Recent trend shows the necessity of the construction of high rise building which is possible due to the development of modern technology. With the increase of the height of the structure, its natural frequency becomes low and hence, it is important to protect these flexible structure from the effect of environmental loadings (e.g., strong winds and earthquake motions) which induces severe vibrations. To protect such structures, it is necessary to inject a lot of control force which is possible by using a suitable active feedback control scheme. In the past, there are lot of research on the active control of the first bending mode of suspension buildings. However, as the tendency of constructing more reliable and lighter building increases, it becomes insufficient to consider the first mode only, since the vibration of higher modes also raises problems for structure strength.
In this paper, a lumped modeling method and a robust control design are proposed for controlling the multiple vibration modes of tall buildings. Two controller design methodology has been discussed in connection with the control of a 20 story benchmark building. These are filtered Linear Quadratic (LQ) optimal and Hinfinity based optimal control theory. Both the evaluation criteria and the vibration control effects are compared using simulation results. Also experience shows that one possible way of improving the structural control efficiency is by placing the actuator and sensors in a suitable locations. This is also a possible way of remedies to remove the spill over instability (excitation of high frequency mode which is neglected in the time of modeling) due to feedback control effects. Here the placement of the actuator and sensors in suitable locations in relation to the feedback control strategy are also discussed.