Abstract

Magnetorheological (MR) and Electrorheological (ER) fluid dampers provide a fail-safe semi-active control mechanism for suppressing vibration response of structures as these smart fluids can change their apparent viscosity immediately under the influence of magnetic and electrical fields, respectively. MR based damping devices have recently received appropriate attention as they have less power demand, provide better dynamic range and are less sensitive to the temperature and external contaminants as compared to their ER counterparts.
This thesis studies physics-based modeling of MR fluid dampers and their application in seismic design of buildings. In the first part of thesis, MR damper modeling and its related subject are studied, while in the second part of the thesis, application of MR dampers in tuned mass damper and bracing system is investigated.
The existing models, namely the phenomenological models for simulating the behavior of MR and ER dampers rely on various parameters determined experimentally by the manufacturers for each damper configuration. It is of interest to develop mechanistic models of these dampers which can be applied to various configurations so that their fundamental characteristics can be studied to develop flexible design solutions for smart structures. This research presents a formulation for dynamics analysis of ER and MR fluid dampers in flow and mix mode configurations under harmonic and random excitations. The procedure employs the vorticity transport equation and the regularization function to deal with the unsteady flow and nonlinear behaviour of ER/MR fluid in general motion. Using the developed approach, the damping force of ER/MR damper can be evaluated under any type of excitations.
While tuned mass dampers are found to be effective in suppressing vibration in a tall building, integrating them with semi-active MR based control system enables them to perform more efficiently under varying external excitations. To study the application of MR damper in tuned mass damper, a forty-storey tall steel-frame building assumed to be located in the Pacific Coast region of Canada (Vancouver), designed according to the relevant Canadian code and standard, has been studied with and without semi-active and passive tuned mass dampers. The response of the structure has been studied under a variety of ground motions with low, medium and high frequency contents to investigate the performance of the optimally designed semi-active MR based tuned mass damper in comparison to that of a passive tuned mass damper. It has been shown that the semi-active MR based system modifies structural response more effectively than the conventional passive tuned mass damper in both mitigation of the maximum displacement and reduction of the settling time of the building.
Finally, the effectiveness of MR damper in structural bracing has been examined. Two steel building structures, five and twenty-storey building designed according to Canadian national building code, have been modeled using the finite element method. These building structures have been equipped with MR dampers in different floors appropriately based on the seismic floor-shear distribution. The governing equations of motion of the structures integrated with MR dampers have been cast into the state space representation for the implementation of the full state LQR combined with clipped optimal control strategies. The response of building structures under passive on and active controlled modes have been obtained for low, medium and high frequency content seismic records and compared.