Estimation formulas for natural frequencies of girder bridge and continuous rigid frame bridge

This paper is concerned with the evaluation of natural frequencies for the design of simply supported girder bridges, continuous girder bridges, and continuous rigid frame bridges. There are two significant parameters affecting the vibration frequencies. The first parameter is called the span ratio γ while the second parameter is called the stiffness ratio κ. The approximate formulas in terms of these parameters are proposed for these three types of bridges. From the analysis results, it is found that the first mode shape of the continuous rigid frame bridge is mainly induced by the pier other than the superstructure, when the stiffness parameter κ is greater than 10. Finally, the method proposed herein may be adopted to investigate the natural frequency of other types of bridges.