Chattanooga 1-75 N to I-24 W Overpass Partial Collapse
Chattanooga 1-75 N to I-24 W Overpass Partial Collapse
(OP)
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




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




RE: Chattanooga 1-75 N to I-24 W Overpass Partial Collapse
RE: Chattanooga 1-75 N to I-24 W Overpass Partial Collapse
The interesting part I got from the news is this bridge was scheduled for 2019 rehabilitation. So the owner new it was bad and they made a plan to fix it but it failed before it was fixed. So is there any real discipline for the owner, unlikely as this is public infrastructure. If this was a private bridge crossing from industry would it be the same outcome, i think not. I believe if this was a private bridge crossing there would be civil and criminal investigations launched with financial penalties and charges against executives and the company.
RE: Chattanooga 1-75 N to I-24 W Overpass Partial Collapse
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
RE: Chattanooga 1-75 N to I-24 W Overpass Partial Collapse
https://www.timesfreepress.com/news/breakingnews/s...
RE: Chattanooga 1-75 N to I-24 W Overpass Partial Collapse
https://newschannel9.com/news/local/watch-live-t-d...
RE: Chattanooga 1-75 N to I-24 W Overpass Partial Collapse
On the link is the inspection report from 2018.
RE: Chattanooga 1-75 N to I-24 W Overpass Partial Collapse
Rather than being scheduled to be fixed, it was actually scheduled for demolition due to the interchange being reconfigured.
RE: Chattanooga 1-75 N to I-24 W Overpass Partial Collapse
The theory is that an oversized load impacted the overpass at some undetermined time prior to the collapse. The evidence supporting this is that five of the tension cables along the base of the beam are cleanly cut in a straight line.
Here are some screen captures of the cut cables.
RE: Chattanooga 1-75 N to I-24 W Overpass Partial Collapse
In the street view shots it looks like the span may have been previously repaired based on the irregular concrete lines. From the incident shots it looks like the tendons are cleanly cut which speaks of a repair, perhaps improperly executed. The failure near mid-span (directly above the left lane) also suggests a pre-existing weakness in the tendons at that point. The bridge file of record should show the repair history.
Interesting that the clearance was not posted on the span.
Edit: Here is a link to the location. The irregular concrete lines could just be distortion where the street view photos are stitched together.
https://www.google.ca/maps/@35.0029472,-85.2119007...
Another edit, sorry:
Is it not irresponsible to say on the one hand that you have no idea why something happened and then simultaneously express confidence that it cannot happen again?
Also what is the point of this kind of amateur damage control by TDOT? Their own spokesperson doesn't seem to understand how the bridge is constructed and the significance of the failure.
RE: Chattanooga 1-75 N to I-24 W Overpass Partial Collapse
RE: Chattanooga 1-75 N to I-24 W Overpass Partial Collapse
Nothing stands out to me, but my specialty is electrical, not civil.
https://goo.gl/maps/ZcJ784ULDdz
RE: Chattanooga 1-75 N to I-24 W Overpass Partial Collapse
Suppose an oversized load on top contacted the railing and forced it off of the support on the left.
Could the damage to the span and railing have happened when one end of the span hit the ground?
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Chattanooga 1-75 N to I-24 W Overpass Partial Collapse
RE: Chattanooga 1-75 N to I-24 W Overpass Partial Collapse
Reading charliealphabravo‘s post got me wondering if a truck hitting the beam would cut the strand cleanly like they show in the picture. If the strand they used in the 50’s is like what we have now I would expect it to bend before breaking. Prestressing plants regularly harp the strands a considerable amount with no problems. Plus to cut the strand the impact would have to cut through the concrete. I would imagine the concrete would take the brunt of the impact.
RE: Chattanooga 1-75 N to I-24 W Overpass Partial Collapse
RE: Chattanooga 1-75 N to I-24 W Overpass Partial Collapse
I am not abandoning my thought that a wide load may have tagged the railing and pushed it off.
I may be wrong so I'll wait and see.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Chattanooga 1-75 N to I-24 W Overpass Partial Collapse
RE: Chattanooga 1-75 N to I-24 W Overpass Partial Collapse
RE: Chattanooga 1-75 N to I-24 W Overpass Partial Collapse
RE: Chattanooga 1-75 N to I-24 W Overpass Partial Collapse
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.
RE: Chattanooga 1-75 N to I-24 W Overpass Partial Collapse
RE: Chattanooga 1-75 N to I-24 W Overpass Partial Collapse
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:
RE: Chattanooga 1-75 N to I-24 W Overpass Partial Collapse
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):
RE: Chattanooga 1-75 N to I-24 W Overpass Partial Collapse
Why was this pic not in early reports?
RE: Chattanooga 1-75 N to I-24 W Overpass Partial Collapse
RE: Chattanooga 1-75 N to I-24 W Overpass Partial Collapse
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
RE: Chattanooga 1-75 N to I-24 W Overpass Partial Collapse
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Chattanooga 1-75 N to I-24 W Overpass Partial Collapse
RE: Chattanooga 1-75 N to I-24 W Overpass Partial Collapse
RE: Chattanooga 1-75 N to I-24 W Overpass Partial Collapse
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.
RE: Chattanooga 1-75 N to I-24 W Overpass Partial Collapse
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: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm
RE: Chattanooga 1-75 N to I-24 W Overpass Partial Collapse
TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm
RE: Chattanooga 1-75 N to I-24 W Overpass Partial Collapse
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.
RE: Chattanooga 1-75 N to I-24 W Overpass Partial Collapse
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.
RE: Chattanooga 1-75 N to I-24 W Overpass Partial Collapse
RE: Chattanooga 1-75 N to I-24 W Overpass Partial Collapse
Link
RE: Chattanooga 1-75 N to I-24 W Overpass Partial Collapse
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.
RE: Chattanooga 1-75 N to I-24 W Overpass Partial Collapse
Obviously the photo is spliced but crack just below the photo splice?
RE: Chattanooga 1-75 N to I-24 W Overpass Partial Collapse
I think your second photograph shows the barrier on the approach span, not the main span that failed.
RE: Chattanooga 1-75 N to I-24 W Overpass Partial Collapse
Yes I agree. I was looking at the incorrect section on the top side. Thanks for your fantastic input. It would be interesting to read the report on this.