Bowstring Truss Bridge


Arch bridge:
Bridge with abutments at each end shaped as a curved arch. The weight of the bridge is thrust into the abutments at either side.  Fixed bridge.

Truss bridge:  Bridge whose load-bearing superstructure is composed of wooden or metal triangle trusses [framework].      Fixed bridge.


Bowstring truss bridge:  an arched beam (the bow) joined at each end by a straight beam (the string), with diagonal support beams joining the two.



1880 ad.   ...   Research by Brian Szafranski




 Partial reprint
Squire Whipple
By Dr. Frank Griggs, Jr., P.E., P.L.S.
StructureMagazine, Sept. 2005 (online July 2018)

Whipple was born in Hardwick, Massachusetts in 1804 the son of a farmer. Between 1811 and 1817, his father designed, built and ran a cotton-spinning mill in nearby Greenwich, Massachusetts. The young Whipple was therefore exposed to construction and materials at an early age. The family then moved to Otsego County just north of Cooperstown, New York to take up farming again.

After receiving the best common school education available he attended Hartwick Academy and Fairfield Academy located in central New York near his home. In 1830 he graduated from Union College in Schenectady, New York after one year of study. He spent the decade of the 1830s serving his apprenticeship working on the Baltimore and Ohio Railroad, the Erie Canal Enlargement, the New York and Erie Railroad and several other railroads. When work was slow, he designed, built and sold mathematical instruments such as transits and engineer’s levels and drafting equipment. He married later in life and had no children.

In 1841, he designed and built a weigh lock scale with a capacity of 300 tons to weigh the canal boats on the Enlarged Erie Canal in Utica. This was the largest weighing device in the country at the time.

Whipple became interested in the design and construction of iron and wooden bridges. Having worked on the enlargement of the Erie Canal, he knew that wooden bridges that crossed the original canal had a short-life. He also knew that the new, wider canal would require longer span bridges and must be made of a modern material-iron.

After some thought, he designed his bowstring iron truss arch and was issued patent No. 2,064 on April 24, 1841 for the “construction of iron truss bridges”.

Between 1842 and 1870, hundreds of Whipple Bridges were built over the Erie and its branch canals, either by Whipple or to his patent. Frequently contractors would build to his patent without paying patent fees, so he never received large sums of money from people using his patent.

Perhaps his major accomplishment was A Work on Bridge Building consisting of Two Essays, The One Elementary and General, the other Giving Original Plans and Practical Details for Iron and Wooden Bridges, which he wrote and published in 1847.

Whipple retired around 1860 but continued to design swing and lift bridges, building many swing bridges over the Erie, Portland and Welland Canals. In December 1872, he designed and patented, #134,338, the first vertical lift bridge in the United States and built it over the Erie Canal in Utica in 1874.

Whipple died in Albany, NY on March 15, 1888 at the age of 84.





Partial reprint

The Whipple Bowstring Truss
By Frank Griggs, Jr.
Structure Magazine (online July 2020)


It wasn’t until Capt. Richard Delafield built an 80-foot span arch bridge, across Dunlap’s Creek near Brownsville, Pennsylvania on the National Road in 1839, that iron was used as a major bridge material.    ....    It wasn’t until Earl Trumbull built a small bridge at Frankfort, New York that cast and wrought iron were used in a truss like bridge.

It was into this environment that Squire Whipple entered the field of bridge engineering. Since graduating from Union College in 1830, he had worked on the B&O Railroad, the Northern Railroad between Ogdensburg and Lake Champlain and the New York and Erie Railroad before moving to the enlargement of the Erie Canal under Holmes Hutchinson. The canal was being enlarged from a 40-foot width at the surface to a 70-foot width and a depth increase from 4 feet to 7 feet. This required a large number of longer span bridges to cross the 363-mile long canal.

After some thought he came up with his bowstring iron truss arch on August 22, 1840.
He submitted his design to the Patent Office, and was awarded Patent No. 2,064 on April 24, 1841.


Detail, Whipple Patent Application Drawing

He was not claiming that he was the inventor of the bowstring truss. He was claiming the use of cast-iron segments in combination with wrought iron diagonal ties or braces to sustain the form of the arch against the effects of unequal loadings. He also claimed the use of thrust ties, the string in the bow and string bridge, to sustain the thrust and spreading of the arch. His last claim was use of a diverging top chord, either in wood or iron, to give the arch or truss lateral stability, hence the independent iron arch truss bridge.

... when the wooden bridge across the canal at First Street in Utica fell, Whipple contracted to build his first bridge over the canal for the sum of $1,000 in the spring of 1841. He now had something to show the doubters, as his bridge was not only durable but, with its arches, was almost graceful and did point the way to materials of the future. Interestingly enough, this bridge served until September 16, 1922 when the canal was closed and the Barge Canal opened using the Mohawk River.

In 1851, the Commissioners adopted the Whipple Independent Iron Arch for use on the canal.

Whipple’s bowstring was the first successful cast and wrought iron bridge built in the United States, and the first bridge with each element sized to carry its load under varying placement of the load on the bridge. It set the stage for the Bollman and Fink Trusses that were to follow. For this, and other reasons, Whipple has been called “The Father of the Iron Truss Bridge.”









2009 photo    ...   Commercial Slip, Buffalo, NY









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