CHANGES IN EIGEN-FREQUENCY OF THE ROAD INFORMATION BOARD FIXED BY THE F TYPE SUPPORT

Abstract

The objectives of this paper are to make clear the vibration characteristics of the road information board fixed by the F type support and to evaluate their sensitivity of eigen frequency to the damage. First, the accelerations of the road information boards in service are observed at three ground sites and three superstructure sites. The observed accelerations are analyzed with ERA (Eigensystem Realization Algorithm). As a result, four common vibration modes are found, and their estimation accuracies are evaluated. The analyzed results also show that the eigen frequencies depend on the site condition. Second, full-scale damage experiments are conducted to investigate the temporal changes in the eigen frequencies due to several patterns of damage. The results show that the failure of anchor bolt in the tension side gives the detectable change in the eigen frequency. Since the full-scale experiments represent the ground site only, the temporal changes in the eigen frequency in the case of a superstructure site are estimated using a simple numerical model that is a cantilever beam with a rocking spring. The simulation results show that the temporal change in eigen frequency is smaller when the rocking spring is softer. Even though the softness of rocking spring in the superstructure site is considered, the failure of anchor bolt might be detectable from the temporal change in eigen frequency.