Optimizing Horizontally Curved, Steel Bridge, Cross-Frame Arrangements to Enhance Construction Performance

Unlike straight bridges where cross frames and diaphragms are considered secondary members that predominantly stabilize the compression zones of noncomposite girders during construction, the interaction of bending and torsion in horizontally curved, steel, I-girder bridges renders these components primary load-carrying members. The effect of curvature on horizontally curved bridge behavior has been shown to be more critical during construction owing to a lack of a large, hardened, concrete deck that helps to stiffen and stabilize the entire system. Therefore, cross frames play important roles with respect to stabilizing the girders and distributing loads in curved bridges during construction. This work examined the effects of a bracing system that involved skewing cross frames relative to a normal to the girder’s web, termed skewed cross frames, on the construction behavior of horizontally curved, I-girder bridges having radially oriented substructure units (abutments and piers). The performance of this skewed cross-frame system was compared to that of more common bracing types, oriented normal to girder web, using three-dimensional, nonlinear, finite-element analyses. Preliminary studies of a single-span, small-radius bridge indicated more uniform load sharing among the girders during construction when a skewed cross-frame system was used. The current study aimed to expand these findings for bridges with other geometries and boundary conditions by investigating single-span and multispan plan geometries containing skewed cross frames at different spacings. In a fashion similar to the preliminary studies, for all cases examined, skewed cross frames were found to reduce deformations and rotations in critical superstructure members while generally requiring fewer intermediate cross frames compared to bracing placed normal to the girder web.