Year constructed: 1876
Bridge type: Pin-Connected Pratt Through Truss
National Register of Historic Places status: Listed
Length: 358 feet
Width: 16 feet
Spans: 2
FHWA: 180690
Jurisdiction: Henry County Conservation Department
Location: County Road W55 over the Skunk River in Oakland Mills State Park, Section 24, T71N-R7W (Tippecanoe Township)
Details
The Oakland Mills Bridge is a long-span combination through and pony truss with seven steel stringers approaches and one Pratt pony approach span on the east end of the structures. Spanning the Skunk River south of Oakland Mills, the 358-foot bridge features pinned connections throughout and is supported by a stone and timber substructure. The bridge's history may be traced to the summer of 1876, when county officials advertised for bids for the construction project. The Missouri Valley Bridge and Iron Company of Leavenworth, Kansas, was ultimately awarded the construction contract with prices set at $15.25 per lineal foot and $7.90 per cubic yard for masonry work. The approximate cost of the bridge therefore amounted to close to $12,000. Using steel components rolled by the Pennsylvania firm Phoenix Iron Company, the bridge was completed by MVB&I under the supervision of county engineer John Schreiner. Although closed to vehicular traffic today, the Oakland Mills Bridge is a popular spot for picnickers in Oakland Mills State Park, where the bridge retains a high degree of structural integrity.
In the early 1880s, the pin-connected Pratt truss superseded the bowstring arch-truss as the iron bridge of choice for medium-span wagon crossings. Patented in 1844 by Thomas and Caleb Pratt, the Pratt design is distinguished by vertical members acting in compression and diagonals that act in tension. Virtually all of the major regional bridge fabricators manufactured Pratt trusses and marketed them extensively to Iowa's counties. This included the Missouri Valley Bridge and Iron Company. Thousands of pinned Pratt trusses were erected throughout Iowa, in both through and pony configurations, and many remain in service today. The Oakland Mills Bridge is distinguished as one of the earliest Pratt through trusses remaining in the state. It is an outstanding multiple-span example of this mainstay structural type [adapted from Crow-Dolby and Fraser 1992].