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and the inside of the damper cylinder housing. The damper has an inside diameter of 20.3 cm and a
stroke of ±8 cm. The electromagnetic coils are wound in three sections on the piston, resulting in four
effective valve regions as the fluid flows past the piston. The coils contain a total of about 1.5 km of
wire. When wired in series, the total coil has an inductance L 0 = 6.6 H and a resistance R Q = 21.9 Q.
The completed damper is approximately 1 m long and has a mass of 250 kg. The damper contains
approximately 5 liters of MR fluid. The amount of fluid energized by the magnetic field at any given
instant is approximately 90 cm 3 .
Figure 13b shows the experimental setup at the University of Notre Dame for the large-scale 20-ton MR
fluid damper. The damper was attached to a 7.5 cm thick plate that was grouted to a 2 m thick strong
floor. The damper is driven by a 560 kN actuator configured with a 57 1pm servo-valve with a bandwidth
of 30 Hz. A Schenck-Pegasus 5910 servo-hydraulic controller is employed in conjunction with a
200 MPa, 340 1pm hydraulic pump. So that reliable tests of the dynamic performance could be obtained,
particular care was taken to minimize compliance in the system.
Analytical and experimental pseudo-static studies of the damper have been conducted at the Structural
Dynamics and Control / Earthquake Engineering Laboratory at the University of Notre Dame. Figure
14a shows the measured force-displacement loops under a commanded 5.4 cm/sec triangular displacement
at the maximum magnetic field and no magnetic field (off state) respectively. At the maximum
magnetic field, the output force of the damper is 201 kN, which is within 0.5% of the design specification
of 200 kN. Moreover, the on/off range of the damper is well over the design specification of 10.
Fig. 14b also shows the measured force-velocity relationship and its comparison with the results of the
axisymmetric model and parallel plate model (Spencer et al 1999). Both analytical models compare
well with the experimental results. The dynamic response of the damper to changes in the commanded
force has also been shown to be excellent (Yang et al 2000; Yang 2001).
Recently, Sunakoda et al (2000) have also presented encouraging results regarding design and construction
of large scale MR dampers. More information regarding MR dampers and their application to
civil engineering structures can be found at: hitpj/cee muc.edu/sstl/.
Max Magnetic Reid (2A)
No Magnetic Field iQA)
Figure 14. (a) Measured force-displacement loops at 5.4 cm/sec; (b) Comparison of measured and
predicted force-velocity behavior (Spencer et aL 1999)