The National Academies

NCHRP 12-113 [Final]

Proposed Modification to AASHTO Cross-Frame Analysis and Design

  Project Data
Funds: $590,000
Research Agency: University of Texas - Austin
Principal Investigator: Dr. Todd Helwig
Effective Date: 6/1/2017
Completion Date: 6/30/2022
Comments: Phase I is published as NCHRP Research Report 962. Phase II is published as NCHRP Research Report 1045.

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.
STATUS: Phase I report is published as NCHRP Research Report 962. Phase II is published as NCHRP Research Report 1045.

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