Last updated Double-beam drawbridge in DelftThe Poortbrug in Leeuwarden bridges the former city moatDouble-beam drawbridge in Vlaardingen
A double-beam drawbridge, seesaw or folding bridge is a movable bridge . It opens by rotation about a horizontal axis parallel to the water. Historically, the double-beam drawbridge has emerged from the drawbridge . Unlike a drawbridge, a double-beam drawbridge has counterweights, so that opening requires much less energy.
Unlike the bascule bridge, the simple drawbridge and the "oorgat" (earhole) bridge[definition needed], the double-beam drawbridge has two hinges. The road surface is connected to the bottom hinge. Above the hinge is a portal, the hamei gate . A rotating arm, the balance, is attached to this hamei gate. On one side of the balance hangs the counterweight, the balance box, on the other side, the arm is connected to the tip of the bridge deck. So when the bridge goes up, the balance and the bridge deck turn parallel.
The drawback of a traditional double-beam drawbridge is that it has a limited clearance height. That is why the balance box sometimes does not hang between the two arms, but on the arms themselves, without the arms being connected to each other. So there are two balance boxes.
Many variants have been made on the basic design of the double-beam drawbridge. They are both double-rotating (with two separate bridge decks) and single-rotating and with a diagonal bridge deck. In the latter case, there is only one tower or Hamei style, which is next to the road.
The pivot point of the balance with the balance box can either fall behind the hamei gate (as in the photo), or directly above it. The latter system is referred to as an 'Amsterdam type'. The advantage of this is that the tower is only loaded under pressure . When the pivot point falls behind the column, the tower is loaded eccentrically; this gives both pressure and flexion .
When double-beam drawbridges are opened and closed electrically, an electric motor with a gear is often located at about half height in the Hamei styles. This engages in a rack that is hinged to the bridge deck. This construction can also be seen in the photo. The rack is often not straight, but with a curvature at the end, like a hockey stick - this is to give the electric motor time to rev up and gradually raise (and lower) the bridge.
Henk de Jong and Nico Muyen: 2000 years of movable bridges: international guide to known and unknown bridge types and movement works . Rijswijk, Elmar Publishers, 1995. ISBN90 389 0286 7
A counterweight is a weight that, by applying an opposite force, provides balance and stability of a mechanical system. The purpose of a counterweight is to make lifting the load faster and more efficient, which saves energy and is less taxing on the lifting machine.
A hinge is a mechanical bearing that connects two solid objects, typically allowing only a limited angle of rotation between them. Two objects connected by an ideal hinge rotate relative to each other about a fixed axis of rotation: all other translations or rotations being prevented, and thus a hinge has one degree of freedom. Hinges may be made of flexible material or of moving components. In biology, many joints function as hinges, like the elbow joint.
Joseph Baermann Strauss was an American structural engineer who revolutionized the design of bascule bridges. He was the chief engineer of the Golden Gate Bridge, a suspension bridge.
A drawbridge or draw-bridge is a type of moveable bridge typically at the entrance to a castle or tower surrounded by a moat. In some forms of English, including American English, the word drawbridge commonly refers to all types of moveable bridges, such as bascule bridges, vertical-lift bridges and swing bridges, but this article concerns the narrower historical definition of the term where the bridge is used in a defensive structure.
A bascule bridge is a moveable bridge with a counterweight that continuously balances a span, or leaf, throughout its upward swing to provide clearance for boat traffic. It may be single- or double-leafed.
A vertical-lift bridge or just lift bridge is a type of movable bridge in which a span rises vertically while remaining parallel with the deck.
A trunnion is a cylindrical protrusion used as a mounting or pivoting point. First associated with cannons, they are an important military development.
A moveable bridge, or movable bridge, is a bridge that moves to allow passage for boats or barges. In American English, the term is synonymous with drawbridge, and the latter is the common term, but drawbridge can be limited to the narrower, historical definition used in some other forms of English, in which drawbridge refers to only a specific type of moveable bridge often found in castles.
A tilt bridge is a type of moveable bridge which rotates about fixed endpoints rather than lifting or bending, as with a drawbridge. The tilting Gateshead Millennium Bridge spanning the River Tyne between Gateshead on the south bank and Newcastle upon Tyne, England, on the north is a pedestrian bridge with two large hydraulic rams at each side that tilt the structure back allowing small watercraft to pass under.
A folding bridge is a type of moveable bridge.
A fly system, or theatrical rigging system, is a system of rope lines, blocks (pulleys), counterweights and related devices within a theater that enables a stage crew to fly (hoist) quickly, quietly and safely components such as curtains, lights, scenery, stage effects and, sometimes, people. Systems are typically designed to fly components between clear view of the audience and out of view, into the large opening, known as the fly loft, above the stage.
A linkspan or link-span is a type of drawbridge used mainly in the operation of moving vehicles on and off a roll-on/roll-off (RO-RO) vessel or ferry, particularly to allow for tidal changes in water level.
The Rolling Bridge is a type of curling moveable bridge completed in 2004 as part of the Grand Union Canal office and retail development project at Paddington Basin, London.
The Glimmer Glass Bridge is a county owned bridge in Monmouth County, New Jersey, United States. It carries traffic from Brielle Road over the Glimmer Glass, a navigable tidal inlet of the Manasquan River, between Manasquan and Brielle. It has also been on the National Register of Historic Places, since 2008.
A balanced-arm lamp, sometimes called a floating arm lamp, is a lamp with an adjustable folding arm which is constructed such that the force due to gravity is always counteracted by springs, regardless of the position of the arms of the lamp. Many lamp brands as well as other devices, such as drawing boards, use this principle.
The Cortland Street Drawbridge over the Chicago River is the original Chicago-style fixed-trunnion bascule bridge, designed by John Ericson and Edward Wilmann. When it opened in 1902, on Chicago's north side, it was the first such bridge built in the United States. The bridge was a major advance in American movable bridge engineering, and was the prototype for over 50 additional bridges in Chicago alone. The bridge was designated as an ASCE Civil Engineering Landmark in 1981, and a Chicago Landmark in 1991.
The Grand Street Bridge was a double-leaf deck-girder bascule bridge in Bridgeport, Connecticut, United States, that spanned the Pequonnock River and connected Grand Street and Artic Street. It was one of three movable bridges planned by the City of Bridgeport in 1916 at the request of the War Department during World War I. Construction was completed in 1919, but the delays surrounding the construction went to the Connecticut Supreme Court in case of Edward DeV. Tompkins, Inc. vs. City of Bridgeport, Connecticut. The court ruled in favor of Tompkins and awarded damages equal to the contract. In 1936, the bridge had excessive settling and required the replacement of its southeast pier. As part of the repairs, a new floor and electrical system were installed. In 1965, the floor was replaced with a steel grate on I-beam floor. In 1984, the eastern approach span was replaced and the northwest trunnion post was reconstructed. The bridge was closed in the 1990s and dismantled in 1999.
Eighth Street Bridge is a road bridge over the Passaic River in northeastern New Jersey, United States. Opened in 1915 as a bascule bridge, the bridge was fixed in place in 1977. The Eighth Street Bridge was closed to traffic permanently on July 24, 2017 so work could begin on its replacement, completed in 2019.
The following outline is provided as an overview of and topical guide to bridges:
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