A bascule bridge is a type of bridge that can be raised to provide clearance for waterway traffic, and is also referred to as a lifting bridge or a drawbridge.
A bascule bridge is a type of bridge that can be raised to provide clearance for waterway traffic, and may sometimes also be referred to as a lifting bridge or a drawbridge. It makes use of a counterweight to balance a span or leaf through its upward trajectory. The balance of the weight is sometimes adjusted according to the frequency of waterway traffic.
The span can be single or double, and in rare cases it may even be triple or quadruple. The word ‘bascule’ is French in origin and translates loosely as a seesaw or a balancing mechanical device. It is thought that bascule bridges were first designed during the mediaeval era in Europe, when they served defensive purposes.
The original version of London Bridge, which was designed in 1176 by Peter Colechurch, was a wooden bascule bridge that remained in operation until the late 1400s. The current structure, which opened in 1973, is a prestressed concrete box girder bridge.
The longest double-leaf bascule bridge in the world is the Broadway Bridge in Portland, Oregon, USA. It was built in 1913 to span the Willamette River and its total length is 1,742ft with a maximum span of 297ft. The bridge is named after the street it carries, and it has four lanes for two-way traffic.
The Broadway Bridge opens to allow the passing of river traffic about 25 times a month, and carries approximately 30,000 vehicles per day, plus thousands more cyclists and pedestrians. The structure was added to the National Register of Historic Places in 2012.
In the UK, the famous Tower Bridge over the River Thames in London has a double-leaf span and also has suspension bridge design elements. It is a Grade I listed structure and was built between 1886 and 1894 to provide improved access to the East End of London.
New Civil Engineer reports that the opening of a new bascule bridge in Great Yarmouth has been delayed until 2024. The £121m twin-leaf Herring Bridge is designed to carry traffic over the River Yare, and opens in the middle to allow taller river traffic to pass. The bridge is due to open to river traffic shortly, but the opening for road traffic has been postponed.
No specific reason was given for the delay, but the bridge is being assessed by specialists. A joint statement issued by Norfolk County Council and Bam Farrans said: “We are in the final stages of preparing Herring Bridge for opening and we would like to thank the public for their continued patience and support.”
“Our team is working closely with the port authority to bring the bridge into operation for river traffic, which we anticipate in the coming weeks. The road section will follow thereafter. We will provide further details on an opening date following the completion of our marine vessel operations phase.”
The project has already been delayed by the discovery of a vole burrow at the site, and also an unexploded 250kg WWII bomb.
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