Pin-Connected Whipple Through Truss
National Register of Historic Places status:
Hardin County Engineer
Pedestrian path over slight depression in park, 3 miles northwest of Steamboat Rock, Section 7, T88N-R19W (Clay Township)
In January 1879 the Hardin County Board of Supervisors visited the site of a proposed bridge over the Iowa River at Hardin City. The supervisors conferred with city residents to secure a right-of-way for the structure. After achieving this, the county advertised for competitive bids to design, fabricate and erect the all-iron span. In April 1879 the supervisors awarded a contract to the Western Bridge Company of Ft. Wayne, Indiana. Using wrought iron components produced by the Passaic Rolling Mills of Paterson, New Jersey, Western Bridge fabricated this pin-connected truss and apparently completed its erection that year. The Hardin City Bridge carried traffic until its replacement in the 1980s. After that time, the truss was moved from its original location and re-erected for display on concrete pedestals beside a county road northwest of Steamboat Rock, where it stands today.
Configured as a pin-connected Whipple (or double-intersection Pratt) through truss, the Hardin City Bridge is one of the only eight such structures known to exist in Iowa. First patented by Squire Whipple, bridge engineer and builder from New York, the Whipple truss was a popular choice for long-span crossings between 1850 and 1890. The Whipple truss differed from the more common Pratt in that its diagonal members extended across, not one, but two panels. Although more costly, this variation provided greater lateral support for the diagonals, a critical consideration on deep, long-span trusses. By the turn of the century, Parker and Camelback trusses (Pratt variants with polygonal upper chords) had supplanted the Whipple as the truss of choice for longer span crossings. Accordingly, all of Iowa's extant Whipples date from before that time. With its Whipple web configuration, cast iron hip blocks and bearing shoes and rolled wrought iron components, the Hardin City Bridge typifies wagon truss construction of the late 1870s. Its subsequent move has diminished its locational and historical integrity substantially, but the truss remains a technologically significant, early transportation-related resource [adapted from Crow-Dolby and Fraser 1992].