Lawrence Bridge

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Description 

In the 1870s Winneshiek County embarked on an ambitious bridge construction program, in which many of the earliest wooden structures were replaced with more substantial iron spans on stone substructures. Beginning in 1873, the county, under the direction of bridge commissioner George Winship, built several bowstring arch-trusses, most of which were supplied by the Wrought Iron Bridge Company, of Canton, Ohio. By 1880 the county had erected a total of 32 iron bridges, all built under Winship's supervision. That year the county contracted with WIBCo for two medium-span bridge superstructures, the Upper Bluffton bridge, and the Lawrence Bridge, an 84-foot span Pratt pony truss. Costing $2,519.35, the Lawrence Bridge featured a pin-connected Pratt truss based on patents held by David Hammond, WIBCo's president. The Upper Bluffton and Lawrence Bridges marked a watershed for bridge building in Winneshiek County. The county supervisors had contracted for small-scale, all-iron trusses in the 1870s (Pratt half-hips and bedsteads, primarily), but these two trusses marked the first time that the county purchased longer-span trusses instead of bowstrings for rural crossings. The bridges presaged the building trend in the county for the rest of the 19th century. Winneshiek County continued to build iron, and later steel, trusses on its rural roads in the 1880s and 1890s. This change in character of bridges occurred well within the mainstream of state and national trends, for after the 1880 bowstring was specified increasingly less frequently for roadway crossings. WIBCo, at the forefront of bowstring innovation in the 1870s, was also a leader in the shift toward other structural configurations a decade later. David Hammond foresaw the decline of the bowstring in the mid-1870s, as his company was reaching its zenith on the basis of bowstring sales, and he directed his patent activities more toward straight-chorded trusses after that point. WIBCo maintained an extensive catalog of bridge types that ranged from the exotic to the commonplace. With its pinned connections and patented Pratt web configuration, the Lawrence Bridge represented the former rather than the latter. It was one of thousand sof such pinned Pratts erected throughout Iowa in the late 19th century. The Lawrence Bridge is technologically significant as a very early, well-preserved example of this mainstay wagon bridge type. In Winneshiek County it represented the first time the county used a truss rather than a bowstring for a rural crossing. A local harbinger of prevailing bridge trends, the Lawrence Bridge is a significant transportation-related resource [adapted from Crow-Dolby and Fraser 1992].

Categories 

19th Century (7,631) 6-panel truss (652) Built 1880 (180) Built during 1880s (2,011) Iowa (6,530) NR-listed (2,962) Open to authorized vehicles (267) Owned privately (1,748) Pin-connected (3,925) Pony truss (16,245)

Pratt pony truss (3,654) Pratt truss (9,352) Preserved (1,195) Span length 75-100 feet (6,454) Structurally deficient (14,098) Total length 75-100 feet (6,598) Truss (32,984) Winneshiek County, Iowa (90) Wooden deck (6,074) Wrought Iron Bridge Co. (375)

Update Log 

• July 22, 2011: Updated by Luke Harden: Added description
• June 24, 2009: Updated by Jason Smith

Sources 

• Jason Smith - flensburg [dot] bridgehunter [dot] av [at] googlemail [dot] com
• Luke

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