Active structural control based on the prediction and degree of stability

Active control of buildings and structures for reducing damage due to earthquake and other environmental forces represents a relatively new research area. Most of the recent studies on this area are based on the applications of traditional linear quadratic regulator (LQR) control to the earthquake-excited structures. This paper presents the analytical solution of the modified linear quadratic regulator (MLQR) problem including a parameter a known as system stability order in the presence of unknown seismic excitation. The resulting closed-open loop active control force depends on the system state, seismic excitation and alpha. An approximate solution of the problem is based on the real-time prediction of near-future excitation. Since the primary focus of this study is on the relation between the system stability order alpha and the prediction of near-future excitation, numerical simulations of a three-storey undamped structure subjected to an El Centro earthquake are performed for different) values. It is shown that the relative displacements can be reduced significantly for each selected alpha value as the near-future excitation is predicted precisely and there is no significant increase in the control forces. The results also show that there is no need to predict the distant-future excitation to be able to achieve a given reduction in relative displacements as the system stability order alpha is increased. It is also shown that the accelerations increase in general after the fourth-step ahead prediction for a given a while they decrease as a increases. (C) 2001 Academic Press.