pont levant à entraînement sur tour

CONT: The vertical-lift bridge has a span similar to that of a fixed bridge, and is lifted by steel ropes running over large sheaves at the tops of its towers to the counterweights, which fall as the lift span rises and rise as it falls. If the bridge is operated by machinery on each tower, it is known as a tower drive. If it is driven by machinery located on the lift span, it is known as a span drive.
CONT: The Roosevelt Island Bridge is a tower drive vertical lift movable bridge ... The structural steel lift span of this bridge is suspended at each corner from twelve wire ropes which are draped over a main counterweight sheave located atop the corresponding corner of a tower. The other ends of the ropes are connected to counterweights. There is one span counterweight at each tower. Raising and lowering the bridge is accomplished by rotating the main sheaves using tower drive systems. As the span is raised the two counterweights descend. The lift span is raised and lowered by two identical tower drives, one located in a machinery room atop each tower.