Chattanooga 1-75 N to I-24 W Overpass Partial Collapse 6

[Sym P. le]

Maintenance? What maintenance?

TDOT indicates this bridge was constructed in 1959 and last inspected July 2018.

The tree at the east support looks out of place and the gap between the beams (visible from underneath) on the west support looks odd. It also seems that the purchase on the west support was less than optimal. I hope the driver makes a complete recovery.

Image posted by Chattanooga Fire Dept.

From Google Earth

 

[charliealphabravo]

The first photograph in Sym P. le's post is a closeup of the second photograph.

The broken/cut strands are just to the left of the left deck drain (I see two drains in the street view) and are directly over the left lane where the member broke. They look like bottom strands, harped pre-stressing strands I'd guess in the box beam, and at the leading edge of the structure with respect to traffic.

Sorry another edit:

Perhaps someone who has more experience with precast could identify the steel plate near the end of the broken strands. I'm thinking that might be an embedded component used to depress the strands during the original prestressing.

 

[BridgeSmith]

Likely cause of collapse was impact from overheight load

 

[charliealphabravo]

It looks like the ENR story is mostly based on the statements of the DOT talking heads from a couple of weeks ago which don't seem to be very sensible. I'd like to see the results of the forensic investigation they mentioned.

It's hard for me to imagine that a vehicle could strike the bridge as described and not leave a debris trail 2 lanes wide and 100 yards long and no witness marks on the other box beams. And to cut half a dozen embedded strands so cleanly with a high speed impact is inconceivable. The ENR story doesn't mention that one "railing" was reported as previously repaired which is where I would think an investigation would start since the strands look like they have been prepared for couplers like these:

 

[Ingenuity]

...sliced through five 3⁄8-in.-dia reinforcing strands in the beam...

It appears the strands are only 3/8" diameter - however, severing strands of any diameter with such a clean-cut does appear unlikely.

FYI - strand couplers of the type above are not usually used in pretensioned strand repairs, usually GRABB-IT splice chucks are used (similar principle), with the added feature of being able to (partially) re-tension the individual strands (like a turnbuckle):

 

[Phil1934]

Why was this pic not in early reports?

 

[3DDave]

Because that photo is a fake.

 

[JohnRBaker]

Yes, look at the tires on the trailer. You can see where they're photo-shopped from an image where they were sitting on pavement as you can see the 'flat' spots.

John R. Baker, P.E. (ret)
EX-Product 'Evangelist'
Irvine, CA
Siemens PLM:
UG/NX Museum:

The secret of life is not finding someone to live with
It's finding someone you can't live without

 

[waross]

Forget the tires. That trailer is defying the law of gravity. What's holding the trailer up in the air?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[3DDave]

Helium delivery. It happens sometimes. If they load up with too much, they send a plane up to shoot them down. It would happen more often but helium is expensive and the bill for shooting a trailer down from 20,000 ft is more than most trucking firms are willing to risk. Thankfully the tractor held this one down.

 

[TenPenny]

That's definitely a comment on the quality of Swift drivers; there are many comments, such as Swift standing for 'sure wish i'd finished training' and ' swing wide, its a fifty-three'.

 

[bridgebuster]

Maybe he was on his way to Party City. I read a story this morning that they're shutting down upwards of 75 stores because of a helium shortage.

 

[IRstuff]

"Maybe he was on his way to Party City. I read a story this morning that they're shutting down upwards of 75 stores because of a helium shortage."

This is getting dire; we need to get the fusion industry up and running so that we can have our party balloon helium as a by product of generating power...

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[IRstuff]

One thing that lends credence to the collision hypothesis is what appears to be a slight shortage of debris after the beam dropped, but one would think that any collision that cut through the cables would have left debris on the roadway that someone had to clean up, so why wouldn't they have reported the damage to the beam?

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[charliealphabravo]

@Phil1934

Don't feel too bad about getting fooled. The photoshops and viral video fakes are getting better and more common. I'm still a bit embarrassed over that video of the kid that built wings and took off by flapping his arms like some kind of pterodactyl. It should have been immediately obvious as impossible but the presentation was good and I forgot my common sense.

 

[3DDave]

CAB, Check Captain Disillusion on YouTube.

Probably the fake was just a jab at Swift. Of the several bad-trucking videos I've seen, I recall more than one trucker getting really angry and not surprised as a Swift driver shaves the mirrors off a parked truck trying to back a trailer into place or tears the fenders off a parked one while taking a turn too tight.

 

[Spartan5]

Looks like another MCAS malfunction to me.

 

[Kwan]

I'm not sure if anyone has already brought this up, but it's interesting to look at the street view from google maps. Looks like cracking in the barrier wall and road.
Link

 

[charliealphabravo]

I hadn't thought to look at the street view for the overpass.

You can see that the spans are continuously paved without exposed expansion joints, perhaps because the spans are short. The transverse pavement cracks appear at the ends of each of the three spans so they probably aren't significant.

There is evidence of a rather hard strike on the barrier, directly above where the span eventually failed.

Edit: Another angle showing direct damage and possible indications of rotation.

 

[Kwan]

This is what I see. The bottom side seems to have crack which is located close to the breaking point. The topside looks like a crack located at breaking point but may just be trash or something. It has a white appearance so maybe someone tried to fill it (however, it's just blurry enough cause question about a crack)? There is definitely strike damage on both sides of the road. Google maps is cool!

]
Obviously the photo is spliced but crack just below the photo splice?

 

[charliealphabravo]

It is hard to distinguish between form lines and cracks with these poor quality photographs, but it does look like a crack in the first and second beam where you indicate. Also from the incident photographs it is hard to tell if only the beam on the leading edge (including the barrier) failed or if maybe more than one beam failed.

I think your second photograph shows the barrier on the approach span, not the main span that failed.