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elSicomoro · 08-02-2007, 11:26 PM

From Wikipedia:

Black ice

In February and December 1996, the Interstate Hwy. 35W bridge over the Mississippi River east of downtown Minneapolis was identified as the single most treacherous cold-weather spot in the Twin Cities freeway system, due to a thin layer of black ice causing spinouts and collisions on the bridge.[23][24] By January 1999, the state Transportation Department began testing liquid magnesium chloride and a mixture of magnesium chloride and a corn-processing byproduct to see whether either would reduce the black ice that appears on the bridge during the winter months.[25] In October 1999, the state embedded temperature-activated nozzles in the bridge deck to spray the bridge with liquid potassium acetate to keep the area free of winter black ice.[26] The system came into operation in 2000.[27][28]

[edit] Structural reviews

In the years prior to the collapse, several reports citing problems with the bridge were issued. In 1990, the federal government gave the I-35W bridge a rating of "structurally deficient," citing significant corrosion in its bearings.[29] A 2001 Minnesota Department of Transportation report indicated weakness at the joints of the steel that held the concrete deck above the river, due to "unanticipated out of plane distortion" of the steel girders. The report also noted a concern about lack of redundancy in the main truss system,[13] which meant the bridge had a greater risk of collapse in the event of any single structural failure. In 2005, the bridge, along with over 70,000 other US bridges[30], was rated as "structurally deficient" and in possible need of replacement, according to the US Department of Transportation's National Bridge Inventory database.[31] In a subsequent report, an inspection carried out June 15, 2006 found numerous problems, including fatigue cracking.[32]

Other topics of concern were the water erosion around the north piers (which were partially toppled in the collapse), steel substructure defects (especially near the south piers which toppled sideways in a scissors motion), problems with the bridge de-icing system,[33] thermal cycling of the structure, recent heavy rains and flooding on the I-35W highway.[34]

08-02-2007, 11:26 PM	#21
elSicomoro Person who doesn't update the user title Join Date: Jan 2001 Posts: 12,486	From Wikipedia: Black ice In February and December 1996, the Interstate Hwy. 35W bridge over the Mississippi River east of downtown Minneapolis was identified as the single most treacherous cold-weather spot in the Twin Cities freeway system, due to a thin layer of black ice causing spinouts and collisions on the bridge.[23][24] By January 1999, the state Transportation Department began testing liquid magnesium chloride and a mixture of magnesium chloride and a corn-processing byproduct to see whether either would reduce the black ice that appears on the bridge during the winter months.[25] In October 1999, the state embedded temperature-activated nozzles in the bridge deck to spray the bridge with liquid potassium acetate to keep the area free of winter black ice.[26] The system came into operation in 2000.[27][28] [edit] Structural reviews In the years prior to the collapse, several reports citing problems with the bridge were issued. In 1990, the federal government gave the I-35W bridge a rating of "structurally deficient," citing significant corrosion in its bearings.[29] A 2001 Minnesota Department of Transportation report indicated weakness at the joints of the steel that held the concrete deck above the river, due to "unanticipated out of plane distortion" of the steel girders. The report also noted a concern about lack of redundancy in the main truss system,[13] which meant the bridge had a greater risk of collapse in the event of any single structural failure. In 2005, the bridge, along with over 70,000 other US bridges[30], was rated as "structurally deficient" and in possible need of replacement, according to the US Department of Transportation's National Bridge Inventory database.[31] In a subsequent report, an inspection carried out June 15, 2006 found numerous problems, including fatigue cracking.[32] Other topics of concern were the water erosion around the north piers (which were partially toppled in the collapse), steel substructure defects (especially near the south piers which toppled sideways in a scissors motion), problems with the bridge de-icing system,[33] thermal cycling of the structure, recent heavy rains and flooding on the I-35W highway.[34]