Drawbridge

A drawbridge (sometimes: drawbridge ) is a moveable bridge, which can be folded with the aid of a mechanical device to control access to a port or to permit the passage of vessels on a waterway. The bridge flap movable, referred to as part of the bridge rotates about a horizontal axis of rotation or at a hinge. Is Hoisted the bridge by means of ropes or chains that begin at the outer end of the bridge flap.

Drawbridges in the fortification

To secure a gate drawbridges were used in medieval castles and fortifications, and even in many modern fortresses. Drawbridges have been handed down from the Middle Ages, found in German-speaking countries, however, only in the late Middle Ages further spread.

In castles and fortifications similar goal represented a particular weak point, and was therefore often protected by various structural devices. By means of a drawbridge in front of the gate of the entrance over the moat could be effectively and quickly interrupted. During this purpose also solid wooden bridges were built, which could be eliminated in the case of a siege, the drawbridge allowed a more flexible control over access and could be used for rapid failures beyond. The bridge flap offered in the raised state additional protection for the door opening. This attacker the bridge flap could not pull down by means of hooks, often a wall recess was applied to the gate around, in which the bridge was hit flush.

In medieval drawbridges two different basic designs were widely used for the wind-up mechanism:

• Chain or rope bridge. In this design, two parallel ropes or chains from the outer end of the bridge plate in a diagonal line through two wall openings above the door to the interior of the gatehouse, where they can be obtained by means of a winch. To facilitate the pulling-up, the counterweights may be placed at the end of the chains, or to an extension of the bridge path behind the axis of rotation.
• Momentum tail bridge. This design takes advantage of the leverage effect by the chains are attached to two so called rods or flywheel Wippbäumen that will run parallel to the bridge flap and continued inside the gatehouse behind the axis of rotation. The rear halves of the swing rods are connected to each other by a stable frame structure, which may be mounted on the additional counterweights. The bridge is pulled up by the rear end of the swing rod is moved downwards.

Drawbridges in hydraulic

In hydraulic drawbridges are used to allow vessels passage through a channel if the mast or chimney of the ship above the level of the bridge rail protrudes. Mostly for two facing drawbridges be built that permit the passage in the middle of the channel when folded. The bridges have usually about swing rods ( see above). The same purpose also meet several other movable bridge constructions, for example, bascule bridges or movable bridges. In the Rotterdam district Sheedam there is a drawbridge of wood, which must still be manually operated by hand crank operation. Another example of a manual and functional folding mechanism is the bridge in Wieck Greifswald.