Equivalent Damping Ratio of Coupled System

Many structures are installed on supports in industrial facilities. The damage by amplitude increases with the coupled vibration is shown. The response magnification is obtained from natural frequency and damping ratio of the coupled system in the seismic design. Therefore, the natural frequency and damping ratio of the coupled system are required. The natural frequency and damping ratio of support and structure are obtained in initial design or vibration test. However, the natural frequency and the damping ratio of the coupled system are not easily obtained. The natural frequency of the coupled system can be calculated from theoretical equation, but the damping ratio cannot be easily calculated. In this study, the equation to calculate the damping ratio of the coupled system with Rayleigh damping is shown. The equivalent damping ratio without Rayleigh damping is estimated.