Design Aids of NU I-Girder Bridges [long report]

2010Final Report115 page pdfPDFTech ReportProject Number: P322Bridge designBridge superstructuresGirder bridgesPrecast concretePrestressed concreteI beamsNebraskaNebraska. Dept. of RoadsHanna, Kromel E.Morcous, GeorgeTadros, Maher K.University of Nebraska--Lincoln. Dept. of Civil EngineeringNebraska. Dept. of Roads. Bridge DivisionUS Transportation CollectionPrecast prestressed concrete I-girder bridges have become the most dominate bridge system in the United States. As a part of the design stages, preliminary design becomes a vital first step in designing an economical bridge. Within the state of Nebraska, the two standard precast prestressed products used are Inverted Tee (IT) girders and University of Nebraska (NU) I-girders. In the early 1990\u2019s, Nebraska Department of Roads (NDOR) developed design charts for NU I-girders in order to assist in member selection and preliminary design. In 2004, design charts were developed for IT girders. However, the NU I-girder charts have since become obsolete because they were developed for low strength concrete (6 ksi) and 0.5 inch prestressing strand. In addition, the charts were based off of AASHTO Standard Specifications. Since then, NDOR has adopted AASHTO LRFD Specifications for superstructure design and the Threaded Rod (TR) continuity systems in their standard practice. Therefore, the new design charts are based on the latest AASHTO LRFD Specifications for superstructure design and NDOR Bridge Operations, Policies, and Procedures (BOPP manual). With the increasing use of 0.6 and 0.7 inch diameter strand as well as increasing concrete strengths, there is a need for new preliminary design charts for NU I-girders. The new design aids provide bridge designers with different alternatives of girder section size (from NU900 to NU2000), girder spacing (from 6-12ft), number of prestressing strands (up to 60), prestressing strand diameter (from 0.6 to 0.7 inch), and compressive strength of concrete (from 8ksi to 15ksi). Three sets of design charts are developed to cover simple span, two-span continuous and three-span continuous bridges. Each set contains two different type of charts: summary charts and detailed charts. Summary charts give designers the largest possible span length allowed given girder spacing, concrete strength, and NU I-girder sections. Detailed charts give designers the minimum number of prestressing strands required given girder spacing, span length, and concrete strength. Both sets of charts provide designers with the limit state that controls the design. If needed, this allows the design to be optimized in an efficient manner. Design tables were developed.92