The Effect of a Rubber Sheet on the Dynamic Response of a Machine Foundation Located over a Small Thickness of Soil Layer

Placing a machine footing over a small thickness of soil layer, which is located over a bedrock, could encounter many challenges due to the bed’s notable stiffness in comparison to the soil. The advantages of using rubbers to protect facilities (structures, machine foundations, nearby footings and equipment, etc.) from vibration and control its consequences are well known nowadays. In this study, the benefits of employing a small thickness of rubber sheet (2 mm) on the dynamic response of a machine foundation which is located over four thicknesses of soil (210, 420, 630, and 840 mm) has been investigated. The soil layer is located over an artificial bedrock that is consisted of a thick concrete layer. The tests have been conducted in a vast test pit of size 2500×2500 mm and a depth of 840 mm by using a semi large-scale machine foundation model with a square concrete foundation of width 400×400×100 mm. It was observed that, by increasing the soil layer thickness, the resonant frequency and amplitude of the vibrating system decreases. Moreover, by employing a rubber sheet beneath the machine footing, the resonant frequency of the vibrating system significantly decreases especially for a small thickness of the soil layer. Although, using a rubber sheet could slightly increase the resonant amplitude, but the benefit of the resonant frequency-changing capability of the rubber sheet is too impressive by taking the resonant frequency of the system far enough from the unchangeable working frequency of the machine and preventing the resonant phenomenon to happen.

Dynamic Analysis of Machine Foundation with and without Geosynthetic Reinforced Soil Beds

Most of the machine foundations are located in the regions with poorly graded soil including loose sand. Hence, the experimental studies are undertaken to evaluate the dynamic parameters of geosynthetics using cyclic PLT. This paper presents the results of the 10 m2 area of the model cyclic plate load test conducted on geosynthetics reinforced soil beds with similar density, supporting square footing, the results of cyclic PLT from the laboratory-model tests on square footings resting on a sand bed. The various intensity of cyclic load (loading-unloading) applying on the footing and then the elastic recovery of the footing alike to each intensity of loading obtains during the tests to determine the coefficient of elastic uniform compression (Cu) of sand. Results showes that the provision of geosynthetics like geogrid and jute the value of Cu decreases due to elastic recovery increases as compared to unreinforced soil bed, by 06% to 94% and natural frequency 03% to 76% . Introduction of planer geogrid at the base of the geosynthetic matress not only enhance the load carrying capacity but also increasing the elastic recovery to making them more elastic and prevents footing to failure due to vibration. In addition to the experiments also analyses various dynamic parameters of the machine foundation using cyclic PLT on the geosynthetics

Effects of Soil-Structure Interaction on Torsionally Coupled Base Isolated Machine Foundation under Earthquake Load

In this paper, the influence of soil-structure interaction (SSI) on a torsionally coupled turbo-generator (TG) machine foundation is studied under earthquake ground motions. The beneficial effects of base isolators in the TG foundation under earthquake ground motions are also studied duly, considering the effects of SSI. A typical TG foundation is analyzed using a three-dimensional finite element (FE) model. Two superstructure eccentricity ratios are considered to represent the torsional coupling. Soft soil properties are considered to study the effects of SSI. This research concludes that the effects of torsional coupling alter the natural frequencies, if ignored, could lead to unsafe design. The deck accelerations and displacements are increased with an increase in superstructure eccentricity. On the other hand, the deck accelerations and displacements are greatly reduced with the help of base isolators, thus confirming the beneficial use of base isolators in machine foundations to protect the sensitive equipment from the strong earthquake ground motions. However, the effects of SSI reduce the natural frequencies of the TG foundation resting on soft soil conditions and activate the higher mode participation, resulting in amplifying the response.

The effect analysis of the stiffness changes of a Traditional Fishing Boat Foundation on Vibration Amplitude

The ship with the outboard engine is intended to make it easier for fishers to operate and maintain. However, the magnitude of the vibration due to the excitation of the engine during operation adversely affects the surrounding structures. It is evidenced by measuring the vibration amplitude of more than 0.02 mm at several points around the ship engine foundation. This study aims to reduce these vibrations by changing the canal's dimensions as a foundation and using damping rubber as the simplest solution. The analysis was carried out by calculating the vibration parameters of 2 types of machines, SR1110 and S1100. The numerical method is used to calculate the vibration's amplitude by varying the value of channel stiffness and rubber damping on the machine foundation. Supporting data is obtained by measuring the vibration amplitude at several points around the foundation. The magnitude of the previous vibration amplitude is 0.078 mm for the SR1110 type and 0.069 mm for the S1100 type, which exceeds the limit still. The amplitude is reduced by changing the foundation's dimensions and using a rubber damper (c). With the new foundation dimensions, the amplitude for the diesel engine type SR1110 becomes 0.0245 mm and type S1100 becomes 0.0238 mm. Increased stiffness and the addition of rubber succeeded in reducing the vibration amplitude by a significant value. The amplitude was reduced by 69% for the SR1110 engine type and 65% for the S1100 engine type within the allowable limit of less than 0.02 mm to 0.03 mm based on Barkan's observation results.

Experimental evaluation of the effect of soil water fluctuations in the dynamic behavior of machines

In this study the dynamic response of a machine-foundation-soil system was investigated experimentally and theoretically. The objective of this work is to analyze the effects of the water table fluctuations in the soil on the response of the foundation and machine subjected to dynamic loads at frequencies ranging from 30 to 50 Hz. A physical model test was developed to simulate a machine-foundation-soil system, with measurements of the machine vibrations and the shear wave velocity of the soil. It is found that the water level produced significant changes in the shear wave velocity of the soil and, thus, in the natural frequencies of the system. For a fully saturated soil the vibration levels increased due to a working condition near resonance. The results showed a good agreement between the experimental vibration measurements and the predictions based on the theory used in foundation design, when considering the appropriate soil parameters. It is concluded that proper estimation of soil parameters is of high importance in the design process of machine foundations.