Experimental Study of Sliding Base-Isolated Buildings with Magnetorheological Dampers in Near-Fault Earthquakes

The increase in bearing displacements of sliding isolated buildings due to near-fault earthquakes, with long-period pulse type of ground motion, is an important problem. Often, supplemental nonlinear passive dampers are incorporated into the isolation system to reduce the base displacements; however, this may increase the interstory drifts and accelerations in the superstructure. Hence, there is a need to examine whether controllable nonlinear dampers can reduce the base displacements without a further increase in superstructure response. In this study, the effectiveness of variable damping, provided by magnetorheological ~MR! dampers, in reducing the response of sliding isolated buildings during near-fault earthquakes is investigated using a 1:5 scale steel two-story model. A nonlinear analytical model is developed with due consideration given to the nonlinearities of the friction bearings and the MR damper. A Lyapunov-based control algorithm is developed for control of the MR damper and the building model, and tested on a shake table. Results of passive low/high damping cases and semiactive cases are compared. It is shown that the variable damping reduces base displacements and superstructure responses further than passive low/high damping cases. DOI: 10.1061/~ASCE!0733-9445~2005!131:7~1025! CE Database subject headings: Base isolation; Damping; Earthquakes; Ground motion; Displacement; Superstructures; Structural response.