The Minnesota Slip Bridge is a pedestrian lift bridge spanning the Minnesota Slip on Duluth’s waterfront. The bridge is heavily used by foot and bicycle traffic to connect Canal Park with the Duluth Entertainment and Convention Center along with other downtown businesses.
H&H performed mechanical and electrical rehabilitation of the bridge. The rehabilitation was in response to a long-standing mechanical problem that resulted in the periodic inoperability of the bridge and inconvenience to the public. The operational problems were linked to the wire rope-driven winch machinery located at the rear portion of the balance truss arm and connected to the base of the towers. The wire ropes would periodically “skip a drum groove” and bunch up similar to a fishing reel mishap, requiring hours of downtime and labor to repair.
In 2016, H&H performed a short assessment and recommendation to replace the system with a bidirectional operating strut arm, driven by a rack gear and pinion arrangement instead of the wire rope pulley system. The operating strut machinery was located to fit in the same location as the wire rope winch drive, and the tower connections were strengthened to account for the new loading arrangement. As part of the work, the span center locks were modified to complement the structural arch load path, replacing the original centering latches. The latches had been reported to disengage under pedestrian live load traffic and bounce at the center the span several inches.
The replacement center locks now act in compression when the arch meets at the seated position and are incapable of disengaging and bouncing under live loads.