Stability of skewed I-shaped girder bridges using bent plate connections

textLateral bracing systems consisting of cross frames and their connections play a significant role in the elastic buckling strength of steel girder bridges. By providing lateral and torsional stability, they prevent lateral torsional buckling of the girder during bridge construction prior to the concrete bridge deck curing. To perform this function, the bracing system must possess adequate strength and stiffness. And since each component of the bracing system acts in series, the overall stiffness of the system is less than the least stiff component. In skewed bridges, cross frames at the ends of the girders are installed parallel to the bridge skew angle, and their connection to the girder requires that the cross frames be at an angle that prohibits welding a stiffener from the cross frame directly to the girder web. To make this connection, many states use a bent plate to span the angle between the web stiffener and cross frame. While this bent plate connection is now being widely used, it has never been rationally designed to account for its strength or stiffness in the bracing system. Results from field studies show that the bent plate connection may be limiting the cross frame stiffness thereby hampering its ability to provide stability to the girder during construction. The result is significant girder end rotations. The purpose of this research is to classify the impact of the bent plate connection on the end cross frame stiffness in skewed straight steel girder bridges and propose methods to improve the end cross frame’s structural efficiency. This research uses laboratory testing, finite element modeling, and parametric studies to recommend design guidance and construction practices related to the end cross frames of skewed steel girder bridges. In addition to recommending methods to stiffen the existing bent plate connection, an alternative pipe stiffener connection is evaluated. The pipe stiffener not only offers the possibility of a stiffer connection, but can also provide warping restraint to the end of the girder which may significantly increase the girder elastic buckling capacity.Civil, Architectural, and Environmental Engineerin

Influence of Plate Stiffener Geometry on LTB Capacity

The standard analytical equations for elastic and inelastic lateral-torsional buckling assume a connection that permits rotation about the strong axis (as well as warping), but prevents twist about the longitudinal axis. The plate stiffener, commonly called a shear tab, is idealized as such a connection. In this paper, the influence of plate stiffener geometry on the lateral-torsional buckling capacities of various wide-flange beams is studied, using high-fidelity computer simulation. Preliminary results indicate that plate stiffener geometries have a significant effect on beam LTB capacity