Open Steel Box Sections with Top Lateral Bracing

Top-braced open thin-walled steel box girders under combined bending and torsion were studied. Two model box girders were tested in the elastic range. Analytically, the top bracing of open box sections was converted to an equivalent plate thus forming an equivalent closed box. Experimental results on top-braced open boxes and computed stresses for the equivalent closed boxes agreed fairly well. Rotations calculated from deflections without adjustment of support rotations were higher than the values computed for the equivalent closed boxes. Deformation of cross section was neglected in the analysis. The stresses in the bracing members were estimated using stresses in the equivalent top plate as loads on a bracing frame. The estimated stresses also compared well with experimental results. Based on the concept of equivalent closed box, a procedure was recommended for the selection of bracing member sizes.