Missouri University of Science and Technology
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International Conference on Case Histories in
Geotechnical Engineering
(1988) - Second International Conference on Case
Histories in Geotechnical Engineering
Jun 1st
On Properties of Damping of Bases
Wang Xikang
Central Research Institute of Building & Construction of MMI, China
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Xikang, Wang, "On Properties of Damping of Bases" (1988). International Conference on Case Histories in Geotechnical Engineering. 14.
http://scholarsmine.mst.edu/icchge/2icchge/2icchge-session4/14
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Proceedings: Second International Conference on Case Histories In Geotechnical Engineering, June 1-5, 1988, Sl Louis, Mo., Paper No. 4.07
On Properties of ·Damping of Bases
Wang Xlkang
Senior Engineer, Central Research lnsl of Building & Construction,
Ministry of Metallurgical Ind., Beijing, China
SYNOPSIS: On the basis of many tests it has been proved that the damping properties of bases not only
Have bearing on magnitude of base area of foundation but also on weight of foundation and on mecha~
nics model adopted.
This paper puts forward the computation formulas of damping parameters to some
soils.
iNTRODUCTION
dynamic rigidity, damping coefficient and soil
mass must be determined the model may be referred to as three parameter model.
The reasonableness of adopting three parameter model had
been discussed in detail in the paper 2 and
is not discussed herein.
In order to compute the vibration response
of structures and foundations under machinery
with satisfactory precision it is necessary
to establish the damping properties of bases
correctly.
In recent years the problem
above mentioned has been researched by the
author and his colleagues under the conditions
of field tests employing vertical forced
vibration with smaller amplitude which were
performed on foundation of different sizes
and different soil conditions.
When researching
the damping properties of bases a new concept
is cited, Whereby the mass participating in
foundation vibration includes not only mass
of foundation but also soil mass.
In consequence of considering the soil mass not 0 nly
the damping parameters established agree wi~h
practice to a ~reater exterit but also the
precision of computation of vibration reaponse
acquires great improvement.
In the following
several main results of research are introduced
in detail.
Under the harmonic vertical exciting force
with constant amplitude as shown in Fig.l the
equation of motion of foundation may be written
as follows:
Pzsinwt
Fi&'·l
Vibration llodel
m
Considerin&' Sol I lless
1. MECHANICS MODEL AND THEORETICAL FORMULAS
FOR DAMPING COMPUTATION
( 1)
Before researching the damping properties
of bases the mechanics model of foundation
vibration must be first developed because
using the different mechanics model wil1
obtain different dynamic parameters.
When
analysing the damping properties of bases,
the model of Mass-Damping-Spring of linearity
is adopted as shown in Fig.l and the following
assumptions are employed: ·
1) Base soils . possess not only elasticity
but also inertia effect.
2) The soil mass participating in vibration
and vertical damping coefficient as well as
veitical dyna*ic rigidity of bases are not
varied within the range of •xciting fre~uen­
cies.
where: m and m = Mass of foundation ~nd soil
s
Maximum value and frequency
of exciting force
c Vertical damping coefficient
Dynamic • rigidity · of · base
K
z
z Verticil displacement - cif · foun~
dation
Limiting our discussion to forced vibration
merely, we take the solution of the question
in the form:
Z = A z Sfn( . Co) . t - 9)
where: Az= Amplitude of vibration
9 :, Phase shift
In order to obtain three dynamic parameters we
Because three dynamic parameters which are
Second International Conference on Case Histories in Geotechnical Engineering
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