Lateral torsional buckling of steel twin plate girder systems with torsional braces only
This paper presents results of both an experimental and a finite element study on the lateral torsional buckling behaviour and strength of twin plate girder systems with only discrete torsional braces. Two scaled twin-beam specimens with different arrangements of lateral and torsional braces were tested and results were used to validate the finite element model. The finite element study considered the effect of individual brace member stiffness and the number of braces. Results showed that for twin plate girders braced with only torsional braces, the critical buckling moment has the most significant increase when the number of interior braces increases from two to three. For a given girder section, the increase in the critical moment capacity by increasing the cross-frame member size is minimal. The lateral torsional buckling moment equation as well as the brace force design procedure contained in the Canadian Highway Bridge Design Code were examined. A relationship between the ratio of provided-to-required torsional stiffness and the effective length factor was discussed.