Geology Reference
In-Depth Information
The value of the optimal damper coefficients
as calculated by Takewaki is as follows: c
1
=
4.8x10
6
N-s/m and c
2
= 4.2x10
6
N-s/m. One fact
to be noted is that Takewaki neglected the con-
tribution of the in-structure damping while cal-
culating these coefficients. From our sensitivity
analysis point of view, this is ideal because the
damper coefficient values obtained do not have
any contribution from in-structure damping;
thereby providing us with a flexibility of incor-
porating different in-structure damping models
with apparently no significant error. The undamped
frequencies of the uncontrolled frame are re-
corded in Table 1.
of both ground motions are presented in Figure
6 and Figure 7.
Figure 6 shows that the Chi-Chi record has a
narrow band spectrum with a predominant fre-
quency content of 1.7Hz. On the other hand, the
Sakaria record has a broad band spectrum with
Fourier peaks occurring between 0.5 and 10 Hz
as is evident in Figure 7.
The choice of the ground motion records is
made with a focus to excite as many modes as
possible. For example, reviewing the modal fre-
quencies given in Table 1 it becomes evident that
in the case of the Chi-Chi record the predominant
excitation is expected to happen in the first 2
modes, whereas the Sakaria record is expected
to excite several higher order modes to varying
degrees. Since our intention is only to highlight the
possible uncertainties arising due to the interac-
tion between the inherent in-structure damping of
the system and the 'added damping' supplied by
the mechanical dampers, the choice of these two
ground motions may be deemed to be appropriate.
Description of the Ground Motions
In order to assess the sensitivity of the optimally
controlled frame to different in-structure damping
models, the controlled frame is subjected to two
different earthquake ground motions: the Chi-Chi
and the Sakaria. The Fourier amplitude spectra
Figure 5. Uncontrolled shear frame building (left) and optimally controlled shear frame building (right)
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