A mechanical model for a 3-dimensional beam-pier-pile system is proposed with finite
element methods for a continuous rigid-frame bridge to analyze its vibration characteristics. The
pile-soil system is simplified to build the space model and to calculate the dynamic behaviors of the
system. Then the dynamic analysis model for the rigid-frame bridge is set up. The dynamic
behaviors of the rigid-frame bridge are calculated and compared with different models, including that
without considering the pile, that with pile base but without considering the effects of soil properties
on vibration of the pile, and that with the interaction of the soil and the pile considered. The results
show that the main factor affecting the third order frequencies are the properties of piles, but the
properties of pile bases have not significant effects on the vibration characteristics of the beam-pier-
pile system..