r - The Hong Kong Polytechnic University

Comparison of SAF-TMD and PF-TMD system responses
In this subsection the experimental seismic responses of the SAF-TMD system are compared to the simulated
responses for two passive systems (PF-TMD-1 and PF-TMD-2). Theoretically, when using the SAF-TMD
model, the response of a PF-TMD can be simulated by pre-selecting an equivalent pre-compression force N 0 and
then setting the control voltage V(t)=0. Table 4 lists the equivalent N 0 for these two PF-TMD systems. For the
PF-TMD-1, N 0 is set to 130 N, which is exactly equal to N 0 of the SAF-TMD used in the test. Restated,
PF-TMD-1 may represent an uncontrolled SAF-TMD. On the other hand, N 0 of the PF-TMD-2 is selected such
that the TMD results in a peak stroke equal to that of the SAF-TMD for a given ground motion. Therefore, N 0 of
the PF-TMD-2 differs for different PGA levels in Table 4. Figure 8 compares the RMS responses (J 2 and J 4 ,
respectively) and peak TMD stroke (J 5 ) of the three TMD systems when data for the the selected earthquake is
applied with different PGA levels. Note that the plots are for the experimental data for the SAF-TMD, and only
the tested PGA levels are shown. Additionally, the data for PF-TMD-1 and PF-TMD-2 in Figure 8, respectively,
are simulation data. The two figures confirm that, (1) for the range of the PGA levels tested, both the
displacement and acceleration performance of the PF-TMD-1 are superior to those of the SAF-TMD and
PF-TMD-1and that, (2) with a lower damping force, the PF-TMD-1 has the best control performance among the
three systems; however, it also results in a peak stroke much higher than those of the SAF-TMD and PF-TMD-2,
especially in earthquakes with high PGA. The maximum stroke for the SAF-TMD observed in the test is only
0.15m. (3) With the same peak TMD strokes, both the displacement and acceleration performance of the
SAF-TMD are superior to those of the PF-TMD-2 cases. Figure 9 compares the time histories of the structural
displacement and TMD stroke for the SAF-TMD and PF-TMD-2 systems subjected to the El Centro earthquake
(PGA=500gal). The figure shows that the SAF-TMD is more effective in suppressing the structural
displacement compared to the PF-TMD-2, which has the same peak TMD stroke (0.12m). Furthermore, the
SAF-TMD can also prevent a residual TMD stroke, which is observed in the PF-TMD-2 system.
Table 4 Pre-compression force (N 0 ) of the PF-TMD-1 and PF-TMD-2
Earthquake
PGA Pre-compression force N 0 (N)
(gal) PF-TMD-1 PF-TMD-2
300 130 253
El Centro 400 130 313
500 130 474
Disp. reduction ratio
1
0.95
0.9
0.85
0.8
0.75
0.7
0.65
SAF-TMD
PF-TMD-1
PF-TMD-2
Index J2 (El Centro)
Acc. reduction ratio
1
0.95
0.9
0.85
0.8
0.75
0.7
0.65
SAF-TMD
PF-TMD-1
PF-TMD-2
Index J4 (El Centro)
Peak TMD stroke (m)
0.6
0.5
0.4
0.3
0.2
0.1
SAF-TMD
PF-TMD-1
PF-TMD-2
Index J5 (El Centro)
0.6
200 300 400 500 600
PGA (gal)
0.6
200 300 400 500 600
PGA (gal)
0
200 300 400 500 600
PGA (gal)
(a) Index J2 (b) Index J4 (c) Index J5
Figure 8 Comparison of performances indices of various TMD systems to the El Centro earthquake with
different PGA levels
(a) Structural displacement
(b) TMD stroke
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