Year constructed: 1913-1914
Alternate name: Hartley Drive Bridge
Bridge type: Rigid-Connected Pratt Through Truss
National Register of Historic Places status: Listed
Length: 122 feet
Width: 16 feet
Spans: 1
FHWA: 063250
Jurisdiction: Allamakee County
Location: Hartley Drive over Upper Iowa River, 4.8 miles southeast of Dorchester, Section 34, T100N-R5W.
Details
The Upper Iowa River Bridge is a medium-span through truss carrying a gravel-surfaced road over the Upper Iowa River southeast of Dorchester, in Union City Township. The road is presently a secondary one, but the crossing was once located on the main road between Dorchester and New Albin. The first permanent bridge was built here around 1870 by Allamakee County. Comprised of a two-span bowstring arch-truss, it had deteriorated to the point of replacement by the early 1910s. In 1913 the county removed the old bridge and solicited competitive proposals for its replacement. Although the project was relatively modest in scale, bids were received from 13 state and regional firms. The contract to build the new concrete substructure was awarded to New Hampton, Iowa, firm Chambers and Dobson for $2,585.00. The Clinton Bridge and Iron Works were hired to fabricate and erect the rigid-connected Pratt truss for $3,490.00. Using steel components rolled by the Illinois Steel Company, Clinton B&I fabricated the truss and shipped it to Allamakee County. The Upper Iowa River Bridge was completed in July 1914. It has functioned in place since in unaltered condition.
When this bridge was let for bids in 1913, the Iowa State Highway Commission was just getting underway with its legislatively mandated program to standardize bridge design in the state. Although the highway commission delineated standards for pony trusses and small-scale concrete structures in 1913, it was not until the following year that through-truss designs were developed. This left counties such as Allamakee to depend--as they had for decades before--largely on the bridge companies themselves for both engineering and construction. The Upper Iowa River Bridge was built during this transitional period. Using a rigid-connected Pratt through-truss, it resembles the 1914 state standards in design but differs slightly in detail, indicative of its independent source. It is thus technologically significant as one of the last of the pre-ISHC trusses in the state. Of interest is the builder's plate on the bridge's portal, consisting of a pierced plate with crenellated top, the only one of its kind identified by Fraser's inventory [adapted from Fraser and McWilliams 1992].