Moveable bridge
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A moveable bridge is a bridge that moves to allow passage for (usually) boats or barges. By making the bridge movable it may be made low, which avoids the expense of high piers and long approaches, greatly reducing the cost of the bridge. The principal disadvantage is that the traffic on the bridge must be halted when it is opened for passages. 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, sometimes remotely using video-cameras and loudspeakers. Generally the bridges are powered by electric motors, whether operating winches, gearing, or hydraulic pistons.
There are often traffic lights for the road and water traffic, and moving barriers for the road traffic.
In the United States, regulations governing the operation of movable bridges, 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[1]; temporary deviations are published in the Coast Guard's Local Notice to Mariners[2].
[edit] Types of moving bridges
- Drawbridge - the bridge deck is hinged on one end
- Bascule bridge - a drawbridge with a counterweight to facilitate raising
- Folding bridge - a drawbridge with multiple sections that collapse together horizontally
- Curling bridge - a drawbridge with multiple sections that curl vertically
- Lift bridge - the bridge deck is lifted up by counterweighted cables mounted on towers
- Table bridge - a lift bridge with the lifting mechanism mounted underneath it
- Retractable bridge (Thrust bridge) - the bridge deck is retracted to one side
- Rolling Bridge - an unhinged drawbridge which remains horizontal as it is retracted
- Submersible bridge - the bridge deck is lowered down into the water
- Tilt bridge - the bridge deck, which is curved, is lifted up at an angle
- Swing bridge - the bridge deck rotates around a fixed point, usually at the center, but may resemble a gate in its operation
- Transporter bridge - a structure high above carries a suspended, ferry-like structure
- Jetway - a passenger bridge to an airplane
[edit] See also
- Bailey bridge, Medium Girder Bridge, and Armoured vehicle-launched bridge - transportable or relocatable bridges.
- Pontoon bridge - may be built with a barge or boat-like section that may be moved for passage.
