Retractable bridge

Retractable bridge

Vindbron (Ultunabron) inUppsala(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
Falseworkrequired	No

Aretractable bridgeis a type ofmoveable bridgein which the deck can be rolled or slid backwards to open a gap while traffic crosses, usually a ship on a waterway. This type is sometimes referred to as athrust bridge.

The bridge is retracted to the right.

Borden Avenue Bridge,Long Island City

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).

Two remaining examples exist in New York City: theCarroll Street Bridge(built 1889) inBrooklyn,and theBorden Avenue BridgeinQueens.A recent example can be found atQueen Alexandra DockinCardiff,Wales,where the bridge is jacked upwards before being rolled on wheels. Helix Bridge atPaddington Basinin 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.TheSummer Street BridgeoverFort Point ChannelinBostonis a variant type called aretractile bridge.This bridge is oriented northwest–southeast, with the northwest-bound lanes of traffic retracting diagonally to the north, and the southeast-bound lanes retracting diagonally to the west.

Some retractable bridges are alsofloating bridges,such as theHood Canal Bridge.Two other floating bridges in Washington state used to have retractable spans but were replaced with new floating bridges without retractable spans: theEvergreen Point Floating Bridge(replaced in 2016) andLacey V. Murrow Memorial Bridge(replaced after it accidentally sank in 1990). This design is popular inGuyana,which has theDemerara Harbour Bridgeand theBerbice Bridge.

Historical examples of designs for retractable bridges include those byLeonardo da VinciandAgostino Ramelli.

In theNetherlands,especially in the province ofNorth Holland,avlotbrugis a design of retractable bridge across acanalin which the roadwayfloatsand can be retracted under fixed structures on the canal banks.

See also

Animation of operation

• Guthrie rolling bridge
• Moveable bridgesfor a list of other movable bridge types

External links

• Carroll Street Bridge history at bridgesnyc.com