Study On Structural Control Based On Fuzzy Control Theory

Today the structural control technique has entered a middle-developed phase. There are many algorithms and practical devices available. However, it is also stepping into a "bottleneck" period. Unfolded before an investigator is such a situation: most practicable methods may be classified into three alternative approaches as isolation, energy-absorbing dampers and active control. All of them are deficient in some aspects. Meanwhile, due to the complexities of structural models, material characteristics and loads information, such theoretical problems as how to design a proper and simple algorithm are not solved well.In this paper presented is a newly developed control strategy OTE (off-and-towards-equilibrium). Its essential idea is to prevent structures from accumulation of dynamic responses by means of limiting the potential crossing velocities at the zero position to seclude every to-and-fro motion circle as possible. If it is combined with fuzzy control theory, then the corresponding OTE algorithm, including the discrete control and the continuous control, can be derived. On the basis of the algorithm, in this paper some different control systems are analyzed and discussed. Some basic conclusions have been have been drawn, and its rationality to use the OTE strategy has been verified. Main contents and results are as follows: In this paper the OTE strategy, where the control operation is formulated according to the relation among the motions of the structures, the exciting force and the control force, is presented. The detailed algorithm can be derived by means of combining the strategy with fuzzy control theory. Based on the OTE algorithm, the active tendon system is studied. During its control, the off-equilibrium control is more important than the to wards-equilibrium control. If in the course of the towards-equilibrium control the structure is restrained from approaching the equilibrium position properly, the accumulation of its dynamic responses will be avoided in the some degree. As is helpful for vibration control of the structure. Based on the OTE algorithm, the variable-damping system is studied. Via researches Symans and Sadek pointed out that for flexible structures (structures with periods beyond 1.5s) such a semiactive control system can be effective in reducing both the relative displacement and the absolute acceleration, whereas for rigid structures (structures with periods below 1.5s) it is doubtful. On the basis of theoretic analysis and numeric calculation, the author verifies that only is the ratio of the fundamental period of the structure to the disturbance period beyond 1.4, it's possible to achieve reductions in both the relative displacement and the absolute acceleration responses. In other words, the effectiveness of viscous variable dampers on reducing the response of structures depends on not the period of the structure, i.e. the rigid structure or the flexible structure, but the ratio of the disturbance period to the structure. The results indicate that while variable dampers significantly reduce the response as compared to the case with no control, no reduction or the worse situation is observed when compared to the same device acting as a passive damper with the upper limit of the damping of the corresponding variable damper. As a result the use of semiactive dampers in structures is positively only in some special cases when compared to passive systems. Therefore more attentions should be paid to such a semiactive control system. In this paper a hybrid control system of variable stiffness and base isolation, i.e. the ISAVS system that can overcome their deficiencies effectively, is studied based on the OTE algorithm. Such a semiacitve control system is not only with a broad frequency range for vibration suppression but also apt to implement. Numerical results show that using the discrete control can generally decrease the displacement response but increase the acceleration response, whereas usin...