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A drawbridge is a type of movable bridge typically associated with the entrance of a castle. The term is often used to describe all different types of movable bridges, like bascule bridges and lift bridges.
Overview
Simple drawbridges may be found in short canal crossings, where the lifting mechanism is a pair of overhead beams with counterweights that are not a part of the bridge's load bearing structure.
The most common type of drawbridge consists of a wooden platform with one fixed side (normally with a hinge), and the other side attached to the wall from a floor higher than the drawbridge.
In the Middle Ages, drawbridges were often used to allow or deny access across a moat or ditch. They could be let down to allow people across, or pulled up to deny entry into the castle.
There are also drawbridges where the cars will stop and the bridge will open to allow large vessels to go through because they are to big to go under and they can't go around.
Road and rail
Now, with cars and trains in need of crossing small waterways without blocking boats from passing, drawbridges have a more peaceful reason for their existence.
In Queensland, diamond crossings between narrow gauge cane tramways and main lines are being replaced by drawbridges, so that the rails of the main line are completely unbroken by gaps or weak spots. This also allows the main line speeds to be raised.
Another rail use of drawbridges was on the Listowel and Ballybunion railway in Ireland. This was a sort of monorail, where trains hung on either side of a fence-like track. Road crossings were either a gate-like Stuart section of track or twin drawbridges, that allowed crossing at rail level.
Gallery
 Drawbridge crossing fortification ditches at Fort Ticonderoga |
 The famous Magere Brug (a double drawbridge) in Amsterdam |
 Another drawbridge in Amsterdam |
 USS Lake Erie, a Ticonderoga-class guided missile cruiser, passes under the Broadway Bridge on the Willamette River |
 Drawbridge, painted by Vincent van Gogh |
.JPG) Drawbridge at Castle Dornenburg |
 Wooden drawbridge in Amsterdam |
 Drawbridge connecting James Island (South Carolina) to the mainland |
Wikipedia content modification information:
- This page was last modified on 5 January 2009, at 19:39.
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