Semi-Active Control Of Steel Mega-Frame With Suspended Floors

On the basis of a thorough analysis of the related research findings home and abroad, this thesis aims at a research of the vibration control of active variable stiffness and active variable damper on steel mega-frame with suspended systems. It comprises the following sections:1). In chapter 1, the development,actuality and application in engineering of huge structure with suspended substructure and semiactive control technology are introduced,and the present research overview and development trend are sketched ,finally,the background and main research contents of this thesis are introduced.In chapter 1, firstly,the reliability of equivalent model is identified by summing up the existing equivalent simplified models to steel mega-frame and by analyzing the seismic response concerning the precise model and equivalent model based on examples separately.2). In chapter 2,the relationship of the parameters such as frequency ratio, mass ratio, damper ratio of megaframe and substructure, and mean-square of random response is given .These parameters is optimized by random analysis method for single-degree and multi-degrees of freedom of steel mega-frame structure with suspended systems. And the practical analysis method for the length of suspension boom is obtained by establishing the relationship between the parameter-length of suspension booms and the mean-square response with the variety of the parameters directly.3). In chapter 3, an active variable stiffness systems, which can provide a live and continuous change of the length of suspension booms of suspension floor, is adopted. The systems is used to change the length of suspension booms so as to change the dynamic characteristic of structure. At the same time, the variety of the length of suspension booms is to bring up elastic restoration force that can work as the control force for semi-active control devices as long as it is designed reasonably. 4). Based on the LQR optimum control theory, this thesis establishes elasticrestoring force that is caused by changing the length of suspender, that is , the relationship between the active variable stiffness control force and quadratic optimal control force, and under the principle of keeping elastic restoring force closest to or follow and realize LQR optimum active control force, the algorithm of solving optimum elastic restoring force can be deduced and obtained , and hereby a method which can solve the real-time optimum variation of suspender length is established. As the example analysis indicates, this active variable stiffness system has better controlling effects on the structural displacement and velocity reaction, but the effects on the supressing acceleration of structure are unsatisfactory.5). In chapter 4, an existing typical active variable damping control system is introduced into the giant steel frame with suspended systems, and the controller is set in a new way that is different from the already researched one, in which an active variable damper is set between the main structure floors alone, and between the sub structure floor alone.6). A concise performance index expression is put forward, and by using the control theory of the SMC(sliding mode control), the switch function and variable structure controller is analyzed and designed, resulting in an algorithmic method of variable structure whose expressing form is relatively concise. As example analysis indicates , the control way of active variable damping has a better control result to the displacement and velocity reaction of the structure, and a certain control result to the acceleration reaction of the structure. So active variable damping control is a vibration control system which has better robustness.7). In chapter 5 , conclusions have been made, and problems remaining to study further are put forward.