Query: machine foundation

title: Stresses and pore water pressure induced by machine foundation on saturated sand
abstract: In this study, the response and behavior of machine foundations resting on dry and saturated sand was investigated experimentally. In order to investigate the response of soil and footing to steady state dynamic loading, a physical model was manufactured. The manufactured physical model could be used to simulate steady state harmonic load at different operating frequencies. Total of (84) physical models were performed. The parameters that were taken into considerations include loading frequency, size of footing and different soil conditions. The footing parameters were related to the size of the rectangular footing and depth of embedment. Two sizes of rectangular steel model footing were used (100 x 200 x 12.5 mm) and (200 x 400 x 5.0 mm) The footing was tested in all parameters at the surface and at 50 mm depth below model surface. Meanwhile the investigated parameters of the soil condition included dry and saturated sand for two relative densities 30% and 80% The response of the soil to dynamic loading includes measuring the stresses inside the soil using piezoelectric sensors as well as measuring the excess pore water pressure by using pore water pressure transducers. It was found that the rate of increase in excess pore water pressure ratio decreased remarkably at a depth of 0.5 B 1.5 B (B is the footing width) for medium and loose dense sand, respectively. Moreover, excess pore water pressure ratio increases with increasing the eccentricity of dynamic load. The generated pore water pressure is always greater under the point of load application. Its value reduces with a certain percentages at any point away from the point of load application. In addition, the rate of variation of pore water pressure with eccentricity for loose sand is less than that for medium dense sand. The dynamic stress increments resulting from the dynamic load on the foundation reduce with depth. In addition, the dynamic stresses under the corner are slightly greater than the stresses at the center by a percentage of about 10.0% The excess pore water pressure increases with increasing the relative density of the sand, the amplitude of dynamic loading and the operating frequency. In contrast, the rate of dissipation of the excess pore water pressure during dynamic loading is more in the case of loose sand.

title: General Principles of Machine Foundation Design

title: Effect of Embedment Depth on Response of Machine Foundation on Saturated Sand
abstract: In this paper, a dynamic analysis of strip machine foundation is carried out. The foundation of multiple thicknesses is placed at different depths above a saturated sand with different states (i.e. loose, medium and dense) and vertical harmonic excitation is applied with build up of the excess pore water pressure being considered. 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 of the dynamic load, the frequency of the dynamic load and the embedment of foundation. It was concluded that increasing the embedment ratio causes a reduction in the dynamic response up to a certain embedment depth; when the depth of embedment increases higher than 1 m, the effect become less pronounced and as strength of the soil increases, the effect of embedment depth in reducing dynamic response will decrease also. The vertical displacements decrease obviously by 46, 37 and 40 for loose, medium and dense sand, respectively, when increasing the embedment of foundation from 0.5 to 1 m, while when the embedment of foundation increases from 1 to 1.5 m, the vertical displacements for loose, medium and dense sand decrease by 45, 38 and 3 respectively. Finally, when the embedment of foundation increases from 1.5 to 2 m, the decrements in vertical displacements are also recorded for loose, medium and dense sand by 42, 36 and 18 respectively.

title: Finite element analysis of a piled machine foundation
abstract: A case study using finite element software for the dynamic analysis and structural design of a machine foundation on piles in homogeneous sandy soil is reported. A parametric study was carried out to investigate the effect of the foundation geometry, the amplitude and frequency of the dynamic load, and the damping ratio. It is concluded that as the pile cap thickness increases the oscillation of displacement decreases due to material damping inherent in the concrete of the pile cap. There is a limit of the pile cap size at which its stiffness governs its dynamic response. Above this size the weight of the pile cap overrides its stiffness effect, and the additional weight leads to an increase in pile displacement. When the pile group size increases, the frequency at which maximum displacement occurs increases, and hence the system becomes more stable against resonance. In the case of changing the pile spacing, the maximum moment factor IM is always at the pile cap centre, where the load is applied. This fa.

title: Dynamic earth pressure on rigid retaining walls induced by a neighboring machine foundation, by the meshless local Petrov Galerkin method
abstract: Dynamic earth pressure induced by machine foundations on a neighboring retaining wall is analyzed with emphasis on factors which control the intensity and location of the design forces. The meshless local Petrov Galerkin (MLPG) method is used to analyze the problem for a variety of retaining wall and machine foundation geometries. The soil medium is assumed to be homogeneous and visco elastic. The machine foundation is idealized as a harmonic sinusoidal dynamic force often encountered in practice. A number of analyses have been made to reveal the effect of the loading frequency, the location and size of the foundation and the soil shear wave velocity on the distribution and magnitude of the dynamic earth pressure. Results indicate that there is a critical frequency and a critical location for which the passive pressure takes the maxima in the entire duration of the dynamic load.

title: Dynamic Analysis Of Machine Foundation
abstract: The analysis and design of machine foundation requires more attention since it involves not only the static loads but also the dynamic loads caused by the working of the machine. The limiting amplitude and operating frequency of a machine are the most important parameters to be considered in analysis of machine foundation. The Elastic half space analogy method with embedment coefficients can be used for coupled modes of vibration to get the natural frequencies and amplitudes of foundation vibrations. With effect to depth of embedment there has been increase in natural frequency but considerable decrease in amplitude of foundation vibrations.

title: Optimization of the machine foundation using frequency constraints
abstract: Faced with the constantly increasing requirements for machine efficiency and reliability, designers have to pay attention to every detail, including machine foundation. Possible outage costs due to foundation damage can easily exceed the costs of design and construction of the foundation. This paper presents a novel and systematic procedure for finding an optimal design of reinforced concrete columns of the spring mounted machine foundation subjected to dynamic loads. The proposed approach assumes considerably decoupled natural modes of the critical structural members which can be optimized as simplified analytical models. It includes the following steps: FE modal analysis of the complete structure, identification of expected dynamic excitation, determination of the critical structural members, optimization of the corresponding analytical models and verification by FE modal analysis of the complete optimized structure. Turbine generator foundation structure was employed as an illustrative example. Operating speeds of the turbine and the generator and their higher order harmonics are taken as a critical dynamic excitation. Therefore, avoiding possible resonance region became the design objective, while the design variables were dimensions of the foundation columns cross section. Lower and upper bounds of the design variables are determined on the basis of structural stability and space limitations regarding condenser and other auxiliary components of the turbine generator system. The results of the analyzed example confirm that the optimization was successfully performed, since the optimized dimensions of the columns yielded natural frequencies outside the critical frequency range.

title: Utilization of the Confined Cell for Improving the Machine Foundation Behavior Numerical Study
abstract: Construction and industrial dynamic sources can produce environmental vibration problems for the supporting soils and adjacent structures. High vibrations and unacceptable dynamic settlements could disturb sensitive devices and even be the cause of structural damage and foundation failure. This paper aimed at investigating the technique to mitigate and control the dynamic effect of vibrating sources like generator using confined cell below the foundation. Numerical modeling of a vibrating source resting on a circular footing with/without confined cell is studied at different cell depth and diameter using Plaxis dynamic version 8.2. A series of axisymmetric model with geometry damping were run via Rayleigh damping after check and validate the program. The effect of confinement on the deformation behavior and dynamic response of supporting soil were investigated. The consequence of such technique on the peak particle velocity and excess pore water pressure in addition to sub grade damping was analyzed. The results showed that, installing the cell with minimum diameter closer to the foundation with sufficient penetration depth significantly improved the dynamic response and decreased the total sub grade deformation. Based on numerical simulations, the peak particle velocity and the excess of pore water pressure for monitored point at the free field are reduced by 90% This method can be considered an alternative technique to increase the sub grade damping by 230% Using barrier in the form of confined cell is an effective screening of vibration that can be achieved by proper interception, scattering and diffraction of surface waves.

title: Vibratory Machine Foundation Design: When to Perform a Dynamic Analysis
abstract: Current codes and standards do not address all aspects of design of soil supported vibratory machine foundations for Petrochemical and other industrial facilities. Many engineers and companies involved in the industry have developed procedures and techniques for calculating loads for analyses on such foundations. The criteria for performing a dynamic analysis can vary significantly from source to source and lead to inconsistent structural reliability. This paper provides a summary of design requirements found in selected current standards and common practices in the industry. A study is presented for small vibratory machinery foundations examples analyzed using commercially available software. Recommendations are provided for determining if it is necessary to perform a dynamic analysis for soil supported vibratory machine foundations based on parameters included in the study. Also included is a discussion of other related issues to vibratory machine foundation analysis. This paper identifies the major considerations for vibratory machine foundation design. It makes recommendations for when it is appropriate to use the rule of thumb methods for foundation systems and when to perform dynamic analysis.

title: Modal Analysis and Fault Diagnosis of Dynamic Machine Foundation under Ambient Excitation
abstract: This paper introduces the modal parameter identification method of a reinforced concrete block foundation under ambient excitation. On this basis, the dynamic characteristics of a stone cutting machine foundation are obtained by modal test under different operating conditions, and test results reveal that the main cause of abnormal vibration lies in lower dynamic stiffness of the whole structure. With the comparison of dynamic response between pre reinforcement and post reinforcement, reinforcement effects of high pressure grouting technique and pre stressed bolt applied to restrain foundation vibration are verified effectively.