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Historic Bridges in Minnesota
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Bridge L5659 in Blue Earth County.

Bridge L5659 on Township Road 96 over Big Cobb River

 

Bridge number: L5659

Year built: 1904

Contractor: Mayer Brothers, Mankato

Overall length: 73 feet

Overall width: 17.7 feet

 

Adapted from the National Register of Historic Places nomination form prepared by Dale Martin, Renewable Technologies, Inc. The Zieglers Ford Bridge was placed on the National Register of Historic Places in 1989.

 

 

Description

The Zieglers Ford Bridge is a steel, single-span, five-panel, pin-connected Pratt through truss. It carries Township Road 96 over the Big Cobb River. Its overall length is 73 feet and its overall width is 17.7 feet. The bridge's upper cord superstructure consists of paired channels with continuous cover plates riveted on top and batten plates underneath. The main verticals are laced paired channels; the hip verticals are paired forged eye-bars. The lower chord and the diagonals in the 2nd and 4th panels are paired punched eye-bars; in the middle panel the diagonals are turnbuckles. The floor consists of wood planks on wood beam stringers, which rest on the upper flanges of the I-beam floor beams, which in turn are suspended from the pin connections by U-bolts. Portal and sway bracing is of paired angle sections. Top and bottom lateral bracing is round rods. The span rests on coursed, quarry-faced sandstone abutments with wing walls, major refacing and repairs in concrete occurred in 1976. The bridge railing is made of angle sections. The movable end is not visible.

 

 

Historic significance

The Zieglers Ford Bridge is historically significant as a surviving example of a pin-connected Pratt through truss, a common bridge type of the late 19th and early 20th centuries. The bridge is also significant as a product of the Mayer Brothers, a Minnesota bridge building company located outside the Twin Cities. The Mayer Brothers was a Mankato firm whose foundry and machine shop produced a wide variety of goods in the late 19th century. Products include ditching and grading equipment, engines, boilers machinery and architectural iron work. Apparently, the company did not make bridge building a major part of its business. In this case, the Mayer Brothers competed against nine other firms, from Minneapolis, Iowa and other Midwest cities.

 

As Minnesota's population grew in the second half of the 19th century, a system of transportation evolved which featured railroad lines and a web a local roads leading from rural areas to shipping points along the railroads. These roads needed bridges over rivers and streams to insure year-round travel. The first bridges in Minnesota were constructed of wood, but in the late 1860s and early 1870s, local governments in the state began to build wrought iron bridges because of long-term cost advantages. Blue Earth County made an especially noteworthy effort to replace wood bridges with metal bridges. After early experimentation with a variety of other structural configurations, the pin-connected Pratt truss became the most widely used type of wrought iron bridge. By the early 1890s, steel had supplanted wrought iron as the structural material of choice, but the pin-connected Pratt remained the most widely used configuration into the 20th century. Most of the early metal bridges in Minnesota were built by out-of-state firms, but by the late 19th century, several Minneapolis based companies had grown to prominence. In the early 20th century, most bridges in the state were erected by these Minneapolis bridge builders, but in some instances, local firms, such as the Mayer Brothers, were successful in bidding against the larger companies.

 

Work on the bridge began in May, 1904, after the Blue Earth County Board of Commissioners selected C.S. Erickson from among four bidders to erect the stone abutments. Erickson bid $1,050 for the job, which the county required completed by early August. At about the same time, the county commissioners sought builders to bid on the construction of five bridges in the county, ranging in length between 20 feet and 80 feet. After opening bids on June 9, 1904, and subsequent negotiations, the commissioners offered the job of building four of the bridges, including this one, to Mayer Brothers of Mankato. The firm accepted, for a total payment of $4,317 ($975 lower than the lowest of the original ten bids).