Site Measuring and Analysis of Ground Vibration Induced By the Large Earthquake Simulation Shaking-Table Operation

Abstract eng:
The large shaking-table operation induced vibration to the free-field is concerned by the nearby users of precise instruments laboratory and refinement processing workshop. In previously researches, theoretical analysis using transfer function method about ground vibration induced by shaking-table operation has not been verified by testing. The present paper focuses on site measuring and analysis of surrounding free-field vibration induced by the large earthquake simulation shaking-table operation. The field vibrations induced by the large shaker were recorded at multiple stations within the steel platen, the reinforce concrete foundation block and the surface of the surrounding soil up to distances of 26 m from the shaker. The results obtained validate that the rigid-body motion pattern of the foundation block for NS excitations of the block have been determined. It has been shown that the foundation of the shaking-table can be simplified as a single-DOF mass-spring-damping model, the foundation soil provides spring restoring force and damping force, the operation of the shaking-table is taken as dynamic loads exerted on the foundation. From the frequency response curve of the foundation obtained with the sweeping-frequency tests for a harmonic force of constant amplitude, the natural frequency of the foundation was determined as 11.8Hz, and this result shown good agreement with the estimated ones as 12.1Hz by using 'Code for design of dynamic machine foundation' combining the geotechnical characteristics of the site. The vibration of reaction foundation block is sufficiently small. For a actual ground motion recorded in a strong earthquake of 60mm,10cm/s and 1.5g corresponding to the maximum displacement, velocity and acceleration that the shaker actuators exert on the foundation, the average rigid-body translation at the top of the block has amplitude of less than 17μm, 0.2mm/s and 5gal respectively, and the latter is less than 0.1%, 0.2%, 0.4% of the former respectively. The vibration attenuation from the foundation to surrounding field versus distance obeys an exponential law, and the measured result is attenuation slowly than estimated ones by the Code. Vibration velocity and acceleration comparison between measured and Code limit value shown that vibration induced by the full load operation of the shaking-table does not have a worse effect on people health and building safety in surrounding field.

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