County-Built Steel Plate Arch Bridge Turns 82

Topics: Buried Bridge, Case Study, Durability

Article provided by Metal Culverts and the National Corrugated Steel Pipe Association

Imagine a time when minimum wage was 30 cents an hour, fuel costs were 12 cents a gallon, and blueprints were actually blue.

In 1941, 82 years ago, Union County, Iowa commissioned a dirt road to provide farmers a better route to get their harvest to the grain bins in nearby Creston, Iowa. The three mile grading project included a structural steel plate arch as well as over 1,000 feet of corrugated steel pipe culverts on a farm-to-market road.

The county contracted out the excavation and culvert installation to Roth Construction of Indianola, Iowa.

Roth moved more than 56,000 yards of dirt and installed the culverts for under $7,000, however, the Union County Engineer decided the county would assemble the structural steel plate arch themselves.

Installed in 1941, ‘Performing Well’

This particular structural steel plate arch (pictured above) has a 15 foot span with a 7 foot 8 3/8 inch rise and a length of just over 30 feet.

Assembly of the structure began on October 14, 1941, and installation was completed in just 13 working days. It took 70 hours to assemble and the total labor costs were $66.00, material costs on the project were $566.15 and the equipment costs were just $41.99. The total assembled cost for the structural plate arch was $674.14.

The primary function of the road has remained unchanged over the years, and despite the substantial changes in agricultural equipment and increased loading capacity, the structural plate arch continues to perform well.

Over the past 80+ years, the county has added concrete footing and headwalls but little else has been done besides several routine inspections.

The latest inspection has the structural plate arch listed in good condition.

Prime Example of Galvanized Material Performing as Expected

There are thousands of structural plate, lock seam, and riveted galvanized corrugated metal pipe in this condition and of this vintage throughout the Midwest.

What is unique to this project is the intact bridge record and blueprints dating back to 1941. This is a prime example of galvanized material performing as expected and living up to its design — making this a hall of fame worthy discovery!

A special thanks to Larry Latham, Assistant to the Engineer, and Union County, Iowa for their assistance in providing detailed cost information and sorting through their archives and to NCSPA member, Metal Culverts Inc., for providing additional information.

Standard structural plates are available in thicknesses ranging from 0.111 inches to 0.380 inches. Plates are furnished curved to various radii and are clearly identified by the fabricator for field assembly.

These plate structures are assembled into various shapes including round, pipe arch, singles-radius arch, horizontal ellipse, low profile arch, high profile arch, pear, underpass and vertical ellipse, with other special shapes also available. Learn more at by clicking here.

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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.

Learn more about buried steel bridges→