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els can be readily supplied by batteries. Table 2 provides a summary of the key physical characteristics
of both MR and ER fluids.
Spencer et al. (1997) and Dyke et al. (1998) (see also: http://www.nd.edu/-quake/) have conducted a
number of pilot studies to assess the usefulness of MR dampers for seismic response reduction. Dyke et
al. (1998) have shown through laboratory experiments that the MR damper, used in conjunction with
recently proposed acceleration feedback control strategies, significantly outperforms comparable passive
configurations of the damper for seismic response reduction.
Table 2 Summary of the Properties of Today's MR and ER Fluids (Carlson 1994).
Property
Max. Yield Stress i y(fjeld)
Operable Temp. Range
Plastic Viscosity, r^
Stability
V
T y(field)
Power Supply (typical)
Response Time
Particle Sedimentation
Raw Materials
MR Fluids
50-100kPa
-50 to 150°C
0.2-1. OPa-s
Not affected by most impurities
10- 10 -10- u s/Pa
2-25V, 1-2 A
milliseconds
Little
nontoxic & environ, safe
ER Fluids
2-5 kPa
+ 10to90°C
0.2-1. OPa-s
Cannot tolerate impurities
l(T 7 -l(r 8 s/Pa
2000-5000 V, 1-1 OmA
milliseconds
Little
nontoxic & environ, safe
DEVELOPMENT OF FULL-SCALE MAGNETORHEOLOGICAL DAMPERS
To prove the scalability of MR fluid technology to smart damping devices of appropriate size for civil
engineering applications, a 20-ton MR fluid damper has been designed and built (Carlson and Spencer
1996; Spencer et al. 1997, 1999). Figure 13a shows the schematic of the MR damper tested herein. The
damper uses a particularly simple geometry in which the outer cylindrical housing is part of the magnetic
circuit. The effective fluid orifice is the entire annular space between the piston outside diameter
Figure 13. (a) Schematic of 20-ton MR fluid damper; (b) Experimental setup