Semi-Active Control Algorithms for Structures With Variable Dampers.
Semi-Active Control Algorithms for Structures With
Sadek, F.; Mohraz, B.
NISTIR 6052; 35 p. October 1997.
Journal of Engineering Mechanics, Vol. 124, No. 9,
981-990, September 1998.
Available from: National Technical Information Service
(NTIS), Technology Administration, U.S. Department of
Commerce, Springfield, VA 22161.
1-800-553-6847 or 703-605-6000;
Order number: PB98-103898
algorithms; seismic design; semi-active control;
structural dynamics; variable dampers
Semi-active control systems combine the features of
active and passive control to reduce the response of
structures to various dynamic loadings. They include:
a) active variable stiffness where the stiffness of the
structure is adjusted to establish a non-resonant
condition between the structure and excitation, and b)
active variable damper where the damping coefficient of
the device is varied to achieve the most reduction in
the response. This study is concerned with examining
the effectiveness of variable dampers for seismic
applications. Three algorithms for selecting the
damping coefficient of variable dampers are presented
and compared. They include: a linear quadratic
regulator (LQR) algorithm, a generalized LQR algorithm
where a penalty is imposed on the acceleration response,
and a displacement-acceleration domain algorithm where
the damping coefficient is selected by examining the
response on the displacement-acceleration plane and
assigning different damping coefficients accordingly.
Two single-degree-of-freedom structures subjected to 20
ground excitations are analyzed using the three
algorithms. The analyses indicate that unlike passive
dampers where for flexible structures, an increase in
damping coefficient decreases the displacement but
increases the acceleration response, variable dampers
can be effective in reducing both the displacement and
acceleration responses. The study indicates that the
generalized LQU algorithm is more efficient than the
other two in reducing the displacement and acceleration
responses. The algorithms are used to compute the
seismic response of two flexible structures - an
isolated bridge modeled as a single-degree-of-freedom
system and a base-isolated six-story frame modeled as a
multi-degree-of-freedom system. The results indicate
that variable dampers reduce the displacement and
acceleration responses of the two structures to a