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Design aids of NU I-girders bridges.
  • Published Date:
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Filetype[PDF-2.35 MB]

  • Publication/ Report Number:
    SPR-P1(09) P322 ; 26-1120-0042-001 ;
  • Resource Type:
  • Geographical Coverage:
  • Edition:
    Final report; May 2010.
  • NTL Classification:
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  • Abstract:
    Precast prestressed concrete I-Girder bridges have become the most dominant bridge system in the United States. In the early 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 1990s, 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 strands. In addition, the charts were based off of American

    Association of State Highway and Transportation Officials (AASHTO) standard specifications. Since then, NDOR has adopted

    AASHTO Load and Resistance Factor Design (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 strands 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 6-12 ft), prestressing strands (up to 60), prestressing strand diameter (from 0.6 to 0.7 inch), and compressive strength of concrete

    (from 8 ksi to 15 ksi). Two sets of design charts are developed to cover simple span and two-span continuous bridges. Each set contains

    two different types 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.

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