This paper proposes a new damper that can change the damping force depending on the response displacement and response velocity. The proposed damper reduces the damage of seismic-isolated structures which undergo excessive deformation during huge earthquakes, without lowering the performance of the seismic-isolation system during medium to small magnitude earthquakes. We investigate the effects of using the proposed attenuator on the responses of a superstructure model to seismic motion that causes collision with retaining walls. An experiment using a shaking table is conducted, and the results from the test are compared with those from numerical analyses. The test results agree approximately with the numerical analysis results except for the absolute acceleration results in collision cases.
KEYWORDS: Buildings, Computer simulations, Earthquakes, Digital signal processing, Electroluminescence, Control systems, Motion models, Magnetism, Fluid dynamics, Systems modeling
The dynamic characteristics of mid-story isolated buildings and seismic response reduction due to a semi-active control system were investigated using a three-lumped-mass model that simplified the sixteen story building with an isolation layer in the sixth story. A semi-active control method using a rotary inertia mass damper filled with magnetorheological fluid (MR fluid) was proposed. The damper shows both mass amplification effect due to rotational inertia and variable damping effect due to the MR fluid. The damping force is controlled by the strength of the magnetic field that is applied to the MR fluid. It is determined by using the electric current, which is calculated by the proposed semi-active control method based on the velocity of the isolation layer relative to the layer just underneath it. Real-time hybrid tests using an actual damper and simulations using a building model were conducted to check the damper model; the test results were in good agreement with the simulation results. The simulation results suggest that the response displacement of the structure above the isolation layer is significantly reduced, without increasing the response acceleration of the entire structure against near-fault pulse and long-period ground motions. The proposed semi-active control using an MR rotary inertia mass damper was confirmed to be effective for mid-story isolated buildings.
Magnetorheological fluid damper (MR damper) has been expected to control the response of civil and building structures
in recent years, because of its large force capacity and variable force characteristics. At first, a series of real-time hybrid
tests was conducted. The important objective of this paper is to verify the validity of real-time hybrid tests by
comparison with the test results of shaking table tests by using the same MR damper. The maximum damping force of
the MR damper is 10 (kN), the stroke is 600(p-p) (mm), and the maximum piston velocity is 1(m/s). To determine the
control force of the MR damper, optimal control theory and skyhook control were employed. The capability of the MR
damper to control the response displacements and accelerations of base isolation system was verified by both shaking
table tests and real-time hybrid tests.
Recent study is to the performance of variable dampers for reducing earthquake response of buildings or wind induced sway. The variable damper using magnetorheological fluid (MR damper) changes its damping force by changing the magnetic field acting on the MR fluid according to an electric current. MR dampers have a simple mechanism and don’t need a large amount of energy. Semi-active control using such a variable damper stabilizes building responses in an earthquake better than the conventional passive control. Basic characteristics of the MR damper have been clarified. This time, authors proposed control algorithm of base-isolated structure, which carried out semi-active control by optimal regulator theory. This control algorithm reduces response displacement and response acceleration for the purpose of, and aims at enhancements, such as safety and amenity. This paper presents a comprehensive study on the performance of the MR damper to base-isolated structure. It's describes shaking table tests on a three-story large-scale test frame with base-isolated structure. The test results verify the controlling system and the control effect as a semi-active device of the MR damper.
A 400kN magnetorheological damper (MR damper) for a real base-isolated building was developed and its dynamic characteristics were verified by experimental tests. The MR damper has 950mm (+/-475mm) stroke and by-pass flow potion.
A new type of Magneorheological fluid is also developed in order to apply to the MR damper. MR fluid had a property of the settlement of particles in dampers. Authors developed a new MR fluid, which keeps the particles in the fluid adequately enough for usual use of MR damper.
Analytical model was discussed in this paper. The force by the bingham visco-plastic model was compared with the results of experimental tests. It was found that this analytical model is useful to predict the capacity of the MR damper.
This study deals with a shake table test on a three-story base-isolated steel frame. The frame rests on four roller bearings for isolation and is equipped with four laminated rubbers as shear spring. An MR damper is used in the test to perform semi-active seismic response control. The basic control algorithm applied in the study is to simulate the load-deflection of an origin-restoring friction damper (ORFD) which is a sort of friction damper that looses its resistance when it moves toward the origin, making sure for the base-isolated system to minimize residual displacement even after an extremely strong ground motion. Also attempted is a hybrid type control that superposes viscous damping on the ORFD when the damper moves from the peak displacement toward the origin.
This paper presents a comprehensive study on the application of the MR damper to base-isolated building structures. It first proposes a simple semi-active control algorithm for a base-isolated structure with an MR damper. The algorithm, in which the MR damper's hysteresis shape is controlled, aims to reduce the isolator's displacement without increasing the acceleration responses of the upper structures. The second part of this paper covers the properties of an MR fluid and an MR damper developed for a base-isolated model structure. The damper has a nominal capacity of 40kN, which can be adjusted in accordance with the applied magnetic fields. In the test, the damper is subjected to cyclic sinusoidal displacements with different amplitudes, velocities and magnetic field intensities. The last part describes shaking table tests carried out using the MR damper and the base-isolated model structure. It is confirmed that the proposed semi-active control method is effective in reducing the isolator's displacement without increasing the acceleration responses.
KEYWORDS: Ferroelectric polymers, Sensors, Actuators, Control systems, Control systems design, Ferroelectric materials, Interference (communication), Passive isolation, Polymers, Digital filtering
Induced strain actuator (ISA) can change their own shapes according to external electric/magnetic fields, and vice versa. Recently these materials have been widely used for the small/precision. The objectives in this study are to develop smart members for building and to realize the smart, comfortable and safe structures. The research items are 1) Semi-active isolation of structures using piezoelectric actuator, 2) Using ISA as sensor materials and 3) Improvement of Acoustic Environment. Semi-active base isolation system with controllable friction damper using piezoelectric actuators is proposed. Simulation study was carried out, and by semi-active isolation, it could be realized to reduce response displacement of the structure to 50% of values of the passive isolation. ISA materials can act as sensors because they cause change of electric or magnetic fields under deformation. PVDF sensors are suitable for membrane structures. We evaluate performance of PVDF sensors for membrane structures by experiment. Polymer based ISA films or distributed ISA devices can control vibration mode of plane members. Applications to music halls or dwelling partition walls are expected. Results of experimental studies of noise control are discussed.
First part of this paper covers experimental studies on mechanical properties of two types of magneto-rheological fluid (MRF) dampers. One is a commercial built-in-pass type damper and the other an original by-pass type damper. In the test, they are subject to cyclic sinusoidal displacements with different amplitudes, velocities and intensities of magnetic field. Not only their hysteretic properties but also their quickness to respond to the applied magnetic field are examined. In the second part, two analytical methods to represent the mechanical properties of the dampers are presented. One is a semi-empirical method making use of a Bingham Model to simulate the hysteretic properties of the damper. The other one, an analytical method based on the theory of non-Newtonian fluid. A design formula to predict the resistance of the damper is so obtained as to take into consideration the damper's dimensions, the properties of the fluid and the intensity of the magnet field applied.
Two kinds of Magneto-rheological fluid damper (MRF damper) have been designed and manufactured. One has a nominal capacity of 2kN and the other 20kN. A bypass flow system is adopted for both dampers and each has the same capacity of electromagnet attached to the bypass portion. The effective fluid orifice is the rectangular space and the magnetic field is applied from the outside. A test was performed by applying different magnetic fields to the orifice portion of the rectangular space. The damping force and the force- displacement loop were evaluated. The test results yielded the following: (1) Two type's of dampers functioned by using one unit of the electromagnet under an appropriate electrical current control. (2) The magnitude of the damping force depends on the input magnetic field, but it has an upper limit. (3) Without an applied magnetic field, the MRF damper exhibits viscous-like behavior, while with a magnetic field it shows friction-like behavior. A mechanical model of the damper is estimated by taking account of the force-displacement loop. It is clarified that MRF dampers provide a technology that enables effective semi-active control in real building structures.
Building Research Institute, Japanese Ministry of Construction, initiated a 5-year research and development project of 'Smart Materials and Structural Systems' in 1998 as a part of U.S.-Japan cooperative research efforts. The U.S. Counterpart is the National Science Foundation. Smart Structural Systems (also called as Autoadaptive Media) are defined as systems that can automatically adjust structural characteristics, in response to the change in external disturbance and environments, toward structural safety and serviceability as well as the extension of structural service life. The research and development of (1) concept and performance evaluation of smart structure system, (2) sensing of structure performance, and (3) development and evaluation of structural elements using smart materials will be conducted.
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