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Some sources have classified this bridge as a Warren truss variant, however this bridge is more appropriately and clearly categorized and recognized as a Thacher truss. The issues with classifying this bridge likely have cropped up because of the history of the Thacher truss as a configuration. Thacher truss bridges defy precise classification and configuration because the Thacher truss was a patented truss configuration that bridge companies could not copy exactly. As a result, they designed bridges that were extremely similar to the Thacher patent truss configuration but which were different enough so as to be protected from infringement. No bridges survive that directly follow the Thacher patent truss... in other words bridges built by Edwin Thacher or the Keystone Bridge Company for which he worked. Other surviving Thacher truss bridges left standing and also the Ditch Road Bridge, were built by the Wrought Iron Bridge Company of Canton, Ohio, and this Ellsworth Ranch Bridge was built by the King Bridge Company of Cleveland, Ohio under the auspices of regional agent Milo Adams. The difficulties in classification are apparent by comparing the Ellsworth Ranch Bridge to the aforementioned Ditch Road Bridge. Both have diagonal members that form the distinctive single "W" shape that spans from endpost to endpost, with the outer diagonals being tension members, and the center members being compression members. However Ditch Road Bridge contains a series of vertical members throughout the truss, while the Ellsworth Ranch Bridge only has hip verticals, with no other verticals present. Despite these differences, all are today considered Thacher trusses because of their extreme significance as one of the rarest surviving truss configurations in the country. Nationwide, only a few examples remain. As such, each surviving example, including the Ellsworth Ranch Bridge, should all receive the highest preservation priority possible.
This bridge was fabricated by the King Bridge Company of Cleveland, Ohio. The actual bridge design was engineered by the King Bridge Company's agent for the region, Milo A. Adams. The bridge design appears to have been the brainchild of Adams alone, and was never adopted by the King Bridge Company as a whole. Milo A. Adams later formed his own company in Minneapolis, called simply Milo A. Adams Bridge Company.
The Ellsworth Ranch Bridge is perhaps the most unique of the surviving Thacher truss bridge designs because in addition to its rare truss design, it features extremely unusual design details that are very bizarre. Perhaps the most obvious and extremely unusual detail is the arrangement of the built-up top chord and endpost, which is configured with front-to-front channels with v-lacing on the sides. The visual appearance of connections along the top chord and end post have an unusual appearance as well as a result of this design. Also, the center two diagonal members, which are compression members and thus not eye bars, are rigidly connected with rivets rather than pin-connected. This combination of riveted and pinned connections, especially with a pre-1900 bridge is noteworthy. The overall design and configuration of the bridge is very lightweight and was designed with economy of materials in mind.
This bridge is seated on caissons (sometimes called Lally columns), consisting of concrete-filled metal tubes.
While this abandoned bridge appears to remain in good condition and appears to be unthreatened in its current location, this bridge would also make a great candidate for relocation and restoration for pedestrian use in a park or on a non-motorized trail. In its current location, the bridge is difficult for the public to enjoy, since the bridge is positioned in the middle of field with tall grass that is liberally infested with ticks. Either way, this bridge should be protected from damage, demolition, collapse, etc. at all costs, whether that means simply leaving it standing where it is, or relocating and restoring the bridge. Given Iowa's tendency to have floods, it is worth a warning that great efforts should be taken to ensure that this bridge is in no danger whatsoever from flood damage. There would be more surviving Thacher truss bridges, if Michigan had not hired an inept engineer to relocate the Ditch Road Bridge onto low piers that were not designed for flood waters.
Information and Findings From Iowa's Historic Bridge InventoryDiscussion of Bridge
Located
in northeastern Emmet County, this short-span through truss extends
north-south across the East Fork of the Des Moines River. The structure
consists of a single pin-connected truss, supported by steel cylinder
piers, with timber retaining walls. The five-panel truss displays
elements of both Pratt and Warren configurations. The end posts and
outside panels are typically Pratt-like, but the interior three panels
feature a triangular, Warren-like configuration, with diagonals acting
alternating in compression and tension. Even in this, the truss's web
differs from the typical Warren configuration, however, because the
inverted V of the center panel diagonals does not parallel the diagonals
in the adjacent panels. Known locally as the Ellsworth Ranch Bridge,
this structure dates to 1895. In January of that year the Emmet County
Board of Supervisors received a petition for a bridge across the Des
Moines River in Lincoln Township. The board laid the matter over until
April, whereupon it approved construction of the bridge and solicited
competitive bids for its fabrication and erection. When the proposals
were submitted the following month, the board adopted the plans of King
Iron Bridge Company as "the most suitable," but rejected all of the bids
as too high. After further discussion, the supervisors rewrote the
specifications for the proposed bridge, reducing its length from 100
feet to 80 feet in the hope that the reduction in materials would result
in a lower cost. This strategy was apparently successful. By the day's
end, the supervisors had awarded a contract to the King Iron Bridge
Company for the construction of three bridges - including this
truss--for $3,400. The Ellsworth Ranch Bridge was completed later that
year. Other than a minor reconstruction in 1937, it remains unaltered
today. Bridge Considered Historic By Survey: Yes |
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