Project Spotlight: Captain William Henry Moore Bridge
Article provided by the National Corrugated Steel Pipe Association
The Captain William Henry Moore Bridge is an historic suspension bridge on the Klondike Highway, crossing Captain William Moore Creek about 10 miles north of Skagway, Alaska. The existing 110 ft span suspension bridge was constructed in 1976 and connects Skagway to the Yukon highway network.
Throughout its history the bridge has carried a lot of traffic, including many heavy trucks loaded with ore. The heavier ore trucks have been causing significant deflection, reportedly causing distress in some of the foundation ties. The Alaska Department of Transportation and Public Facilities (ADOT&PF) engaged DOWL Engineers of Juneau, AK to evaluate potential replacement structures.
After evaluating several potential options, DOWL and ADOT&PF elected to use a large span deep corrugated structural plate Buried Bridge to provide a hydraulic opening for the fast moving Captain William Moore Creek while filling in the rest of the gorge with roller compacted concrete. The 75 ft span x 15 ft rise Buried Bridge bears on foundations over 100 ft below the Klondike Highway and was design to act as a stay in place form for placement of the concrete in the gorge.
The structure had to be built on a 16 degree skew to the highway because of the rough terrain and site limitations.
Hamilton Construction, LLC also requested that the structure be fabricated so that it could be built in place completely from the outside because of insufficient space to operate equipment on the inside of the structure during construction. Contech/Big R Bridge worked with Hamilton to design an external bracing system to allow for the support of the skewed ends of the structure without a concrete collar.
The structure was also manufactured with special splicing hardware to allow it to be pre-assembled in a staging area in three large sections, lowered into its place on the footing, and each of the large sections connected completely from the outside. This helped to speed up assembly in an area where the construction weather window is short as well as improve the quality and safety of the installation since much of the assembly could be completed in a more controlled setting. After the sections were connected, the external bracing to support the skewed ends was attached.
The backfill material consisted of concrete placed in lifts up to a height of about 5 ft above the crown of the structure. Roller compacted concrete (RCC) was placed above that level up to the road subgrade 75+ ft above. One key component to the success of the project was that DOWL and ADOT&PF involved manufacturers in evaluating the feasibility of the project early on and allowed for flexibility in means and methods for construction as the installation details were being developed. The original bridge remains in place for recreation uses.
For More Information:
CONTECH Engineered Solutions LLC
9025 Centre Pointe Drive
West Chester, Ohio 45069
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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.
Buried steel bridge is constructed with local crews in Buchanan County Iowa.
Steel buried bridges are durable and resilient, with the ability to support very heavy loads.