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West Fork West Nishnabotna River Bridge

Photos 

Iowa Department of Transportation

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BH Photo #270812

Map 

Description 

During World 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 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 Nishnabotna River Bridge I northeast of Manilla 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 Nishnabotna River Bridge I 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].

Facts 

Overview
Bowstring pony truss bridge over West Fork West Nishnabotna River on T Avenue
Location
Crawford County, Iowa
Status
Open to traffic
History
Built 1945
Builder
- Des Moines Steel Co. of Des Moines, Iowa
Design
Bowstring pony truss
Dimensions
Length of largest span: 77.1 ft.
Total length: 97.1 ft.
Deck width: 18.0 ft.
Recognition
Eligible for the National Register of Historic Places
Approximate latitude, longitude
+41.93550, -95.21893   (decimal degrees)
41°56'08" N, 95°13'08" W   (degrees°minutes'seconds")
Approximate UTM coordinates
15/316042/4644996 (zone/easting/northing)
Quadrangle map:
Manilla
Land survey
T. 82 N., R. 38 W., Sec. 12
Inventory numbers
IA 126410 (Iowa bridge number)
BH 13280 (Bridgehunter.com ID)
Inspection (as of 04/2015)
Deck condition rating: Poor (4 out of 9)
Superstructure condition rating: Fair (5 out of 9)
Substructure condition rating: Poor (4 out of 9)
Appraisal: Structurally deficient
Sufficiency rating: 27.9 (out of 100)
Average daily traffic (as of 2012)
30

Update Log 

  • August 8, 2016: New photos from Kevin Skow
  • November 22, 2013: Updated by Luke Harden: Added type, builder & Description
  • May 6, 2010: Updated by J.R. Manning: Added Road Name

Sources