120th Street Bridge
Located west of West Liberty, this small-scale steel and concrete bridge carries a gravel-surfaced county road over an unnamed stream. The bridge consists of a single-span steel rigid-frame structure, supported on a skew by steel posts embedded in concrete abutments. Although its dimensions are modest--spanning only 35 feet--the structural configuration of the beams was noteworthy. The four slightly arched beams are made up of steel plates welded continuously to form variable depth I-beams, braced by concrete beam diaphragms. The Iowa State Highway Commission designed the structure in the spring of 1937. Using the ISHC design, Muscatine County solicited competitive proposals and in June awarding a contract for this bridge and two others to Otto Wendling of Muscatine. Presumably completed later that year, this structure has functioned in place since, in unaltered condition.
With notable engineers such as Thomas McDonald and Conde McCullough on its staff, the Iowa State Highway Commission was from the beginning a leader among state highway agencies in the standardization of bridge design. Immediately after the re-organization in 1913, ISHC began developing design standards for several short-span structural types. But within this framework of standardization, ISHC was continuously experimenting with innovative applications of existing and new technologies. This diminutive bridge in Muscatine County is evidently the result of ISHC experimentation. It and the other bridges let in the June 1937 contract employed rigid-frame configurations - this one using welded steel beams and the others reinforced concrete beams. Further research is needed to determine the purpose and circumstances of this exercise, but it appears that the bridge is a formative application by ISHC in welded steel technology. It is today distinguished as the oldest welded beam bridge in Iowa - an important transportation-related resource [adapted from Fraser 1991].
- Rigid frame bridge over an unnamed creek on 120th Street
- Muscatine County, Iowa
- Open to traffic
- Built 1937
- - Iowa State Highway Commission of Ames, Iowa
- Otto Wendling of Muscatine, Iowa (Designer)
Span length: 35.1 ft.
Total length: 35.1 ft.
Deck width: 19.7 ft.
Posted to the National Register of Historic Places on May 15, 1998
- Approximate latitude, longitude
- +41.56806, -91.32313 (decimal degrees)
41°34'05" N, 91°19'23" W (degrees°minutes'seconds")
- Approximate UTM coordinates
- 15/639811/4603178 (zone/easting/northing)
- Land survey
- T. 78 N., R. 4 W., Sec. 16
- USGS topographic map
- West Liberty
- Inventory numbers
- IA 258410 (Iowa bridge number)
NRHP 98000491 (National Register of Historic Places reference number)
BH 14151 (Bridgehunter.com ID)
- Inspection (as of 09/2011)
- Deck condition rating: Poor (4 out of 9)
Superstructure condition rating: Poor (4 out of 9)
Substructure condition rating: Satisfactory (6 out of 9)
Appraisal: Structurally deficient
Sufficiency rating: 30.9 (out of 100)
- Average daily traffic (as of 2006)
- September 15, 2013: New photos from J.R. Manning
- May 10, 2012: Updated by Luke Harden: Added builder
- January 11, 2012: Photo imported by Luke Harden
- July 22, 2011: Updated by Luke Harden: Added description
- June 12, 2011: Updated by Luke Harden: Fixed design type and added photograph
- June 11, 2011: Updated by Luke Harden: Added National Register information