Year constructed: 1946
Bridge type: Rigid-Connected Bowstring Pony Arch-Truss
National Register of Historic Places status:
Listed
Length: 134 feet
Width: 18 feet
Spans: 1
FHWA: 130550
Jurisdiction: Crawford County
Location: 180th Street between B and C Avenues over Beaver Creek, 4.5 miles northwest of Schleswig, Section 9, T85N-R40W (Morgan Township)
Details
During War II the War Department developed a "Priorities Critical List" of materials deemed essential to the war effort. As a component of almost every major piece of war materiel, steel was, of course, included on the list, making the construction of steel bridges problematic for Iowa's counties. In response, most of the counties reverted to timber construction for their small-scale bridges, and timber pile bridges outnumbered all other types by a substantial margin in the 1940s. Crawford County, too, relied on timber construction, until heavy flooding in May 1945 washed out 27 bridges and culverts in the county.
The county board of supervisors resolved to build new bridges using emergency funds, purchasing several steel superstructures from the Des Moines Steel Company as replacement spans. These structures featured a bowstring arch-truss configuration, with the upper chord in compression and the lower chord in tension to resist the springing action of the curved upper chord (although the all-riveted construction made this action structurally indeterminate). The trusses employed only small-profile steel angles for the web members. They employed angled gusset plates to which the vertical and diagonal members were riveted to the chords. Each web was fabricated in the shop in two halves and field-bolted at the site by a county work force. The trusses were carried by relatively simple bearing shoes, and angle outriders provided lateral support for the truss webs. The Beaver Creek Bridge northwest of Schleswig was one of several such hybrid trusses build by Crawford County during the war years. Comprised of the riveted truss, supported by a timber substructure, the Beaver Creek Bridge remains in unaltered condition today. It, like the five other, almost identical spans that remain in Crawford County, is a noteworthy example of wartime bridge construction in Iowa [adapted from Fraser 1993].