Lake Shore Drive Bridge
Location: Chicago, Illinois
Program: Moveable Pedestrian Bridge
The Lake Shore Drive Bridge is a unique butterfly concept composed of a combination bascule and vertical lift bridge. Movement of the bascule arch spans provides the mechanism to raise the 250 ft. pedestrian bridge span as a vertical lift bridge. The drive mechanism to move the arches consists of hydraulic cylinders at each quadrant, near the arch springings. Arches will be counterweighted to minimize the force needed to move the individual arches. Cylinders are designed to move the balanced arch spans, raise the pedestrian lift span and supporting cables, and overcome associated friction, rope bending and related mechanical design loads. A mechanical locking system will hold the bridge in the open and closed positions. Bumper blocks within the pier provide a positive stop at the range of motion limits. Trunion bearings and roller bearing assemblies allow movement of the arch span while accommodating associated arch loads at the base of the arch. A positive connection between arch crowns serves to stabilize the arch system for wind and live loading. A hinged floor system on the pedestrian span accommodates geometric variations as the lift cables raise the span. Spooled anchor cables maintain lateral control of the moving span. In the closed position, a mechanical tensioning system stabilizes the span for wind loading.