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Response Control by Magneto-Rheological (MR) Fluid
Magneto-rheological (MR) dampers have been expected to control the response of civil and building
structures in recent years because of their large force capacity and variable force characteristics. In
general, passive control has a limitation of damping effects within a certain range of frequency and
input levels. Semi-active control reduces both response displacements and accelerations. The MR
damper generates a damping force, which does not depend on the piston speed (Fujitani 2000). The
target of this subject is to improve the safety, functionality and habitability by controlling the response
displacements and accelerations by using MR dampers. For this purpose, MR dampers and a control
algorithm have been developed, and their validity is discussed by an analytical study and shaking table
tests.
MR damper
(a) Control of base isolation system
Damage Detection by Sensors
(b) Two types of story drift control
Figure 2: Test frame for response control by MR
dampers
Monitoring the structural soundness of a building effectively reduces its life cycle cost. A series of
experimental tests for a monitoring system has been conducted by measuring the process in which a
concrete device is broken. Devices are inserted in the central structural plane in each frame layer
(Figure 3). The same device is installed in each layer, and the purpose of the test is to detect damage.
The input earthquake wave is El Centro 1940 NS. The table was shaken three times with maximum
velocities of lOcm/sec, 30cm/sec, and 40cm/sec. White noise excitation and micro tremor
measurement were carried out before and after shaking.
Two identification methods were carried out: one using the data of before and after shaking, and the
other using the data during shaking. For the first, we used the flexibility method, the layers stiffness
method and the identification method using multiple natural frequency changes, etc. For the second,
we used the ARX model and parallel processing identification method (Morita 2001).
Several types of "smart sensors" (such as line-saving systems, RDIF tags, maximum value memory
sensors, smart temperature sensors, and AE sensors) are examined.
Rocking Energy Dissipation System
Rocking systems that cause rocking vibration under appropriate control during earthquakes are now
under development (Midorikawa et. al. 2002). Some researchers have pointed out that the effects of
rocking vibration can reduce seismic damage to buildings subjected to strong earthquake ground