Abstract:
The vertical dynamic behaviour of machine foundations subjected to vertical dynamic loading
was investigated for surface and embedded foundations. The responses of these machine
foundations were determined using analytical and numerical solutions ranging from simple to
complex. An accurate prediction of impedance functions for the foundation system is a key step
in the design procedures. The prediction accuracy depends on how close the modelling
procedures are to reality. The subject of soil dynamics is complex. At times, the choice of the
analysis model is based on the experience of the engineer with the model. The chosen model
may or may not result in an optimal, efficient, and accurate design.
The current advancement in manufacturing technology calls for machine foundation systems
with high performance, availability and reliability. The analysis and design of such complex,
large and sensitive machine foundations requires good understanding of their dynamic
behaviour.
The aim of this thesis is to investigate and evaluate the most accurate analytical and numerical
models for determining the dynamic behaviour of surface and embedded machine foundations.
Surface and embedded footings were cast at the experimental station at the University of
Pretoria. The vertical dynamic behaviour of these foundations was determined by vertical
harmonic loading. The measured impedance functions were compared with predicted responses
obtained from analytical solution of the Winkler model, elastic half-space theory, simplified
Lysmer (1965) model, Veletsos and Verbic (1973) models, the Dyna5 program and numerical
solution of finite element method (Abaqus). The dynamic responses of the surface foundation
predicted by the analytical solution proposed by Veletsos and Verbic (1973) soil with mass,
compared reasonably well with the results obtained from field-measured data. The measured impedance functions of the embedded foundation were compared with the
predicted results ascertained using the analytical solution proposed by Novak and Beredugo
(1972), Dyna5 program and numerical solution of the finite element method (Abaqus). It is
shown that embedment increases stiffness, natural frequency, natural frequency ratio, and
damping ratio. The embedment reduces resonant amplitude, resonant amplitude ratio and has an
insignificant effect on resonant frequency and resonant frequency ratio. The measured dynamic
responses compared favourably with the results predicted by the finite element method
(Abaqus).
The conclusion is that the analytical model proposed by Veletsos and Verbic (1973) soil with
mass, and the finite element method (Abaqus) can be used to accurately predict the dynamic
response of surface and embedded machine foundations respectively.
