Effects of Distortion on Strength of Curved I-Shaped Bridge Girders

The curved I-shaped plate girders used in bridges with curved alignment are subjected to forces that cause significant distortion of the cross section during construction and during application of live loads after the deck has hardened. Furthermore, the addition of curvature reduces the vertical bending stiffness, increases deflection nonlinearities, and changes stability characteristics of behavior. Although the design equations of the AASHTO Guide Specifications for Horizontally Curved Highway Bridges are formulated to address these behavioral issues, design and construction engineers often are not familiar with the difficulties curvature introduces and do not understand the relationship between distortion and deflection amplification with the design equations. Analytical research conducted as part of the FHWA Curved Steel Bridge Research Project was used to highlight and describe the effects of curvature on the strength and stability of curved I-girder bridge superstructures. Issues described include the following: ( a) effects of cross-frame and diaphragm spacing on system behavior, ( b) effects of curvature on the lateral-torsional stability of curved I-shaped beams, ( c) effects of warping stresses on flange buckling, ( d) effects of curvature on web behavior, and ( e) effects of curvature on initiation and propagation of yield stresses in the girders of curved I-girder frames.