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CR-71 Bridge

Monroe Road 859 Bridge

CR-71 Bridge

Primary Photographer(s): Nathan Holth and Rick McOmber

Bridge Documented: July 3, 2009

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Key Facts

Facility Carried / Feature Intersected
CR-71 (Monroe Road 859) Over Long Branch Creek
Location
Rural: Monroe County, Missouri: United States
Structure Type
Metal 4 Panel Pin-Connected Pratt Bedstead Pony Truss, Fixed and Approach Spans: Metal Stringer (Multi-Beam), Fixed
Construction Date and Builder / Engineer
1911 By Builder/Contractor: Illinois Steel Bridge Company of Jacksonville, Illinois

Technical Facts

Rehabilitation Date
Not Available or Not Applicable
Main Span Length
61 Feet (18.6 Meters)
Structure Length
91 Feet (27.7 Meters)
Roadway Width
11.8 Feet (3.6 Meters)
Spans
1 Main Span(s) and 2 Approach Span(s)
NBI Number
14617

Historic Significance Rating (HSR)
View Information About HSR Ratings

Bridge Documentation

View Archived National Bridge Inventory Report - Has Additional Details and Evaluation

The CR-71 Bridge is a beautiful and well-preserved example of a bedstead truss bridge of relatively large size. The bridge contains a main bedstead span featuring four panels and a single stringer approach span at each end of the bridge. The bridge appears to retain a high degree of historic integrity. Structural integrity of the truss appears to be good as well. The bridge displays barely any pack rust, even on the top chord cover plate which is  a typical trouble zone for pack rust. Very little section loss is present on the bottom chord as well. There is nothing on the bridge that would be difficult to restore as part of a preservation project. Original lattice railings remain on the bridge, except on the southern stringer approach on the east side, where the lattice was replaced with a very slightly different style of lattice railing, probably salvaged from another bridge. The bridge includes a traditionally composed wooden deck surface. Because of its size and historic integrity, this bridge should receive preservation priority.

 There is a ford crossing next to the bridge, probably used by farm traffic that may exceed the weight limit or width of the bridge.

The bedstead truss is a rare form of  truss bridge that was mostly built between 1890 and 1915, usually using pinned connections and a Pratt configuration. In Missouri however, they continued to be built after that  date for a while, with riveted connections and a Warren truss configuration. The bedstead truss (also known as a truss leg bedstead) was a design in which the end post was vertical and this end post extended down below the bottom chord to act as a substructure (bridge-supporting structure). The design was an economical one, since it reduced abutment costs, since the legs of  the bedstead did most of the job of the abutments. Bedstead truss bridges were marketed to local governments as a less expensive alternative to more traditional truss bridge forms. Bedstead truss bridge construction did not last long however, since it was found that  the design had some functional problems. The truss legs made the bridge susceptible to flooding, since flood debris could collide with the truss legs and damage them, drastically reducing their support strength. Worse, the bridge might be picked up completely and pushed away into the river. Another problem was with the way the forces act on a bridge with vertical endposts, which is a reason why truss bridges of any kind with vertical end posts is rare. One feature that bedstead truss bridges sometimes have to try to counteract these problems is a compression member for the first panel of the bottom chord.

To label a truss bridge as a bedstead, the vertical endpost must extend below the bottom chord to be considered a bedstead. A vertical endpost along is insufficient for a bridge to be called a bedstead. In some cases, a bedstead truss's legs may be encased in a concrete abutment or pier. Close examination of such bridges in the field is often needed to confirm whether or not such bridges are bedsteads or simply truss bridges with vertical end posts.

The bedstead truss is one of the rarest type of truss bridges today. Many states today do not have a single example within their borders, and others might have less than a handful. Neighboring Arkansas has only one example listed. In contrast, Missouri has perhaps the largest number of bedstead truss bridges in the entire country. When the first Historic Bridge Inventory was completed, there were in fact over one hundred examples! The problem with this is that at that time the inventory found most of them non-historic because there were so many. However many years have passed since that initial inventory, and while Missouri may still have the largest number of bedsteads in the country, the current number is nowhere near where it was initially since many of these bridges have been demolished. It is unclear if the Historic Bridge Inventory has been updated to reflect the rarity of the bedstead truss bridge: on a relative scale within the state and on an absolute scale on a national level. If the surviving examples in Missouri are not determined Eligible For the National Register of Historic Places like they should be, this will increase the difficulty of preservation. The high level of integrity, rarity of the design on the national level, and increasing rarity on the state level make the preservation of each surviving bedstead something that should take a high level of priority. In addition, the small size of the bedstead truss makes it  conducive to relocation and preservation in a park or on a non-motorized trail if it is considered insufficient for its current use. In addition, the smaller size makes a preservation project less costly and easier to tackle. Sadly however, the CR-214 Bridge demonstrates that these bridges are still being demolished in Missouri. This must end before it is too late. 

Information and Findings From Missouri's Historic Bridge Inventory

Discussion of Bridge

Other features: end post and truss legs: 2 channels with cover plate and lacing; upper chord: 2 channels with cover plate and lacing; lower chord: 2 angles with batten plates (outer panels), 2 punched rectangular eyebars (inner panels); vertical: 4 angles with lacing; diagonal: 2 punched rectangular eyebars; counter: round eyerod with turnbuckle; lateral bracing: round rod with threaded ends; floor beam: I- beam, field-bolted below lower chord; Guard-rail: steel lattice

Bridge Considered Historic By Survey: No

View Original PDF Historic Bridge Inventory Sheet

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Maps and Links: CR-71 Bridge

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