An underspanned suspension bridge (also upper deck suspension bridge[1]) is a rare type of suspension bridge that was developed in the early 19th century.
Ancestor | Simple suspension bridge |
---|---|
Carries | Pedestrians, livestock |
Span range | short |
Movable | No |
Design effort | low |
Falsework required | No |
It differs from its ancestor, the simple suspension bridge, in that the deck is raised on posts above the main cables. The raised deck is less stable than a deck laid on or hung below the cables, and very few underspanned suspension bridges have been built. Examples include Guillaume Henri Dufour's Pont des Bergues (1834);[2] and James Smith’s Micklewood Bridge.[3] Similar bridges were proposed by Robert Stevenson in 1820 for a bridge over the River Almond between Edinburgh and Queensferry, and by a Mr. Armstrong for a bridge at Clifton.[3] Part of the roadway on the land side of the piers of the Hammersmith Bridge was constructed in this manner. In the late 19th century and into the 20th century a few bridges of this type were constructed.[1]
The Micklewood Bridge, constructed at Doune in Scotland, was the very first of this type. [citation needed] It had a span of 103 feet (31 m), and the main cables were chains, making this an instance of a chain bridge. The deck was stiff and relatively stable, owing to heavy cross-braces.[3]
The only remaining underspanned suspension bridge in the United States is the Kellams Bridge crossing the upper Delaware River between New York and Pennsylvania. It is named for its builder.