Critters complicate bridge inspections

Bridge breaker?: An unusual factor that may have contributed to the I-35W bridge collapse is a build-up of pigeon poop in the box beams of the bridge. To keep pigeons from getting into the box beams, plastic covers were put over inspection holes on the bridge.
Bridge breaker?: An unusual factor that may have contributed to the I-35W bridge collapse is a build-up of pigeon poop in the box beams of the bridge. To keep pigeons from getting into the box beams, plastic covers were put over inspection holes on the bridge.
As the blame game starts to heat up in the aftermath of the I-35W bridge collapse, members of the animal kingdom are getting fingers pointed at them.

Tuesday’s Star Tribune carried a story about how problems with pigeons and spiders complicated bridge inspections over the past 13 years. How could those creatures play a part in a bridge going down? Read on.

Pigeon poop is a nuisance in all urban areas and was chronicled in this post to Science Buzz a few months ago. And evidently at the I-35W bridge, pigeon droppings were a big problem. Large numbers of pigeons were nesting in the box beam sections of the bridge structure from as far back as 1994. The box beam is vertical support beam between the bridge deck and the supporting floor beam below the bridge. The box beams had holes in them for inspectors to look inside, but that was also the access that pigeons were using to get inside and build nests.

With large numbers of pigeons in the bridge came heavy amounts of pigeon droppings. And the waste matter in those droppings can be very corrosive to metal. The solution taken in 1999 to solve that problem was to put plastic covers over the box beam holes. And those areas were some of the most critical areas for fatigue cracking that was occurring in the bridge. Some are now wondering if those plastic covers limited inspectors’ views of these critical areas of the bridge.

As for the spiders, inspectors said that the huge number of spider webs in and under the bridge could often be confused for bridge structure cracks.

The story also mentioned one other species that made inspections more challenging to engineers: humans. While the inspection work would be targeted to non-rush hour times from 9 a.m. to 3 p.m., inspectors said they still were often the targets of road rage from passing motorist who felt inconvenienced by having one lane of the bridge shut down during the inspection. Inspectors said they even had object thrown by passing drivers as they were trying to do an inspection.

Your Comments, Thoughts, Questions, Ideas

Tom Starling's picture

I'm glad that somebody is taking the factor of bird droppings seriously. In the quantity in which they were present the bird droppings very well could have been seriously corrosive, as well as the visual obstruction they provided.

A simple bird control program, like bird spikes in some key areas, could have eliminated this factor all together.

posted on Fri, 08/10/2007 - 12:11pm
sandy09's picture
sandy09 says:

This is a very interesting thing to blame the collapse on!!!

posted on Wed, 10/15/2008 - 8:37am
mkp_rocks's picture
mkp_rocks says:

Weird how a bird could have contributed to the collapse. It's really not their fault!

posted on Wed, 10/15/2008 - 8:38am
gcy09's picture
gcy09 says:

I didn't know that pigeon poop could be such harm!!! Acidy??? What the HECK!!!

posted on Wed, 10/15/2008 - 8:44am
dennisvang's picture
dennisvang says:

i think the poop from the pigeons made the briged more brittle

posted on Wed, 10/15/2008 - 9:46am
chang's picture
chang says:

Very intresting of how they think that the pigeons poop contributed to the collapse of 35W.

posted on Wed, 10/15/2008 - 9:57am
Cristian's picture
Cristian says:

I find surprising that big accident could have been related to those little birds

posted on Wed, 10/15/2008 - 9:59am
guallpa321's picture
guallpa321 says:

WOW!!! I never knew pigeons nest in a box in the bridge

posted on Wed, 10/15/2008 - 10:00am
Petey28's picture
Petey28 says:

so how exactly did pidgeons do all that?!

posted on Wed, 10/15/2008 - 10:03am
darcyb's picture
darcyb says:

wow didn't know pigeon droppings would lead to decay of a bridge.

posted on Wed, 10/15/2008 - 10:05am
margarita's picture
margarita says:

so in this article i found that it was interesting that spider webs kinda had something to do witth that bridge collapse. i aslo found out that pigeion droppings [poop] caused the bridge to collapse as well!

posted on Wed, 10/15/2008 - 10:06am
jorge sanchez's picture
jorge sanchez says:


posted on Wed, 10/15/2008 - 10:07am
rayiaharris's picture
rayiaharris says:

that must have been a lot of pigeon poop in order to help the bridge collapse!!!

posted on Wed, 10/15/2008 - 10:10am
Alvarado's picture
Alvarado says:

Its hard to believe that pigeons could cause such bad damage.

posted on Wed, 10/15/2008 - 10:10am
Ahus1102's picture
Ahus1102 says:

I am really suprised that spider webs had to do something with the clopse of the bridge but Could the spider have some more effects of the next bridges how could we control the spiders not to cause any more bridges to clop.

posted on Wed, 10/15/2008 - 10:10am
warda05's picture
warda05 says:

this article was very intresting, funny, weird, and sad.
it was interesting because, you would never think peigons or birds would cause all of this.

posted on Wed, 10/15/2008 - 10:12am
Alvarado's picture
Alvarado says:

Why would people think that a spider web can look like a crack?

posted on Wed, 10/15/2008 - 10:12am
Najah Abdirahman's picture
Najah Abdirahman says:

Very interesting, I would have never thought that pigeons would be such a problem or produce droppings that would actually corrode steal beams.

posted on Wed, 10/15/2008 - 10:21am
msanchez's picture
msanchez says:

I was surprised that pigeons had to do with the bridge collapsing because I didn't think pigeons were a big problem. However, they were.

posted on Wed, 10/15/2008 - 10:24am
Marisol's picture
Marisol says:

I was surprised thet pigeons had anything to do with the bridge collapsing and that they had made it more fragile.

posted on Wed, 10/15/2008 - 1:03pm
wilson's picture
wilson says:

I think that the pidgeons poop could probably be a cause to the collapse. Also because it human or animal waste theirs some acid and it can cause for it to make holes in steel. The collapse was really tragic but i never had any idea or clue that pidgeons or spiders had anything to do with it.

posted on Wed, 10/15/2008 - 1:16pm
lmen1001's picture
lmen1001 says:

That's kind of sad that something like a pidgon's poop help cause this tradgy. o.o'

posted on Wed, 10/15/2008 - 1:22pm
JenniferSwanberg8's picture
JenniferSwanberg8 says:

I thought it was interesting that the pigeon poop was a problem for the inspections of the bridge!

posted on Wed, 10/15/2008 - 1:23pm
linda-thao's picture
linda-thao says:

Its surprising that they would think its pigeon poop that effect the 35w bridge to collapse. But at the same time, they said it did make the bridge heavy. Some spots were cover with plastic and makes it more difficult for inspectors.

posted on Wed, 10/15/2008 - 1:24pm
ccha1002's picture
ccha1002 says:

They say tha the pigeons dropping made the bridge corrosive faster, but on the news they said that plates was not big enough. The plates was thinner and it rust faster. Humans tend to try blame things on other things and don't want to face the fact how things go down.

posted on Wed, 10/15/2008 - 1:30pm
wraithdrudge's picture
wraithdrudge says:

i agree, the fact that someone is looking into all the possible scenarios as to what caused the bridge collapse.the fact is the bridge was crudly built,and was an eye-sore.the pigeon poop was not what brouht the bridge could have helped but alone it would have taken far longer than given.

posted on Wed, 10/15/2008 - 3:00pm
birdmaster bird control's picture

The acidity in pigeon (bird) droppings defaces stone and metal, attacking the substrate of a building to cause permanent damage. It is important to understand when and where pigeons come home to roost. It can save businesses countless dollars by knowing which parts of a building to bird proof and which parts don't need it.

posted on Wed, 11/11/2009 - 8:16am

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