Sabo Bridge closed for repairs until early December

Nearest crossing at 28th a ‘mess’ during Xcel construction being completed at same time

by Tesha M. Christensen

Sabo Bridge is closed to all pedestrian and bicycle traffic until early December.

Crews are making final repairs to the five-year-old bridge, which was first closed earlier this year when a pair of suspension cables broke loose.

“We’re pleased to see the final bridge repair underway,” said Midtown Greenway Coalition Soren Jensen. “I know many people join me in hoping the repair goes smoothly and quickly.  I think the most important thing is to do it right and ensure the bridge is safe, however long it takes.”

NEW PARTS WILL WITHSTAND WIND-INDUCED FATIGUE

Diaphragm plates on the bridge’s pylon will be installed and retrofitted while the bridge is closed.  After extensive tests, Wiss, Janney, Elstner Associates, Inc., an engineering firm hired by the city, identified the cause of the cable connection failure to be wind-induced cable vibrations that caused fatigue cracking in the diaphragm plates. These plates secure the cables to the bridge’s main pylon.

According to the city, the retrofitted and replacement plates being installed are designed to withstand the fatigue that caused the cracking.

After the bridge was closed in February 2012, the broken plates were analyzed by Lehigh University in Pennsylvania. Strain gauges, displacement transducers and accelerometers installed on the bridge provided actual stress range movement, amplitude and frequency of cable vibrations experienced by the bridge during wind events. These two pieces of information presented investigators with a complete picture of what happens to the bridge in all kinds of weather. From this, the repair plan was developed.

The 215 foot-long cable-stayed suspension bridge 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.

INTERSECTION AT 28TH A ‘MESS’

The nearest crossing to the Sabo bridge for bicyclists and pedestrians is at 28th and Hiawatha. However, that is an area of concern right now for the Midtown Greenway Coalition. Xcel has began construction there on the substation and two 115-kilovolt transmission lines that will travel 1.5 miles underground from Hiawatha to Oakland Ave. S. via 28th.

“It’s really quite a mess right now. ” observed Jensen.

He added, “Fixing the Sabo bridge is a top priority, so bicyclists and pedestrians can at least avoid most of the construction and safely cross Hiawatha/55.”

Construction of the transmission lines will be complete in the fall of 2013. The substation work will be done in 2014. The bike trails around the Hiawatha substation will remain open during the construction; however, at times the trail will be temporarily rerouted by 10 to 20 feet.

The Hiawatha Transmission Line will carry 55 megawatts of power, enough to serve 50,000 customers, and bolster existing capacity infrastructure.

Jensen encourages bikers and walkers to remain patient through the construction process. “The power company’s original idea was to place giant overhead power lines in the Midtown Greenway.  What a terrible idea! With the support of neighborhood organizations and residents along the Greenway, our coalition took the lead in the fight to keep the lines out of the Greenway -- and we won!  

“So, while the construction on 28th will disrupt things for a while, we see it as a reminder of the power of neighborhoods and citizens standing up to protect vital community assets like the Midtown Greenway.”