Concrete Through Girder
National Register of Historic Places status:
40th Street over Otter Creek, 1.7 miles northwest of Oelwien, Section 19, T91N-R9W (Jefferson Township)
Located northwest of Oelwein, in Jefferson Township, this medium-span concrete bridge carries a gravel-surfaced county road over Otter Creek. The bridge is comprised of two through girder spans, with reinforced concrete substructure, deck and guardrails that double as the girders. The Otter Creek Bridge dates to 1917. In July of that year the Fayette County Board of Supervisors approved the bridge's design by the state highway commission and solicited competitive bids for its construction. When no bids were received, the county resorted to using day laborers to build the structure for a cost of $5,153.38. Since its completion in 1917, the Otter Creek Bridge has functioned in place, in unaltered condition.
"Fayette County has pinned considerable faith to the day laborer system of bridge and culvert building and has made good," the state highway commission reported. "This is contrary to the general experience of Iowa counties with day labor work." Among the structural types that the county employed during this period of intense bridge construction was the concrete through girder. Carrying the roadway deck between the two structural beams, the through girder bridge was one of the first standard designs developed by the state highway commission after its re-organization in 1913. Several of Iowa's counties built through girder bridges in the 1910s. The advantage of this structural type was that it required less clearance between the roadway and the high water mark than did the deck girder. Its disadvantages were that it required slightly more material than the deck girder and it was not as flexible: with the structural members above the deck, the through girder could not be widened later. Ultimately the disadvantages outweighed the advantages, and the through girder was phased out of common use in Iowa by the early 1920s. Most of the state's through girders are relatively short, single-span structures over minor watercourses. A handful of two-span girders remains in Fayette County, however, of which the Otter Creek Bridge is a well-preserved example. It is a typically configured example of ISHC standard concrete through girder design, distinguished somewhat by its two-span configuration [adapted from Fraser 1992].