Retractable bridge

From Wikipedia, the free encyclopedia

Retractable bridge
Ultuabron 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

The bridge deck of a retractable bridge 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.

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.

Many retractable bridges are also floating bridges, such as the Hood Canal Bridge, where a retractable span can be withdrawn between two lines of pontoons in the shape of a "U".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]

[edit] See also

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