Field and Numerical Evaluation of Lateral Bending in Skewed Steel I-Girder Bridges during Deck Placement

Abstract

Steel I-girder bridges are subjected to unique loading conditions when they are under construction, and, in particular, lateral bending of skewed bridges during deck placement is of interest. Proper evaluation of skew effects on girder lateral bending stress in precomposite steel superstructures under concrete dead load is necessary for ensuring safety and economy in design for construction-stage loading. To provide new data on bridge response during deck placement, strains at selected cross sections were monitored for two steel I-girder bridges skewed around 45°, with variation in support conditions at the abutments. Girder stress components associated with strong-axis bending and lateral bending were calculated from field strain measurements, and complementary three-dimensional (3D) finite-element numerical simulations were conducted. Modeling methods that properly incorporate field girder boundary conditions and deck overhang loading for precomposite bridges were validated using field data from the two instrumented bridges, and parametric studies were then conducted on 33 bridges to evaluate skew effects on flange lateral bending stress. A staggered cross-frame layout provided additional load paths that transferred lateral load internally from an exterior girder, which was observed to be most significant near the midspan of a skewed bridge. Development of flange lateral bending near supports of a skewed bridge was found to be primarily caused by superstructure stiffness along the skewed bearing lines; large flange lateral bending stress occurred when the lateral movement induced from girder rotation along the skew is restrained at the support. For a skewed bridge with a staggered cross-frame layout along its length, standard design recommendations from the AASHTO LRFD Bridge Design Specification regarding skew-related lateral bending stress were observed to be effective for interior girders, except near ends of some bridges with skew over 45°, but inadequate for exterior girders.