Natural frequency for torsional vibration of simply supported steel I-girders with intermediate bracings

Natural frequency is essential information required to perform the dynamic analysis and it is crucial to thoroughly understand natural frequency in order to study the noise and vibration induced by cars or trains, which is the major disadvantage of the steel I-girder bridge. In this study, analytical solutions for the natural frequencies and the required stiffness for torsional vibration of the I-girder with intermediate bracings are derived. The derived equations have simple closed forms and they can be applied to an arbitrary number of bracing points. The proposed equations are then verified by comparing them with the results of finite element analyses. From the results, it is found that the proposed equations provide good prediction of natural frequency for torsional vibration of the I-girder with intermediate bracings. Finally, the derived equations are applied to a twin I-girder system as an example of a practical civil engineering application and a series of parametric studies is conducted to investigate the effects of a number of bracing points and total torsional stiffness on torsional vibration.