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Fourpoints Bridge

   


Fourpoints Bridge

Primary Photographer(s): Nathan Holth and Rick McOmber

Bridge Documented: July 9, 2008
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Key Facts

Facility Carried / Feature Intersected
Keysville Road Over Toms Creek
Location
Rural: Frederick County, Maryland
Construction Date and Builder / Engineer
1876 By Builder/Contractor: Wrought Iron Bridge Company of Canton, Ohio

Technical Facts

Rehabilitation Date
1997
Main Span Length
103 Feet (31.4 Meters)
Structure Length
103 Feet (31.4 Meters)
Roadway Width
12.8 Feet (3.9 Meters)
Spans
1 Main Span(s)
NBI Number
200000F-0502010

Historic Significance Rating (HSR)

Bridge Documentation

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

View The Historic Bridge Inventory Report For This Bridge

 

This eight panel bridge is a textbook example of a Wrought Iron Bridge Company through truss based on their 1876 patent. In this case the "textbook" so to speak is actually a pamphlet that the company put out advertising its bridges. In this document, the Pratt though truss design they offer is the one seen on Keysville Road. Click here to view the page from the pamphlet. A number of other bridges remain elsewhere similar to this bridge, but extremely few include (or retain) the distinctive caps on the endpost / top chord connection and in an intact fashion. An example of such a bridge lacking the caps is Michigan's Maple Road Bridge.

 Hurricane Fran washed this ancient bridge right off of its abutments in 1996, however the bridge was restored and reset on the abutments a year later. Despite damage from the hurricane, the bridge sits today a functional crossing with good historic integrity. While some alterations such as a replaced flooring system are present, the key distinctive details that make this bridge an important example of Wrought Iron Bridge Company work remains on this bridge. As such it should be considered an extremely important historic bridge, as well as an example of a difficult preservation project completed successfully. Images taken by Frederick County showing the damage and subsequent restoration are available below. In the middle photo, challenges such as bent eyebars and sway bracing are clearly visible.

There are a number of important details to note on the Fourpoints Bridge. To aid in this discussion, the diagram on this page serves as a guide and key to the text that follows. First and foremost is the caps on the endpost / top chord connection (B). These caps are cast iron and display a patent date on the front and a decorative star shape on the side. They serve both an aesthetic and functional purpose, covering up and protecting the unusual connection detail at those locations, a connection detail which Wrought Iron Bridge Company would use also in its pony truss bridges such as Smith Road Bridge. The nature of the connection can be seen in that Smith Road Bridge because the pony truss bridges did not feature caps, so the connection is exposed. The detail is visible on Fourpoints bridge from below as seen at (E) in the diagram. Instead of having the diagonal and hip vertical members be an eye bar to fit around a pin, they are threaded at the rounded end and large bolts hold it in place at that connection. The thinking behind this connection is also visible with the end post / bottom chord connection (C).  The lower connection of the hip vertical (G) was another place where the company often used an unusual design. This was typically an strange four-pronged/looped eye that attached to a hanger loop on the floor beam. At least part of this connection has been altered with the flooring system replacement on Fourpoints Bridge. The actual vertical may represent the original design (and perhaps materials) however, but if this is the case, than this bridge displays a more standard eye shape at the end. Another unusual detail is the presence of a very lightweight rod that runs the length of the truss (A). This rod is seen on other early bridges by the company, and its purpose is unknown. It may have been an attempt to provide additional stability to the truss. No other prolific bridge company appears to have placed such a rod on their bridges. Compared to other pin-connected truss bridges, their is a lack of v-lacing or lattice on the bridge. This is again typical for an early bridge by Wrought Iron Bridge Company. The company instead used either rolled beams, as seen in the sway bracing, or their built-up beams such as the vertical members (D) were small and relatively lightweight and as such their design did not have room for or require large lacing and lattice to hold them together. Finally, the observant visitor to this bridge may notice, particularly on the cast iron elements of the bridge, that there are numbers on them (F). These may have been originally to aid in bridge assembly.

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Photos and Videos: Fourpoints Bridge

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