Analysis Of Seismic Response Of Passive And Smart Isolated Structures And Investigation To Control Algorithms

Structural vibration control is widely recognized as an effective way of mitigating catastrophic damage of structures induced by earthquakes. Among various techniques for structural vibration control, base isolation is the most widely used method in the world because of its simplicity, stability, and cost effectiveness. However, in passive isolated structures, the base drift is always very large. When the earthquake excitation is strong, the overall performance of the structural system is largely suppressed by the response of base isolator. Therefore, a lot of research work has been carried out to improve the adaptiveness of base isolation by combining active or semi-active devices with the passive isolation system, resulting in so-called "smart" isolated system. To calculate the seismic response of passive isolated structures, non-proportional damping must be handled, and to analyze the response of smart isolated structures, control algorithms must be worked out. Besides, seismic excitation is of strong randomness, evaluating controlled response using random vibration analysis can provide better statistical information. This paper investigates several key issues concerning passive and smart isolated structures, and mainly focuses on the following things:41) Base isolated building is usually a kind of non-proportionally damped system. But, this paper revealed that base isolated structure is a special type of non-proportionally damped system by showing the damping decoupling effect of base isolation. A real mode superposition method for analyzing time domain response of non-proportionally damped base isolated structures is derived for general MDOF system, and the results calculated by the proposed method are verified using the dynamic simulation tool of Simulink method in Matlab, and compared with those from the complex mode superposition, the Wilson- method coded in double precision Fortran. The result shows that under the design damping level defined in this paper, the proposed method in this study has good accuracy, which shows the applicability of the proposed method for the large class of isolated building in common use. Besides, the proposed general MDOF model of real mode superposition method can be used to derive a spectral estimation of maximum response for 2-DOF isolated structures which is similar to the method proposed by Kelly, but the method proposed in this study has a wider range of validity, and the result is more reasonable when examined by direct simulation.2) For linear structure implemented with ideal controller, optimal control is a powerful tool for determining control force, and has found wide application in civil engineering. However, when classical optimal control is applied to seismic control, a non-homogeneous term will appear in the traditional Riccati equation, which causes the model not to be solved directly. Two current optimal control algorithms, i.e., the approximate classical optimal control algorithms (COC) and instantaneous optimal control algorithms (IOC), were derived based on a lot of simplification. In this paper, the control objective function is reconstructed using impulse response of both seismic excitation and the control force, which leads to a new styleoptimal control model. By defining a dual system according to the resemblance between the companion equation and the state equation, the optimal control force is directly calculated by state transition algorithm. An improved optimal control algorithm is thus developed, and is named as Sequential Optimal Control (SOC). The proposed SOC not only improved the two current optimal control algorithms conceptually, but also numerically. Simulation result shows that the proposed method is advantageous over the two current optimal control algorithms in terms of the ability of reducing the peak response, the control efficiency, and has almost the same stability range with the classical optimal control algorithms.3) Under strong earthquakes, a structure will always come to its elasto-plastic stage, and thus becomes a kind of...