INFLUENCE OF SUPPORT BOUNDARY CONDITIONS ON THE NATURAL VIBRATION CHARACTERISTICS OF CONCRETE BEAMS - ANALYSIS USING THE FINITE ELEMENT METHOD

Abstract

The natural vibration characteristics of concrete beams constitute an important basis for structural dynamic analysis and structural health monitoring. In many studies, the boundary conditions at supports are commonly idealized as rigid supports. However, in practical bridge structures, bearings always exhibit a certain degree of flexibility, which can significantly alter both the spectrum and the nature of the natural vibrations of the structure. This paper investigates the influence of rigid and elastic support boundary conditions on the natural vibration characteristics of a concrete beam using a three-dimensional finite element model. The results indicate that when the finite stiffness of the supports is taken into account, the lower-order vibration modes are no longer dominated by the bending deformation of the beam, but are primarily governed by rigid-body motion modes of the coupled beam-support system. The bending-dominated modes of the beam appear only at higher vibration orders, leading to a noticeable change in the sequence of mode occurrence compared with the rigid support case. The findings clarify the role of realistic boundary conditions in the vibration analysis of concrete beams and are of significant importance for the interpretation and mode identification of vibration measurement data in practical applications.