Year constructed: 1961
Bridge type: Steel Continuous Stringer/Beam/Girder
National Register of Historic Places status:
Eligible
Length: 245 feet
Width: 30 feet
Spans: 3
FHWA: 043270
Jurisdiction: Iowa DOT
Location: U.S. 6 over Silver Creek at 350th Street west of Oakland, 1.0 mile east of SR L66, Section 13, T75N-R41W (Washington Township)
Details
According to the ISHC, the bridge was the first prestressed steel bridge in the United States. In July 1960, ISHC structural engineer Bill Barnard posited the idea of prestressing steel for bridges based on the successful experimentation of prestressing concrete for the same purpose. The process involved adding weight to a beam to cause it to bend (or deflect). Then T1 heat-treated cover plates are welded to the deflected beams. Once the plates are welded, the weight on the beam is removed and the deflected beam is inverted for use in a bridge. This process strengthens the beam, allowing it to be used in place of larger beams. The process was thought to save up to 25% in steel weight (ISHC 1961:7-9).
The US 6 Highway Bridge meets several registration requirements outlined in the MPD and as such is eligible for inclusion in the NRHP under Criterion C. The bridge is an early, well-preserved example of a prestressed welded steel girder bridge, the first of its kind in the U.S. according to the ISHC. The bridge is also an exceptional example of work by ISHC structural engineer Bill Barnard, who created and tested the concept of prestressing steel for bridges. The bridge has a high degree of integrity with no major repairs noted in the SI&A database or eRMS.