Improved Cross-Frame Connection Details for Steel Bridges with Skewed Supports

Abstract

Cross frames and diaphragms play an important role in stabilizing straight steel girders. Commonly used connections between these braces and the steel girders can introduce flexibility, which can have detrimental effects on the bracing behavior, particularly on bridges with skewed supports. This paper documents a research investigation sponsored by the Texas Department of Transportation on connection details for stability bracing in steel bridges with skewed supports. One goal of the study is to propose an improved connection method. One detail being investigated is a round half-pipe stiffener connected to the top and bottom flanges. The round stiffener allows perpendicular connections to the cross-frame connection tab, regardless of the skew angle. Additionally, there are substantial structural improvements when the tubular stiffener is used. Fastening the tubular stiffener to the flanges provides a significant increase in the warping stiffness of the cross section at the support. Finite element modeling has predicted increases in buckling capacity as high as 80% because of this warping restraint. As a result, in the vicinity of the half-pipe stiffener, the brace spacing can likely be increased. The increased spacing in these regions will simplify fabrication and reduce the number of fatigue-sensitive details in the congested support region. This paper describes a method to calculate the increase in girder buckling capacity due to the warping restraint provided by the pipe stiffener as well as the size of pipe for a required buckling capacity or unbraced length with design tools already widely used by structural engineers.