Dynamic Analysis of Electrohydraulic Shaking Tables,

摘要

The frequency response characteristics of two shaking tables have been determined experimentally. The lighter table,weighing 2,000lb (900kg),was used primarily to determine the effects of a resonant structure on a shaking table's frequency response. The heavier table,weighing 100,000lb (45,300kg),was used primarily to determine the effects of foundation compliance on a shaking table's frequency response. Mathematical models were formulated for both tables,and the models were refined by adjusting parameters to obtain the best correspondence between the computed and experimental frequency responses. The mathematical models were then used to study the effects of a resonant structure and of foundation compliance on the frequency responses of shaking tables and on the ability of shaking tables to reproduce earthquake-type motions. It was found that the magnitudes of the peak and notch distortions in the frequency response of a shaking table are sensitive to the amount of force feedback employed by the control system. In addition,the magnitudes depend on the ratio of the mass of the structure to the mass of the shaking table and to the transmissibility function of the structure with respect to the table. Although the peak and notch effect may cause difficulties in determining the frequency response of structures by means of shaking tables,it has little effect on the accuracy to which a shaking table can reproduce earthquake-type motions. It was found that foundation compliance affects the frequency response of a shaking table only at low frequencies,and the magnitude of the effect is limited to an amount which depends on the transmissibility function of the foundation with respect to the table.