Optimal Control of Accelerations in a Base-isolated Building Using Semi-active Mr Dampers

This article presents a theoretical study aimed at improving effectiveness of the isolation system of a building by adding magneto-rheological (MR) dampers that act in parallel to the rubber bearings (RB). To this end, the building itself is modeled with uni-axial elements that consider axial, shear and flexural deformations. Nonlinear elements that include RBs and MR dampers, whose response is velocity dependent, are added at the base of the building. Properties of the MR dampers are obtained from laboratory tests previously performed. Genetic algorithms with local improvement of chromosomes that represent a fuzzy logic control system are used to optimize operation of the MR dampers. Maximum acceleration at the top of the building is taken as the variable to be minimized. Several records of destructive earthquakes that could affect the site are used as input. Structural responses for three different conditions are compared: a) building with the actual isolation system, but without any additional dampers. b) building with rubber isolation and the MR dampers as passive energy dissipaters, and c) building with rubber isolation and MR dampers that are controlled semi -actively. Results show that the average absolute peak acceleration, considering different types of earthquakes, can be reduced by up to 20% in comparison with the case where no dampers are installed.