Evaluation of Top Flange Bracing Systems for Curved Box Girders

Abstract

In recent years, steel trapezoidal box girders for curved highway interchanges have become popular. For these bridge systems, significant steel girder cross-sectional stresses occur during the concrete casting sequence. To help resist construction loads, a lateral truss system is installed at a level close to the top flanges to form a “pseudo-closed” section, which has a higher torsional stiffness than an open U-section. Several recent incidents, ranging from the buckling of individual bracing members to the complete failure of a trapezoidal box-girder bridge, suggest a lack of understanding of curved box-girder behavior and the use of inadequate analysis tools by designers. In order to provide an improved understanding of these systems, computational software to analyze steel trapezoidal box-girder bridges with a cured or semicured concrete deck has been developed. In this paper, a brief description of this computationally efficient and easy-to-use software is provided. In addition, results are presented from computational studies evaluating the performance of different girder bracing configurations in conjunction with different deck placing sequences. Based on these results, recommendations for design are given.