Structural support of Sabo Bridge moving forward

City crews have installed two sets of the four support structures that need to be put in place on the Sabo Bridge, where a suspension cable connection broke loose late Sunday evening, Feb. 19. It is anticipated that the remaining shoring supports will be in place in the next day or two. Once all four sets of shoring are in place, it is anticipated that crews can safely begin the work to release the tension from a second set of cables that were also compromised.

Since Sunday evening, City engineers have been consulting with the Sabo Bridge’s original designers and others to inspect, stabilize and repair the bridge. Besides complex computer modeling and measuring the loads on jacks on the shoring structures, engineers are also directly measuring tension in the cables. Understanding the changing tensile loads in the cables is an important part of judging stability. Inspectors are also measuring deflections of the bridge deck and looking for any new visible signs of cracking, bowing, or frayed strands of bridge cable.

The City of Minneapolis and Hennepin County have contracted with Wiss, Janney, Elstner, Associates, Inc., a forensic engineering firm to assist in determining the cause of the failure. Understanding the cause of the failure will be critical to developing plans to move forward. The bridge was originally designed and constructed as a Hennepin County project and “ownership” was turned over to the City of Minneapolis after the bridge opened in 2007.

Because of safety concerns, traffic on Hiawatha Avenue will continue to be closed from 26th Street East to Lake Street. In addition, Metro Transit will continue to use buses to replace Light Rail trains serving Franklin Avenue, Lake Street/Midtown and the 38th Street stations. City and County bridge and engineering staff, in collaboration with MnDOT and Metro Transit, will determine when the bridge is stabilized enough to reopen Hiawatha Avenue to traffic and the Hiawatha Light Rail line. The Sabo Bridge itself will remain closed until repair work is completed.

Annual bridge inspections

The bridge is one of 373 inspected annually by the City of Minneapolis. The City’s licensed bridge inspectors examine and rate bridges using federal and state guidelines. Since its opening, the Sabo Bridge has undergone inspections every year with the most recent inspection taking place in September 2011. Those inspections did not find any problems with the bridge’s cable support system. 

The Sabo Bridge is a 215 foot-long cable-stayed suspension bridge that opened in November of 2007 to carry Midtown Greenway bicycles and pedestrians over Hiawatha Avenue. The bridge was built by Hennepin County and turned over to the City of Minneapolis when construction was completed.

The bridge, which carries bicycle and pedestrian traffic over Hiawatha Avenue, was closed early Monday morning after a cable connection broke on the bridge’s mast or pylon, causing a pair of suspension cables to break loose. The bridge design includes 18 cables on each side of the bridge, for a total of 36 cables.

Published Feb 22, 2012