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This paper investigates the effectiveness of two adaptive control strategies for modulating control force of piezoelectric
friction dampers (PFDs) that are employed as semi-active devices in combination with laminated rubber bearings for
seismic protection of buildings. The first controller developed in this study is a direct adaptive fuzzy logic controller. It
consists of an upper-level and a sub-level direct fuzzy controller. In the hierarchical control scheme, higher-level
controller modifies universe of discourse of both premise and consequent variables of the sub-level controller using
scaling factors in order to determine command voltage of the damper according to current level of ground motion. The
sub-level fuzzy controller employs isolation displacement and velocity as its premise variables and command voltage as
its consequent variable. The second controller is based on the simple adaptive control (SAC) method, which is a type of
direct adaptive control approach. The objective of the SAC method is to make the plant, the controlled system, track the
behavior of the structure with the optimum performance. By using SAC strategy, any change in the characteristics of the
structure or uncertainties in the modeling of the structure and in the external excitation would be considered because it
continuously monitors its own performance to modify its parameters. Here, SAC methodology is employed to obtain the
required force which results in the optimum performance of the structure. Then, the command voltage of the PFD is
determined to generate the desired force. For comparison purposes, an optimal controller is also developed and
considered in the simulations together with maximum passive operation of the friction damper. Time-history analyses of
a base-isolated five-story building are performed to evaluate the performance of the controllers. Results reveal that developed adaptive controllers can successfully improve seismic response of the base-isolated buildings against various types of earthquakes.
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