Unformatted text preview: il. In order to express this tendency of the imaginary part,
the first natural frequency fg of the surface stratum is
particularly termed “cutoff frequency”.
The frequency characteristic of the imaginary part is
depicted in the figure: Both the real and the imaginary
parts of the horizontal D.I.F are
fluctuating in higher
frequencies over 2.5Hz. The
fluctuations are particular for
the layered strata. The fluctuations for the
rotational D.I.F are also
observed in far higher
frequencies. Comparing the raft foundation to the pile foundation, slight
differences in the horizontal D.I.F are observed between
both foundations. Distinct differences are recognized in the
real parts of the rotational D.I.F. The real parts of the pile foundation are much larger than
that of the raft foundation.
The rotational stiffness of the pile group foundation is
composed of:
(1) The rotational stiffness at each pile caps
(2)The stiffness estimated by a product of the vertical
stiffness at the each pile caps and the distance of the
caps from a neutral axis of the foundation.
In a case of the pile group foundation, the latter (2)
becomes significant. Consequently, the rotational
stiffness of the pile foundation becomes larger than the
raft foundation.
We can understand the differences in D.I.F between both
the foundation types arise distinctly in the real parts of the
rotational and the other components exhibit only trivial
differences. 3.4 Damping Factor of Dynamic Impedance Function
A damping factor, which is evaluated from the hysterics
loops of the structural components, is employed for a
dynamic analysis of a superstructu...
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 Summer '14
 DrGRD
 pile foundation, surface stratum

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