Vibration Analysis and Design of Block-Type Machine Foundations Interacting with Soil

Anteneh, Mulugeta (2003) Vibration Analysis and Design of Block-Type Machine Foundations Interacting with Soil. Masters thesis, Addis Ababa University.

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Until recently, the design and analysis of block-type machine foundations did not properly consider impedance functions. This thesis aims at incorporating impedance functions by making use of recently compiled closed form expressions and dimensionless graphs for the purpose of determining dynamic stiffness and dashpot coefficients. Based on these expressions and the well-known solutions of the dynamic equations of motions, a computer programme is written in FORTRAN. The general requirements and criteria to be fulfilled for machine foundations are compiled. The input soil parameters essential for the design including shear modulus, G, Poisson’s ratio, υ, damping ratio, D, spring stiffness K, and shear wave velocity, Vs, are reviewed. The basic concepts in vibration of structures like frequency, free vibration (undamped and damped), forced vibration and foundation vibration are discussed. In addition, the performance requirements and the basic steps employed in the design of a machine foundation are presented. The older approaches of machine foundation analysis are also reviewed. The basic steps and relations used to calculate the uncoupled vertical and torsional vibration amplitudes as well as the coupled rocking and horizontal vibration amplitudes are provided.Based on the basic relationships for the vibration amplitudes and the relatively simplified and well-compiled recent works of G. Gazatas [2] for the determination of static stiffness, dynamic foundation soil stiffness as well as radiation dashpot coefficient, a computer program in FORTRAN is written to analyze block-type machine foundations for the following four conditions in a rational approach. (a) Foundation on the surface of a homogeneous half space (b) Partially of fully embedded foundation in a homogeneous half space. (c) Foundations on the surface of a homogeneous stratum overlying the bedrock. (d) Partially of fully embedded foundations in a homogeneous stratum overlying the bedrock. Finally, practical examples are solved for the above four cases using the programme and the results are checked against each other. The same example is also solved using the classical method even though this method does not appropriately incorporate the impedance functions. A comparison of the results obtained using the classical approach and the more rational method adopted in this work indicates that the latter is a substantial improvement over the former. A comparison of the results obtained showed that embedding a foundation is a very effective way to reduce to the acceptable levels of the anticipated amplitudes of vibration, especially if these amplitudes arise due to rocking or torsion. Such an improvement would be effected mainly by the increase in radiation damping produced by waves emanating from the vertical sidewalls.

Item Type: Thesis (Masters)
Uncontrolled Keywords: Civil Engineering
Subjects: Q Science > QC Physics
T Technology > T Technology (General)
T Technology > TA Engineering (General). Civil engineering (General)
Divisions: Africana
Depositing User: Andriamparany Edilbert RANOARIVONY
Date Deposited: 11 Jul 2018 12:15
Last Modified: 11 Jul 2018 12:15

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