The National Academies

NCHRP 20-07/Task 133 [Completed]

Improved Live Load Deflection Criteria for Steel Bridges
[ NCHRP 20-07 (Research for AASHTO Standing Committee on Highways) ]

  Project Data
Funds: 50000
Research Agency: University of Washington
Effective Date: 11/16/2000
Completion Date: 5/15/2002
Comments: Completed

Task 133, FY 2001, "Improved Live Load Deflection Criteria for Steel Bridges" (University of Washington,Charles Roeder). Deflection limits are commonly applied to steel bridges. These deflection limits may control the design of the superstructure elements. The AASHTO LRFD Specifications (C2. note that calculated deflections are difficult to verify in the field because of numerous sources of stiffness that have not been accounted for in the calculations. Research is needed to determine how live load deflection requirements affect the long-term performance of the superstructure and if such requirements are needed. The research should determine if the requirements are unnecessarily restrictive for slab-and-girder type bridges and if they adversely affect the economy of bridge design. The deflection limits may have some beneficial effect on controlling the overall performance of some bridges, which may not be apparent when examining bending stresses only. For example, bridges that are designed as composite but have heavily cracked decks may be more flexible than a bridge with an uncracked deck. On the other hand, deflection limits may restrict the use of newer materials such as high performance steel (HPS) and other innovative materials.

The objective of this research is to develop recommendations on live load deflection limits for steel bridges for consideration by the AASHTO Highway Subcommittee on Bridges and Structures. The project panel has approved the interim report.

Work on a comparative analysis of variations in the application of deflection limits, parametric studies of bridge vibration, and a detailed analysis of bridges believed to exhibit damage due to excess bridge deflection is complete and the project panel has approved the contractors draft report. The contractors final report has been distributed to the project panel and is available online as NCHRP Web Document 46. This project is complete. (NCHRP Staff: D.B. Beal)

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