Effect of mode of vibration on the response of machine foundation on sand (original) (raw)
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Response of Different Machine Foundation Shapes Resting on Dry Sand to Dynamic Loading
Tikrit Journal of Engineering Sciences, 2020
In this paper, the effect of footing shape resting on dry sand when subjected to machine dynamic loading is experimentally investigated. A laboratory set-up was prepared to simulate the case at different operating frequencies. Nine models were tested to examine the effects of the combinations of two parameters, including different frequencies of (0.5, 1, and 2 Hz) and different footing shapes (circular, square and rectangular). The tests were conducted under a load amplitude of (0.25 ton) using sand with medium and dense relative densities corresponding to (R.D. = 50% and 80%) having unit weights of (17.04 and 17.96 kN/m3) respectively. A shaft encoder and a vibration meter were used to measure the strain and amplitude displacement, while the stress in the soil at different depths was measured using flexible pressure sensors. It was found that the shape of footing has a considerable influence on the bearing capacity of the supporting soil under dynamic loading. For instance, the str...
An experimental investigation of vertical vibration of model footings on sand
Soil Dynamics and Earthquake Engineering, 1996
Many free and forced vertical vibrations tests were conducted on surface and embeded models for footings on dry and moist poorly graded sand that has the following properties: Dl0 = 0-21 ram, D30 = 0-305ram, Dt0 = 0.423mm, Cu = 2, Cc = 1-05, Gs = 2.66, "rnm = 1"74cm-3 and 7rain = l'4g cm-3-The tests were conducted at relative density Dr = 82%. The effect of mass, area, geometry, embedment, saturation, load amplitude and frequency were studied. For this purpose square, rectangular and circular models of concrete footings were chosen. Swieleh sand was chosen as the foundation soil. Results have been obtained for models having different mass, same base shape and area; models of different base area and equal base shape and mass; and models of different base shape geometry and about equal masses and base areas.
In this study, the response and behavior of machine foundations resting on dry and saturated sand was investigated experimentally. A physical model was manufactured to simulate steady state harmonic load at different operating frequencies. The effect of relative density, depth of embedment, foundation area as well as the imposed harmonic load was investigated. It was found that the amplitude of displacement of the foundation increases with increasing the amplitude of dynamic force and operating frequency meanwhile it decreases with increasing the relative density of sand, degree of saturation, depth of embedment and contact area of footing. The maximum displacement was noticed at 33.34 to 41.67 Hz. The maximum displacement amplitude response of the foundation resting on dry sand models is more than that on the saturated sand by about 5.0 to 10 %.
Response of Circular Machine Foundation Resting on Sandy Soil to Harmonic Excitation
2020
This paper focuses on the effect of the machine's circular foundation on the variation of surface settlement, vertical displacement and stress with a number of cycles. A special setup was designed and manufactured to simulate the vertical vibration of a machine foundation. Six laboratory model footings were prepared on medium and dense dry sand separately. A circular steel model of (150 mm) diameter was used to represent the footing. The models were tested under dynamic load amplitude of 0.25 ton and different frequencies of 0.5, 1, and 2 Hz. It was found that the rate of increase in settlement decreased remarkably when increasing the frequency for both types of sand. While increasing the soil relative density under the same load and frequency resulted in a decrease of the settlement. Moreover, the amplitude displacement decreased when increasing frequency and relative density. The resulting stress due to the dynamic load below the foundation decreased with depth. Besides, there...
Strain and strain rate effects on the rocking response of footings subjected to machine vibrations
16th European Conference on Earthquake Engineering (Thessaloniki 2018), 2018
Footings subjected to dynamic loads are commonly designed under the simplifying assumption of linear or equivalent-linear soil behaviour. Even though this approach is simple to implement and, in some cases, could take advantage of available closed-form solutions, the outcomes remain a gross approximation. Although considerable research has been conducted for the case of high-amplitude footing vibrations, where uplift, slippage or even failure may occur, there remains a research gap for small to medium strain amplitudes, for which the behaviour is also non-linear. To address this problem, a numerical methodology is developed herein, for the analysis and design of shallow footings, while taking into consideration shear modulus degradation and hysteretic damping increase effects for the foundation subsoil. The analysis methodology is based on the implementation of the modified hyperbolic model as a user-defined formulation into the explicit finite difference code FLAC. Focus is then given on a rigid strip surface foundation subjected to a harmonic rocking motion, and results from preliminary analyses are presented in terms of the variation of the dynamic impedance with the dimensionless frequency of the excitation. Different excitation amplitudes are examined to demonstrate the effects of soil non-linearity, while strain rate effects are also investigated.
Strain and strain rate effects on the rocking response of footing subjected to machine vibrations
2018
Footings subjected to dynamic loads are commonly designed under the simplifying assumption of linear or equivalent-linear soil behaviour. Even though this approach is simple to implement and, in some cases, could take advantage of available closed-form solutions, the outcomes remain a gross approximation. Although considerable research has been conducted for the case of high-amplitude footing vibrations, where uplift, slippage or even failure may occur, there remains a research gap for small to medium strain amplitudes, for which the behaviour is also non-linear. To address this problem, a numerical methodology is developed herein, for the analysis and design of shallow footings, while taking into consideration shear modulus degradation and hysteretic damping increase effects for the foundation subsoil. The analysis methodology is based on the implementation of the modified hyperbolic model as a user-defined formulation into the explicit finite difference code FLAC. Focus is then gi...
elsevier, 2022
The difficulty that arises in the design of a machine foundation is how to know the behavior of the soil at different soil conditions. Therefore, there are many indications of a need to study machine foundation on soil of different degrees of saturation, covering all the important aspects of clay soil. Experiments on machine foundation (circular and rectangular) were carried out resting on clay soil with different degrees of saturation (100 % and 60 %), in order to find the amplitude displacement of the foundation under different operating frequencies. In addition, the paper describes the vertical stress and displacements inside the soil distributed at three points under the foundation (0.5 B, B, and 2B, B is the foundation width). The experiments results showed that the effect of increasing the degree of saturation is to reduce the amplitude displacement of the foundation to about 61 %. The increase in degree of saturation of soil reduced the vertical stress by about 77 %. The change in the degree of saturation leads to significant action on displacement inside the soil. These influences depend on the distance of the point from the foundation
Experimental Investigation for Dynamic Response of Saturated Clay Under Machine Foundation
springer , 2021
A machine foundation is considered important and because of that the foundation design under dynamic loads must be governed by serviceability limit states performance considerations rather than strength requirements. The dynamic response is carefully calculated to ensure high-quality and efficient performing for machinery. This paper presents a model for estimating the dynamical response of a machine foundation on saturated clay by experimental work. The machine is produced to simulate forced vibrations by harmonic loading at various operating frequencies. The depth influence of embedding and load frequency onmodel footings on soft clay soil is investigated. As well as, stresses and excess pore water pressure get measured at different depths in the soil below the footing. It was concluded that the maximum displacement increases as the operating frequency increases, as well as, there is an increase in the excess pore water pressure when the dynamic load increases.
Analysis of machine foundation vibrations: state of the art
International Journal of Soil Dynamics and Earthquake …, 1983
The paper reviews the state-of-the-art of analysing the dynamic response of foundations subjected to machine-type loadings. Following a brief outline of the historical developments in the field, the concepts associated with the definition, physical interpretation and use of the dynamic impedance functions of foundations are elucidated and the available analytical/numerical methods for their evaluation are discussed. Groups of crucial dimensionless problem parameters related to the soil prot~ile and the foundation geometry are identified and their effects on the response are studied. Results are presented in the form of simple formulae and dimensionless graphs for both the static and dynamic parts of impedances, pertaining to surface and embedded foundations having circular, strip, rectangular or arbitrary plan shape and supported by three types of idealized soil profdes: the halfspace, the stratum-over-bedrock and the layer-over-half space. Consideration is given to the effects of inhomogeneity, anisotropy and non-linearity of soil. The various results are synthesized in a case study referring to the response of two rigid massive foundations, and practical recommendations are made on how to inexpensively predict the response of foundations supported by actual soil deposits.
Numerical Analysis of Machine Foundation Resting on Saturated Sandy Soil
ABSTRACT The behavior of machine foundation on saturated porous medium can be considered as a complicated geotechnical problem due to nature of dynamic loads and plasticity of soil which make the analysis and design of foundation subjected to dynamic loads more complex. The main criteria for safe performance of machine foundations subjected to dynamic loads are to control excessive displacements. In this paper, a dynamic analysis of strip machine foundation with multiple thicknesses is placed at the middle of the top surface of saturated sand with different states (i.e. loose, medium and dense), and vertical harmonic excitation is carried out and building up of the excess pore water pressure. The dynamic analysis is performed numerically by using finite element software, PLAXIS 2D. The soil is assumed as elastic perfectly plastic material obeys Mohr-Coulomb yield criterion. A parametric study is carried out to evaluate the dependency of machine foundation on various parameters including the amplitude and the frequency of the dynamic load. The dynamic response (displacement and excess pore water pressure) generally increases with increasing of loading amplitude, but the displacement and excess pore water pressure versus frequency are not smooth and exhibit undulations (peaks and troughs). Keywords: Machine foundation, dynamic loads, finite elements, saturated sand, elastic perfectly plastic.