Nonlinear viscous damper characterization tests
Baiping Dong, Richard Sause, James M. Ricles
Lehigh University
Damper Characterization Test
Characterization tests of nonlinear viscous dampers under sinusoidal displacement loading
protocol (Figure 1). This loading protocol has a total of 12 sinusoidal cycles, including 2 ramp
up cycles, 7 full cycles and 3 ramp down cycles. Different displacement amplitudes and different
excitation frequencies were used since it is known that the behavior of nonlinear viscous
dampers is sensitive to displacement amplitude and excitation frequencies. Majority of tests were
done at the ambient temperature of 20 ~25˚C, however for tests with excitation frequency of
0.5Hz and 1Hz, there were tests with controlled ambient temperatures of 10˚C, 20˚C and 30˚C.
Damper Displacement (in)
1.5
2 ramp
up cycles
1
3 ramp
down cycles
7 stable full cycles
0.5
0
-0.5
-1
-1.5
0
2
4
6
Time (sec)
8
10
12
Figure 1. Sinusoidal displacement loading protocol
Test Setup
The experimental setup for the characterization test is shown in Figure 2. The viscous damper is
pinned to the foundation beam using a clevis, and at the other end connected to the NEES
hydraulic actuator through a short segment of ‘rigid’ steel beam. The reason of adding the ‘rigid’
steel beam is to extend the arm of actuator piston and thus to accommodate for the spacing of
damper anchored to the strong floor. The actuator and ‘rigid’ steel beam are both vertically
supported through rollers to ensure the actuator is lined up with the damper horizontally. The
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actuator has a force capacity of 382 kips and a maximum stroke of +/- 20inches, and the
maximum velocity the actuator can reach is 45 in/second.
Figure 2. Setup of characterization test
Test Instrumentation
Load and displacement transducers are two major types of instrumentation implemented in the
characteristic tests, shown in Figure 3. A load cell with a capacity of 150 kips is mounted
between the viscous damper and ‘rigid’ steel beam to measure the damper force during the tests.
LVDTs are installed to measure the damper deformation and clevis deformation; LVDT-1 and
LVDT-2 measure the relative displacement of damper endplate to floor; LVDT-3 and LVDT-4
measure the relative displacement of clevis to floor; LVDT-5 measure the relative displacement
of damper clevis to floor; the damper deformation is the difference between the average
measurement of LVDT-1and LVDT-2 and measurement of LVDT-5. Thermocouples are used to
monitor the temperature of the damper; one thermocouple is attached to the surface of the
damper cylinder housing along the circumference at mid-length of the damper to monitor damper
temperature change in tests, and meanwhile another thermocouple is exposed in the air close to
damper to monitor the ambient temperature.
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Figure 3. Instrumentation implementation
Data uploaded to NEES hub
Experiment 4 (VD-1)
Characterization tests on nonlinear viscous damper #1. For this damper, the sinusoidal displacement
amplitude varies from a full range of 0.5~4.0 inches, and the excitation frequency varies from a
full range of 0.25~4.0Hz. The test matrix is shown in table 1and table 2. With the combination of
displacement amplitude and frequency, the velocity range the damper experienced in the tests
varies from 0.785 in/sec to 37.7 in/sec.
Table 1. Test matrix of characterization tests on damper #1
Displacement amplitude (inches)
Frequency
(Hz)
0.25
0.5
0.75
1
1.25
1.5
2
3
4
0.5
0.75
Note:
1 valve
1
2 valves
1.25
1.5
1.75
2
2.5
3 valves
Table 2. Test matrix of temperature check on damper #1
Frequency
(Hz)
0.5
1
Displacement amplitude (inches)
1.25
2
10 °C, 20 °C, 30 °C
10 °C, 20 °C, 30 °C
10 °C, 20 °C, 30 °C
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3
4
Experiment 5 (VD-2)
Characterization tests on nonlinear viscous damper #2. For this damper, the characterization tests were
done at a sample of selected excitation frequency. The test matrix is shown in table 3.
Experiment 6 (VD-3)
Characterization tests on nonlinear viscous damper #3. For this damper, the characterization tests
were done at a sample of selected excitation frequency. The test matrix is shown in table 3.
Table 3. Test matrix of characterization tests on damper #2 and #3
Displacement amplitude (inches)
Frequency
(Hz)
0.25
0.5
0.75
1
1.25
1.5
2
3
4
0.5
0.75
1
1.25
1.5
1.75
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2
2.5
3
4