No abstract

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.

Abstract. Magnetorheological (MR)

Abstract. Magnetorheological (MR)

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.

Abstract-Magnetorheological (MR) dampers have received special attention as semi-active devices for mitigation of structural vibrations. Because of the inherent nonlinearity of these devices, it is difcult to obtain a reasonable mathematical inverse model. This paper is concerned with two related concepts. On one hand, it presents a new inverse model of MR dampers based on the normalized Bouc-Wen model. On the other hand, it considers a hybrid seismic control system for building structures, which combines a class of passive nonlinear base isolator with a semi-active control system. In this application, the MR damper is used as a semi-active device in which the voltage is updated by a feedback control loop.The management of MR dampers is performed in a hierarchical way according to the desired control force, the actual force of the dampers and its capacity to react. The control is applied to a numerical three-dimensional benchmark problem which is used by the structural control community as a state-of-the-art model for numerical experiments of seismic control attenuation. The performance indices show that the proposed semi-active controller behaves satisfactorily.

No abstract

Abstract. In this paper, a semi-active control technique is presented to mitigate the seismic vertical response of suspension bridges using Magneto-Rheological (MR) dampers. MR dampers, as semi-active control devices, have received signi cant attention in recent years because of their adaptability of working as active control devices without requiring large power of sources. The most challenging problem in this study is how to install the dampers at the degrees along the bridge span far from the towers. In the present paper, to solve this problem, a \rigid truss", which is attached to the bottom of the bridge deck, is proposed. The MR damper can be installed between the bridge deck and free-end of the truss. For numerical study, the Vincent-Thomas suspension bridge is chosen and di erent schemes, in point of number and location of the dampers view, are proposed to get optimal performance of the dampers in reducing the bridge vertical responses. To reach this goal, all of the schemes are optimized, and the controlled and uncontrolled responses of the bridge are calculated under application of 15 major world-wide earthquake accelerogrames. The results indicate that the proposed models can e ectively reduce the vertical responses of the example bridge.