Dynamic Behavior of the Bumpy Road Shaking Table System

Vibration tests were performed on the "bumpy road shaking table" system at the Cambridge University Geotechnical Centrifuge to investigate its dynamic behavior under operating conditions. In these tests, steel plates of known weights were fastened onto the base of the model container. The container was then subjected to "earthquake motions" simulated by the shaking table system and the accelerations of various parts of the system measured by means of accelerometers. The test results show that the bumpy road wheel acceleration has a substantial amount of high-frequency components. During earthquake tests, the bumpy road container is isolated from this high-frequency motion by the flexibility of the package-transmission assembly. The results also suggest that the bumpy road package-transmission assembly has a resonance mode at about 85 Hz while the centrifuge arm has a resonance mode at about 104 Hz. If the excitation frequency is close to the package-transmission frequency of 85 Hz, a strong response is obtained from the bumpy road system, and package motion is highly harmonic and relatively "clean." On the other hand, if the excitation frequency is close to the resonance frequency of the centrifuge arm, the latter is excited into motion instead of the container and soil model.