US 6 Highway Bridge over Silver Creek

Year Constructed:  1961
Bridge type:  Steel Continuous Girder 
National Register of Historic Places Status:  Eligible 
Length:  245 feet
Width:  30.0 feet
Spans:  3
FHWA:  43270
Jurisdiction (and direct contact, email phone):  Iowa DOT; District 4; Wes Mayberry (Assistant District engineer); Wes.Mayberry@iowadot.us
Location: US 6 over Silver Creek
Sections: 13 Township: 75 North Range: 41 West
 

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 proposed using prestressed steel for bridges, building on the successful experimentation with prestressed 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. This process was thought to save 25% in steel weight.

The US 6 bridge (78-02342) is a three-span steel continuous-girder bridge measuring 245 x 30 feet. It’s an early, well-preserved example of a prestressed welded steel girder bridge, the first of its kind in the United States. 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 maintains a high level of historic integrity and is eligible for the NRHP under Criterion C.