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Earthquake Engineering Research - HKU Libraries - The University ...

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235<br />

modes. An energy drop will be obtained in the second mode as the first mode. Figure 4(b) shows that the<br />

energy drops about 17 dB in the second mode when compared with the uncontrolled system response.<br />

with control<br />

time(s)<br />

Fig. 2 Free response of the building<br />

time(s)<br />

Fig 3 PPF controlled system response<br />

Table 1 PPF result for 1st mode<br />

Gain 1st modal dB drop Controlled damping ratio % Change in damping<br />

5<br />

10<br />

12.5<br />

15<br />

44.75<br />

50.9<br />

50.4<br />

48.8<br />

0.0313<br />

0.0467<br />

0.0499<br />

0.0519<br />

286.42<br />

476.54<br />

516.05<br />

540.74<br />

with control<br />

without control<br />

Frequency (Hz)<br />

Frequency (Hz)<br />

(a)PPF with first mode under control (b) PPF with first two modes under control<br />

Fig. 4 PSD plot comparison for PPF control

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