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1.
Stresses and excess pore pressure induced in saturated poroelastic halfspace by moving line load 总被引：2，自引：0，他引：2
This paper examines stresses and excess pore fluid pressure that are induced in a saturated poroelastic soil of halfspace extent by a concentrated line load. The line load is moving at a constant velocity along the surface of the poroelastic halfspace. The governing equations for the proposed analysis are based on the Biot's theory of dynamics in saturated poroelastic soils. The governing partial differential equations are solved using Fourier transforms. The solutions for the stresses and excess pore pressure are expressed in the forms of inverse Fourier transforms. The numerical results are obtained by performing the numerical inversion of the transform integrals. A parametric study is presented to illustrate the influences of the velocity of moving load and the poroelastic material parameters on the stresses and excess pore pressure. At a high velocity, the maximum values of the stresses in a poroelastic halfspace are smaller than those in an elastic solid, whilst at a low velocity the stresses in a poroelastic halfspace are larger than those in an elastic halfspace. The potential of diffusivity has an important influence on the stresses and excess pore pressure. 相似文献
2.
Christopher Bode Reinhold Hirschauer Stavros A. Savidis 《Soil Dynamics and Earthquake Engineering》2002,22(4)
A time-domain formulation is proposed for the transient response analysis of general, three-dimensional structures resting on a homogeneous, elastic halfspace subjected to either external loads or seismic motions. The formulation consists of two parts: (a) the time domain formulation of the soil behaviour and (b) the coupling of the corresponding soil algorithms to the Finite Element Code ANSYS. As far as the structure is concerned, this coupling opens the way for the analysis of non-linear soil–structure interaction. The approach is based on halfspace Green's functions for displacements elicited by Heaviside time-dependent surface point loads. Hence, the spatial discretisation can be confined to the contact area between the foundation and the soil, i.e. no auxiliary grid beyond the foundation as for conventional boundary element formulations is required. The method is applied to analyse the dynamic response of a railway track due to a moving wheel set by demonstrating the influence of ‘through-the-soil coupling’. 相似文献
3.
Coherency functions are used to describe the spatial variation of seismic ground motions at multiple supports of long span structures. Many coherency function models have been proposed based on theoretical derivation or measured spatial ground motion time histories at dense seismographic arrays. Most of them are suitable for modelling spatial ground motions on flat‐lying alluvial sites. It has been found that these coherency functions are not appropriate for modelling spatial variations of ground motions at sites with irregular topography (Struct. Saf. 1991; 10 (1):1–13). This paper investigates the influence of layered irregular sites and random soil properties on coherency functions of spatial ground motions on ground surface. Ground motion time histories at different locations on ground surface of the irregular site are generated based on the combined spectral representation method and one‐dimensional wave propagation theory. Random soil properties, including shear modulus, density and damping ratio of each layer, are assumed to follow normal distributions, and are modelled by the independent one‐dimensional random fields in the vertical direction. Monte‐Carlo simulations are employed to model the effect of random variations of soil properties on the simulated surface ground motion time histories. The coherency function is estimated from the simulated ground motion time histories. Numerical examples are presented to illustrate the proposed method. Numerical results show that coherency function directly relates to the spectral ratio of two local sites, and the influence of randomly varying soil properties at a canyon site on coherency functions of spatial surface ground motions cannot be neglected. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
4.
Based on the Betti–Rayleigh Dynamic Reciprocal Theorem, the reciprocal property of the Green's functions is demonstrated, on the basis of which the analytical solution of soil vibration subjected to moving loads is derived. By application of the Betti–Rayleigh Dynamic Reciprocal Theorem, the moving source problem is converted to the fixed source problem with receiver point moving in opposite direction, which greatly simplifies the complex analytical solution of soil/ground vibration induced by a moving load. A computer code for solving the ground responses subjected to the moving constant load and harmonic load is developed via MATLAB and is employed to perform a case study. The analyzed results show that the ground vibration induced by moving constant load is of typical low-frequency feature; the frequency range of ground vibration is controlled by the Rayleigh's wave velocity of the top layer soil; when the receiver nears the source path, the R-wave contributes to the ground vibration more than the P-wave and the S-wave; while when the receiver is far from the source path, the contribution of the P-wave is more obvious. 相似文献
5.
Scattering of SH waves by a scalene triangular hill 总被引：1，自引：1，他引：0
<正>The influence of local landforms on ground motion is an important problem.The antiplane response of a scalene triangular hill to incident SH waves is studied in this paper by using a complex function,moving coordinates and auxiliary functions.First,the model is divided into two domains:a scalene triangular hill with a semi-circular bottom;and a half space with a semi-circular canyon.Wave functions that satisfy the zero-stress condition at the triangular wedges and at the horizontal surface are constructed in both domains.Then,considering the displacement continuity and stress equilibrium, algebraic equations are established.Finally,numerical examples are provided to illustrate the influence of the geometry of the hill and the characteristics of the incident waves on the ground motions. 相似文献
6.
Three-dimensional simulation of track on poroelastic half-space vibrations due to a moving point load 总被引：1，自引：0，他引：1
An analytical approach is used to investigate dynamic responses of a track system and the poroelastic half-space soil medium subjected to a moving point load under three-dimensional condition. The whole system is divided into two separately formulated substructures, the track sub-system and the ground. The ballast supporting rails and sleepers is placed on the surface of the ground. The rail is modeled by introducing the Green function for an infinitely long Euler beam subjected to the action of the moving point load and the reaction of sleepers represented by a continuous mass. Using the double Fourier transform, the governing equations of motion are then solved analytically in the frequency–wave-number domain. The time domain responses are evaluated by the inverse Fourier transform computation for a certain load velocities. Computed results show that dynamic responses of the soil medium are considerably affected by the fluid phase as well as the load velocity. 相似文献
7.
Dynamic analysis of slab track on multi-layered transversely isotropic saturated soils subjected to train loads 总被引：1，自引：0，他引：1
The dynamic responses of a slab track on transversely isotropic saturated soils subjected to moving train loads are investigated by a semi-analytical approach. The track model is described as an upper Euler beam to simulate the rails and a lower Euler beam to model the slab. Rail pads between the rails and slab are represented by a continuous layer of springs and dashpots. A series of point loads are formulated to describe the moving train loads. The governing equations of track-ground systems are solved using the double Fourier transform, and the dynamic responses in the time domain are obtained by the inverse Fourier transform. The results show that a train load with high velocity will generate a larger response in transversely isotropic saturated soil than the lower velocity load, and special attention should be paid on the pore pressure in the vicinity of the ground surface. The anisotropic parameters of a surface soil layer will have greater influence on the displacement and excess pore water pressure than those of the subsoil layer. The traditional design method taking ground soil as homogeneous isotropic soil is unsafe for the case of RE 1 and RG 1, so a transversely isotropic foundation model is of great significance to the design for high train velocities. 相似文献
8.
System identification (SI) methods are used to determine empirical Green's functions (EGF) for soil intervals at the Port Island Site in Kobe, Japan and in shake table model tests performed by the Port and Harbor Research Institute (PHRI) to emulate the site during the 17 January 1995 Hyogo‐ken Nanbu earthquake. The model form for the EGFs is a parametric auto‐regressive moving average (ARMA) model mapping the ground motions recorded at the base of a soil interval to the top of that interval, hence capturing the effect of the soil on the through‐passing wave. The consistency of site response at Port Island before, during, and after the mainshock is examined by application of small motion foreshock EGFs to incoming ground motions over these time intervals. The prediction errors (or misfits) for the foreshocks, the mainshock, and the aftershocks, are assessed to determine the extent of altered soil response as a result of liquefaction of the ground during the mainshock. In addition, the consistency of soil response between field and model test is verified by application of EGFs calculated from the shake table test to the 17 January input data. The prediction error is then used to assess the consistency of behaviour between the two cases. By using EGFs developed for small‐amplitude foreshock ground motions, ground motions were predicted for all intervals of the vertical array except those that liquefied with small error. Analysis of the post‐liquefied ground conditions implies that the site response gradually returns to a pre‐earthquake state. Site behaviour is found to be consistent between foreshocks and the mainshock for the native ground (below 16 m in the field) with a normalized mean square error (NMSE) of 0.080 and a peak ground acceleration (PGA) of 0.5g. When the soil actually liquefies (change of state), recursive models are needed to track the variable soil behaviour for the remainder of the shaking. The recursive models are shown to demonstrate consistency between the shake table tests and the field with a NMSE of 0.102 for the 16 m to surface interval that liquefied. The aftershock ground response was not modelled well with the foreshock EGF immediately after the mainshock (NMSE ranging from 0.37 to 0.92). One month after the mainshock, the prediction error from the foreshock modeled was back to the foreshock error level. Copyright © 2001 John Wiley Sons, Ltd. 相似文献
9.
Linear and especially non-linear analyses of spatially extended structures, such as pipelines and bridges, often requires specification of time histories of ground motion at an array of closely spaced points. As the number of dense accelerograph arrays worldwide is small, and the number of earthquake observations is limited, synthetic motions with desired characteristics become necessary. This paper presents a method for synthesizing such motions, which is an extension of the SYNACC method, developed first in the early 1970s for synthetic accelerations, velocities and displacements at a point, and later extended to synthetic near surface strains, rotations and curvatures of ground motion at a point. It consists of unfolding in time a site specific Fourier amplitude spectrum of ground acceleration, obtained by an empirical scaling model, by representing the ground motion as a superposition of traveling wavelets of Love and Rayleigh waves and body waves, which propagate with phase and group velocities consistent with the dispersion characteristic of the site geology, approximated by parallel layers. Uniform hazard Fourier spectra or any specified target Fourier spectrum can also be used. Derivations of the point strains, rotations and curvatures are also presented. The method is illustrated for scenario M6.5 and M7.5 earthquakes and three dispersion models. 相似文献
10.
Using a thin-layer method enhanced by continued-fraction absorbing boundary conditions, dynamic responses of a layered half-space subjected to a series of constant and time-harmonic line loads moving at a constant speed are studied. The thin-layer method for moving line loads is formulated for plane-strain as well as antiplane-shear conditions and is verified by comparison of computed responses of a homogeneous half-space subjected to a single constant load on its surface against available analytical solutions. Next, time-harmonic loads on a homogeneous half-space are examined. The study continues with both constant and time-harmonic loads on a layered half-space. Finally, multiple constant and time-harmonic loads are considered. The formulation and results demonstrate the effectiveness and versatility of the method in problems of dynamic response of layered media to moving loads. 相似文献
11.
The effect of seawater on vertical ground motions is studied via a theoretical method and then actual offshore ground motion records are analyzed using a statistical method. A theoretical analysis of the effect of seawater on incident plane P and SV waves at ocean bottom indicate that on one hand, the affected frequency range of vertical ground motions is prominent due to P wave resonance in the water layer if the impedance ratio between the seawater and the underlying medium is large, but it is greatly suppressed if the impedance ratio is small; on the other hand, for the ocean bottom interface model selected herein, vertical ground motions consisting of mostly P waves are more easily affected by seawater than those dominated by SV waves. The statistical analysis of engineering parameters of offshore ground motion records indicate that:(1) Under the infl uence of softer surface soil at the seafl oor, both horizontal and vertical spectral accelerations of offshore motions are exaggerated at long period components, which leads to the peak spectral values moving to a longer period.(2) The spectral ratios(V/H) of offshore ground motions are much smaller than onshore ground motions near the P wave resonant frequencies in the water layer; and as the period becomes larger, the effect of seawater becomes smaller, which leads to a similar V/H at intermediate periods(near 2 s). These results are consistent with the conclusions of Boore and Smith(1999), but the V/H of offshore motion may be smaller than the onshore ground motions at longer periods(more than 5 s). 相似文献
12.
列车引起场地振动的建模需要能够表达地层的动力格林函数.本文兼顾饱和土的流固两相耦合性、场地土的分层性和波动的三维传播性,构建了半解析的场地动力格林函数.首先,基于Biot方程,在傅里叶变换域求解固体骨架和流体的位移和应力.然后采用传递矩阵方法建立地表位移和应力间的关系,得到格林函数矩阵.进而讨论矩阵的一些固有特征,提出改善竖向位移计算效率的措施.最后利用推导的格林函数计算了几个典型算例.数值结果与文献中其他方法得到的结果十分接近,与场地振动的现场观测试验基本符合.软土场地振动的计算结果高于饱和砂土场地,高速列车场地振动强度高于低速列车.当车速接近场地瑞利波速,模拟结果中显示出马赫锥.数值结果还显示,即使车速略低于瑞利波速,马赫锥也可能出现.本文推导的格林函数将有助于深入理解列车等移动激励作用下层状饱和土场地的振动特征. 相似文献
13.
This paper presents a novel approach to model and simulate the multi-support depth-varying seismic motions (MDSMs) within heterogeneous offshore and onshore sites. Based on 1D wave propagation theory, the three-dimensional ground motion transfer functions on the surface or within an offshore or onshore site are derived by considering the effects of seawater and porous soils on the propagation of seismic P waves. Moreover, the depth-varying and spatial variation properties of seismic ground motions are considered in the ground motion simulation. Using the obtained transfer functions at any locations within a site, the offshore or onshore depth-varying seismic motions are stochastically simulated based on the spectral representation method (SRM). The traditional approaches for simulating spatially varying ground motions are improved and extended to generate MDSMs within multiple offshore and onshore sites. The simulation results show that the PSD functions and coherency losses of the generated MDSMs are compatible with respective target values, which fully validates the effectiveness of the proposed simulation method. The synthesized MDSMs can provide strong support for the precise seismic response prediction and performance-based design of both offshore and onshore large-span engineering structures. 相似文献
14.
Using reciprocal theorems for dynamic and static boundary value problems, boundary integral equations are presented for wave propagation in elastic, isotropic media and compressible, inviscid fluids in the time domain as well as in the frequency domain. For the analysis of fluid–soil and fluid–structure systems, suitable coupling conditions are prescribed along the interfaces. The numerical treatment of the boundary integral equations consists of a point collocation and of a discretization of the boundary, in which constant and linear approximation functions are assumed. Step-by-step integration is applied to the time-dependent equations, where again the states are taken to be linear and constant over each time interval. These boundary element procedures are used to analyse the response of dams due to horizontal and vertical ground motions considering dam–water interaction and absorption of hydrodynamic pressure waves at the reservoir bottom or at the far end into the soil medium. Both the frequency response and the impulse generated transient response are investigated. 相似文献
15.
Seismic risk analysis and mitigation of spatially extended structures require the synthesis of spatially varying ground motions in the response history analysis of these structures. These synthetic motions are usually desired to be spatially correlated, site reflected, nonstationary, and compatible with target design response spectra. In this paper, a method is presented for simulating spatially varying ground motions considering the nonstationarity, local site effects, and compatibility of response spectra. The scheme for generating spatially varying and response spectra compatible ground motions is first established for spatial locations on the ground surface with varying site conditions. The design response spectrum is introduced as the “power” spectrum at the base rock. The site amplification approach is then derived based on the deterministic wave propagation theory, by assuming that the base rock motions consist of out-of-plane SH wave or in-plane combined P and SV waves propagating into the site with assumed incident angles, from which tri-directional spatial ground motions can be generated. The phase difference spectrum is employed to model ground motions exhibiting nonstationarity in both frequency and time domains with different site conditions. The proposed scheme is demonstrated with numerical examples. 相似文献
16.
Iya Abubakar 《Pure and Applied Geophysics》1964,59(1):10-20
Summary TheSH-type of motion in an isotropic elastic halfspace with infinite electrical conductivity subjected to an uniform magnetic field and disturbed by a buried source is investigated. Expressions for the surface displacements for various type of sources are obtained by an application of Cagniard technique. Numerical calculation has been performed for the case of a diapole source moving parallel to the surface of the halfspace with an uniform velocity. 相似文献
17.
Kemal Hacıefendioğlu Emre Alpaslan 《Stochastic Environmental Research and Risk Assessment (SERRA)》2014,28(2):415-427
This paper presents the dynamic response analysis of industrial masonry chimney subjected to artificially generated surface blast induced ground shock by using a three-dimensional finite element model. The effects of surface blast-induced ground shocks on nearby structures depend on the distance between the explosion centre and the structure, and charge weight. Blast-induced ground motions can be represented by power spectral density function and applied to each support point of the 3D finite element model of the industrial masonry system. In this study, a parametric study is mainly conducted to estimate the effect of the blast-induced ground motions on the nonlinear response of a chimney type masonry structure. Therefore, the analysis was carried out for different values of the charge weights and distances from the charge center. The initial crack and propagation of the crack pattern at the base of the chimney were evaluated. Moreover, the maximum stresses and displacements through the height of the chimney were investigated. The results of the study underline that blast-induced ground motions effects should be considered to perform the non-linear dynamic analysis of masonry type chimney structures more accurately. 相似文献
18.
A comprehensive analysis is made of the harmonic response of vertically excited, massless, rigid ring foundations supported at the surface of an homogeneous elastic halfspace. The parameters considered include the thickness to radius ratio for the ring, the frequency of the exciting force and of the resulting steady-state response, and Poisson's ratio for the supporting medium. The response quantities examined include the stiffness and damping coefficients of the system in an equivalent spring–dashpot representation of the supporting medium, the displacements of the foundation and of points on the ground surface away from the foundation, and the normal pressure at the foundation–medium interface. The results in each case are compared with those obtained for a solid disk having the same radius as the outer radius of the ring, and a simple approximate model is used to interpret the results and to provide insight into the action of the system. The reported data are computed by a method of analysis that takes due account of the mixed boundary conditions at the surface of the halfspace, and are believed to be of high accuracy. 相似文献
19.
G. Lefeuve-Mesgouez A. T. Peplow D. Le Houdec 《Soil Dynamics and Earthquake Engineering》2002,22(6):692
The transmission of vibrations over the surface of the ground, due to high-speed moving, vertical harmonic rectangular loads, is investigated theoretically. The problem is three-dimensional and the interior of the ground is modelled as an elastic half-space or a multilayered ground. The transformed solutions are obtained using the Fourier transform on the space variable. A new damping model in the spatial wavenumber domain, presented in Lefeuve-Mesgouez et al. [J. Sound. Vibr. 231 (2000) 1289] is used. Numerical results for the displacements on the surface are presented for loads moving with speeds up to and beyond the Rayleigh wave speed of the half-space. 相似文献
20.
Reduction of ground vibration by means of barriers or soil improvement along a railway track 总被引：3，自引：0，他引：3
Trains running in built-up areas are a source to ground-borne noise. A careful design of the track may be one way of minimizing the vibrations in the surroundings. For example, open or infilled trenches may be constructed along the track, or the soil underneath the track may be improved. In this work, the influence of the track design and properties on the level of ground vibration due to a vehicle moving with subsonic speed is examined. A coupled finite element-boundary element model of the track and subsoil is employed, adopting a formulation in the moving frame of reference following the vehicle. The computations are carried out in the frequency domain for various combinations of the vehicle speed and the excitation frequency. The analyses indicate that open trenches are more efficient than infilled trenches or soil stiffening–even at low frequencies. However, the direction of the load is of paramount importance. For example, the response outside a shallow open trench may change dramatically when horizontal load is applied instead of vertical load. 相似文献