Year constructed: 1891
Bridge type: Pin-Connected Pratt Half-Hip Pony Truss
National Register of Historic Places status: Bridge is un-evaluated in its current location
Length: 60 feet
Width: 13.6 feet
Spans: 1
FHWA: 232150
Jurisdiction: Madison County Historical Society
Location: Northeast of the Winterset County Historical Society building in Winterset, Section 6, T75N-R27W (Scott Township)
Details
Previously located at the end of an unimproved county road, this short-span pony truss crosses a branch of Clanton Creek. The structure is comprised of a pinned Pratt truss, with timber stringer approach spans on both ends, all supported by a timber substructure. The truss web composition is unusually light, consisting of riveted angles for the upper chords and end posts and thin eyebars for the lower chords, and features both pinned and rigid connections. This is contrasted by the relatively heavy "fishtail" girder floor beam U-bolted to the lower chord pins at the center panel point. Known locally as the Morgan Bridge, the structure was built here in 1891 by Winterset contractor Benton Jones for $376.39. Jones used a wrought iron or steel superstructure fabricated by the King Iron Bridge Company of Cleveland, erecting the truss on timber pile bents with 22 feet of timber approaches. The substructure has evidently been replaced subsequently, as have the approach spans, but the truss itself remains in essentially unaltered condition. Always a relatively remote crossing of this minor watercourse, the Morgan Bridge is now closed to traffic, its deck in deteriorating condition.
With their pinned connections and standardized fabrication, Pratt pony trusses were the iron bridge of choice for short-span applications in the late 19th century. Thousands of such trusses were fabricated by the major bridge firms such as King, WIBCo, and in Iowa, the Clinton Bridge and Iron Works. Many remain in place to day. The Morgan Bridge is noteworthy among the remaining Pratts for its unusual web composition and its relatively early construction date. Although altered somewhat through the replacement and deterioration of its timber members, it is still a relatively well-preserved early wagon truss [adapted from Fraser 1992].