Sliding mode control and nonlinear spectra of smart base isolated structures
Master of Science thesis
One of the main challenges in structural design is to protect the structures from the damaging effects of destructive environmental forces such as wind loads and earthquakes. In this research, flexibility and energy dissipation capability are introduced into the base isolation interface by Magneto-Rheological (MR) Dampers and Semi-Active Independently Variable Stiffness Devices (SAIVS), which act as the connections between the ground and the building base. MR damper alters the damping coefficient and SAIVS switches the stiffness continuously and smoothly. The main objectives of this research are generation of nonlinear spectra of smart base isolated structures and development of new sliding mode control algorithm. To achieve these goals, analytical models of a two-story base isolated building and the corresponding computer program are developed to calculate the dynamic response of structures. The nonlinear spectra demonstrate the efficiency of two types of new dissipative mechanisms in reducing the dynamic response of the base isolated structures subjected to near fault ground motions. It is shown that a combination of MR dampers and SAIVS devices is most attractive in reducing the base displacements substantially without appreciably increasing base shear and superstructure accelerations. In the second part of this study, a new control algorithm based on sliding mode is developed for variable stiffness systems. The response of the structure to different earthquakes is computed using the new sliding mode controller. It is shown that the new sliding mode controller is effective in reducing base displacements and verified by comparing the simulated response with experimental results of the two-story 1:5 scale model tested on the shake table.