Load Rating of Complex Bridges

2010PDFTech ReportSPR-1(10) P32926-1120-0049-001Load factorDesign loadMechanical properties by mathematical limits or valuesArch bridgesConcrete bridgesLoad ratingTied-arch bridgeLegal loadsPrmit loadsRating factorAASHTLRFRNebraskaNebraska Transportation CenterMorcous, GeorgeHanna, KromelTadros, Maher K.Mid-America Transportation CenterUnited States. Department of Transportation. Research and Innovative Technology AdministrationUnited States. Federal Highway AdministrationUnited States. Department of Transportation. Federal Transit AdministrationNTL-HIGHWAY/ROAD TRANSPORTATION-Bridges and StructuresUS Transportation CollectionThe National Bridge Inspection Standards require highway departments to inspect, evaluate, and determine load ratings forstructures defined as bridges located on all public roads. Load rating of bridges is performed to determine the live load thatstructures can safely carry at a given structural condition. Bridges are rated for three types of loads, design loads, legalloads, and permit loads, which is a laborious and time-consuming task as it requires the analysis of the structure underdifferent load patterns. Several tools are currently available to assist bridge engineers to perform bridge rating in aconsistent 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 researchprojects with the University of Nebraska-Lincoln. An example of these systems is tied-arch bridge system adopted inRavenna Viaduct and Columbus Viaduct projects. The research projects dealt mainly with the design and construction ofthe new system, while overlooking the load rating. Therefore, there is a great need for procedures and models that assist inthe load rating of these new and complex bridge systems. The objective of this project is to develop the procedures andmodels necessary for the load rating of tied-arch bridges, namely Ravenna and Columbus Viaducts. This includesdeveloping refined analytical models of these structures and performing rating factor (RF) calculations in accordance to thelatest Load and Resistance Factored Rating (LRFR) specifications. Two-dimensional and three-dimensional computermodels 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 mostcommon legal and permit loads in the state of Nebraska in addition to AASHTO LRFD live loads. In addition, the twostructures were analyzed and RFs were calculated for an extreme event where one of the hangers is fully damaged92