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Author Topic: Bridges and Infrastructure  (Read 1224 times)
DougMacG
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« on: August 22, 2007, 11:53:07 PM »

This post could have gone into 'Science' but I think the topic, if discussed, will quickly move to politics.  I wrote earlier that  "I twice drove over an 8-lane, 2000 ft. bridge within 3 hours of it tumbling into the Mississippi."  The story is national but it is a particularly big deal here since it is still down and quite a few people died, 13 I think.  My flippant mind tells me the force that brought the bridge down was gravity and the onus was on the engineers to tell us why it shouldn't fall.

First hunch on cause that makes so far is good news in a sense because it was only installed on a few bridges including the I-35W Minneapolis bridge that fell and the counterpart I-35E bridge over the Mississippi in St. Paul.  It turns that they installed an automatic spraying system for Potassium Acetate on the bridge which is likely a weld and bolt corrosion accelerator.  That's a side effect; its primary purpose is to rust and rot our cars, it also melt snow and ice.

My lesson so far from this ordeal is to question whether these are the people we want to run our health care system.

(Repeating from above, this is only a hunch, the cause of the collapse won't be determined for a long time)

http://www.startribune.com/10204/story/1377743.html

Oct. 19, 1999: I-35W bridge getting de-icer system

By Laurie Blake, Star Tribune

Starting today, the most notorious winter slick spot on the Twin Cities-area freeway system - the Interstate Hwy. 35W Bridge over the Mississippi River - is being fitted with an automatic de-icing system.

Using temperature- and precipitation-activated nozzles embedded in the bridge deck, the system will spray the bridge with liquid potassium acetate in a bid to rid the surface of the treacherous black ice that has caused more than 120 accidents in the past five winters.

The potassium retains its melting power at 20 to 30 degrees below zero. Keeping the bridge clear of black ice has been difficult at sub-zero temperatures when salt is no longer effective. The State Patrol occasionally has closed the bridge to protect drivers.

The automatic system will apply the liquid potassium to the bridge from 68 spray heads in the driving surface placed 59 feet apart and from eight additional spray heads on the north end of the bridge in the median barrier and on the sides of the bridge, said Ia Xiong, project engineer.

Sensors in the bridge detect freezing temperatures before ice forms and activate the potassium spray to prevent ice formation.  The liquid will squirt out of nozzles in an arc 4 to 6 inches high, so motorists will see the spray. The deck surface will be wet.  The plastic nozzles are about an inch thick and 11 inches in diameter. The spray will reach most of the bridge and vehicles will spread it across the entire deck.
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