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Semi-Active Control Algorithms for Structures With Variable Dampers.

pdf icon Semi-Active Control Algorithms for Structures With Variable Dampers. (2328 K)
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.
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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 significant degree.