Fuzzy logic control of vibrations of multi-degrees-of-freedom structure

The damage on buildings caused by the earthquake on August 17th, 1999 at Kocaeli has madevibration control of buildings against earthquakes popular again. Vibration in structures caninduce added displacement, stress and many results in significant damage. A number ofstudies on structural vibration control have recently been done and practical applications havebeen realized. Seismic protective systems, in general, consist of two categories, namelyPassive Control Systems and Active Control Systems.In this study, a fuzzy logic based controller and PID controller are designed for an activecontrol device considering a multi-degree-of-freedom structure against earthquakes. PIDcontrollers are most widely used in industry for years, due to their simple structure and easyof design. However classic PID controllers are not well suited to nonlinear systems. Fuzzytype controllers are candidates to be used in this area. After fuzzy logic was defined by Zadehin 1965, it has been applied for many areas. It finds an important place in control applicationssince it gives the opportunity of describing the systems especially, which are difficult todescribe mathematically, linguistically. The advantage of this approach is its robustness andability to handle non-lineer behavior of the system. The simulated system has fifteen degreesof freedom. Structural system was simulated against the ground motion of the destructiveKocaeli earthquake (Mw=7.4), which resulted in more than 20.000 deaths in Turkey on 17August, 1999. In this study a lineer motor is used as the active isolator. At the end of thestudy, the time history of the storey displacements, accelerations and frequency response ofboth the uncontrolled and controlled analytical structures are presented and the results arediscussed. It was shown that a designed fuzzy logic controller brought better active controlperformance than a PID controller. The improvement in resonance values and decrease invibration amplitudes support this result.Keywords: Earthquake induced vibration, multi-degree-of-freedom structure, seismicisolation, PID control, fuzzy logic control.