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Siting Considerations for Prefabricated Buried Open-Bottom Precast Concrete Bridge Structures
Course Information
Open-bottom buried bridges are structures built with side walls and a top that’s either flat or in an arc formation. With either configuration, the bottom is not constructed as part of the bridge structure, which provides a foundation design that’s separate from the bridge’s structural design. The structure sides support the surrounding soil, while the open bottom has the flexibility for a variety of site adaptations.
This feature is useful with existing streambed conditions where it’s essential to reduce site disturbance. Where the bridge spans over the streambed, the natural soils can be preserved, assisting in the sustainability of wildlife and fish passage. A buried bridge structure limits the exposed structural elements, reducing maintenance time and costs by protecting the bridge against exposure to de-icing materials. A prefabricated concrete structure is constructed at an offsite precast plant location and delivered to the site, reducing the overall construction time as compared with onsite conventional stick-built-type bridge structures.
Prefabricated, buried bridges can be used in several site intersections. These include—but are not limited to—railway over/under roadway, roadway over roadway, airplane passage over roadway and roadway over streambed. Because the roadway over streambed application is the most common site intersection for buried, three-sided structures, this article describes the conditions related to that type. Many of the site considerations presented in this article can be adapted if a different intersection is under consideration.
Author
JULIA FRAZIER, P.E., AND RACHEL LAGEMAN, P.E.Learning Objectives
This article focuses on the unique considerations required for three-sided, prefabricated concrete structures installed below grade along with general site considerations for bridge construction. At the conclusion of this article, the reader should be able to understand the following:
• Application options for open-bottom structures.
• Terminology used to describe a buried bridge structure.
• Items needed to complete a layout of a structure.
• The procedures to properly align and specify the lengths for wingwalls.
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