This paper investigates the effectiveness of force-derivative feedback semi-active control control scheme for seismic protection of base-isolated building structures employing magnetorheological (MR) fluid dampers. The base-isolation of the building is considered linear and represented by elastomeric bearings. Elastomeric bearings provide a clear advantage due to manufacturing development and long term efficacy if they are protected to environmental exposure. However, this type of isolation does not supply any energy dissipation to the building under seismic excitations because they lack of a hysteretic component like lead-rubber bearings. Nevertheless, these devices have one inadequacy when it comes to a near-fault earthquake, which is the high potential for excessive displacement at the base, producing total shear failure of the bearing. In the last years there has been an increasing interest to MR dampers and their applications to civil engineering structures. Base-isolated structures employing MR fluid dampers have gained the attention of many researchers in this field. These devices are highly nonlinear and thus accurate models of these devices are important for effective simulation and control system design. A hysteretic model based on the normalized Bouc-Wen model represents an experimentally identified large-scale MR fluid damper. The MR fluid damper is scaled up to represent both a real-manufacturable MR fluid damper and a compatible benchmark damper. The performance of the proposed force-derivative feedback semi-active control algorithm at the base-isolated building employing MR fluid damper is compared with passive-off, passive-on and clipped-optimal controllers. The proposed control scheme reduces the base-displacement without increasing the floor accelerations. Its main advantage is that only requires local measurements. The proposed MR fluid damper could be considered as a promising candidate for a real application of a base-isolated building employing MR fluid dampers as semi-active devices.
Summary
Seismic base isolations are well‐established passive control systems, used for reducing structural responses and preventing interior sensitive equipment and nonstructural elements from damaging. However, in a base‐isolated structure under near‐fault earthquakes, isolated layers sustain large displacements that might not be allowable. Further, any passive limitation in these displacements amplifies vibration transmissions to the superstructure. Smart hybrid base isolations using magnetorheological (MR) dampers, as well‐known semiactive devices, can overcome this problem by smart dampening. Nonetheless, highly nonlinear hysteretic behavior of MR dampers is one of the challenges for model‐based control algorithms. In this study, a smart multi‐objective fuzzy‐genetic control for dampening the vibrations of structures in an irregular base‐isolated benchmark building subjected to different earthquake scenarios is presented. The control aims, on one hand, to conserve (or even improve) top isolation characteristics in unique restraining of floor accelerations and drifts and, on the other hand, to mitigate large base displacements under near‐fault earthquakes using MR dampers simultaneously. Unlike many smart controls with a black‐box performance, the proposed fuzzy core is constructed conceptually employing control expertise with respect to the plant. To achieve control objectives, a conceptual innovative feedback is proposed for fuzzy decision making. To optimize this human‐designed controller, a multi‐objective genetic algorithm is applied. For evaluation, a three‐dimensional nonlinear irregular base‐isolated benchmark building planned by the American Society of Civil Engineers is employed. In comparison with classical and smart controls, the results demonstrate that despite having the smallest structure with fast performance, the proposed control effectively diminishes conflicting responses and has better performance than other controls.
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