Semi-active Control Of Long-span Spatial Structures Under Multi-dimensional And Multi-point Seismic Excitation Using Magnetorheological Dampers

In recent years, lots of long-span building structures have been constructed in China. Because of the huge degree-of-freedom and its complex spatial characteristic, their safety under earthquake excitation has received more and more attention. Magnetorheological (MR) damper have been widely used in the field of civil engineering structures to protect them from earthquake and high winds. However, few efforts have been devoted to the application of MR damper to long-span spatial structures. In this dissertation, MR damper-based semi-active control system is introduced to long-span spatial structure for seismic protection. The main work and achievement are as follows:(1) The feasibility of the application of semi-active control system on long-span spatial structure is first studied. The expression of linear quadratic regulator (LQR) optimal control force in three-dimensional cases is deduced. Numerical simulation is performed on a seismic excited lattice structure installed with MR damper. The results show that both the displacement and acceleration responses of the spatial structure can be reduced greatly by the semi-active control system.(2) Based on the dynamic characteristic of MR damper, a semi-active control problem is described as a constrained optimization problem by using precise integration method. And a trust-region based instantaneous optimal semi-active control (TIOC) algorithm for magnetorheological (MR) dampers is proposed. The effectiveness of the semi-active control algorithm is verified through a numerical example of a seismic excited three-story frame and a control experiment on an MR damper controlled cantilever beam. Both simulation and experimental results indicate the better control effectiveness of the proposed controller on reducing the root-mean-square responses, and the superiority of the proposed controller during multi-dampers situation is also demonstrated. It is found that the time interval of the controller may greatly affect the control effectiveness of the semi-active controller.(3) By using trust-region based instantaneous optimal semi-active control algorithm, the semi-active control of long-span spatial structure is studied. The basic control equation of long-span spatial structure under multi-dimensional and multi-point excitation is first set up. Then the effectiveness of the TIOC controller is evaluated though a numerical example of a long-span spatial structure under both multi-dimensional uniform earthquake excitation and travelling-wave excitation with different apparent velocities. The simulation results indicate that the MR fluid damper-based semiactive control systems have the potential for mitigating the responses of full-scale long-span spatial structures under earthquake hazards. The superiority and stability of the proposed TIOC controller is demonstrated by comparing the control effectiveness with that of the traditional semi-active controller in different cases.(4) Because of the huge degrees-of-freedom and the close-spaced natural frequencies of long-span spatial structure, a novel modal controller incorporated with wavelet packet transform (WPT) is proposed. In the proposed control system, the WPT method is utilized to decompose the acceleration measurement and select those modes containing most of the WPT energy component as the dominant modes. Then, a modal controller is designed to control these dominant modes. A Kalman-filter observer, which estimates the full controlled modal states from local accelerometer outputs, is designed for reducing the number of required sensors and the dimension of control equation and rendering the controller to be more applicable to spatial structures with a large number of degrees of freedom (DOFs). The effectiveness of the semi-active controller is demonstrated through two numerical examples: An MRF-04K damper controlled stadium roof structure subjected to vertical excitation, and a long-span spatial structure subjected to multi-dimensional and multi-point earthquake excitation. Simulation results show that the control effectiveness of the traditional modal controller can be improved by WPT-based modal controller. And comparing to TIOC controller, WPT modal controller can be more efficient and more practical in real project application.