Moveable bridge

in Chicago, IL river in Utrecht, Netherlands in New York City 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 , 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. An advantage of making bridges moveable is the lower cost, due to the absence of high piers and long approaches. The principal disadvantage is that the traffic on the bridge must be halted when it is opened for passage of traffic on the waterway. For seldom-used railroad bridges over busy channels, the bridge may be left open and then closed for train passages. For small bridges, bridge movement may be enabled without the need for an engine. Some bridges are operated by the users, especially those with a boat, others by a bridgeman (or bridge tender); a few are remotely controlled using video-cameras and loudspeakers. Generally, the bridges are powered by electric motors, whether operating winches, gearing, or hydraulic pistons. While moveable bridges in their entirety may be quite long, the length of the moveable portion is restricted by engineering and cost considerations to a few hundred feet.…

in Chicago, IL]] river in Utrecht, Netherlands]] in New York City]] 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 , 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. An advantage of making bridges moveable is the lower cost, due to the absence of high piers and long approaches. The principal disadvantage is that the traffic on the bridge must be halted when it is opened for passage of traffic on the waterway. For seldom-used railroad bridges over busy channels, the bridge may be left open and then closed for train passages. For small bridges, bridge movement may be enabled without the need for an engine. Some bridges are operated by the users, especially those with a boat, others by a bridgeman (or bridge tender); a few are remotely controlled using video-cameras and loudspeakers. Generally, the bridges are powered by electric motors, whether operating winches, gearing, or hydraulic pistons. While moveable bridges in their entirety may be quite long, the length of the moveable portion is restricted by engineering and cost considerations to a few hundred feet. There are often traffic lights for the road and water traffic, and moving barriers for the road traffic. The Steel Bridge in Portland, Oregon is believed to be the only example of a double-deck bridge where both decks can be moved independently. In the United States, regulations governing the operation of moveable bridges (referred to as drawbridges)  – for example, hours of operation and how much advance notice must be given by water traffic – are listed in Title 33 of the Code of Federal Regulations; temporary deviations are published in the Coast Guard's Local Notice to Mariners.

Types

Vertical motion Vertical-lift bridge – the bridge deck is lifted by counterweighted cables mounted on towers; road or rail Table bridge – a lift bridge with the lifting mechanism mounted underneath it Submersible bridge – also called a ducking bridge, the bridge deck is lowered into the water Horizontal motion Retractable bridge (Thrust bridge) – the bridge deck is retracted to one side Vlotbrug, a design of retractable floating bridge in the Netherlands Guthrie rolling bridge Transporter bridge – a structure high above carries a suspended, ferry-like structure Rotation about a vertical axis Swing bridge – the bridge deck rotates around a fixed point, usually at the centre, but may resemble a gate in its operation; road or rail Rotation about a horizontal axis Bascule bridge – a drawbridge hinged on pins with a counterweight to facilitate raising; road or rail Rolling bascule bridge – an unhinged drawbridge lifted by the rolling of a large gear segment along a horizontal rack Drawbridge (British English definition) – the bridge deck is hinged on one end Double-beam drawbridge Fan Bridge – a drawbridge with longitudinal divisions between multiple bascule sections that rise to various angles of elevation, forming a fan arrangement. Tilt bridge – the bridge deck, which is curved and pivoted at each end, is lifted at an angle Other motions Folding bridge – a drawbridge with multiple sections that collapse together horizontally Curling bridge – a drawbridge with transverse divisions between multiple sections that curl vertically By function Jet bridge – a passenger bridge to an airplane. One end is mobile with height, yaw, and tilt adjustments on the outboard end Linkspan – for a roll-on/roll-off vessel or ferry Ferry slip Locks are implicitly bridges as well allowing ship traffic to flow when open and at least foot traffic on top when closed

Visual index

File:Drawbridge.gif|Drawbridge File:MovableBridge_draw.gif|Bascule bridge File:MovableBridge_fold.gif|Folding bridge File:MovableBridge curl.gif|Curling bridge File:MovableBridge_lift.gif|Vertical-lift bridge File:MovableBridge table.gif|Table bridge File:MovableBridge thrust.gif|Retractable bridge (Thrust bridge) File:MovableBridge roll.gif|Rolling bascule bridge File:MovableBridge subm.gif|Submersible bridge File:MovableBridge tilt.gif|Tilt bridge File:MovableBridge_swing.gif|Swing bridge File:MovableBridge_transport.gif|Transporter bridge

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