The Bollman Truss Railroad Bridge across the Little Patuxent River at Savage, Maryland, is one of the oldest standing iron railroad bridges in the United States and the sole surviving example of a revolutionary design in the history of American bridge engineering.[5] The 160-foot (48.8 m) double-span was built in 1852 at an unknown location on the main line of the Baltimore and Ohio Railroad. It was moved 35 years later to its present location, where it replaced the very first Bollman bridge.[2][5] Today, it carries the Savage Mill Trail.
The Bollman design, a through truss bridge, was the first successful all-metal bridge design to be adopted and consistently used on a railroad.[1][2] The type was named for its inventor, Wendel Bollman, a self-educated Baltimorecivil engineer.[2] Bollman formed two companies in Baltimore, the W. Bollman and Company and the Patapsco Bridge Company, to market the bridge in North and South America.
The bridge's paired end posts at mid-span showing connection of diagonal tension members with anchor casting
The bridge was built for an unknown location on the main line of the Baltimore and Ohio Railroad in 1852 and was moved to its present location, spanning the Little Patuxent River on the spur to the Savage Mill, in 1887. This spur line dates to around 1840 and originally crossed the river on a stone arch bridge; however, due to alterations to the mill in the 1880s and topographical restrictions, a replacement bridge was needed. The bridge remained in service until the mill closed in 1947; switching crews used additional cars in order to avoid crossing the bridge with locomotives, and thus there was never a need for a more substantial structure. A smaller, narrower example was installed next to the railroad bridge for road traffic, which was removed sometime after World War I.[6][7]
Bollman Truss Bridge At Harpers Ferry
It was the first successful all-metal bridge design to be adopted and consistently used on a railroad. The design employs wrought iron tension members and cast iron compression members. It was an improvement over wooden structures, as the independent structural units lessened the possibility of structural failure. After receiving a patent on January 6, 1852,[8][9] the company built about a hundred of these bridges through 1873. Their durability and ease of assembly greatly facilitated expansion of American railroads in this period. Bollman's Wills Creek Bridge has also survived, but it employs a different type of truss system.
The bridge was surveyed for restoration in 1978 by Modjeski and Masters, which noted deterioration of the floor trusses. A $214,200 restoration contract was let to Dewey-Jordan of Frederick, Maryland, in September 1982.[12] The bridge was restored by Wallace, Montgomery & Associates, LLP, for the Howard County Department of Recreation and Parks in 1983. In 2000, it received additional preservation work and was rededicated on September 16. Today it receives regular maintenance as part of Savage Park. Nearby Bollman Bridge Elementary School takes its name from the historic bridge.
Description
The Bollman Bridge is a two-span through-truss, resting on granite abutments at each end and a granite pier in the middle of the river. The truss structure is a mixture of wrought and cast iron. The truss configuration is the design patented by Bollman as the "Bollman suspension truss" in 1852. Each span is 79.5 feet (24.2 m) long, 25.5 feet (7.8 m) wide and about 21 feet (6.4 m) tall. The Bollman truss suspends the deck from a network of tension members, while the top chord resists compressive forces. The system is therefore referred to as a suspension truss.[2][13] Bollman published a booklet describing the Harpers Ferry bridge and the system in general as a “suspension and trussed bridge,” which is accurate as the design lacks an active lower chord required of a strict truss bridge. Later descriptions used "suspension truss" for the design.[2]
The truss includes decorative elements, such as Doric styled vertical members. The cast iron end towers, which transfer the weight of the structure to the abutments and pier, are also detailed. A decorative and protective metal enclosure at the top of the towers was lost to vandalism but was replaced during the restoration work. Metal strips at each portal read "W. BOLLMAN, PATENTEE", "BALTIMORE, MD.", "BUILT BY B&O R.R. CO.", "1869" AND "RENEWED 1866". Replicas of the original strips were installed during the restoration.[13]
The bridge is brightly painted, using red oxide for the towers and the heavier compression members and an ivory color for the lighter tension members.[13] The bridge was originally painted in a three-color scheme, documented in black-and-white photography, with specific shades unknown.[12]
^ abcdefVogel, Robert M. (1964). "The Engineering Contributions of Wendel Bollman". Contributions from the Museum of History and Technology (Smithsonian). 240. Washington, D.C.: U.S. Government Printing Office: 79–104. Retrieved October 12, 2020.
^ abMaryland State Highway Administration (October 1995). Historic Highway Bridges in Maryland: 1631-1960(PDF) (Report). Baltimore, Maryland: Maryland State Department of Transportation. pp. 22–24, 75, 82. Retrieved October 12, 2020.
^Howard County Historical Society. Images of America Howard County. p. 117.
^Digital Collections, The New York Public Library. "(still image) Harper's Ferry. B.&O. R.R." The New York Public Library, Astor, Lennox, and Tilden Foundation. Retrieved December 19, 2015.
^Witcher, T.R. (January 2020). "Preserving the Profession's Achievements: The ASCE Historic Civil Engineering Landmark Program". Civil Engineering. 90 (1). American Society of Civil Engineers: 36–39.
^ abDeLony, Eric (1996). "The Bollman Bridge at Savage, Maryland: Restoring America's Quintessential Metal Truss". APT Bulletin. 27 (1–2): 24–31. doi:10.2307/1504496. JSTOR1504496.
