I-85 fire: Section of Atlanta highway collapses

[knight1fox3]

http://www.cnn.com/2017/03/30/us/atlanta-i-85-fire/index.html

 

[canadagoose]

Aren't highways in the US mostly concrete?  How does that burn?

 

[NJmike PE]

Hmm, steel structure collapsed from only a fire load.....

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[Road Guy]

the one good thing about a fire is that they will be able to trace what started it within a few days. My ATL friends are already pointing to some conspiracy theory about some old rolls of conduit stored under the bridge from a project that went south a few years ago as the "fuel".. But I would think you would need some major accelerate (gasoline, etc) to get a bridge to burn.. but yes anything can burn..

Traffic is going to be so ******....

 

[roadwreck]

This is the image that is being circulated that is prompting the "rolls of conduit" theory.  The conduit wouldn't just spontaneously combust so there had to be something else that sparked the fire.  My guess would be urban outdoors-men...

GDOT stores a lot of crap under this bridge.  I know they park HERO (Highway Emergency Response Vehicles) under another portion of the bridge.  When the fire was initially reported I assumed it was those burning.  I'm betting there will be a new directive from GDOT soon dictating that nothing should be stored or placed under bridges.  

 

[Road Guy]

that (storage) probably happens all around the country though.

So is that photo from before the fire "went crazy"?  I am not fire expert but it just doesn't seem to me that there is enough plastic there to generate enough heart to burn a concrete bridge?

 

[NJmike PE]

that (storage) probably happens all around the country though.

So is that photo from before the fire "went crazy"?  I am not fire expert but it just doesn't seem to me that there is enough plastic there to generate enough heart to burn a concrete bridge?

It all depends on how long the fire continued to grow. In it's "growth" stage, a fire doubles in size every 30 seconds. If it's inaccessible, then that would only add to the delay in supressing it

 

[NJmike PE]

another thing to consider is what was in those "storage" containers. They clearly were not empty and I doubt it was plastic alone that generated that heat. Whatever the accelerant was, it burned hot enough and long enough to weaken the steel connections.

 

[thekzieg]

I don't do road design, so I'm not sure about the typical assembly, but it looks to me like the fire melted the expansion joints causing the rebar to become exposed, the rebar then weakened and the whole section collapsed under its own weight. I don't think there's any other way to get such clean break lines on both sides of the collapsed span without it being an expansion joint failure.

 

[Road Guy]

its just rolls of conduit, no containers that I could see (google street view)

 

[Road Guy]

the bridge beams usually sit on the bridge "cap" (abutment) usually there is a foot or so of the concrete beam that rests on the cap, which supports the load. It would have had to burn hot enough to melt that overhand enough to allow it all to break clean.. from the pics I saw on news it looks like the "caps" are still intact somewhat

not sure how old this google street view pic is but there is a lot of conduit, maybe that would be enough. but you have to think it would have taken some serious flame to get that going..

 

[NJmike PE]

The report should be interesting. Definitely going to be some finger pointing involved

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[Ship Wreck PE]

Did RG design that road?

 

[TNSparky]

the bridge beams usually sit on the bridge "cap" (abutment) usually there is a foot or so of the concrete beam that rests on the cap, which supports the load. It would have had to burn hot enough to melt that overhand enough to allow it all to break clean.. from the pics I saw on news it looks like the "caps" are still intact somewhat

not sure how old this google street view pic is but there is a lot of conduit, maybe that would be enough. but you have to think it would have taken some serious flame to get that going..

View attachment 9284

Holy cow! That street view pic is from November! I doubt they had moved any of that material since then (assuming that's the portion that collapsed). I didn't realize conduit could burn that hot. Guess I learn something new every day.

 

[Road Guy]

Did RG design that road?

lol - I did some design on I-85 further north and way further south back in the day, but that's not my viaduct!

 

[Road Guy]

this pic shows the cap is still mostly "there"  check out the column (can barely see at the bottom) looks like another section of the bridge each side will also have to go.

 

[NJmike PE]

damn, so the girders failed..... all together?

 

[csb]

I'm glad they are tied off and wearing hard hats. 

 

[thekzieg]

Safety first. Always.

 

[EB NCEES REP]

those look like surveyors who are not smart enough to listen

I think this will work until they get it fixed - just change direction for AM / PM Rush Hour