Truss Bridging in the Civil War
by
Luke Eames, Artificer
Co. A US Engineer Bn.
Herman Haupt, The Man behind the Bridges
(Meredith, 1979)

Herman Haupt graduated from West Point in 1835 which he then became a civilian engineer.  He specialized in railroad surveying and railroad bridge construction.  In 1862, he was summoned by the Secretary of War, Edwin Stanton, to serve as the U.S. Railroad Superintendent (Harris, 2012).  According to Edwin Stantons’s biographer, Haupt “began by demanding that he should have no rank, title, or uniform, no compensation beyond his expenses, and that he could go back to his Western Massachusetts railroad tunnel after the campaign was over. The conditions he set wore away under the tooth of time; Haupt did not see his tunnel again until nearly the close of the war, when he retired as a general. In the meanwhile, he recruited his own labor force, built railroads and bridges furiously, and told military officers to go to hell." (Pratt, 1970)  In 1864, Haupt took all of his documentation and published a book, “Military Bridges.”     


Truss Bridge

Truss bridges were designed and built to be self-supporting with cross braces and arches.  They were, and still are, the most common railroad bridge because of their strength.  Haupt designed templates which allowed the bridges to be built by unskilled men.  Chords and braces could be interchanged with one another to avoid complicated setup.  If the templates were followed correctly, each board can be put into place without altering (Haupt, 1864).  


(Russell, Building Military Railroad Truss Bridge Across Bull Run, April 1863)

Each truss bridge contained two lower and two upper chords made from four to six stacked pine boards measuring 3” by 12”, cross braces made from 2” by 10” pine boards and two arches that would span the length of the bridge.  Each arch was built with eighteen 1” by 12” oak boards.  The arch was an essential piece of the bridge keeping it rigid and able to hold the load which was put upon the bridge.  The height of each bridge was dependent on the height of the smoke stacks of the train engines (Haupt, 1864). 


When sawmills were not available, truss bridges must have been built with round sticks.  Because of the amount of support the lower chord provides, it must be built with sawn lumber.  Trains or wagons could carry enough lumber for the chord.  The rest of the bridge could be built with round sticks.  The main arch would be replaced with arch braces and 2” iron truss-rods.  The arch braces ran from the bottom ends of the bridge to the top of the second panel.  These arches provided enough strength to become essential to the bridge’s structure.  Truss-rods ran vertical, connecting the top of the top chord to the bottom chord.  The rods did not run through the chords but through saddles.  Both the top and bottom chord contained a saddle, clamping the chords.  The truss-rods created a tension between the top and bottom chord.  Scaffolding was required for these bridges however, the chords were used to hold the scaffolding.  This allowed the bridge to be built at both ends (Haupt, 1864).


(Russell, Yard at Alexandria, construction corps finishing portable bridge trusses, 1862 or 1863)

The Portable Truss Bridge had a similar structure to a regular truss however, the bottom chord was arched and joined the top chord at the ends.  The roadway would lay on the top chord with the truss braces below the roadway.  Sides were pre-manufactured in 60 foot lengths, with each side consisting a bottom chord of six 1” by 12” pine boards, a top chord of five 1” by 12” pine boards and braces of 4’’ to 5’’ pine boards. (Haupt, 1864).

The bridges were designed and built to be efficiently packed and assembled.  Bridge sides could stack on one another in one railroad car, with the bed of the road sitting on one of the sides.  If needed, the train could get close to the bridge site, then oxen could pull the bridge sides to their final destination.  Despite the 1,000 feet that was constructed, portable truss were never used in the field (Haupt, 1864).        

Trestle Bridge

Trestle bridges were constructed of timbers and highly robust. They were popular for crossing great spans of a valley or over flood plains.  Because of their importance for railroad transportation, trestle bridges were highly guarded and sought after to be destroyed by the enemy.  Some trestle bridges were built with guard posts on each end.  

Similar to the truss bridges, Haupt developed a standard template that could be used on all trestle bridges, regardless of length.  Templates could be used by unskilled men, many of whom did not have bridge building skills.   The “W” style trestles were only used for heights not exceeding 30 feet.  These trestles were constructed using round sticks no less than 9” in diameter at the small end.  Each stick would have a girder on the end where wooden pegs would be used to hold all the sticks together.  These trestles were very simple but highly effective (Haupt, 1864).

Separate templates were used when the bridge exceeded 30 feet in height.  With similar style to the “W” trestle, the lower level trestles were wider with a center support.  The next level of trestle would sit on the cap of the lower level, while being braced by pegs (Haupt, 1864). When assembled, braces on the sides would hold the trestles in place.

Despite the simple design, they were highly effective with great strength.  These bridges could be built in a short amount of time.  With the use of a thousand men, the 400 foot Lincoln Bridge over the Potomac was completed and carried a fully loaded train in nine days (Thomas, 1864).

Experimental Board Suspension Bridge

During 1863 in Alexandria, VA there was a test of a board truss suspension bridge. This suspension bridge was designed with boards acting as cable.  Six 1” by 12” pine boards were stacked on each other creating a 6” by 12” cable that span the length of the bridge.  One cable per side of the bridge was required.  The ends of each cable were fanned to prevent them from slipping through horizontal post anchorage.  Trusses were placed on the tops of the cables which the roadway would sit on (Haupt, 1864).
 

(Russell, Experimental suspension trusses of boards. Loading the board suspension bridge with railroad iron for the purpose of breaking it , 1862 or 1863)

Board suspension bridges required no scaffolding.  Each cable could be built on the roadway at either side, then pulled across with ropes.  Once the cables were in place, men could walk out and start assembling the trusses and the roadway from both sides of the bridge.  During the experiments, the cables slid out of the anchorage at 84,000 pounds of weight, without breaking the actual bridge (Haupt, 1864).

Throughout the American Civil War, great advancement had been made for the future of railroad bridging.  Standardization and efficiency allowed for quick and effective bridge building.  Many other style of bridges had been made, however the ones described here were the most common on the railway.  Haupt’s knowledge and skill made him one of the great leaders to the Union victory.

References


Harris, D. B. (2012, May 25). The Opinion Pages. Retrieved from The New York Times: http://opinionator.blogs.nytimes.com/2012/05/25/rules-for-the-road/

Haupt, H. (1864). Military Bridges. New York: D.Van Nostrand.

Meredith, R. a. (1979). Mr. Lincoln's Military Railroads: A Pictorial History of the United States Civil War Railroads, 1861-1865. New Your: W.W. Norton & Co.

Pratt, F. (1970). Stanton: Lincoln's Secretary of War. Westport: Greenwood Press.

Russell, A. J. (1862 or 1863). Experimental suspension trusses of boards. Loading the board suspension bridge with railroad iron for the purpose of breaking it .

Russell, A. J. (1862 or 1863). Yard at Alexandria, construction corps finishing portable bridge trusses.

Russell, A. J. (n.d.). Building Military Railroad Truss Bridge Across Bull Run, April 1863.

The Generals and Admirals: Herman Haupt (1817-1905). (n.d.). Retrieved from Mr Lincoln's White House: http://www.mrlincolnswhitehouse.org/inside.asp?ID=653&subjectID=2

Thomas, G. H. (1864, January 14). January 14, 1864: The Railroad War in Tennessee. Retrieved from The American Civil War: http://www.civilwar-online.com/2014/01/january-14-1864-railroad-war-in.html