Failure of ‘good’ cables stuns Sabo Bridge’s inspector

Nickalas Tabbert

 Minneapolis bridge inspector John Beetsch said he was in shock after learning the cables from the Martin Olav Sabo Bridge he inspected failed Sunday evening.

Beetsch and colleague Kent Madsen spent a half-day in October examining the 18 sets of cables and cable anchors, the Star Tribune said.  They gave them their highest rating for soundness and lack of corrosion, saying "cables are good" on their report on the four-year-old bridge.

Officials said in the Tribune article published Wednesday that it is still too early to identify a cause for the failures on the city-owned pedestrian and bicycle bridge.  The emergency closing of the cable-stayed bridge has diverted vehicles off Hiawatha Avenue and disrupted service of the Hiawatha light-rail line indefinitely.

Minneapolis officials gave the cable system on the 2,200-foot span – along with its other parts – top marks in every inspection going back to 2008.  The additional inspection of the cables in October, aimed at going beyond the annual inspection, returned parallel remarks.

Beetsch said it is unlikely for a bridge opened as recently as late 2007 to have problems. 

Engineers will look into whether the bridge's design, construction or some outside force caused the cable supports to crack.  Such an investigation typically takes months to complete, Mike Kennedy, director of transportation, maintenance and repair for the Minneapolis Department of Public Works said.

The city is also getting assistance from the bridge's design consultant, San Francisco-based URS Corp.  The engineering firm  was a consultant for the state-owned 35W Bridge that collapsed in 2007.

City workers have struggled in their attempts to install timber and steel shoring structures on the east end of the Sabo bridge because of soft soil.  They cannot fix the compromised anchor without ensuring the span is sound, according to Kennedy.  He said concerns remain about the second cracked cable support, which is still connecting a pair of cables to the mast.

"We are having to sort of rethink the plan … and it's all taking time," Kennedy said.