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Poffenberger Road Bridge

   


Poffenberger Road Bridge

Primary Photographer(s): Nathan Holth and Rick McOmber

Bridge Documented: July 9, 2008
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Key Facts

Facility Carried / Feature Intersected
Poffenberger Road Over Catoctin Creek
Location
Rural: Frederick County, Maryland
Construction Date and Builder / Engineer
1878 By Builder/Contractor: Penn Bridge Company of Beaver Falls, Pennsylvania

Technical Facts

Rehabilitation Date
2006
Main Span Length
123 Feet (37.5 Meters)
Structure Length
126 Feet (38.4 Meters)
Roadway Width
13.5 Feet (4.1 Meters)
Spans
1 Main Span(s)
NBI Number
200000F-2203010

Historic Significance Rating (HSR)

Bridge Documentation

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

View Historic American Engineering Record (HAER) Documentation For This Bridge

HAER Data Pages, PDF

View The Historic Bridge Inventory Report For This Bridge

The Poffenberger Road Bridge is right off a very important bridge because it is an ancient 1878 structure displaying the uncommon Whipple truss configuration. Its age shows in its lightweight design. The vertical members and original rolled floorbeams on this bridge are surprisingly small on this bridge. However the bridge is far more than just that.

This bridge clearly displays numerous design details that immediately associate it with the Penn Bridge Company just as surely as a builder plaque (which is missing from the bridge) would. It does have some traits that the Wrought Iron Bridge Company also used, and this confused some people including those who conducted the state historic bridge inventory. However some other details on the bridge are unique only to Penn Bridge Company, it is those details that HAER and this website both used to arrive at Penn Bridge Company with extremely high confidence.

The Poffenberger Road Bridge features the unusual termination of the top chord at the end post that allows a small date plaque to be present at the end of the top chord. Another company did this also on its oldest Pratt truss bridges, the Wrought Iron Bridge Company. However the presence of two pins at the top chord / end post connections is something that is extremely unusual but something Penn Bridge Company did often. It is most similar in appearance and design to a smaller bridge in Michigan that is a Pratt rather than a Whipple, the Bauer Road Bridge. These two bridges share a distinctive portal knee bracing and a bottom chord whose eye bars are a single piece of fabricated iron for  a length of two panels rather than the usual one panel. By the way, be sure to look closely at the knee bracing on these bridges. You will note the shapes are not "cut" smoothly, and instead have a jagged teeth-like edge to them. This is because they lacked machinery to simply cut the metal. Instead the shapes had to be laboriously cut out by punching or drilling tiny holes in the metal, like using a one hole-punch tool to cut a sheet of paper in half. This is the effort that companies went to just to make sure the bridge was not only functional, but was attractive as well.

A detail that is not shared with many other Penn Bridge Company bridges that is present on this bridge is the fact that although they went overkill with two pins at the top chord and end post, there are no pins for the diagonals on the rest of the top chord connections. Instead the diagonals terminate in a threaded rod which is held to the top chord by a large bolt. This connection technique is something likely brought from the way members on bowstring truss bridges like Bennies Hill Road Bridge were connected. The Wrought Iron Bridge Company is the only other noteworthy company that continued using this unusual connection technique beyond the bowstring era, employing it for some of their pony truss bridges.

As an extremely old 1878 example of a pin-connected truss bridge, as a bridge with the unique design details of its builder, and as a bridge with the uncommon Whipple truss configuration, the Poffenberger Road Bridge is an extremely significant historic bridge that should continue to receive high preservation priority.

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