Abstract
After the Hyogo-Ken Nanbu Earthquake occurred, the steel bearings underneath the girder bridges came to be substituted with rubber bearings in order to prevent seismic damage to the bridges. However, in this change of design, the concern of vibration increased by response amplitude has been overlooked and, therefore, the new design (with rubber bearings) had to be verified safer for also normal traffic conditions. In the process of analysis, data were collected from three span girder bridges those are equipped with only rubber bearings or steel bearings. In a consequence of analysis, it was revealed that rubber bearings caused not only damping difference but also the difference of vibration mode shapes, which was accountable enough for the phenomena that response from unit sinusoidal load of rubber bearings exceeded that of steel bearings.
