When the Schuylkill river was a conduit for coal, lumber, refined petroleum products, stone, and other finished goods, nearly every crossing south of the mound dam at Fairmount was of sufficient height to allow barge traffic. Some like the University Ave Bridge, the South Street Bridge, the CSX rail bridge (that carries our vaunted trash trains to us), and a tiny one track ex-PRR railroad swing bridge south of the Grays Ferry Bridge had mechanical appurtenances enabling them to open, swing, and elevate around river traffic.
The PRR swing bridge locked in the open position and the currently-used railroad bridge just south have the distinction of being the only two swing bridges in the city of Philadelphia. During the heyday of civil engineering, swing bridges were some of the most innovative — and trickiest — bridges to execute. Unlike a drawbridge or a bascule bridge, swing bridges were almost exclusively dependent on their central pivot point which is situated within the ship channel. Barges striking the central pier could damage either the central span or its pivot or bring the entire structure out of true with its approaches. The central pivot also had to be maintained, cleaned, and lubricated. New York City’s Third Avenue Swing Bridge, the only in that city, still requires consistent upkeep.
The PRR bridge was built in 1902 by the American Bridge Company, one year after Andrew Carnegie’s massive horizontal integration project, the subsidiary bridge building division of United States Steel Corporation. The American Bridge Co. is still in operation, spun off by US Steel in 1987. So send them an email thanking them for their fine work.
And if you thought that swing bridges went out with steam locomotives and coal barges, Japanese engineers have recently (2001) completed a combined floating/swing bridge at the port of Osaka. Called the Yumemai Bridge, it is detachable from its approaches and movable by a fleet of barges. Read all about that here. Despite the growing attraction of bioengineering, aeronautics, nanotechnology, and materials science, great minds are still attracted to not-so-sexy civil engineering. According to the Corus construction company, engineers have pushed back the frontiers of adaptable spans in such projects as the Gateshead Millenium Bridge:
“The Gateshead Millenium Bridge is perhaps unique in the way it opens. Being nether a lift nor a swing bridge, it opens by rotating and the movement has been likened to the blinking of an eye. This 125m long footbridge over the River Tyne links Gateshead with Newcastle comprises a pair of arches (one forming the deck and one supporting it) which pivot around their common springings. The bridge is opened by hydraulic rams housed in the supports.”