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1.
In this paper the free vibrations of simply supported rectangular plates, resting on two different models of soils, are considered. The first model called Hetényi, by the name of the deviser, assumes a continuous plate, embedded in a Winkler‐type soil to realize the foundation partial continuity. The upper plate rests on a multiple layer characterized by a Winkler‐type soil, a continuous plate and another Winkler‐type soil in sequence. The two Winkler‐type soils have different modules. In the second model, the plate will be embedded in two layers of soils, whose behavior is similar to that of the Pasternak–Kerr‐type soil. The two models have been already used for the study of the double beam system. The free motions, in both cases, are described by a homogeneous set of partial differential equations, based on Kirchhoff–Love theory. Next, the homogeneous equations of motion are solved by using the classical Navier method. The free frequencies and associated vibration mode shapes of double plate system are found and numerical examples are illustrated to compare the two models. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
2.
INTRODUCTIONUnderstanding dynamic response andits correla-tion to the effects of traffic , wind and earthquake hasbecome one of the engineering challenges of cable-stayed bridges , since the cable-stayed bridges arepresently extending to medium- and long-spanlengths .Investigations of both the aerodynamic sta-bility and earthquake response of cable-stayed bridgesare dependent upon knowledge of the dynamic char-acteristics ,such as natural frequencies , mode shapesand modal damping values ,… 相似文献
3.
作为一种柔性支挡结构,加筋土挡墙相较于传统重力式挡墙具有优越的抗震性能。由于结构在地震等动荷载作用下的动力响应大小与其自身的固有频率大小有关,因此,固有频率的研究显得尤为重要,特别是其最小值基频。以整体刚性面板加筋土挡墙为研究对象,分别用弹性地基梁模型、线性弹簧模型表示面板、填土及筋材,提出了一种加筋土挡墙固有频率计算方法。计算求得的基频值与既有瑞利能量法计算值具有较好的一致性。参数分析表明：填土中铺设筋材可以增大墙体的基频;对于加筋土挡墙,筋材长度以及筋材-填土界面摩擦系数对墙体基频影响较小;随着筋材竖向间距的增大,加筋密度对加筋土挡墙基频的影响逐渐减小;墙体基频随着面板宽度的增大先减小后增大;随着面板模量的减小,墙体基频趋于恒值。 相似文献
4.
隧道近距下穿山坡楼房爆破振动测试研究 总被引：3，自引：0，他引：3
以成渝客运专线新红岩隧道为工程背景,测试了隧道近距下穿山坡楼房爆破时引起的地面振动。通过对隧道浅埋侧（隧道地表斜坡下部）和深埋侧（隧道地表斜坡上部）的地表振动数据分析,研究了地表的振动速度、振动主频及振动安全评价方法。结果表明：在浅埋隧道爆破的近区,入射纵波为主要载体,地表水平和竖直方向振动的主要成分可以认为是入射纵波在水平和竖直方向的投影,浅埋侧和深埋侧地表水平和竖直方向振速的大小取决于爆心距和入射纵波与竖直方向的夹角两个因素;隧道采用电子雷管进行单孔连续起爆,相比非电雷管爆破,可以有效降低地表振动强度,同时能够提高地表振动主频;地表振动主频方面,地表竖直方向振动主频普遍高于水平方向,而且浅埋侧地表竖直和水平方向主频大多高于深埋侧地表对应方向的主频;隧道近距下穿山坡楼房进行爆破施工时,建议在浅埋侧和深埋侧地表同时布置爆破振动监测测点,并根据浅埋侧和深埋侧地表测点的峰值振速、爆破振动主频与建筑物固有频率的关系对地表振动安全进行评价,以减少隧道施工爆破对地表环境和周围建筑物造成的振动破坏。 相似文献
5.
The consistent transmitting boundary condition is a powerful numerical technique for frequency domain analysis of wave problems in unbounded elastic media. A second-order complex-valued eigen-problem is associated with this method and the computed eigenmodes are used to formulate the nodal forces acting on the lateral boundaries of a Cartesian computational domain. Usually, all eigenmodes are computed and used in the consistent transmitting boundary conditions to simulate the infinite extent of the elastic medium. In this paper, it is demonstrated that by selecting a reduced number of relevant eigenmodes it is possible to produce similar results and consequently reduce the overall computational cost. This is highly desirable for soil–structure interaction problems involving wide ranges of frequencies and large-size domains with many sub-layers. The efficiency of the proposed approach is investigated by considering, first, the case of foundation vibration over rigid bedrock and, second, the effectiveness of a wave barrier to reduce the transmitted vibrations caused by a surface harmonic loading. 相似文献
6.
Environmental problems such as vibration and air blast are often faced and discussed in mining, quarrying, civil construction, shaft tunnel, pipeline, and dam operations, where blasting is inevitable. It is necessary to establish national standards in order to minimize environmental problems induced by blasting and judicial matters in our country as it is in the USA, European Union (EU) countries, and other developed countries. This necessity and the obligation of Turkey, which has started the procedure of joining the EU, to accept EU criteria emphasize the importance of this study. In other words, the establishment of a particular national standard related with this subject is inevitable for Turkey. This will be possible only by studying and applying scientific methods and techniques by experts. This paper presents a new damage criterion norm for blast-induced ground vibrations in Turkey. In this study, first, numerous vibration records were taken in blasting operations performed at different sites and rock units. For these rock units, particle velocity predictions and frequency analysis were done. At the same time, structures in the neighborhoods of these blasts were also observed and investigated. Finally, a damage criterion norm based on risk analysis was established and proposed by using these collected data. In light of the norm to be obtained from the data that were collected in the research, it will lead the excavation work in our country to be performed in such way that they are more effective and will cause minimum environmental problems. 相似文献
7.
A. J. Prakash P. Palroy D. D. Misra 《Fragblast: International Journal for Blasting and Fragmentation》2004,8(1):51-60
This paper presents the influence of various discontinuities, natural or artificial, on magnitude and frequencies of blast induced ground vibrations. These discontinuities were geological faults, a pond, a shaft incline, a trench and a pre-split plane interposed in the path of vibration propagation. In the post-trench region, ground vibrations in terms of peak particle velocity were significantly reduced and dominant frequencies in higher bands were consequently observed. Depth of trench with respect to blastholes were varied and consequent vibration characteristics were analyzed. The techniques of creating a trench and pre-split plane were successfully implemented in controlling vibration and in increasing the explosives charge to meet the scheduled production target of an opencast mine. Comparisons of ground vibration characteristics affected by a trench and a pre-split plane of the same depth are described in the text. The findings lead to the conclusion that such experimental data are necessary for production blasting in open cast mines under constrained conditions. 相似文献
8.
Assessment of predominant frequencies using ambient vibration in the Kachchh region of western India: implications for earthquake hazards 总被引：1，自引：1，他引：0
The Kachchh region is the second most seismically active region in India after the Himalaya. One of the disastrous Indian earthquakes of the millennium was the Bhuj earthquake of January 26, 2001, which caused about 14,000 casualties and huge property damage. The main reason for such devastation is due to lack of earthquake awareness and poor construction practices. Hence, an increase in the knowledge and awareness, based on improved seismic hazard assessment, is required to mitigate damage due to an earthquake. Natural predominant ground frequencies have been investigated in the Kachchh region of western India using ambient vibrations. The horizontal-to-vertical spectral ratio technique has been applied to estimate the predominant frequency at 126 sites. The ambient vibration measurements were conducted for about 1 h at each site in the continuous mode recording at 100 samples/s. We have validated the estimated predominant frequency with earthquake data recorded at six broadband stations in the region. It has been observed that geological time period has a significant effect on predominant frequency of the ground. The estimated predominant frequencies vary from 0.24 to 2.25 Hz for the Quaternary, 0.41–2.34 Hz for the Tertiary, 0.32–4.91 Hz for the Cretaceous, and 0.39–8.0 Hz for the Jurassic/Mesozoic. In the Deccan trap, it varies from 1.30 to 3.80 Hz. We found distinct variation of predominant frequencies of sites associated with hard rock and soft soil. The predominant frequencies were related to the thickness of the sediments, which are deduced by other geophysical and geological methods in the region. Our results suggest that frequencies of the region reveals the site characteristics that can be considered for studying the seismic risks to evolve a plan for disaster risk mitigation for the region. 相似文献
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In this paper, a progressive asymptotic approach procedure is presented for solving the steady-state Horton–Rogers–Lapwood problem in a fluid-saturated porous medium. The Horton–Rogers–Lapwood problem possesses a bifurcation and, therefore, makes the direct use of conventional finite element methods difficult. Even if the Rayleigh number is high enough to drive the occurrence of natural convection in a fluid-saturated porous medium, the conventional methods will often produce a trivial non-convective solution. This difficulty can be overcome using the progressive asymptotic approach procedure associated with the finite element method. The method considers a series of modified Horton–Rogers–Lapwood problems in which gravity is assumed to tilt a small angle away from vertical. The main idea behind the progressive asymptotic approach procedure is that through solving a sequence of such modified problems with decreasing tilt, an accurate non-zero velocity solution to the Horton–Rogers–Lapwood problem can be obtained. This solution provides a very good initial prediction for the solution to the original Horton–Rogers–Lapwood problem so that the non-zero velocity solution can be successfully obtained when the tilted angle is set to zero. Comparison of numerical solutions with analytical ones to a benchmark problem of any rectangular geometry has demonstrated the usefulness of the present progressive asymptotic approach procedure. Finally, the procedure has been used to investigate the effect of basin shapes on natural convection of pore-fluid in a porous medium. © 1997 by John Wiley & Sons, Ltd. 相似文献
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A boundary element approach for time harmonic axisymmetric problems using the complete space point load fundamental solution is presented. The fundamental solution is integrated numerically along the azimuthal co-ordinate of each axisymmetric element. To increase the accuracy of the numerical integration a simple co-ordinate transformation is proposed. The approach is applied to the computation of the dynamic stiffness functions of rigid circular foundations on layered viscoelastic soils. Three different sites are considered: a uniform half-space, a soil layer on a half-space, and a soil consisting of four horizontal layers and a compliant half-space. The numerical results obtained by the proposed approach for surface circular foundations are very close to corresponding published results obtained by different procedures. 相似文献
13.
George Gazetas 《国际地质力学数值与分析法杂志》1982,6(2):219-241
Closed-form solution to the problem of free vibrations of vertically inhomogeneous earth dams, modelled as truncated-wedge-shaped shear beams, has been obtained by implementing an inverse procedure in which the determination of the function descrbing the inhomogeneity constitutes part of the problem. The resulting cube-root variation of the shear-wave velocity with distance from the crest compares very favourably with measurements in two Japanese dams. The results of the method are presented in theform of natural periods, modal shapes and average seismic coefficients for a number of truncation ratios. Compared with an ‘equivalent’ homogeneous dam, the inhomogeneous experiences sharper amplification of modal displacements and greater averge seismic, coefficients near the crest and has natural periods which are closer to each other. This behaviour is in better agreement with the observed response of a 37m-high dam during five earthquake motions. 相似文献
14.
Investigations were carried out at three underground coal mines in India to study the response of surface structures to underground
blasting and the likelihood of damage to the structures. The structures in the vicinity of the underground blasting area were
single and multistoried residential houses. The amplitudes of vibration due to underground blasting were monitored simultaneously
on the ground surface near the foundation of the structures and on various floors of the structures. The vibrations were also
monitored near the important surface installations. It was observed that the magnitude of vibration in structures decreased
with the increase in the height of the structures. The frequency of blast vibration from underground blasting was higher than
the natural frequency of the structures. Little energy was transmitted into the structures, which caused reduction in the
vibration level in the structures. The reduction in the vibration levels was up to 45% in the houses. It indicates that the
dominant frequency of blast vibration plays an important role in persistence of vibration and its amplification or reduction
characteristics in the structures. This paper deals with the effect of the vibrations on structures/houses standing above
the blasting faces in underground workings and their potential to likely damage to the structures at different Indian geo-mining
conditions. 相似文献
15.
This paper deals with the computational aspects of nonaqueous phase liquid (NAPL) dissolution front instability in two-dimensional
fluid-saturated porous media of finite domains. After the governing equations of an NAPL dissolution system are briefly described,
a combination of the finite element and finite difference methods is proposed to solve these equations. In the proposed numerical
procedure, the finite difference method is used to discretize time, while the finite element method is used to discretize
space. Two benchmark problems, for which either analytical results or previous solutions are available, are used to verify
the proposed numerical procedure. The related simulation results from these two benchmark problems have demonstrated that
the proposed numerical procedure is useful and applicable for simulating the morphological evolution of NAPL dissolution fronts
in two-dimensional fluid-saturated porous media of finite domains. As an application, the proposed numerical procedure has
been used to simulate morphological evolution processes for three kinds of NAPL dissolution fronts in supercritical NAPL dissolution
systems. It has been recognized that: (1) if the Zhao number of an NAPL dissolution system is in the lower range of the supercritical
Zhao numbers, the fundamental mode is predominant; (2) if the Zhao number is in the middle range of the supercritical Zhao
numbers, the (normal) fingering mode is the predominant pattern of the NAPL dissolution front; and (3) if the Zhao number
is in the higher range of the supercritical Zhao numbers, the fractal mode is predominant for the NAPL dissolution front. 相似文献
16.
This paper presents an analytical method for modeling the dynamic response of a rigid strip footing subjected to vertical-only loads. The footing is assumed to rest on the surface of a viscoelastic half-space; therefore, effects of hysteretic soil damping on the impedance of the foundation and the generated ground vibrations are considered in the solution. To solve the mixed boundary value problem, we use the Fourier transform to cast a pair of dual integral equations providing contact stresses, which are solved by means of Jacobi orthogonal polynomials. The resulting soil and footing displacements and stresses are obtained by means of the Fourier inverse transform. The solution provides more realistic estimates of footing impedance, compared to existing solutions for elastic soil, as well as of the attenuation of ground vibrations with distance of the footing. The latter is important for the estimation of machine vibration effects on nearby structures and installations. 相似文献
17.
A Feasibility Study on Controlling Ground Vibrations Caused by Blasts in Malmberget Underground Mine
Z. X. Zhang P. -A. Lindqvist T. Naarttij rvi K. Wikstr m 《Fragblast: International Journal for Blasting and Fragmentation》2004,8(1):3-21
In order to control or reduce the ground vibrations caused by underground blasts in Malmberget mine, a number of blast tests were carried out during production blasts and a series of single shot waveforms were obtained. Then the single shot waveforms from the same ring or different rings were analysed and compared with each other. The results showed that the single shots are reproducible, meaning that the ground vibrations caused by underground blasts can be controlled by means of the interference of the vibration waveforms measured. Finally, a formal test using electronic detonators and employing an optimum delay time of 8 ms was done in production. The test for an 11-borehole ring shows that the maximum vertical ground vibrations are reduced to the maximum vertical vibrations of a single shot. Particularly, the total vibration history for the 11-borehole-ring blast is shortened to about 200 ms over a velocity of 2 mm/s. However, the total vibration history of a normal production blast of 11-borehole ring is always 1400 ms over a velocity of 2 mm/s, namely the total vibration time of a production blast can be reduced to one seventh of that of the common production blasts by using the vibration control method. This indicates that the vibration control method introduced in the paper is feasible for underground mining blasts. 相似文献
18.
Potential field data is generally contaminated by random noise. The high-frequency noise contained in the data brings unfavorable influences to subsequent data processing. Therefore, suppressing the adverse effects of noise has always been a crucial step which is desirable prior to applying other transformations. Over the past decades, numerous mathematical approaches have been proposed for noise cancelation of potential field data. In the work discussed in this paper, the application of the empirical mode decomposition for denoising of potential field data is briefly described, and a new stopping criterion for this filtering method is introduced. Using the proposed method, the empirical mode decomposition is firstly performed on the original potential field data to get numerous intrinsic mode functions corresponding to components with different frequencies. Each intrinsic mode function is subtracted from the original data to get different residual datasets. The correlation coefficients associated with the original data and various residual datasets are calculated and plotted. The inflection point of the correlation coefficient curve is adopted as the last intrinsic mode function to be selected. The new stopping criterion offers a quantitative way to determine which intrinsic mode functions should be removed during filtering and can be easily implemented within the algorithm. Tests on synthetic noisy gravity data demonstrate that the empirical mode decomposition based noise cancelation method along with this new stopping criterion yield acceptable filtering results for potential field data. The newly developed method is also investigated on real gravity data collected over a magnetite zone in Jilin Province, China. 相似文献
19.
Monia Aloui Yannick Bleuzen Elhoucine Essefi Chedly Abbes 《Arabian Journal of Geosciences》2018,11(21):686
Blasting constitutes a beneficial industrial technology, used in quarries and mining production processes, which ensures the achievement of the expected results in a short period of time with relatively low cost. Nevertheless, a significant part of the used blasting energy is wasted in the form of ground vibration and air blast. Hence, blasting-induced ground vibrations are one of the fundamental problems in the mining industry which may cause severe damage to structures and plants nearby. Therefore, a vibration control study plays an important part in the minimization of the environmental effects of blasting in mines. This study represents an investigation reporting ground motion (measured in terms of peak particle velocity (mm/s)) and air blast overpressure measurements around the open-pit phosphate mine near Metlaoui area (southwestern Tunisia). It aimed to calculate the site’s constants: K (ground transmission coefficient) and n (site attenuation curve slope). The obtained site parameters allowed determining the propagation equation of the blast-induced seismic waves in the study area. The scope of this study was to predict the peak particle velocity when the amount of explosive charge and/or the distance were altered with minimum spoil to the environment. Also, a frequency overview of the study area revealed the dominance of low frequencies (>?40 Hz). Such values can cause damage to the nearby structures when a specific peak particle velocity value is reached by blasting. Moreover, this study demonstrated that all overpressure magnitudes were less than 134 dB, which is the safe limit of air blast level. 相似文献
20.
Piles and drilled shafts are commonly used to stabilize potentially unstable natural and engineered slopes. Estimation of
lateral pressures on piles or shafts used to stabilize potentially unstable sites continues to be a fundamental problem in
geotechnical engineering. Several methods are available to estimate the lateral force on piles or drilled shafts used to stabilize
a site. An approximate procedure to estimate the lateral force on drilled shafts supporting structures, i.e., installed at
relatively large spacings on a potentially unstable site with a fixed slip surface is proposed, which is based on a widely
referred theory of plastic deformation. Lateral pressures estimated using the method proposed show good agreement with a more
rigorous method, which in turn has been reported to provide results close to field measurements. An approximate procedure
to estimate a limiting (maximum) value of lateral pressure on shafts or piles when they are installed at close spacings is
also proposed. Although, the limiting pressures estimated using the approximate procedure are in agreement with the pressures
calculated using more rigorous method, verification of both methods with field measurements is recommended. 相似文献