Comparison of Direct and Superposition Methods of The Coupled Horizontal and Rocking Vibration of Block Machine Foundations

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Addis Ababa University


The analysis and design of machine foundation requires more attention since it involves both the static loads and the dynamic loads caused by the machine. The response of such foundation under machine induced vibration depends on several parameters such as the shape and size of the foundation, depth of embedment, static load, dynamic excitation frequency, and other geotechnical parameters. The main objective of this study focuses on the sensitivity and comparative study of coupled horizontal and rocking vibration of block machine foundation by applying a direct approach which directly considers the combined effect of force and moment without simplifications. This direct approach is compared with a superposition method which uses simple superposition of the separate action of the force and the moment. In both methods impedance functions are utilized by making use of compiled closed form expressions and dimensionless graphs for the purpose of determining frequency dependent dynamic stiffness and dashpot coefficients. Theoretical results are also validated by comparing results from existing experimental investigations on field test. The comparison showed an encouraging agreement in the case of surface foundation for prediction of natural frequency. Furthermore, a sensitivity study has been conducted on reciprocating compressors based on the dynamic response of surface and embedded block foundations for different aspect ratio under coupled mode of vibration for different embedment ratio for clay, gravel and sand. The results indicate that as the embedment depth increases, the resonant amplitude decreases and resonant frequency increases. In the case of the damped natural frequency when the aspect ratio increases horizontal and angular amplitude increase and damping ratio decreases. On the other hand, in the case of the undamped natural frequency horizontal amplitude, angular amplitude and frequency ratio decrease.



Rocking Vibration, Superposition Methods, Block Machine Foundations