Retractable bridge

Retractable bridge

Vindbron (Ultunabron) in Uppsala (retracted)
Ancestor	Plate girder bridge
Related	Lift bridge, submersible bridge, folding bridge
Descendant	None
Carries	Automobile, pedestrians
Span range	Short
Material	Steel
Movable	Yes
Design effort	Medium
Falsework required	No

A retractable bridge is a type of movable bridge in which the deck can be rolled or slid backwards to open a gap for crossing traffic, usually a ship on a waterway. This type is sometimes referred to as a thrust bridge.

The bridge is retracted to the right

Retractable bridges date back to medieval times. Due to the large dedicated area required for this type of bridge, this design is not common. A retractable design may be considered when the maximum horizontal clearance is required (for example over a canal).

Several examples exist in New York City, (e.g., Carroll Street Bridge (built 1889) in Brooklyn, Borden Avenue Bridge in Queens). A recent example can be found at Queen Alexandra Dock in Cardiff, Wales, where the bridge is jacked upwards before being rolled on wheels. Helix Bridge [1] at Paddington Basin, London is a more unusual example of the type, consisting of a glass shell supported in a helical steel frame, which rotates as it retracts. The Summer Street Bridge over Fort Point Channel in Boston is another variant type. This bridge is oriented northwest-southeast, with the NW-bound lanes of traffic retracting diagonally to the north, and the SE-bound lanes retracting diagonally to the west.

Borden Avenue, Long Island City

Many retractable bridges are also floating bridges, such as the Hood Canal Bridge, where a retractable span can be withdrawn between two lines of pontoons in the shape of a "U". A similar arrangement exists on the Evergreen Point Floating Bridge and Lacey V. Murrow Memorial Bridge.

Historical examples of designs for retractable bridges include those by Leonardo da Vinci [2], and Agostino Ramelli. [3]

See also

Animation of operation

• Movable bridge for a list of other movable bridge types
• Guthrie rolling bridge