Guilford Quarry Pratt through Truss Bridge

NOTE:  On June 2, 2021 the Guilford Quarry Pratt Through Truss Bridge was officially listed on the National Park Service's National Register of Historic Places (SG100006648)!

This bridge was constructed at this site in either late 1901 or early 1902 to complete the extension of B&O Patuxent Branch rail line to Guilford that opened to freight in April of 1902. The Interstate Commerce Commission Valuation report in 1919 wrote that this bridge was moved to its current location and was previously Bridge No. 10 of the B&O District 2, Middle Division (likely in Ohio where the only "Middle Division" was found and many of those bridges did make their way out of state ).  

This bridge is an excellent example of an early truss bridge design that dominated bridge building in the late 1800s.  This bridge helped to open up the Guilford quarries to the transportation route needed to make the quarries an economic and social force for the area.    Please read the original Maryland Historical Trust nomination form for the Guilford Pratt Through Truss Bridge.  Also, please see the current Historical Marker for the Pratt Through Truss Bridge along the Patuxent Branch Trail.  

Below is an excerpt from the National Register Form recently approved by the National Park Service.

"General Description:

The Guilford Quarry Pratt Through Truss Bridge was constructed circa 1902 as a single-span wrought-iron, 83-foot long, five panel, pin-connected Pratt through truss bridge. The bridge connected the B&O Patuxent Branch railroad to the quarry across the Little Patuxent River. The truss is fifteen feet wide to accommodate a single track with a 2-86 ton live load. It is 21 feet high supported with large granite abutments; the end points of the truss rest on the massive granite block abutments, spaced 83’ apart center to center. Atypically, this truss bridge doesn’t cross the river at a right angle as do most truss bridges; it has a 35-degree left-hand skew with inclined end-posts at each end (ICC 1919).

A skew is not common and provides more engineering difficulty to construct, but it allows a train to cross a river in a straight line if the banks are not perpendicular to the railroad alignment. This feature is recognized by transportation authorities for ranking a bridge’s historical and engineering significance as part of systems for establishing maintenance priorities. For example, the Indiana Department of Natural Resources adds a point to its significance because “Fewer than 15% of Indiana’s surviving metal bridges are built on a skew or angle. Skewed bridges represented an additional engineering challenge to the designer and are a testament to their skills.” (IDNR, 1999).

Pratt bridges are named for Caleb and his son Thomas Willis Pratt, who patented their design in 1844 (patent #3,523, Pratt 1844). Their design used wood as the upright compression members and wrought iron as the diagonal tension members which was the opposite of the predecessor Howe truss bridge. However, with the success of the all-metal Bollman bridges, the Pratt truss bridges were eventually made of all wrought iron and became increasingly popular due to their simplicity of design and construction in the field (MSHA 1995).

The Pratt design not only simplified construction, but also made the bridges amenable to dismantlement and reuse in a new location. According to Interstate Commerce Commission records (ICC 1919), the Guilford Quarry bridge was originally located on the Middle Division of the B&O Railroad in Ohio – its precise location remains undetermined – and reconstructed at its current location in about 1902. As increasing loads rendered pin-connected Pratt bridges functionally obsolete, they were readily moved to less heavy service. Industrial historian Patrick Harshbarger (email communication May 9, 2019) wrote that “What you have here is a pin-connected Pratt through truss, which was the most common type of railroad through truss of the 1880s to 1890s, covering the transition from wrought-iron to steel. After 1900, the pin connections give way to riveted connections, which were more rigid and suited to the heavier construction needed for the ever-increasing live loads of locomotives. Pratt trusses also gave way to Warren trusses, which were more suited to riveted connections. This meant that pre-1900 or so truss bridges on main lines, in particular, became under-performing even though they were barely 20 years old, sometimes less. The B&O, and other railroads, moved some of the pin-connected trusses to branch lines or to overhead (highway) use where they were still adequate.”

"The Pratt design and its many variations were exceedingly popular, and in the 1995 compilation of previous bridge surveys, the majority of the remaining Maryland truss bridges were of the Pratt design including pony, through and other truss types. (MSHA, 1995, p. 77). A recent search of the Maryland State Historic Preservation office’s database yielded only six surviving Pratt through truss bridges in Maryland, including the Guilford quarry bridge. A well-known example is Governor's Bridge, a single-lane Pratt through truss bridge with a span of 105 feet over the Patuxent River near Bowie, Maryland that was built between 1907 and 1912 (MHT 2001). The only other survivor in Howard County besides the Guilford Quarry bridge is the 1903 Ilchester B & O Pratt Through Truss across the Patapsco River (MHT, 2019). This review shows that what was once a popular bridge type is now relatively rare in Howard County and Maryland. The Guilford Quarry Pratt Through Truss Bridge is a well-preserved representative example of this type".

 The Guilford Quarry Pratt Through Truss Bridge was determined eligible  in 1999 by the Maryland Historical Trust to be nominated as a site in the National Register of Historic Places.  In 2021, we prepared a National Register Nomination Form, submitted it to the Maryland Historical Trust who then submitted it to the Governor’s Consulting Committee on the National Register of Historic Places - here is the process for the nomination and approval - https://mht.maryland.gov/research_nationalregisterprocess.shtml

I am happy to report that in April 2021 the Governor's Consulting Committee unanimously approved the nomination and sent it for listing to the National Park Service.  On June 2, 2021, this is now one of the two bridges fully in Howard County that appear on the National Register of Historic Places - the other being the Bollman Bridge.  A fitting tribute to our Between the Bridges efforts.  Please view the final nomination form to the right or on our Documents page.