Cross-Frame and Diaphragm Layout and Connection Details
Record Type: DOT
Cross-frames and diaphragms play an important role in the behavior of straight and curved steel bridge systems. These braces provide stability to straight girders during construction and serve as primary structural members in resisting torsion in curved bridges. Due to complexities in fabrication details and difficulties during erection and construction, these braces are often a large component of the cost of the overall bridge system. The costs associated with the braces can be increased further by maintenance issues during the service life of the bridge, as the cross-frame or diaphragm connections are often the most frequent locations of fatigue problems in steel bridges. Because of the many factors that affect the behavior of the braces, designers are often faced with difficult decisions regarding cross-frame and diaphragm detailing in steel bridges-particularly in bridges with skewed supports. The research will consider both the stability and fatigue performance of the bracing connections, as well as practical issues related to fabrication and erection. While the bent plates are likely satisfactory for small skew angles, at large skew angles the brace forces cause large bending deformation of the plates, greatly reducing the stiffness of the brace. Large skew angles would require very thick bent connection plates to provide the required stiffness and strength. The limiting magnitude of the skew angle that economical bent plates can be used will be identified. The performance of cross-frames and diaphragms oriented along a staggered layout will also be evaluated. The use of staggered cross-frames can be useful: they permit the perpendicular stiffener orientation while also minimizing live load induced forces because they connect to adjacent girders at similar positions along the respective girder lengths. The work will be accomplished with laboratory testing, parametric finite element analysis, as well as soliciting feedback from designers and fabricators so that the resulting connection satisfies both functional and practical criteria. The resulting recommendations will provide designers with practical detailing options and guidance relating to skewed diaphragm connections and configuration of torsional bracing systems.
Start date: 2007/9/1
End date: 2010/8/31
Contract/Grant Number: 0-5701
Source Organization: Texas Department of Transportation
Date Added: 09/12/2007
Index Terms: Bridge design, Bridge members, Bridges, Steel structures, Girders, Torsion, Fatigue (Mechanics), Research projects,
University of Texas, Austin
Center for Transportation Research, 3208 Red River, Suite 200
Autsin, TX 78712-1075
Engelhardt, Michael D.
Phone: (512) 471-6837