transmission coefficients underlying medium J as does monoclinic medium M. This means that the underlying monoclinic medium M can be replaced by isotropic medium E without changing the reflection and transmission coefficients for all values of the angle of incidence. Thus no set of SH seismic experiments performed in the isotropic medium in the symmetry plane of the underlying half-space can reveal anything about the monoclinic anisotropy of that underlying half-space. Moreover, even when the underlying monoclinic half-space is stratified, there exists a stratified isotropic half-space that gives the identical reflection coefficient as the stratified monoclinic half-space for all angles of incidence and all frequencies. 相似文献
13.
Scattering of elastic waves by two dimensional multilayered dipping sediments of arbitrary shape embedded in an elastic half-sapce is investigated by using a bondary method. The displancement field is evaluated throughout the elastic media for both steady state and transient incident SH waves. The unknown scattered field is expressed in terms of wave functions which satisfy the equation of motion, traction-free boundary condition and appropariate radiation conditions. The transient response is constructed from the steady state solution by using the fast Fourier transform technique. The numerical results presented demonstrate that scattering of waves by subsurface irregularities may cause locally very large amplification of surface ground motion. The motion can be affected greatly by the scattered surface waves in the sediments. The results clearly indicate that the surface ground motion depends upon a number of parameters present in the problem, such as frequency and the angle of incidence of the incoming wave, impedance contrast between the layers and location of the observation point. 相似文献
14.
Scattering of elastic waves by three-dimensional canyons embedded within an elastic half-space is investigated by using a wave function expansion technique. The geometry of the canyon is assumed to be non-axisymmetric. The canyon is subjected to incident plane Rayleigh waves and oblique incident SH, SV and P waves. The unknown scattered wavefield is expressed in terms of spherical wave functions which satisfy the equations of motion and radiation conditions at infinity, but they do not satisfy stress-free boundary conditions at the half-space surface. The boundary conditions are imposed locally in the least-squares sense at several points on the surface of the canyon and the half-space. Through a comparative study the validity and limitations of two-dimensional approximations (antiplane strain and plane strain models) have been examined. It is shown that scattering of waves by three-dimensional canyons may cause substantial change in the surface displacement patterns in comparison to the two-dimensional models. These results emphasize the need for three-dimensional modelling of realistic problems of interest in strong ground motion seismology and earthquake engineering. 相似文献
15.
A closed-form analytical solution of surface motion of a semi-elliptical cylindrical hill for incident plane SH waves is presented. Although some previous analytical work had already dealt with hill topography of semi-circular and shallow circular, our work aims at calculating surface motion of very prolate hill for high incident frequency, and explaining the special vibrating properties of very prolate hill. Accuracy of the solution is checked by boundary conditions, numerical results for surface motion of oblate and prolate hills are calculated, and some conclusions are obtained. 相似文献
16.
弹性孔隙介质分界面上的反透射系数特征,在岩性划分、流体识别、储层边界判识等方面有重要的应用.本文研究上层为含两项不混合黏性流体孔隙介质、下层为含单项黏性流体孔隙介质分界面上的反透射理论.首先根据两种孔隙介质分界面上的能量守恒得到边界条件,再将波函数、位移、应力与应变关系代入边界条件,推导出完全连通孔隙情况下,第一类纵波入射到孔隙介质分界面上的反透射系数方程.通过建立砂岩孔隙介质模型,分别分析不同孔隙流体类型、不同含油饱和度及不同入射角情况下,各类波的反透射系数特征.研究表明,第二、三类纵波反透射系数数值比第一类纵波小多个数量级,且两者对入射角的变化不敏感,但对孔隙流体性质、含油饱和度的变化较敏感,而横波反透射系数特征恰好与此相反;第一类纵波反透射系数特征比较复杂,入射角、孔隙流体的性质及含油饱和度的变化都对其产生影响.不同孔隙流体弹性物性的差异、孔隙介质中含油饱和度的变化及不同入射角引起垂向和切向应力分量的变化都会影响各类波的反透射系数特征,分析这些特征可以为研究储层含油气性提供理论基础. 相似文献
17.
The impact of the incident angle of earthquake motion on the seismic response of the long lined tunnels is studied. Based on the time‐domain finite element method with the viscous‐spring artificial boundary condition, the earthquake motion of oblique incidence is transformed into the equivalent nodal forces acting on the truncated boundary of finite element model. In the present work, the formulas of equivalent nodal forces for the plane P wave with arbitrary incident angle are deduced and implemented into the commercial software abaqus 1 . The effectiveness of the formulas and its implementation are demonstrated by two numerical examples with the reference solutions. The proposed method is applied to investigate the seismic responses of the long lined tunnels under the obliquely incident P waves. The numerical results indicate that the seismic responses of the long lined tunnels are highly affected by the incident angles of P waves. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
18.
The dynamic soil-tunnel interaction is studied by indirect boundary element method (IBEM), using the model of a rigid tunnel in layered half-space, which is simplified to a single soil layer on elastic bedrock, subjected to incident plane SH waves. The accuracy of the results is verified through comparison with the analytical solution. It is shown that soil-tunnel interaction in layered half-space is larger than that in homogeneous half-space and this interaction mechanism is essentially different from that of soil-foundation-superstructure interaction. 相似文献
19.
M. D. Trifunac 《地震工程与结构动力学》1972,1(3):267-281
The two-dimensional scattering and diffraction of plane SH waves by a semi-cylindrical canyon is analysed for a general angle of wave incidence. The closed-form solution of the problem shows that the surface topography can have prominent effects on incident waves only when the wavelengths of incident motion are short compared to the radius of a canyon. The surface amplification of displacement amplitudes around and in the canyon changes rapidly from one point to another, but the amplification is always less than 2. The over-all trends of amplification pattern are determined by two principal parameters: (1) γ, the angle of incidence of plane SH waves, and (2) η, the ratio of radius of the canyon to one-half wave length of incident waves. The higher η leads to greater complexity of the pattern of surface displacement amplitudes characterized by more abrupt changes of amplification from one point to another, while γ mainly determines the over-all trends of displacement amplitudes. For grazing and nearly grazing incidences, for example, a strong shadow zone is developed behind the canyon. The qualitative analysis of the topographic effects on the Pacoima Dam accelerogram,1 based on the semi-cylindrical canyon, suggests that this strong-motion record was not seriously affected by surface topography of the recording site. 相似文献
20.
常规完全匹配吸收边界(PML)对以近掠射角入射到界面上的波以及低频波、损耗波都会产生虚假边界反射.基于递归积分的不分裂复频移PML算法,利用复频移拉伸函数,极大地改善了PML边界条件的性能,我们进一步推导出基于递归积分的不分裂复频移PML弹性波方程交错网格高阶差分法,对长条形介质模型进行数值模拟,与常规PML算法进行比较说明该算法对以掠射角入射到PML界面的波以及PML层内损耗波的吸收效果. 相似文献