Investigation on Effect of Elastic Supports Stiffness on Natural Frequencies and Modes of Two Span Beams under Free Vibration

Elastic bearings are used to improve the structural behavior of the bridges. The existence of such bearings has a considerable effect on the change of vibration behavior in bridges and beams; i.e. change of structure's natural frequencies and vibration modes. In technical texts, theoretical studies can be found on one-span bridges with elastic bearings and numerical methods are used for multi-span beams. In the present paper, the equations governing the vibration of two-span beams with elastic bearings under free vibration were deduced and equation coefficients were calculated in Matlab environment. The results were compared with the simulation results in finite element software ANSYS. Finally, changes of natural frequencies and vibration modes with change of bearing stiffness and span length were investigated. The obtained results indicated that frequency changes in the first and second modes had a descending order for low stiffness; with the increase of stiffness, this change became almost constant. However, frequency increased continuously in higher modes. Moreover, in terms of performance, elastic bearings showed their best performancein equal spans.