Developments in bridge design and analysis in recent years have created the need for improvements to cross-frame analysis and design for steel girder bridges. In the past, the configuration of cross-frame systems was generally based upon standard designs in which member sizes and layouts were dependent upon geometry and minimum member cross-section requirements. The opportunities for improvements to cross-frame analysis and design cover a variety of topics including: (1) improved definition of fatigue loading for cross frames in curved and/or severely skewed steel girder bridges analyzed using refined analysis methods; (2) implementation of stability bracing strength and stiffness requirements in the context of AASHTO Load and Resistance Factor Design (LRFD) bridge design; and (3) additional guidance for adjustment of the effective stiffness of cross-frame members in refined analysis models to reflect the influence of end connections on cross-frame member stiffness. Addressing these topics could result in a dramatic improvement in reliability and economy of cross frames for steel I-girder bridges.
The objective of this research is to propose modification to the AASHTO LRFD Bridge Design Specifications to provide quantitatively based guidance on: (1) the calculation of the fatigue design forces in cross frames in steel I-girder bridges; (2) the calculation of strength and stiffness requirements for stability bracing; and (3) the influence of cross-frame member end connection upon the cross-frame stiffness. Accomplishment of the project objective will require at least the following tasks.