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Townline Brook Bridge

Bennett Park Bridge

Townline Brook Bridge

Primary Photographer(s): Nathan Holth and Rick McOmber

Bridge Documented: October 21, 2009 and November 6, 2011

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Key Facts

Facility Carried / Feature Intersected
Private Drive Over Townline Brook
Location
Rural: Eaton County, Michigan: United States
Construction Date and Builder / Engineer
1875 By Builder/Contractor: Wrought Iron Bridge Company of Canton, Ohio

Technical Facts

Rehabilitation Date
1967
Main Span Length
Not Available
Structure Length
Not Available
Roadway Width
Not Available
Spans
1 Main Span(s)
NBI Number
Not Applicable

Historic Significance Rating (HSR)

Bridge Documentation

Above: Courtesy of the Digital Bridges collection, a through truss variation of this patented bridge design marketed by the Wrought Iron Bridge Company appearing in a period pamphlet distributed by the company. Click the image for a larger version with a description.

This bridge is the only remaining 1870s bowstring truss bridge in the entire state of Michigan! Bowstring truss bridges were the metal bridge of choice during the 1870s, a very short period of time, because by the 1880s the pin-connected Pratt truss and other variants became the standard. Surviving examples are extremely rare today, and because they usually predate 1880, are among the oldest surviving metal bridges in the country. The bridge is today distinguished as one of the two oldest and most important metal bridges in Michigan.

Bowstring truss bridges are very easy to associate with  a builder because during this time a lot of experimentation was occurring with bridges, both in terms of overall design but also down to the forms of structural iron used to compose the trusses. Builders frequently patented and defended those patented designs aggressively. This bridge is a product of the Wrought Iron Bridge Company of Canton Ohio, an assessment made by an observation of the design of the bridge. This extremely prolific company produced a variety of truss bridges in the late 19th Century. This bowstring bridge is an excellent surviving example of one of the designs that this bridge company offered, which was marketed as a "plate and channel arch bridge." Although composing a top chord using a plate and channel (back-to-back channels with riveted cover plate) top chord was a method that actually became the most common way to build most late 19th century truss bridges of any kind by any company, very few of the bowstring bridges built by the Wrought Iron Bridge Company that remain today exhibit the plate and channel top chord. Most surviving examples instead display the Keystone column top chord. Keystone columns themselves are rare, and indeed the one place they are most frequently found is on the Wrought Iron Bridge Company bowstrings.

In the Wrought Iron Bridge Company's 1880s illustrated pamphlet, the plate and channel bowstring appears in the pamphlet with some interesting comments. As mentioned earlier, new bridge ideas were frequently being patented and aggressively defended by the patentee. The pamphlet description of the plate and channel bowstring remarks that "The Lattice Posts, whether made of Star, Angles or Tees, are covered by patents owned exclusively by this Company, and all other makers or users will be held liable for damages." Indeed, the Wrought Iron Bridge Company did use built-up vertical members with lattice on this and many of their bowstring truss bridges, and even their Pratt pony truss bridges which became popular in the early 1880s. The Townline Brook Bridge's lattice vertical members are composed using the "Tee's" which are T-shaped rolled beams. The "Stars" that the aforementioned quote describes are in fact also present on the Townline Brook Bridge, but not with the lattice, instead appearing on their own, acting as vertical members on all panel points that do not contain the latticed members. These aptly named beams/rods, are truly star-shaped and are quite attractive. Star-shaped beams/rods were only used for a short time, mostly in the same 1870s period that the bowstring truss bridges were being built. Later, more common structural steel elements like rods and angles became the preferred design.

The Townline Brook Bridge is as a result an example of a rare structure type and a good representative example of the work that the Wrought  Iron Bridge Company. The bridge's original location is unknown, but up until 1967 it was located in Bennett Park in Charlotte. In 1967, it was relocated onto a private property to serve as a crossing to access a home. In this location, away from heavy traffic and salt, the bridge has not deteriorated and appears to be in excellent condition. In addition, despite its age and apparent relocation two times, the bridge has no notable alterations. The only structural issues observed on the bridge was some evidence of old collision damage that bent a couple verticals. The owner of the bridge commented that they had the bridge redecked with new wood planks a few years ago, and these appear to be holding up very well. The only work HistoricBridges.org would recommend for the bridge at this time would be to remove the dirt which appears to have built up around the ends of the truss. Because the ends of the bridge are buried in this dirt, moisture can build up there and could cause deterioration. 

Information and Findings From Michigan Historic Bridge Inventory

Narrative Description

There is no information about the history of the Residential Drive Bridge in county or local records. According to its owner, Zygmunt Brzycki, the bridge was moved to this site from Bennett Park in Charlotte in 1968. A photograph in a booklet prepared for Charlotte's centennial in 1963 appears to show the bridge in the park. The bridge was probably originally erected in another location in the late nineteenth century, then salvaged by the city for park use when it became inadequate to handle farm machinery and car traffic in the twentieth century.

Inveterate bridge designer Squire Whipple obtained a patent for a bowstring truss in 1841. Other bowstring designs soon joined the many truss forms developed in the nineteenth century. As bridge engineer and historian J. A. L. Waddell observed: "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." The bowstring's curved top chord, which was in compression, required less material than the more common truss form with a horizontal top chord and inclined end posts. The lower chord, which tied together the bow's two ends, was also relatively light, as were the vertical members that dropped from the top chord to support the deck.

While adequate for traffic in the horse-and-buggy era, the bowstring truss could not handle the heavier and faster traffic that developed in the late nineteenth and early twentieth centuries. "Each form as it appeared," Waddell noted, "was tested by subjecting it to the ordeal of actual use, which showed conclusively both its merits and its defects; hence by a process of elimination, based upon the principle of the survival of the fittest, a few forms have been retained and the others have been relegated to the history of bridge-building." The latter was the fate of the bowstring truss. Stronger and more efficient truss forms prevailed, particularly after structural steel became widely available in the 1890s.

By the end of the 1930s, truss bridges of almost any design had fallen out of favor as steel stringer and other bridge types became easier and cheaper to produce. In the last half of the twentieth century, the population of truss bridges in Michigan has declined rapidly. The loss of bowstrings is even more dramatic: by the early 1990s, only one bowstring truss, the Elm Circle Drive Bridge over the Lower Rouge River in Wayne County, still carried highway traffic.

Statement of Significance

This bowstring truss bridge is eligible for the National Register as an excellent example of the bowstring pony truss, a once common bridge type that is now extremely rare.

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Photo Galleries and Videos: Townline Brook Bridge

 
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