構造物の常時微動における振動システム

抄録

The properties of the first-mode vibration system of structures under ambient excitations and the influences of wind forces on it are investigated through both observed data and a model simulation. Transfer functions and coherence functions, which calculated statistically between two vibrations, are used for evaluating the vibration systems. Among these, coherence functions give effective information on the degree of correlation, which indicate system nonlinearities derived from the mixing of several linear input-output relations. As a result, it is clarified that the system consists of two major ingredients : one is the response excited by microtremors of ground, the other is the component caused by wind excitations, and the ratio of these two ingredients varies with the wind force. A model with this properties are made in the form of eq. (8), in which the pa- rameter Cw is indicating the degree of wind influences. The evaluation of some parameter-estimating methods applied to transfer functions of ambient vibration is also performed on the basis of the properties of the vibration system above mentioned. The estimated parameters, especially damping factors, are affected to a great extent by wind excitations.