It has been reported that the vibration generated in a live hall located in an urban area during a live performance causes unpleasant vibration to surrounding buildings. This is because the vertical motion performed by a large number of audiences in accordance with a song and music. This vertical motion works as an excitation force to generate vibration and the vibration propagates to surrounding buildings through the ground. As a countermeasure against this vibration problem, we have developed a vibration-proof floor system using inertial mass devices. The feature of this vibration-proof floor system is that the forces of the spring supporting the floor and the inertial mass device arranged in parallel with the spring cancel each other out in opposite phases. Due to this feature, the force transmitted to the ground within a certain frequency range can be greatly reduced.
In this paper, first, we show the response characteristics of the vibration-proof floor system in the frequency domain. From this response characteristics, it is confirmed that this vibration-proof floor system is effective countermeasure for the vibration problem caused by vertical motion of audiences in a live hall. Next, an excitation test of the principle model of the vibration-proof floor system is reported. Four disc spring units support weight of the model and an inertial mass device composed of a ball screw and a rotational weight is arranged in parallel. In this test, the model was excited with a sinusoidal wave using an excitation device. As a result of this excitation test, it is confirmed that the expected response characteristics for sinusoidal excitation can be realized. In addition, since the disc spring units and the inertial mass device have a slight hysteresis, it is necessary to evaluate this hysteresis damping in order to determine the performance of the vibration-proof floor system.
The vibration-proof floor system is installed in an actual live hall with standing seats of 1,600. The specifications of the hall, the device configuration and the design performance of the vibration-proof floor system are shown. An excitation test was conducted in which the vibration-proof floor was excited by vertical motion of 1025 people. In this test, the verticals motions to the tempo of 2.0, 2.5 and 3.0 Hz and free verticals motions to the actual song were performed. From the measurement value obtained by the test, the vibration-proof floor behavior at the time of vertical motion was almost as designed. The reaction force response magnification of the vibration-proof floor system applied to the actual hall during the excitation test is obtained through a simulation analysis of the test. In this analysis, the device characteristics are evaluated using bilinear model that expresses friction of devices. The excitation wave used in this analysis is created as a combination of a sinusoidal wave of excitation frequency and twice and three times frequency of that. As a result of this analysis, it was confirmed that the reaction force reduction effect of proposed vibration-proof system is higher than that of the vibration-proof floor without inertial mass device.
Through this paper, it is proved that the proposed vibration-proof floor system is very effective for the vibration problem caused by vertical motion of audiences during live performance.
