Session: SE-09-01 Advanced Seismic Evaluation and Code

Paper Number: 61720

Start Time: Tuesday, July 13, 2021, 08:00 PM

61720 - Acceleration and Displacement Response of Base Isolation System With Friction Subjected to Random Vibration 

Various types of devices have been developed in order to reduce seismic response of the mechanical systems such as pressure vessels and piping systems. In such devices, friction characteristic is used in some dampers and base isolation systems. Some devices with friction are practically used. The authors have developed a base isolation system for preventing overturning of relatively small structures and shown the effectiveness of the system by experiment and numerical analysis. In ordinary case, response of the system with friction decreases with the increase of the friction coefficient. However, during experiment to examine the effectiveness of the base isolation system, it is observed that acceleration response takes minimum value at some friction coefficient in some condition. In this paper, this fact is examined for the mechanical system subjected to random vibration.

  For simplicity, the mechanical system is modeled as a single-degree-of-freedom system with friction. As friction characteristic, Coulomb friction is introduced. As input, seismic ground motions are considered. In order to simulate seismic motions, stationary white noise, stationary filtered white noise and nonstationary filtered white noise are used. In filtered white noise, the dynamic characteristic of the ground is considered. Tajimi model is introduced as the dynamic characteristic of the ground. The standard deviations of the response are obtained from moment equations using the equivalent linearization method. The maximum value of the standard deviation of the absolute acceleration and relative displacement to the ground are obtained because those values correspond to the maximum response.

  Parameters for the dynamic characteristic of the ground are selected considering a standard ground. The natural period of the base isolation system is selected as longer than that of the ground. The damping ratio of the mechanical system is selected considering actual structures. For stationary white noise excitation, acceleration response takes minimum value at some friction coefficient. The friction coefficient which takes minimum response decreases with the decrease of excitation. Reduction rate of acceleration and displacement response increases with the decrease of excitation. Displacement response decreases with the increase of the friction coefficient. For stationary filtered white noise, there are the regions where the mechanical system does not move to the ground for large friction coefficient. The acceleration response also takes the minimum value at some friction coefficient. The friction coefficient which takes the minimum response decreases with the decrease of excitation. Reduction rate of acceleration and displacement response increases with the decrease of excitation. Displacement response decreases with the increase of the friction coefficient. For nonstationary filtered excitation, same results as stationary filtered white noise are obtained.

Presenting Author: Shigeru Aoki Tokyo Metropolitan College of Industrial Technology

Authors:

Shigeru Aoki Tokyo Metropolitan College of Industrial Technology
Katsumi Kurita Tokyo Metropolitan College of Industrial Technology