Steel Bridge Design Handbook Design Example 5: Three-Span Continuous Horizontally Curved Composite Steel Tub-Girder Bridge

Tub girders, as closed-section structures, provide a more efficient cross section for resisting torsion than I-girders, which is especially important in horizontally curved highway bridges. The increased torsional resistance of a closed composite steel tub girder also results in an improved lateral distribution of live loads. For curved bridges, warping, or flange lateral bending, stresses are lower in tub girders, when compared to I-girders, since tub girder carry torsion primarily by means of St. Venant torsional shear flow around the perimeter of their closed sections, whereas I-girders have very low St. Venant torsional stiffness and carry torsion primarily by means of warping. This design example illustrates the design calculations for a curved steel tub girder bridge, considering the Strength, Service, fatigue and Constructibility Limits States in accordance with the AASHTO LRFD Bridge Designs specifications. Calculations are provided for design checks at particular girder locations, a bolted field splice design, an internal pier diaphragm design, and a top flange lateral bracing member design.\n