United States Department of Transportation
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NTL Classification:NTL-HIGHWAY/ROAD TRANSPORTATION-Bridges and Structures
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Abstract:The National Bridge Inspection Standards require highway departments to inspect, evaluate, and determine load ratings for
structures defined as bridges located on all public roads. Load rating of bridges is performed to determine the live load that
structures can safely carry at a given structural condition. Bridges are rated for three types of loads, design loads, legal
loads, and permit loads, which is a laborious and time-consuming task as it requires the analysis of the structure under
different load patterns. Several tools are currently available to assist bridge engineers to perform bridge rating in a
consistent and timely manner. However, these tools support the rating of conventional bridge systems, such as slab, Igirder,
box girder and truss bridges. In the last decade, NDOR has developed innovative bridge systems through research
projects with the University of Nebraska-Lincoln. An example of these systems is tied-arch bridge system adopted in
Ravenna Viaduct and Columbus Viaduct projects. The research projects dealt mainly with the design and construction of
the new system, while overlooking the load rating. Therefore, there is a great need for procedures and models that assist in
the load rating of these new and complex bridge systems. The objective of this project is to develop the procedures and
models necessary for the load rating of tied-arch bridges, namely Ravenna and Columbus Viaducts. This includes
developing refined analytical models of these structures and performing rating factor (RF) calculations in accordance to the
latest Load and Resistance Factored Rating (LRFR) specifications. Two-dimensional and three-dimensional computer
models were developed for each structure and RF calculations were performed for the primary structural components (i.e.
arch, tie, hanger, and floor beam). RFs were calculated assuming various percentages of section loss and using the most
common legal and permit loads in the state of Nebraska in addition to AASHTO LRFD live loads. In addition, the two
structures were analyzed and RFs were calculated for an extreme event where one of the hangers is fully damaged
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