Year constructed: c1945
Bridge Type: Riveted Bowstring Pony Arch-Truss
National Register of Historic Places status: Listed
Length: 134 feet
Width: 17.7 feet
Spans: 2
FHWA: 129750
Jurisdiction: Crawford County
Address: 120th Street over East Soldier River, 2.5 miles southwest of Charter Oak, Section 28/29, T84N-R41W (Charter Oak Township)
Details
During World 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 East Soldier River Bridge east of Charter Oak was one of several such hybrid trusses built by Crawford County during the war years. Comprised of the riveted truss, supported by a timber substructure, the East Soldier River Bridge remains in unaltered condition today. It, like five other, almost identical spans that remain in Crawford County, is a noteworthy example of wartime bridge construction in Iowa [adapted from Fraser 1993].