Martin Olav Sabo Bridge

Martin Olav Sabo Bridge

The Martin Olav Sabo Bridge viewed from the south, from around 28th Street.
Coordinates 44°57′17″N 93°14′33″W / 44.9547°N 93.2425°W / 44.9547; -93.2425Coordinates: 44°57′17″N 93°14′33″W / 44.9547°N 93.2425°W / 44.9547; -93.2425
Carries Pedestrian and bicycle
Crosses Minnesota State Highway 55 (Hiawatha Avenue) and METRO Blue Line
Locale Minneapolis
Official name Martin Olav Sabo Bridge
Maintained by Minneapolis Public Works
Characteristics
Design cable-stayed suspension
Total length 2,200 feet (671 m)
Height 100 feet (30 m)
Longest span 220 feet (67 m)
History
Opened Ribbon cutting November 8, 2007, at 4:00PM CDT
Downtown Minneapolis and the Martin Olav Sabo Bridge from the Hiawatha Avenue bridge over Lake Street, on the METRO Blue Line light rail train.

The Martin Olav Sabo Bridge is a bridge in the city of Minneapolis and the first cable-stayed suspension bridge in the U.S. state of Minnesota. Formerly the Midtown Greenway Pedestrian Bridge, it was renamed in honor of former Representative Martin Olav Sabo, a fourteen-term member of Congress from Minnesota.

Opened and dedicated in November 2007, the bridge crosses Hiawatha Avenue (Trunk Highway 55) north of 28th Street East and just south of 26th Street East, joining Phase 2 and Phase 3 of the Minneapolis Midtown Greenway at Hiawatha Avenue, allowing a continuous biking connection across the city. The bridge also links Longfellow community (Longfellow and Seward neighborhoods) to Phillips community (East Phillips neighborhood).

The bridge was built by Hennepin County and transferred to the City of Minneapolis, which owns and maintains the bridge.[1]

The bridge was closed on February 20, 2012 when two of the cables that support the bridge fell due to cracks in their attachment points; additional significant cracks were subsequently found in two other support plates. The bridge, supported with temporary bracing, was reopened June 1, 2012. A summary report of the failure analysis released June 8, 2012 determined that unaccounted for wind-induced cable vibrations led to the failures of the attachment points. The bridge was again closed for repairs on September 23, 2012.[2] Repairs were completed, and the bridge reopened, on November 19, 2012.[3]

Configuration

The new bridge eliminates the need for bicyclists and pedestrians to cross busy Hiawatha Avenue with a stoplight at grade-level. Instead, the bridge brings them north one block, over the highway, and back south, introducing a new grade-level crossing of 28th Street East west of Hiawatha. Users are still able to use the at-grade Hiawatha crossing after completion.[4]

Structure

The bridge has a total length of 2,200 feet. Its main span passes 220 feet over Hiawatha Avenue, with the cable-stay tower rising 100 feet above the bridge-deck level. The Martin Olav Sabo Bridge is the first true cable-stayed suspension bridge in the State of Minnesota. Its design was the product of engineering consulting firm URS, with community input.[5]

History

During Congressman Martin Olav Sabo's tenure, he earmarked $2.9 million in federal funding to the project. He is also recognized for acquiring federal funding to complete many capital improvements throughout Minneapolis. City advisory boards and committees forwarded the recommendation to rename the bridge after Sabo in 2005, which was done by the City Council.[6] Hennepin County provided additional funding to total $5.1 million for the final project.[7]

2012 structural failures

Late on the night of February 19, 2012, the two longest support cables on the bridge were found detached and lying across the bridge deck below. The bridge was closed shortly thereafter to all traffic. The portion of Hiawatha Avenue that passes underneath the bridge was also closed, and light rail service was suspended on the tracks that pass beneath the bridge.[8][9]

The light rail resumed service on February 24, 2012, after emergency supports were placed underneath the bridge and a second pair of cables were removed due to cracks in their anchor points.[10] Hiawatha Avenue was reopened to traffic underneath the bridge on February 27, 2012.[11]

The original cable failure was due to cracks in diaphragm plates that anchor the ends of the cables to the steel tower, and significant cracks have subsequently been found in three of those anchorages. The engineering firm Wiss, Janney, Elstner Associates, Inc. was hired to investigate how the diaphragm plates became compromised.[12] On June 8, 2012, a summary report[13] of the investigation was released in which the failure was attributed to wind-induced "cable vibrations that induce damaging stress range cycles at fatigue sensitive details in the cable diaphragm plates." The effect of cable vibrations caused by wind was not included in the original design package for the bridge.[14]

The bridge reopened for bicycle and pedestrian traffic on June 1, 2012, with temporary support structures in place.[15] New plates were designed, and the bridge was closed once more between September 23, 2012, and November 19, 2012, to allow them to be retrofitted as permanent repairs.[3]

References

  1. ↑ "Bridges". Midtown Greenway Coalition. 2008. Retrieved 26 February 2012.
  2. ↑ Adams, Jim (September 23, 2012). "Sabo pedestrian/bike bridge closed for repairs". Star Tribune. Retrieved September 30, 2012.
  3. 1 2 Brandt, Steve (November 20, 2012). "Sabo Bridge reopens after repairs". Star Tribune. Retrieved January 20, 2013.
  4. ↑ "Roadguy blog: Check out the new Greenway bridge". Star Tribune. December 8, 2006. Archived from the original on September 26, 2007. Retrieved August 31, 2007.
  5. ↑ "Midtown Greenway Coalition Board Meeting Minutes April 18, 2002". Midtown Greenway Coalition. April 18, 2002. Retrieved August 31, 2007.
  6. ↑ "City Council resolution" (PDF). Archived from the original (PDF) on September 29, 2007.
  7. ↑ "From the Department of Public Works" (PDF). City of Minneapolis. August 9, 2005. Archived from the original (PDF) on September 29, 2007. Retrieved August 31, 2007. This contains official documentation from the Minneapolis Department of Public Works.
  8. ↑ Rao, Maya (February 21, 2012). "Failure of good cables stuns Sabo Bridge's inspector". Star Tribune. Archived from the original on February 25, 2012.
  9. ↑ Mador, Jessica (February 24, 2012). "Sabo Bridge remains closed over safety concerns". Minnesota Public Radio. Retrieved February 24, 2012.
  10. ↑ Gilyard, Burl (February 24, 2012). "Hiawatha LRT service restored to all stations". Finance & Commerce. Archived from the original on February 25, 2012.
  11. ↑ Márquez, Heron (February 27, 2012). "Hiawatha Av. at failed bridge reopens to traffic". Star Tribune. Retrieved 3 March 2012.
  12. ↑ Rao, Maya (February 29, 2012). "More cracks in Sabo Bridge". Star Tribune. Archived from the original on March 3, 2012. Retrieved March 3, 2012.
  13. ↑ "Summary Report" (PDF). Wiss, Janney, Elstner Associates, Inc. Retrieved 10 June 2012.
  14. ↑ Rao, Maya (June 29, 2012). "Sabo bridge findings: Winds caused fractures in plates". Star Tribune.
  15. ↑ "Sabo Bridge re-opens to bicycle and pedestrian traffic". City of Minneapolis. June 1, 2012. Retrieved June 1, 2012.
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