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Historic Bridges in Minnesota
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Bridge 1482 in Rock County.

Bridge 1482 on Hwy 75 over Schoneman Park

 

Bridge number: 1482

Year built: 1908

Contractor: Hewett Bridge Company

Overall length: 29.8 feet

Overall width: 15.7 feet

 

 

Adapted from the National Register of Historic Places nomination form prepared by Charlene K. Roise and Robert M. Hybben. Bridge No. 1482 was listed on the National Register of Historic Places in 1992.

 

 

Description

Bridge No. 1482 is a steel, single-span, king-post pony truss bridge located in a rural setting in Schoneman County Park, just east of U.S. Highway 75. Roadway width is 15 feet, overall width is 15.7 feet. The structure is oriented on a northeast-southwest axis across a shallow channel by a small pond. Most connections are riveted. Verticals, however, are attached by pins top and bottom. Steel for the bridge was provided by Cambria and Inland Steel. Steel members are painted green, the bridge's original color. The upper chord consists of two back-to-back channels covered by a plate on top and connected by battens below. Two looped, rectangular-section bars make up the bottom chord. Verticals are a pair of looped, square rods, encircling a pin at each end. Diagonal bracing stretches from the top chord to a plate at the lower end of the vertical. The single floor beam, a rolled I-beam, is connected to the lower vertical pin by a U-bolt. I-beam stringers are bolted to the floor beam. Continuous curved sections of corrugated metal provide bracing between the stringers. The metal apparently served as form work to facilitate pouring the concrete deck. Bands of steel and low concrete curbs edge the deck. Two angles form the railings. The bridge is braced at the verticals by outriggers formed from back-to-back angles. The superstructure rests on concrete abutments surrounded by dirt. No builder's plate is attached to the bridge, although a modern, free-standing sign near the southeast abutment describes the history of the bridge.


 

Historic significance

Bridge No. 1482 is historically significant as a rare example of a king-post pony truss bridge. One of the few king-post bridges built in Minnesota during the late 19th and early 20th centuries, Bridge No. 1482 provides a fine example of that style's distinctive A-shaped truss configuration. It retains excellent integrity of design, materials, workmanship, feeling and association. The bridge, originally erected over the Rock River on a rural road between Luverne Township and Clinton Township, was moved to its present location in 1990. While the new location is in Schoneman Park, bounded to the west by two-lane U.S. Highway 75, the setting remains rural. The bridge is situated at the northern end of the park, which is relatively undeveloped. The structure is approached by an unpaved road and is surrounded by trees. Farm fields are adjacent to the east. National Register registration requirements for metal truss bridges specifically allow relocation of a bridge to a compatible new setting where the structure can span "a channel or body of water, railroad tracks, or some other barrier to vehicular travel." The bridge is also significant for its association with the Hewett Bridge Company, the firm responsible for construction of Bridge No. 1482. The Hewett Bridge Company was an important Minnesota bridge builder in the early 20th century.

 

Bridge No. 1482 was built during a period of great bridge building activity in Rock County. The supervisor of Luverne Township, encouraged by a 1907 Minnesota law which required counties to pay half of the cost of any bridge built within their borders, petitioned the county board for its construction on July 13, 1908. The board accepted the petition and awarded the contract to the Hewett Bridge Company of Minneapolis one week later. According to the July 31, 1908, Rock County Herald, the contract specified a bridge with "steel piers and frames and [a] cement [concrete] floor." The newspaper also noted that the bridge, approved as one of a group of six new bridges, would give the county 20 new bridges for 1908, one of the largest yearly totals in its history. When it became necessary to replace the bridge in 1990, the Rock County Highway Department, in deference to the structure's historic significance, moved it to Schoneman Park in Section 23 of Luverne Township.

 

The king-post ranks among the oldest truss-bridge forms. While originally built entirely of wood, the style adopted new materials as they were introduced to bridge construction. In the mid- to late 19th century, cast and wrought iron members created timber and metal structures known as "combination" bridges. By the late 1890s, king posts were built of steel, as were virtually all truss bridges at that time. Despite the design's flexibility, however, it fell victim to intensifying economic pressure. Writing in Bridge Engineering in 1916, J.A.L. Waddell, a prominent bridge engineer and historian, noted that "for many years American bridge designers exercised their ingenuity in devising new forms of trusses and girders, the principal object of their endeavors being to find forms involving the use of the smallest amount of metal." As a result, the "A" truss, another name for the king-post, was among those that had become "antiquated." In 1909, only a year after Bridge No. 1482 was built, a popular engineering text, A Text-book on Roofs and Bridges, Part I: Stresses in Simple Trusses, observed that the king-post truss was "formerly employed for highway bridges of very short span" but was "now rarely seen." Waddell singled out the Pratt and the Warren as among the few truss designs that "survived the test of time." These styles were embraced by the Minnesota Highway Commission for their initial standard plans early in the 20th century, while the Commission never promulgated plans for the king-post. Only seven metal king-post trusses are known to survive in Minnesota, making Bridge No. 1482 an extremely rare and valuable example of an important early truss type.