Tadashi Kotera

Study on Isolation Device by Friction

When an isolation device is exposed to earthquakes, the relative displacement between the device and the ground increases. The purpose of this research is to decrease the relative displacement by using the friction force. An analytical model in consideration of the friction force is proposed, and simulation analysis under the famous earthquake waves is performed. Consequently, as the friction force increases, the results show that the relative displacement decreases. However, it is found that the response acceleration increases. It is thought that optimal friction force exists, and this force decreases both the response acceleration and the relative displacement. This is considered to change with the properties of earthquake waves. It is shown that the relation between the optimal friction force and the maximum input acceleration is approximately linear from the results of many seismic waves. It is thought that the response acceleration and the relative displacement can be decreased changing the friction force to the most suitable value for each earthquake according to this relation. This isolation device is examined with simulation analysis.

Study on Isolation Device for Decrease of Displacement by Using Control of Friction

This paper deals with reduction of horizontal relative displacement by using a frictional force for a seismic isolator. First, a compression spring is attached to the base. Next, a slope plate is superimposed on it. The frictional force acts on the slope plate. The restoring-force is given to the seismic isolator by the compression spring attached to the base. In the equation of motion of the analytical model, the frictional force changes in proportion to the displacement. The restoring-force is also proportional to the displacement. The restoring-force always works in the direction of the center. Therefore, the frictional force and the restoring-force are both proportional to the displacement. Simulation analysis was performed under various conditions using this analysis model. As a result of conducting the analysis and an experiment with this model, it was shown that response acceleration and relative displacement can be reduced successfully. In order to reduce response acceleration and relative displacement more, analysis was carried out with the actual earthquake waves under the conditions to change the coefficient of friction by relative displacement. As a result, the coefficient of friction that reduces relative displacement most effectively without impairing the performance of the seismic isolator was established. However, the coefficient of friction that reduces the response acceleration and relative displacement effectively depends on by seismic waves. Therefore, in this report, the coefficient of friction that reduces response acceleration and relative displacement most effectively is determined by using white noise. It is analyzed with actual seismic waves by using the decided parameters. The performance of the seismic isolator is examined.Copyright

Study on Nonlinear Vibration of Continuum System With Gaps Considering Energy Dissipated by Collision

This paper deals with nonlinear vibration of a continuum system with gaps under random waves considered collision phenomena. In order to investigate this nonlinear vibration characteristic, experiments are carried out with an experimental apparatus consisting of a nonlinear vibration system. Moreover, an analytical model of the cubic equation is proposed based on the restoring force characteristics in the experiments. This analytical model is used for the simulation analysis, and its results are compared with the experimental results. However, the results show differences between thick plates and thin plates in the root-mean-square (R.M.S.) value of the response acceleration and the transfer function. The ratio of the kinetic energy of the experimental results and the simulation results is investigated. Consequently, energy is dissipated in the experiments. It is found that the energy dissipated by collision phenomena causes these results. In order to measure the coefficient of restitution by the collision phenomena between the plate and the mass, an experimental apparatus for the collision effect is made. Experiments are carried out with this apparatus. The experimental results agree with part of the results of the ratios of kinetic energy. It is clear that the analytical model in consideration for the energy dissipated by the collision effect is required.© 2004 ASME