Benjamin Franklin Bridge - Pushing the Limits: New Adventures in Engineering - page 15

indispensable guidebook, Great American Bridges and Dams, as “the most stunning and visually
compelling engineering structure built in the early United States.” Unfortunately, like many a con-
temporary wooden bridge, the Colossus was destroyed by fire—in its case, in 1838.
The Schuylkill was also spanned by two historically significant early suspension bridges, the en-
gineers of which were the pioneers of the form in America. The first was the design of James Fin-
ley, who is generally acknowledged to have built the earliest iron-chain bridges. The second was
the first of that type built by Charles Ellet, Jr. His bridge, with a 358-foot span suspended from wire
cable passing over stone towers, was completed in 1842. It provided a replacement for the Colos-
sus.
The much wider Delaware River was not bridged nearly so early nor so readily. An 1818 proposal
for a bridge between Philadelphia and Camden, New Jersey, was unusual in that the span did not
go all the way across the river. The scheme consisted of a bridge from New Jersey to Smith Island,
which then existed close to the Pennsylvania shore, in combination with a ferry connecting the is-
land and the foot of Market Street. The island itself was removed in 1893 to improve navigation,
but other bridges reaching across the entire river were proposed even before that time.
There is always more than one way to cross a river, of course, and a multispan suspension bridge
was proposed in 1851 by the Philadelphia-born engineer John C. Trautwine. Trautwine had gained
extensive experience on railroad and canal projects, including surveying work on a railroad across
the Isthmus of Panama, prefiguring the route of the future canal. His proposal for a bridge at Phil-
adelphia with four spans of one thousand feet each would have been a daring stretch of the state
of the art. Just two years earlier, Ellet's 1,010-foot suspension bridge had been completed over the
Ohio River at Wheeling, West Virginia. Unfortunately, the roadway of that bridge was destroyed
in a windstorm in 1854 and had to be reconstructed. Such a structural failure would naturally give
pause to any community then contemplating a similar but larger bridge.
The collapse of the Wheeling span might have struck an even more severe blow to suspension-
bridge building in America had not another bridge, designed by John Roebling, been completed at
about the same time. His Niagara Gorge Suspension Bridge, with a clear span of 821 feet, was the
first of that genre to carry railroad trains. Roebling's unique structure owed much of its success to
his study of the effects of wind on large bridges. It was only by understanding how earlier suspen-
sion bridges had failed, Roebling believed, that he could design ones that would withstand the great
forces of nature.
Roebling went on to design the great bridge across the Ohio River at Cincinnati. Though its con-
struction was interrupted by the Civil War, the 1,057-foot span was completed and opened to traffic
by 1867. The bridge at Cincinnati set the structural stage for Roebling's masterpiece, the Brook-
lyn Bridge, the construction of which was approved only because Roebling proposed a bridge high
enough to give ample clearance to tall-masted river traffic.
Nevertheless, plans to cross the East River in New York with a span of almost 1,600 feet appear
to have rejuvenated talk of a crossing of the Delaware River. An 1868 joint report by committees
representing the interests of Philadelphia and of Camden put forth what they considered an im-