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Precast alternative for flat slab bridges : final report.
  • Published Date:
    2013-10-26
  • Language:
    English
Filetype[PDF-26.89 MB]


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Precast alternative for flat slab bridges : final report.
Details:
  • Publication/ Report Number:
  • Resource Type:
  • Edition:
    Final report
  • Abstract:
    The cast-in-place (CIP) concrete slab bridge and the hollow core flat slab bridge are two very common bridge types utilized by the

    South Carolina Department of Transportation (SCDOT). The CIP bridge is durable but has a long construction time while the hollowcore

    bridge has a short construction time but produces durability concerns. Trying to balance the speed of construction for hollow-core

    and the durability of CIP, the SCDOT commissioned this study to provide a recommendation for an alternative bridge type that could:

    1) eliminate or minimize longitudinal cracking, 2) have a shorter erection time than the CIP flat slab system, and 3) have no restriction

    on ADTT and can be used on the National Highway System.

    There were two distinct phases in this research. In Phase 1, a thorough online survey and telephone interviews were conducted to

    investigate the pros and cons of existing short-span bridge systems used by other state departments of transportation. In addition,

    feedback from contractors and precast element fabricators in the Southeast region was also solicited. Based on this work, a precast

    bridge system known as the NEXT-D (Northeast Extreme Tee) beam was selected by the SCDOT for further testing and validation.

    The experimental and analytical validation along with the design of a 6 ft. wide section (NEXT-6) and an 8 ft. wide section (NEXT-8),

    with span lengths from 22 ft. to 40 ft., was the focus of Phase 2.

    The results of the experimental study indicated that U-shaped reinforcing bars and poly-vinyl alcohol (PVA) fiber reinforced ultrahigh

    performance concrete (UHPC) were an effective combination when used for the shear key located between precast NEXT

    elements. These results were also used to calibrate analytical models which were used to better understand and quantify the load

    demands associated with this beam type. Using this new understanding, a set of new design guidelines for the new NEXT-6 and

    NEXT-8 bridge systems was developed. For the beam design, the AASHTO live load distribution factors for tee beams are

    recommended to be used. For the deck design, the AASTHO strip method is recommended with some modification. A simplified fourstep

    procedure was developed to assist bridge engineers in determining the design demands (positive and negative moments) on a onefoot

    strip of deck for Strength I and Service I limit states.

    The results of this study, field experience with existing cast-in-place and precast bridges and sound engineering judgment allow the

    investigators to believe with a reasonable degree of confidence that the construction of a bridge using the provided recommendations

    and new system will lead to durable bridges that are cost effective and can be constructed using an accelerated schedule. One of the

    immediate needs is to now share the results of this study with neighboring states, so that the investment of needed steel forms by

    precasters can result in similar precast pieces sold to multiple states.

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