DRAW-Bridge, a bridge made after the manner of a float, to draw up or let down, as occasions serve, before the gate of a town or castle. See BRIDGE.
A draw-bridge may be made after several different ways; but the most common are made with plyers, twice the length of the gate, and a foot in diameter. The inner square is traversed with a cross, which serves for a counterpoise; and the chains which hang from the extremities of the plyers to lift up or let down the bridge are of iron or brass.
In navigable rivers it is sometimes necessary to make the middle arch of bridges with two moveable platforms, to be raised occasionally, in order to let the masts and rigging of ships pass through. This kind of draw bridge is represented in Plate CLXVIII. where AB is the width of the middle arch; AL and BL, the two piers that support the draw-bridge NO, one of the platforms of which is raised, and the other let down, having the beam PQ for its pleyer. To NO are suspended two moveable braces EH, EH; which resting on the support E, press against the bracket M, and thereby strengthen the draw-bridge. These braces are conducted to the rest by means of the weight S, pulling the chain SLF.