Year constructed: 1901
Bridge type: Pin-Connected Pennsylvania Through Truss
National Register of Historic Places status:
Listed
Length: 180 feet
Width: 17.8 feet
Spans: 1
FHWA: 116790
Jurisdiction: Clay County
Location: 210th Avenue over the Little Sioux River, 2.4 miles northwest of Spencer, Section 1, T96N-R37W (Summit Township)
Details
This long-span through truss carries county road 210th Avenue over the Little Sioux River near the northwestern city limits of Spencer. Now located at a rural crossing in Riverton Township, the structure was originally located on Main Street, south of downtown Spencer over the Little Sioux River. The first bridge at this heavily trafficked crossing was built in 1875 by J. Olson for $3,200. A timber pile structure, it lasted only six years before it was destroyed by an ice floe. The bridge was rebuilt, and then rebuilt again in 1889. Ten years later, the bridge needed a major rehabilitation, as the river had shifted its channel from under the truss. This time the Clay County Board of Supervisors opted to build a long-span steel truss, separated from the original truss by a series of timber pile spans. In the spring of 1900 the county contracted for its fabrication and erection with the Clinton Bridge and Iron Works. The Clinton, Iowa company was a prominent early twentieth-century Iowa bridge builder, responsible for constructing most of the major bridges in Clay County into the 1910s. Clinton B&I completed the pinned Pennsylvania span in 1901. The Main Street Bridge served this important route until 1915, when a new concrete arch bridge was erected. The 1901 truss was moved to this site and placed on concrete abutments prepared by the Thor Construction Company of Cedar Falls, Iowa. Here it remains today in essentially unaltered condition.
Serving as a major crossing of the Little Sioux River, the Main Street Bridge was important to transportation and commerce in Spencer, the Clay County seat. The structure's 1901 span is technologically noteworthy as a relatively well-preserved example of a Pratt truss subtype - the Pennsylvania truss. With its polygonal upper chords and subdivided panels, the truss exemplifies this relatively uncommon type, which was used primarily for long-span applications around the turn of the century. Few Pennsylvania trusses were ever built in Iowa, and only a handful remains today. The two spans in Clay County are important representatives of this uncommon early wagon truss configuration [adapted from Zibell, Roise, and Fraser 1992].