I-girder with discrete torsional bracings: Lateral-torsional buckling and torsional vibration

Discrete torsional bracing systems are widely used in practice to increase the strength of Igirders bridges. This paper presents equations for lateral-torsional buckling strength, torsional natural frequency and stiffness requirements of I-girders with discrete torsional bracings. Firstly, the equations to calculate the critical moment of the I-girder with discrete torsional bracings are introduced. An equivalent moment factor C _b in terms of the number of bracing points is proposed for I-girder subjected to linear moment gradient when full bracing is provided. The equations to calculate the torsional natural frequency are also presented in the same manner. The proposed equations are then compared with the results of finite element analyses and those from previous studies. From the results, it is found that proposed equations agree well with results of finite element analyses regardless of the number of bracing points. Finally, the reduced formula for the total torsional stiffness requirement is proposed for the design purpose.