Subway Tile Stagger Framing Arrangements for Straight Steel I-Girder Bridges with Parallel Skew

Straight skewed I-girder bridges exhibit three-dimensional (3D) behavior due to deformation compatibility considerations. Most pertinent is the development of a stiff transverse load path between the obtuse corners of skewed bridge spans, which results in undesirable 3D effects causing large cross-frame (CF) forces and girder flange lateral bending stresses. Recent research has demonstrated that the CF framing arrangement significantly impacts the stiff transverse load path and the overall 3D behavior of these structures. Limited studies have found that the subway tile stagger framing arrangement, derived from a contiguous framing arrangement by eliminating every other intermediate CF from interior girder bays, is highly effective in mitigating the stiffness of the transverse load path and reducing undesirable 3D effects. The reduction of undesirable 3D effects improves the applicability of line girder analysis methods, thereby simplifying the bridge design. This paper evaluates the impact of CF framing arrangements on the 3D behavior of straight skewed bridges under dead, live, and fatigue loads based on the 10th edition of the AASHTO LRFD Specifications. A 3D finite-element analysis parametric study was conducted, encompassing a wide range of geometric variables and CF framing arrangements. Three framing arrangements, consisting of contiguous, parallel stagger, and subway tile stagger patterns, are studied for highly skewed steel I-girder bridge geometries. The influence of the framing arrangement on the bridge’s 3D behavior is assessed, and guidelines are provided for developing effective framing arrangements that significantly mitigate transverse load path effects in straight skewed bridges. A framework is established for simplified design, selection of framing arrangements, and sizing of CFs.