Math Is Fun Forum

mikau

Member

Registered: 2005-08-22

Posts: 1,504

Bridge Collapse in Minneapolis

Geez..

yesterday, August 1st 07, the 35W bridge in Minneapolis collapsed under the weight of heavy traffic during rush hour. Supposedly the bridge was undergoing repairs and maintenance.

This is just speculation but when i heard about it, the first thing that ran through my mind was either lousy structural engineers, or greedy contractors. My dad is an architect and you wouldn't believe how much cheating and code breaking he sees behind closed doors just to save a buck. I'm also suprised by the incompetant math skills of the engineering students in my school and i'm wondering if some engineers are getting lazy or careless in their calculations. Not to bash on engineers of course, but its their job to do these calculations and give their approval. Who's going to question them if they grow slack?

Of course, the bridge could have been well designed originally snd just in bad condition.

My prayers and best wishes go out to all the victims and their families.

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A logarithm is just a misspelled algorithm.

Math_Girl

Member

Registered: 2007-07-27

Posts: 23

Re: Bridge Collapse in Minneapolis

I heard about this on the new today. Very sad incident and my prayers also go out to everyone who may have been affected by this tragic event.

Here's a link to an article on the incident

http://www.bloomberg.com/apps/news?pid= … refer=home

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MathsIsFun

Administrator

Registered: 2005-01-21

Posts: 7,713

Re: Bridge Collapse in Minneapolis

Bridges are "over-designed" by the engineers ... but there can be unforeseen weak spots, either through poor work practices, substituting cheaper materials, wear-and-tear, etc (a long list!).

No doubt they will investigate this and we will then know why. Until then we can only feel sorry for the innocent victims.

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"The physicists defer only to mathematicians, and the mathematicians defer only to God ..."  - Leon M. Lederman

mikau

Member

Registered: 2005-08-22

Posts: 1,504

Re: Bridge Collapse in Minneapolis

what exactly do you mean, "over designed"?

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A logarithm is just a misspelled algorithm.

John E. Franklin

Member

Registered: 2005-08-29

Posts: 3,588

Re: Bridge Collapse in Minneapolis

I think MIF means you design for stress and weight about 3 times the maximum you'll actually get or something.  As for steel, I know little about how it is made, and what could go wrong, and the variation in possible ingredients.

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igloo myrtilles fourmis

MathsIsFun

Administrator

Registered: 2005-01-21

Posts: 7,713

Re: Bridge Collapse in Minneapolis

Yes ... you figure out the greatest likely sum of forces (strong wind, flowing current, trucks parked) to work out the stresses, and assume the lowest strength of material to work out the "Factor of Safety" (how many times stronger the material is than the stress).

Safety Factors of 3 or more are common.

But over time the cross section of a beam can be greatly reduced, by corrosion or "fatigue" (cracks that grow with repeated stresses) to the point where it snaps.

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"The physicists defer only to mathematicians, and the mathematicians defer only to God ..."  - Leon M. Lederman

Mathskido

Member

Registered: 2007-07-20

Posts: 18

Re: Bridge Collapse in Minneapolis

Maybe it happened because the metal was rusting away or it was loosely screwed by the builders in the 1960's.

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Ricky

Moderator

Registered: 2005-12-04

Posts: 3,791

Re: Bridge Collapse in Minneapolis

But over time the cross section of a beam can be greatly reduced, by corrosion or "fatigue" (cracks that grow with repeated stresses) to the point where it snaps.

Here is a doctoral thesis done on this particular bridge in 2001.  It reports that there was less fatigue than expected.  It also calls for regular inspections of certain sections of the bridge that were receiving the highest amounts of stress.

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"In the real world, this would be a problem.  But in mathematics, we can just define a place where this problem doesn't exist.  So we'll go ahead and do that now..."

Laterally Speaking

Real Member

Registered: 2007-05-21

Posts: 356

Re: Bridge Collapse in Minneapolis

Here are some big factors to take into account: extreme temperatures (mostly low), salt used to prevent the formation of ice, poor construction, underfunded repairs (the governor cut the bridge repair budget by 20% a couple years ago), the wear of the bridge under the weight of 200000 vehicles a day, all year long, for several years.

My uncle, who I recently talked to, went over this bridge just 3 hours before it collapsed, so I am very thankful.

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"Knowledge is directly proportional to the amount of equipment ruined."
"This woman painted a picture of me; she was clearly a psychopath"

Ricky

Moderator

Registered: 2005-12-04

Posts: 3,791

Re: Bridge Collapse in Minneapolis

the wear of the bridge under the weight of 200000 vehicles a day

The average per day was around 30,000.

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"In the real world, this would be a problem.  But in mathematics, we can just define a place where this problem doesn't exist.  So we'll go ahead and do that now..."

MathsIsFun

Administrator

Registered: 2005-01-21

Posts: 7,713

Re: Bridge Collapse in Minneapolis

My uncle, who I recently talked to, went over this bridge just 3 hours before it collapsed, so I am very thankful.

That is a pretty close call, really, as the bridge was ready to go.

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"The physicists defer only to mathematicians, and the mathematicians defer only to God ..."  - Leon M. Lederman

fruitloop

Member

Registered: 2007-09-29

Posts: 15

Re: Bridge Collapse in Minneapolis

oh wow laterally speaking! that is really scarey!
right after it happened, they had a lot of research and they said that there are about 50 bridges unsafe in michigan (pretty big amount).. its really creepy.... i hope none of them collapse

Laterally Speaking

Real Member

Registered: 2007-05-21

Posts: 356

Re: Bridge Collapse in Minneapolis

Yes. There are about 150, I think, in Oregon, including one in downtown that has been known to be unsafe for several decades now. The Portland mayor said that he would continue to use said bridge every day, thus bringing about (for me) questions about his sanity...

Pardon me for my exaggerated numbers; I got them through... Well, I´m not sure how I got them, really.

Last edited by Laterally Speaking (2007-10-06 06:30:04)

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"Knowledge is directly proportional to the amount of equipment ruined."
"This woman painted a picture of me; she was clearly a psychopath"