Year constructed: 1919
Bridge type: Concrete Marsh Arch
National Register of Historic Places status:
Listed
Length: 52 feet
Width: 18 feet
Spans: 1
FHWA: 078080
Jurisdiction: Boone County
Location: 210th Street over Beaver Creek, 5.9 miles northwest of Ogden, Section 32, T84N-R28W (Amaqua township).
Details
This concrete fixed arch spans Beaver Creek in the northwestern corner of Boone County. Consisting of one 50-foot span, the structure features slotted guardrails with paneled concrete bulkheads and is supported by a concrete substructure. Dating from 1919, the bridge was erected by the Des Moines-based N.E. Marsh & Son Construction Company, who used a design by James Marsh, engineer and patent holder for the rainbow arch configuration. The Beaver Creek Bridge has functioned in place some six miles northwest of Ogden, in Amaqua Township, since its completion in 1919.
This medium-scale arch marks a noteworthy innovation in bridge design, an achievement engineered and patented by James Marsh in 1912. Marsh's design represented the hybridization of continuous concrete and segmental steel-arch designs, a radical departure from standard engineering practice. Concrete can withstand a nominal amount of tension. For this reason, most previous concrete arches--both reinforced and mass arches in filled and open spandrel configurations--were built with the arch below the deck, where the downward force of the deck could be carried in compression by the arch ribs and spandrel wall or columns. Marsh's suspended arch reversed this.
His arches, of course, act in compression; but the hangers and floor beams carry the deck in tension. Furthermore, the novel treatment of the deck over sliding steel plates on the floor beams and the use of pin-connected, articulated steel hangers for the end panel points were devices more suited to steel construction than concrete. To make the concrete thus act against its nature, Marsh inserted large amounts of structural steel. His bridges may look like concrete spans, but the arch ribs and hangers carry such heavy and complicated reinforcing that they are, in reality, steel structures encased in concrete. Marsh designed his bridges with either tied (with the arches attached to the abutments at the floor beam level) or fixed (arches extending below the floor beams to the abutments) configurations. Aside from this, all of his rainbow arches were similar, varying only in span length, arch rise and number of hangers.
Marsh's invention did not foretell a new direction in reinforced concrete design. The industry would later turn to other, simpler slab and beam configurations as it developed more sophisticated reinforcing techniques in the 1930s and 1940s. The rainbow arch did, however, denote one of the more interesting early experiments in concrete engineering and represented the proliferation of concrete for road and bridge construction. It is not known how many Marsh arches were built in Iowa in the 1910s and 1920s: judging from county records perhaps not more than one hundred. The large amount of reinforcing steel sheathed within a relatively thin skin of concrete has made them particularly vulnerable to rusting and spalling. As a result, only a few are known to remain. The Beaver Creek Bridge is distinguished as a well-preserved example of an indigenous structural type [adapted from Fraser 1992].