Historic Bridges

Mallory Township Bridge

Clayton county

Bridge information

Year constructed: 1890
Bridge type: Pin-Connected Pratt Half-Hip Pony Truss
National Register of Historic Places status : Listed 
Length: 38 feet
Width: 15.6 feet
Spans: 1
FHWA: 118210
Jurisdiction: Clayton County
Location: Kale Avenue over Carlan Creek, 1.3 miles southwest of Osterdock, Section 3, T91N-R3W (Mallory Township)

Details

Spanning a small stream a mile southwest of Osterdock in southeastern Clayton County, this structure carries an unpaved county road. A Pratt half-hip Pratt pony truss with steel or wrought iron components and stone abutments, the bridge features pinned connections throughout. The bridge dates to 1890. That summer the Clayton County supervisors solicited competitive bids from bridge companies for several small-scale iron and combination spans. In July the supervisors awarded a contract to D.H. Young of Manchester, Iowa, to supply eight superstructures for the aggregate sum of $2730.00. Using wrought iron components rolled in Pittsburgh by Lackawanna, Young delivered the spans that year, and they were erected by local laborers. This truss continues to carry local traffic in its rural setting while retaining a high degree of both physical and historical integrity.

From the early 1880s to the establishment of state bridge standards in 1913, the pin-connected Pratt truss was virtually the exclusive structural type for short- to medum-span roadway crossings in Iowa. Its standardized fabrication, economy of materials and ease of erection made it a mainstay among the various state and regional bridge companies. The Pratt was marketed in both full-hip and half-hip configurations. The half-hip truss was used primarily for short-span applications, where the savings in materials from the omission of a hip vertical outweighed the loss of structural strength from this omission. This inherently short-span structural type was well suited for Iowa's myriad small streams and ditches, and, as a result, thousands of half-hip pony trusses were receted throughout Iowa in the late 19th century. This bridge in Clayton County is distinguished as the oldest remaining example in the state of the Pratt half-hip pony truss.

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