Abstract. This paper provides a brief description of MR fluid technology and MR fluid based devices. Analytical and experimental investigations about MR dampers covering their rheo-Manuel T. Braz-César, Rui C. Barros INTRODUCTIONThe so-called "smart materials" has received the attention of researchers and engineers due to their capability to create smart devices that can be easily controlled by a small external perturbation like temperature or a magnetic field. Some of the most promising smart devices are based on fluids with controllable properties like Electrorheological (ER) and Magnetorheological (MR) fluids. The performance of MR fluids is less sensitive to temperature because the magnetic polarization mechanism remains unchanged over the operating temperature range and MR fluids behaviour is not affected by impurities, which means that is insensitive to contamination, while ER fluids are highly sensitive to moisture or impurities as result of manufacture and usage process.MR fluids are non-Newtonian and rheologically stable suspensions with a shear yield strength, which can be controlled by a magnetic field. These fluids react promptly to the application of an external magnetic field (in a few milliseconds) exhibiting a reversible and adjustable transition from a free-flowing state to a semi-solid state. Due to this property these materials exhibit a significant change in their rheological behavior (viscosity and plasticity).The expression "apparent viscosity" is used because the carrier fluid viscosity does not change as the magnetic field intensity H is modified. The rheological behavior of MR fluids depends on the magnetic field strength H, however it is possible to define a pre and post yield areas as shown in Figure 1a. In the pre-yield region the MR fluid exhibits visco-elastic behavior and in the post-yield region it behaves like a viscous Newtonian fluid.
Abstract. This work contributes to a better understanding of the seismic response of
The presence of dynamic loads, such as seismic and wind excitations in framed building structures requires the structural control of the consequent lateral displacements in the structure. This control can be made by the implementation of a vibration control system. This paper presents an investigation about the influence that the presence of infill walls in a system with one degree of freedom (SDOF), has on the control action of a passive vibration control system, a Tuned Mass Damper, and vice-versa. A Macro-Simulink model is implemented with the goal of simulate the hysteretic behavior of the infill wall subjected to cyclic loading, contemplating the stiffness and strength degradation and the pinching effect. Numerical results will be presented and discussed, regarding the assessment of the influence that the hysteretic behavior of the infill wall has on the structure.
Earthquake-induced pounding among contiguous building structures with insufficient separation distance, common in highly populated areas, may generate large impact forces that can significantly modify the overall dynamic behavior of the intervenient buildings. Serious structural damage or global collapse is among the negative consequences of building pounding. Inelastic behavior is inherent in building structures subjected to moderate to severe seismic excitations. Hence, the consideration of the inelastic behavior of building structures in the occurrence of pounding is extremely important to obtain more realistic results in the study and modeling of these phenomena. To this end, a Matlab-Simulink model was developed to emulate the elastic and inelastic behavior of two lumped mass SDOF structural systems under an earthquake excitation, where pounding is likely to occur. Using a smooth hysteresis model different hysteresis cases will be considered in the inelastic behavior of the structural systems, namely, stiffness degradation, strength deterioration, and pinching effect, arising in cyclic behavior of materials that compose civil engineering structures. A non-linear viscoelastic impact model will be used to assess the magnitude of pounding forces and their relation with the interpenetration depth. It was verified that the consideration of elastic behavior in buildings prone to pounding overestimates the magnitude and number of impacts that the structures experience, and underestimates structural displacements, especially in flexible structures.
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