SUMMARY This paper presents a new type of electromagnetic damper with rotating inertial mass that has been developed to control the vibrations of structures subjected to earthquakes. The electromagnetic inertial mass damper (EIMD) consists of a ball screw that converts axial oscillation of the rod end into rotational motion of the internal flywheel and an electric generator that is turned by the rotation of the inner rod. The EIMD is able to generate a large inertial force created by the rotating flywheel and a variable damping force developed by the electric generator. Device performance tests of reduced‐scale and full‐scale EIMDs were undertaken to verify the basic characteristics of the damper and the validity of the derived theoretical formulae. Shaking table tests of a three‐story structure with EIMDs and earthquake response analyses of a building with EIMDs were conducted to demonstrate the seismic response control performance of the EIMD. The EIMD is able to reduce story drifts as well as accelerations and surpasses conventional types of dampers in reducing acceleration responses. Copyright © 2013 John Wiley & Sons, Ltd.

We propose a semi-active control of civil structures based on a one-step-ahead prediction of the seismic response. The vibration control device (VCD), which has been developed by authors, generates two types of resistance forces, i.e., a damping force proportional to the relative velocity and an inertial force proportional to the relative acceleration between two stories. The damping coefficient of the VCD can be changed with a command signal to an electric circuit connected to the VCD. In the present paper the command signal for changing the damping coefficient of each VCD is assumed to take two values, i.e., the command to take the maximum or minimum damping coefficient. The optimal command signal is selected from all candidates of command signals so that the Euclidean norm of the one-step-ahead predicted seismic response, calculated by a numerical integration, is minimized. As an example a semi-active control of a fifteen-story building with three VCDs is considered. The simulation results show that the proposed semi-active control achieves superior performance on vibration suppression compared with a passive control case where the damping coefficient of each VCD is fixed at its maximum value.

We address a simultaneous optimal design problem of a semi-active control law and design parameters in a vibration control device for civil structures. The Vibration Control Device (VCD) that is being developed by authors is used as the semi-active control device in the present paper. The VCD is composed of a mechanism of a ball screw with a flywheel for the inertial resistance force and an electric motor with an electric circuit for the damping resistance force. A new bang-bang type semi-active control law referred to as Inverse Lyapunov Approach is proposed as the semi-active control law. In the Inverse Lyapunov Approach the Lyapunov function is searched so that performance measures in structural vibration control are optimized in the premise of the bang-bang type semi-active control based on the Lyapunov function. The design parameters to determine the Lyapunov function and the design parameters of the VCD are optimized for the good performance of the semi-active control system. The Genetic Algorithm is employed for the optimal design.

The particle sedimentation of the dispersed particles in magnetorheological (MR) fluids when off-working has been a challenging problem, causing adverse effect to their practical applications. In order to solve this problem, ‘MR fluid porous composite’ made of porous materials impregnated with MR fluid has been fabricated in this work. Its effect to prevent the particle sedimentation has been proved through contrast experiment. Its MR effect has also been measured and verified using a hand-made oscillatory rheometer. Utilizing the MR fluid porous composite, a small-scale seismic linear MR damper has been developed. The unique design of this seismic linear MR damper has enabled it to convert the linear motion (damping force) of the MR damper to the rotations (braking torque) of the MR brake with almost no transmission loss. The damping properties of the developed small-scale seismic MR damper were investigated experimentally to be found that the design target with the damping force to be 20 kN has been achieved when applying an electric current of 0.5 A. Then a theoretical model was derived to estimate the damping force. The simulation results demonstrate that the proposed model is good at describing the properties of the seismic linear MR damper.

This paper presents a response evaluator which evaluates the response of the system and decides the control input to the system. It is applied to a base isolated structure with a semi-active oil damper whose damping coefficient has large or small values. Absolute acceleration of a top story and displacement of an isolated layer are the input signals of the response evaluator, and switching parameter for the damping coefficient is the output signal of the response evaluator. The response evaluator consists of a layered neural network, and a genetic algorithm is used to adjust the neural network parameters which decide the performance of the response evaluator. A computer simulation is carried out using several kinds of earthquake motions, and absolute acceleration and displacement of each story which are trade off relations of each other are reduced to the intermediate value of the response in case where constant damping coefficients are large or small. From the result of simulations, the effectiveness of the response evaluator is verified.