Active Control in Structures

In this paper the application of control theory to structural engineering has been presented from a structural engineering perspective. The objective of this paper is to summarize key steps that are required to design an active control system for a structure. Total acceleration feedback with H2/LQG controller is used in this paper. The structural control device is made of tendon/pulley system. Multiple-input and single-input control systems were compared. It was shown that multiple-input control system could provide a more efficient design. 1.0 Introduction Conventional seismic design of structures permits the reduction of forces for the design below the elastic level on the premise that inelastic action in well-detailed structures will dissipate significant amount of energy and as a result the structure will survive a severe earthquake without collapse. Significant damage in critical regions of structural members followed by degradation in hysteretic behavior results in inelastic behavior and therefore dissipation of energy. In this design philosophy the designer relies upon inherent ductility of structure to prevent catastrophic failure, while accepting a certain level of structural and nonstructural damage. In order to reduce the damage in structural elements, protective systems are ideal ways of modifying stiffness and viscous damping of structures. Designer can identify the distribution of damage and minimize it. Considerable attention has been paid to active and semi-active control research in recent years, with particular emphasis of wind and seismic response [Soong (1991), Spencer (1997)]. 2.0 Background The objective in a typical H2/LQG method is to find a control scheme that minimizes the control index given by equation (1). Based on the values of measurements the control force, u, will be computed, using the weighting factors of the designer choice (Q and R in equation 1). The control law that minimizes the value of J is given by a linear-state feedback.