Fuzzy logic control of bridge structures using intelligent semi-active seismic isolation systems

Passive supplemental damping in a seismically isolated structure provides t he necessary energy dissipation to limit the isolation system displacement. However, damper forces can become quite large as the passive damping level is increased, resulting in the requirement to transfer large forces at the damper connections to the structure which may be particularly difficult to accommodate in retrofit applications. One method to limit the lever of dam ping force while simultaneously controlling the isolation system displaceme nt is to utilize an intelligent hybrid isolation system containing semi-act ive dampers in which the damping coefficient can be modulated. The effectiv eness of such a hybrid seismic isolation system for earthquake hazard mitig ation is investigated in this paper. The system is examined through an anal ytical and computational study of the seismic response of a bridge structur e containing a hybrid isolation system consisting of elastomeric bearings a nd semi-active dampers. Control algorithms for operation of the semi-active dampers are developed based on fuzzy logic control theory. Practical limit s on the response of the isolation system are considered and utilized in th e evaluation of the control algorithms. The results of the study show that both passive and semi-active hybrid seis mic isolation systems consisting of combined base isolation bearings and su pplemental energy dissipation devices can be beneficial in reducing the sei smic response of structures. These hybrid systems may prevent or significan tly reduce structural damage during a seismic event. Furthermore, it is sho wn that intelligent semi-active seismic isolation systems are capable of co ntrolling the peak deck displacement of bridges, and thus reducing the requ ired length of expansion joints, while simultaneously limiting peak damper forces. Copyright (C) 1999 John Wiley & Sons, Ltd.