Iowa County Saves Costs by Choosing Buried Steel Bridge for Replacement Project
The 200th Street Bridge is located about 3.5 miles outside of Jesup, Iowa. During the summer of 2015, the old wooden bridge ― built in 1956 ― was replaced with a new short span steel buried bridge system.
The timber piling for the old 32 foot X 20 foot bridge ―a timber stringer/multi-beam or girder―was deteriorating, and the bridge was in need of replacement. The wooden bridge was demolished in June. Construction on the new bridge began in August.
Buried Bridge Specifications
The buried bridge system was constructed of deep corrugated galvanized steel plate with a corrugation profile of 15 inches wide (peak-to-peak) and 5.5 inches deep (peak-to-valley), with a bolt spacing of 16 inches center-to-center on the neutral axis around the periphery.
Each ring consists of three plates and has a nominal width of 30 inches. Section properties of the plates conform to ASTM A796-13, Table 34 and Tables A12-14 and A12-15 in Section 12 of the most current AASHTO LRFD Bridge Design Specifications. The soft soil conditions of the bridge site required that the new buried bridge structure be supported by H-pile foundations. The completed 200th Street Bridge is 39 feet, 4 inches long and 45 feet wide.
According to Buchanan County Engineer Brian Keierleber, the buried bridge system offers several key benefits to county engineers. It is economical, simple to construct and can be built by local crews. It can also be constructed with excavation equipment and doesn’t require heavy equipment, such as a crane.
This buried bridge system uses a design comparable to those generated by eSPAN140, a complimentary web-based design tool which provides customized steel solutions for bridges up to 140 feet. eSPAN140 is available from the Short Span Steel Bridge Alliance and can be accessed at http://www.espan140.com.
The 200th Street Bridge was completed in September 2015 and is open to service.
Learn more about buried steel bridges in this video from the Short Span Steel Bridge Alliance.
What are buried steel bridges?
Buried steel bridges provide an economical choices for bridge replacement or bridge rehabilitation.
They essentially are a corrugated steel pipe or structural plate pipe systems that is “buried” with backfill to carry loads through soil-structure interaction. This means the bridge structure itself and the backfill soils surrounding the structure interact with each other to support the loads. In effect, the backfill material is part of the bridge.
Because of this interaction, the bridge structure is typically lighter, and there can be significant savings in structure costs.
There are also many cases where buried bridges can carry heavier loads than traditional bridges because of the benefits of spreading vehicle loads through the fill. Buried bridges do not require abutments; and unless foundation soil conditions are poor, do not typically
require deep foundations.
An additional benefit with buried bridges is that they can be tailored to site conditions and geometric requirements. The design includes inputs for site soils and backfill, meaning that locally available materials can often be used in construction and the structure can be tailored to fit the needs of the site and the owner’s requirements.
Steel buried bridges are durable and resilient, with the ability to support very heavy loads.