Well that is definitely "Breaking" News!
On I-40 no less.

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There's an earlier thread (by six minutes) on this topic:

https://www.eng-tips.com/viewthread.cfm?qid=483070

John R. Baker, P.E. (ret)
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Old news.

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It's hard to see what's happening there with the structure. I wonder if it's passed tension into the bridge deck?

Also, that's a weird looking failure. It's not what I would picture for a tension failure, but it doesn't look like anything else I can think of. I can't say I've even seen a photo of a tension failure at that scale, so maybe it's just too big for the things you would expect to see. Or maybe it was brittle. It's also kind of surprising that it didn't happen at the connection zone chocked full of holes half a member depth away.

Is that what a progressive fatigue fracture looks like on a tension member?

Tied arch bridge. When the tie fractured, it didn't go far, so the bridge compensated by taking the load on that side in truss action. I am not a bridge engineer, but to me, that looks like the desirable redundant type design often talked about.

Yes, that does not look like a typical tension failure of a ductile material. Could it possibly be the result of very low temperatures during the winter?

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I think it may have to do with the earthquake damage mitigation changes that put high alternating loads into those members via friction pads rather than the typical rocker arrangements. That was 20 years ago, so 5000-7000 fully reversing cycles found a weak spot. It was last inspected about 2 years ago, so that's up to 700 cycles; if the fracture started on the inside at a weld defect it could have gone this distance since then.

There are other longitudinal members than the one that fractured. The structure along the sides seems to be intended to distribute any uneven loads to multiple cables and to stiffen the overall bridge deck to prevent unwanted deformations. The bottom chord is not the only one resisting the thrust load from the arch.

3DDave,

Do you have some drawings of the bridge? By the limited photos we have seen, I fail to understand what other tie members you mean.

EDIT: Scratch my comments below. I, like others was assuming the deck was a truss it isn't. You can see quite clearly from google street view:

It seems that the 'beam' in question is a strut in the lateral restraint system.

Quote (TLHC)

Also, that's a weird looking failure. It's not what I would picture for a tension failure

I don't think that area is tension I believe it would be compression from hogging about the supporting tie.

Quote (hokie66)

Tied arch bridge. When the tie fractured, it didn't go far, so the bridge compensated by taking the load on that side in truss action. I am not a bridge engineer, but to me, that looks like the desirable redundant type design often talked about.

Did the tie fracture? I didn't hear or see about this detail.

From what I can see the truss failed at a spot that is likely under compression due to the hogging close to the tie support. Load was likely redistributed to other sections of the truss and more tension on the deck.

Cause of failure likely corrosion/fatigue but certainly outside my area of expertise.

Brittle fracture? no signs of triaxiality, stress risers, or weld? Dunno why it 'broke'.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

Kinda looks like shear rupture. Especially noting that is about one section depth away from the end of the portion reinforced with plates.

and more...
"The US Coast Guard also put a waterway restriction in place on the river below, and there were at least 44 vessels with more than 700 barges waiting to travel the river in either direction Thursday morning, according to Lt. Mark Pipkin of Coast Guard Sector Lower Mississippi River."

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

The purpose of the tie is to keep the arch from kicking out. The broken tie could be affecting the stability of the foundations.

That would be my main concern, bridgebuster. They should make at least a temporary repair quick smart. Just because it hasn't moved much yet doesn't ensure it won't.

I guess they would need to 'jack' it back in place so that sides of the box beam line-up, and then weld some scab plates all around. Granted, it would only be a temporary repair, but it should be good enough to get by until they decide how they're going to proceed overall.

John R. Baker, P.E. (ret)
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If that is the arch tie that was severed, I think you need to find out where that force went before you can propose a 'fix'. Is that tension force now going through the deck? Or lateral bracing system? Can the foundations handle any new longitudinal forces/deflections from the sudden thrust? So much we don't know and we're all making our best guesses from some online photos. But my gut is telling me this isn't going to be a quick fix by any sense.

Another photo, under the bridge.


Bigger image: Link

epoxybot, that picture jibes better with this description I read of the crack here:

https://www.usatoday.com/story/news/nation/2021/05...

Quote:

Degges explained the structure and the crack like this: The box beam is made of steel panels that are a little under 2 feet wide and about 32 inches tall. Those four plates of steel are welded together, but three of the plates have separated, by a fraction of an inch. The bottom, fourth piece of the box beam has a crack that's about 20% the width of the steel, he said.

Maybe that helps people here hypothesize about the failure mechanism.

JohnCE920,

That is the arch tie, and is also a chord of the lateral truss. The force is not there anymore, so the gravity load is being carried by the arch/truss, I suspect mostly by bending of the two span truss, but still partially by overall compression of the arch. As noted before, this structure has exhibited excellent redundancy, as total separation of one vital member has resulted in only minor movement. But it needs at least temporary restoration of the tie before it can be placed back into service.

hokie66,

I agree with all you've said. And yes, the redundancy of this structure clearly saved lives this week (or whenever the fracture actually occurred).

I was referring that when the tie fractured and the arch thrust was no longer contained by that member, something had to have taken its place. Maybe the foundations simply 'handled' it. Maybe it went through the deck / lateral bracing system. I do agree there is now no forces in that tie. I get the feeling we're saying the same thing just differently.

My question for the board is HOW do you restore an arch tie? Seems like you'd need to post tension a tie to try and reclaim some of that dead load thrust back into the tie.

That is a good question, and I don't know the answer. My inclination would be to live with the displacement, and just restore the member. But the bridge engineers may have different ideas.

Does anyone have a clearer image of the bridge drawing? It might show the member forces.

How did they tighten those bolts. Someone had to hold the nut from the inside. I wonder if there is a hand hole anywhere near.

Could there be some torsion in the main tie beam. The main transverse floor beam is suspended by a single rod and pin. When a truck is on the bridge, the floor beam deflects down, which causes the end to rotate. This rotation imparts a torsion into the tie beam.

It seems to me that the arch truss would have a significant ability to span on its own as a normal truss (i.e compression in the top chord and tension in the bottom chord), if it needed to once the tension tie is removed.

Although, I'm guessing it wasn't designed that way. I assume the arch action was considered and the overall behavior of the arch truss was that of a single compression arch member with these tension ties at the deck level resisting the thrust. I'd very curious to know how that was analyzed at the time of design 50 years ago.

I agree with that assessment abusementpark. That arch looks stout and able to take a lot. But those end piers aren't very stiff in the longitudinal direction (maybe that's a good thing for today). I doubt they were analyzed for taking that thrust and wonder how they're holding up right now.

I'd be curious to know how a bridge like this was analyzed back in the day too. I'd also settle for a set of As-Builts that are scanned in a little crisper than the one sheet the DOT released.

Is the subject arch connected to the second arch in a way that it may be proving some counter to the longitudinal thrust?

Roy,

It is a two span tied arch bridge, and the trusses forming the arch are integrated at the center support. However, the thrust at the end where the tie is broken is still there. Continuity in the trusses means that the thrust is less than would be the case if these were two simple spans, and that is part of the fortunate redundancy here.

Thanks for the explanation. I only recently found this site, and, having more thorough grounding in railroad investigations, this site and its' participants are very much appreciated.

Apparently crack has been there since 2019. Link

Interesting that the crack is two years old, and only recently was it a problem... maybe somebody not doing their job?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

The seismic prep report in the other thread tells what the loading is like on these members.

https://www.tntech.edu/engineering/pdf/cee/Alexand...
STRUCTURAL HEALTH MONITORING OF THE HERNANDO DESOTO BRIDGE

There was a crack which got to critical crack length... Its no longer a crack after fast fracture..

I don't give that Tweet much credence. To me, it doesn't look like the same place on the bridge, and I can't tell if that line is a crack or not.

It certainly seems like the same spot to me. Many details do line up.

(Though I won't bet all my credibility on it as I already feel slightly abashed by not recognising earlier in this thread that this was an tie for the arch.)

I see it now, human909. It is on the north (upstream) side of the bridge. I thought it was on the south side.

Here’s the 911 call from the inspector stating the need to stop traffic immediately.

https://www.commercialappeal.com/story/news/2021/0...

He was quite a bit more calm than I would have been. I feel my reaction would have been more akin to Bruce Willis in Die Hard when he's talking to the dispatcher on top of Nakatomi plaza.

https://www.youtube.com/watch?v=MTb7UQrHofQ

"To demonstrate the power of Flex Tape, I broke this bridge in half!"

CrabbyT-
This is a serious engineering forum.
That was hilarious. [bigsmile]

Brad Waybright

The more you know, the more you know you don't know.

Not a bridge engineer, but just looking at the number of bolts in the that box beam's web splice plates there looks to be better than a 1,000,000 pounds of bolt shear capacity. Assuming such significant tension? load I would have expected major/significant splice plates on the top and bottom also to better engage the entire box beam and smooth out the load transfer and associated stresses when load is transferred from the splice plates to the box beam section. Wonder if that splice detail gives rise to unforeseen stress concentrations then along with cycling/fatigue you have what you see. Of course this is assuming that entire box beam section is required design wise. Going to be interesting to see the final report on the root cause.

River traffic has been reopened, and an an interim fix using "steel rods to span the fractured section" is in design:

https://www.commercialappeal.com/story/news/2021/0...

Update: more details from TDOT:

https://www.tn.gov/tdot/news/2021/5/14/update-on-t...

Structure was behaving unsymmetricaly back in 2017. If I'm interpreting structural monitoring report properly (from 3DDave above), span with fracture was showing reduced loading from temperature forces back in 2017, which resulted in new bearings not moving anywhere near the amount as the ones on the other end. This was interpreted as possibly the result of foundation movement. In light of this failure one could draw other conclusions.

And it looks like the tension ties had strain gages on them. Assuming they were still collecting data, it's hard to imagine that this crack propagation was not immediately noticed.

Two more photos




Link

Given that photo, I feel like opus might be on to something and this is maybe shear lag related.

From the amount of rust visible, it would seem that this break has been there for awhile.

John R. Baker, P.E. (ret)
EX-'Product Evangelist'
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https://www.ardot.gov/divisions/public-information/40-ms-river-bridge/

More photos in here.

Not recent, and I don't think I could have cut that member that nicely; I cannot imagine how it failed so cleanly... as the doc noted... maybe the duct tape failed.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

No bifurcation to indicate fatigue and no plastic deformation. Not qualified to make this observation but this failure looks brittle.

Such a clean, straight break - I can't help wondering if it's a failure of a butt weld, rather than failure through parent metal?

http://julianh72.blogspot.com

Quote (https://www.ardot.gov/divisions/public-information...)

"In May 2019, a video shows the evidence of the damage on the lower side of the bridge. ARDOT is now investigating to see if that damage was noted in a September 2019 inspection report and, if so, what actions were taken." ... The agency likely will release an image from the May 2019 inspection Monday, Parker added.

Stay Tuned

I cannot imagine a weld failing that cleanly...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

My understanding is that highway departments have long has a distrust of welded structures, and particularly field welds. The box section could be a weldment, built in a shop. The field connections are all bolted. The box looks big enough that a worker can get inside so handholes for access to tighten the nuts are not necessary

While this beam acts as an arch tie, it was installed after the arches were complete. Here is a picture from the March_1972_issue_of_Memphis_Press, showing the arch prior to the arch sections being joined. Note that construction support towers were used at this stage of the construction to balance the structure.

Quote (handholes for access to tighten the nuts are not necessary)

I hope he got out OK...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

It looks like there was a weld that split.; I don't think that's a shadow.

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...in a straight line?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

Since the failed member is no longer carrying load, it would seem to be appropriate to removed the failed section and replace it with a another section, The failed section would need to be sent to a metallurgist for analysis, and the new section ( and others ) monitored with strain gauges attached to a data aquisition system and the real loading measured and analyzed after passing a significant load across the bridge. Nowadays, with the low cost of such monitoring, it might become normal for all bridges to have such as-built stresses monitored after initial construction.

The original equipment QC documents should be accessed and reviewed to confirm that initial material specs and fabrication details were not compromised. The metallurgical analysis might give a clue to possible fabrication issues- there have been other material issues with metals supplied from overseas ( aka PRC) steel mills with false shipping documents. It could also open up a host of other issues, disqualifying other sections.

It also happens that some truckdrivers know how to bypass the weigh scales and there may have been higher than design axle loads ; it is not clear how to review past load history.Tennessee does have some industries that ship XX heavy loads.

"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick

To my eye, the second image I posted on 14 May 21 21:50, does not look like the member has completely separated. It also looks like a small crack is progressing from the opposite side, just to the right.

Quote (there have been other material issues with metals supplied from overseas ( aka PRC) steel mills with false shipping documents.)

I was involved with a major project in Winnipeg several years back where the 8" and 10" pipes failed at 1/10 their rated capatity. The mill test certs were identical with the exception of the test number... also from your overseas location.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

If fatigue or metallurgical, I wonder what other parts of the structure are affected. I understand with fatigue, it is often difficult to determine the extent.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

This image shows it better; the top plate of the beam is separated from the inboard vertical plate.

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Here is another photo linked above by @azcats : https://www.ardot.gov/wp-content/uploads/2021/05/c...

I assume this is the same location, so it appears that the cracking started at the bottom, outer corner. (the current photos show that the bottom plate is not yet fractured).
I can't believe they would leave a crack at least 80% of the web height, without even trying to drill out the crack tip to prevent it from progressing.

This is from this video which was made in 2019.

Bridge inspector also fired this morning.

https://www.youtube.com/watch?v=qmbeDO53TK8

per Wiki, the bridge was constructed in the period 1967-1972, prior to trade with the PRC, so that issue is not applicable. It may yet be a metallurgivcal issue, so let the metallurgical experts figure it out.

During that time period, some CS components fabricated in Spain had metallurgical issues, so it might be useful to review the QC documents , at least regarding the source of the steel.

"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick

Some of the information starts to make sense - the picture from above (IRstuff) indicates that the shape of the crack has turned the beam (Really stiff in tension) to a sort of spring (still stiff but much softer than the opposite side, which is uncracked), This could explain the asymmetrical behavior reported by TheGreenLama.

Incredible video. They certainly like flying their drone.

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and...

Well ... they're more interested in the paint on the gusset plate.

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Funny harmonic and unsymmetrical normal road loads?

Ie there are lorry's full always going in one direction and then empty going in the other direction?

No lorries on this bridge, but lots of trucks. Most of them would be loaded.

An example of the common language which divides us.

Quote (https://www.merriam-webster.com/dictionary/lorries)

lorry noun
lor·​ry | \ ˈlȯr-ē
, ˈlär- plural lorries
Definition of lorry

chiefly British
: motortruck

Also in the new image is the bolted cover for the access hole. They likely has some very small workers on the crew to use an access hole in this location. I would think stress would be higher at the access hole, then the crack location.

You can only think that someone thought that crack was just some sort of surface mark unless they were only watching it live on the little screen the inspector is using. You just wouldn't see it on that.

That pole sparweb pointed to isn't structural, it's a drain pipe from the roadway, but has been hit by something.

Were the vertical cross spars added later?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

A few thoughts on the photo. Repairs are going to be extensive.

The vertical 'pipe' that appears on the right in the photo above is likely just a drain pipe extension, i.e. non-structural.

I can't help coming back to just being thankful that this bridge had enough internal redundancy to prevent a collapse. This bridge was labeled by the DOTs as Fracture Critical and that tie is likely the main reason for the designation. And this FCM has had an enormous fracture for the last few years.... Just thankful no one ended up getting hurt or killed by this.

And that inspection drone video is hard to watch. I know we're all looking for the crack while the inspector is looking at the hangar... but wow. Its such a large crack even then. How do you miss that?

Perhaps they just thought it couldn't be a crack, but some oil or bird sh1t or something like that.

As said we don't know if they looked at it ever again on a big screen or just that little 9 inch hand held thing in the bright day light.

This time the crack was visible to the naked eye looking down from the deck so a lot more visible.

But there do appear to be more visible cracks in the tie so I wonder if they are now doing a rather more thorough inspection while the bridge is closed...

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

HUA looking through a dirty navel lens.

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I am glad we are speculating about how the inspector missed an obvious clue, rather than discussing how a major bridge collapsed in operation!

Possibly the "gorilla" problem? While fixated on one topic, the brain ignores others. But I would have thought an inspector would be proactively looking at every detail, certainly I often find faults while looking for something unrelated. I would be at least tempted to fly the drone in for a closer look, if not break out the climbing gear. I guess their employer felt the same.

> How do you miss that?

Yeah.

To be fair, according to ARDOT, that drone video came from the contractor (Michael Baker) who was only hired to inspect the arch and cables, and that snippet was apparently part of a 5 hour long video that included a similar video of every other cable. I certainly wouldn't expect the operator staring at a tiny screen in broad daylight to find features like that, I assume it's all meant to be reviewed later.

I'm not at all familiar with how these inspections work, but perhaps the drone video is 'backup material' used when you have some question about a more primary type of inspection? Drones being a 'new technology', I could well imagine it is not considered a primary source for such processes.

ARDOT themselves inspected the bridge 6 and 18 months later, supposedly focusing only on these fracture critical elements, and didn't see it. So two different teams, on three separate occasions, all missed it. Lots of 'opportunity' for process improvement, it would seem.

This is all in the press conference video:

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

Craig Neth,

If that drone is a team that specifically looking at the hangar / arch system. Sure I can see not getting that. But the fracture critical member of the structure would have been looked at closely. My experience in working with bridge inspectors doesn't cover a structure like this but I would assume a snooper truck being used to check under the bridge and get the inspector about arms length away from this.

I do agree that there is a lot of room for improvement here. And knowing the inspector was let go, its likely a person that didn't follow the inspection process. Its just a scary thought to think this crack was present for over 2yrs.

Quote (https://www.tn.gov/tdot/news/2021/5/17/tdot-awards...)

We now have a webpage dedicated to the bridge repair: https://www.tn.gov/tdot/projects/region-4/i-40-her.... You can also follow @myTDOT on social media for the latest.

just for my interest whats the likely fix for this?

Replace the whole beam or just strap patch it

First thing I would do is to find the cause, and if there are other locations where this could happen. I've not seen a failure like this and I'm not sure why it happened. Then I consider the manner of fixing it.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

Per one of the TNDOT press releases, sequence is something like

• Stabilize the crack
• Design permanent repair
• Install jig to allow installation of replacement beam
• Install replacement Beam

If more cracks are found - repeat as many time as necessary.

Reopen for traffic

Design of the permanent repair should take into account understanding the cause of the crack, to prevent a repeat.

I'm not into bridges, but the crack is very unusual IMHO; it should have cracked at the first line of bolts. It's odd that there would have been a joint at that location. Other than making things temporarily safe, my first objective is to find out why it cracked, else repair may only be temporary. I'm surprised there wasn't a catastropic failure.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

The DOT site shows a great picture of what I was trying to get at earlier, the top surface of the beam is clearly separated from the rest of the beam

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Some repair info from: https://www.ardot.gov/divisions/public-information/40-ms-river-bridge/

Is this beam two C-sections with plates welded top & bottom? Given the photos by IRstuff & the ding in the drain pipe noted by SparWebl, what are the chances that during a past inspection, the snooper truck smacked the beam while looking at the beam splice and initiated the cracked weld shown in IRstuff's photos?

There is more repair info on the TDOT site; TDOT is responsible for the repairs.

https://www.tn.gov/tdot/projects/region-4/i-40-her...

Sounds like the patch is pretty substantial:

It's a box beam:



Snooper truck definitely sounds like a plausible source of some of those dents and dings...

Apparently its been cracked since at least 2016!!
Link

^ based on the box beam having 1-3/8" (35mm) vertical plates and 1/2" (13mm) top and bottom plates, it takes away from the theory the shear lag is the culprit (with the connection on the vertical plates only.
The source is more likely the weld that formed the box. By the 1970's, they should have been smart enough to not have stitch weld connecting members on a cyclically loaded structure. There is a close up photo above, it looks like the thinner top plate runs over the vertical plate about half way, and it's connected by a fillet weld. That shouldn't be a too bad fatigue category.

Quote (That shouldn't be a too bad fatigue category.)

No body seems to be curious about why it broke, it would appear.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

How about this theory



Traffic is always braking going in one direction and accelerating going in the other.

I know the King George V bridge in Glasgow Scotland has problems due to this effect.

Or it's more likely to be stationary or slow moving on one carriageway and moving freely on the other?

The original Severn bridge had that issue when the queue for the toll booth backed onto the bridge on a regular basis on one side. They worked out that in strong winds the thing could fail. They partly solved it by making the tolls one way, hence the issue that you paid to get into Wales, but it was free to escape. tolls all gone now.

But uneven loading probably wasn't thought about in 1970...

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

yep that's what my theory revolves round. Basically one side is different loading to the other possibly including ROT degree of freedom as well as the main axis. Condensed traffic heading into town slowing down, Out of town everything accelerating and much lower load density.

Severn this bridge and KGV all built in the same period.

Alistair, here's another example.

The Patroon Island Bridge (Interstate 90 over the Hudson River in NY) opened in 1968. It has interchange ramps just west of the main span. It's also downhill approaching the ramps.

Cracking in the floor beams was attributed to trucks braking for the westbound offramp. IIRC, braking forces were twisting them.

My glass has a v/c ratio of 0.5

Maybe the tyranny of Murphy is the penalty for hubris. - http://xkcd.com/319/

So it could have been fatique... could the clamping forces from the bolts on the plate have attenuated the stress to cause the failure to occur outside the bolt holes... I would have thought the crzck wouid be at the first line.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

I've been intrigued by the end of the broken bits seemingly showing a castelated joint. This is a blow up of one of the photos above.

Anyone an idea of what this could be?

It seem too regular to be the result of the fracture.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

I don't think uneven loading would be the case but I definitely could be wrong. This is an arch tie and should be absorbing the majority of its vertical force loads from the arch bearings. By the time live load makes it to the bearings, I suspect there has been adequate redistribution through that truss arch.

My thought is that since the tie is also the chord member for the lateral system, the design didn't account for lateral forces in fatigue stresses. AASHTO Bridge Design Spec really only evaluates truck loads in fatigue. But with this being a long span and susceptible to large wind loads - there is a stress range there as well. That's where my guess is without having ANY knowledge about bridge design standards in the 60s.

Might be a broken weld...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

Is it possible to develop enough force to close that gap with post tensioning strands and jacks to allow the beam to be replaced?

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

waross - that's a good question and I don't know. But if repairs are moving forward, I can only assume that either they can or that the locations the engineers expect the forces to transfer to can handle the additional loads. Maybe even a combo of the two.

dik - definitely could have stemmed from the box weld. I'm still thinking fatigue but we can both be right on this.

I wonder if there is some sort of torsional stress that happens at this location. Like the wind is hitting the tie beam and cause some wind galloping, fluttering, or something and the beam is torsionally restrained at the connection. This cause some sort of torsional stress concentration, its not large but enough to become a fatigue issue.

From the press conference, it appeared that the initial thoughts for the repair would be creating a collar and using tie bolts to pull the beam back together then welding the tie beam.

I seem to remember a conference FEA paper on a 4th or 5th torsional mode causing a tie failure in a offshore structure. It was also designed symmetry but ended up with unsymmetric loads.

Another possible asymmetrical loading scenario might be thermal expansion due to sun hitting only one side of the bridge? Would be interesting to see how that affects the member forces.

Also, in that bridge bearing study that someone linked to, they were seeing unexpected results during thermal expansion. They expected a build up of axial compression in the struts but weren't seeing it on one side of the bridge. They guessed it could be due to one of the piers tilting, but perhaps it had to do with this strut failing and redistributing the load into other members (that didn't have strain gauges).

Sounds sensible

Sorry I screwed up my bridge names It was the Kingston bridge that they have issues with. The M8 motorway goes over it everything blocks up at Anderson

To be quite honest with you, John, I have no idea... I think it could be 2 or 3 things, but would not be surprised if it were a 4th thing...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

I have a gut feeling there is a materials factor in the mix as well. I would be wanting some sharpies and a hardness survey run up that box section before finalising the fix.

Truck weight limits were increased on the interstate system to 80,000 lbs in 1974. Arkansas was one of the states holding back on increased truck weights, only permitting heavier weights for a fee in 1983, completely accepting the full new 80,000 lb limit in 1986 after the trucking industry sued the state.

Link

The bridge was designed in the period prior to the increase in traffic weight. I also seem to recall that the bridge originally had fewer lanes. Is this another example of ever-creeping bridge use and load requirements leading to issues? Similar to some of the problems behind the Minneapolis I-35W Bridge Collapse (but the I-35W bridge also had an overlooked design flaw).

Two questions:
1. Are those strips backing strips for longitudinal welds?
2. Did those strips break or did they end there?

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

I took them to be ribbing to stop hungry horse deformation. And that they broke with the fast fracture mode.

1. Are those strips backing strips for longitudinal welds?
Probably
2. Did those strips break or did they end there?
My opinion is that the weld crack propagated into the backer bar. The pieces of backer bar on the left are visible. The backer bar on the right id hidden by the camera position.

While welds are often made with backer bars, the design needs to consider these welds - just like all fillet welds have "crack like features" in the root of the weld. This sometimes drives a requirement to stress relieve beams when manufactured. If the situation can not tolerate weld root cracks, the backside gouging and welding is necessary, which probably can not be done in this case as the box is too small.

If the base metal is hot short it could also promote weld cracking. Hot short is possible even with a mill test report being to spec. Root cracks can also result from a welder having a bad day defect, and many other things.
WELD CRACKS, DEFINITIONS, CAUSES, PREVENTION & REPAIR

Members with a high proportion of alternating stress with respect to continuous stress are particularly prone to fatigue cracking. It is relatively easy to calculate the tension in the tie beams. It is significantly harder to quantify the variable load for fatigue calculations. Additionally in 1966 (a guess, based on the bridge opening in 1973) when the bridge was designed fatigue theory was not as well understood as it is now.

Here is a link to the Daily Update May 22, 2021.

TDOT released some pictures today of the temporary, 'phase 1' repair plates being installed. They've finished one side, working on second today.

From today's Daily update: https://www.tn.gov/content/dam/tn/tdot/region-4/i-...




Wonder how those bolts were installed, by someone crawling around inside?

Geez. Someone had to run calculations to include the weight of those plates in the dead load.

Brad Waybright

The more you know, the more you know you don't know.

So, someone is sitting inside the beam with a bag of bolts for the guy on the outside to put nuts on...

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
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Unless the bolts pass all of the way through. That might explain the extra thickness in the plates.

The extra thickness can also be explained by needing to use the plate on hand that was thicker than the minimum required. The alternative might have been additional lead time.

Through bolts on a box girder splice would be a poor joint design. The squeezing forces would wind up stressing the box beam corners - which already are cracked.

Can you imagine being in that beam while someone with a 1" impact wrench is wailing away on the other end of the bolts?


I'm impressed that guy with the mag-drill could punch that many holes that line-up well enough to match all those plate holes.

Hey! How did they get the bridge beam re-aligned so holes could be accurately drilled? (chicken and the egg issue)

Can anyone see the crack? I can't see it in the work pictures.


Keith Cress
kcress - http://www.flaminsystems.com

They will have tack welded the bolt heads on the other side.

I am wondering how they captured the fracture without interrupting the node connections just adjacent to the repair.

Brad Waybright

The more you know, the more you know you don't know.

My thought now is that this plate does not span the damaged area. Are these fixtures, installed adjacent to each side for connection of members to stabilize the area to be cut out and repaired afterward?

Brad Waybright

The more you know, the more you know you don't know.

The plate does span the damaged area; the repair plate looks to be about 30 feet long, the bolted section in the foreground is about 10 ft from the break, and the bolted section on the other end of the repair plate is on the other (left) side of the plate that's adjacent to the break.

Something like this:


TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
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Assuming this spans the break, then the original splice plate was removed to allow this to sit flat against the existing surface. I can't see a way that the bolt holes in the new plate would align with the existing arrangement of 8 rows from the original plate. Maybe it's just an illusion.

Brad Waybright

The more you know, the more you know you don't know.

https://twitter.com/TDOTCommish/status/13965904299...

https://www.youtube.com/watch?v=XL9LH1UVRmo

Looks like they've spaced the main plate out away from the surface of the box and it spans across that node.

What are they going to do? Cut out the old box beam and field weld in a new section?

It appears the plate is at least 2 layers, I expect so that the bolted area can be against the original member while the single layer is spaced out enough it clears the existing splice plates. That'd explain why it's so thick. The part that is hard to understand is how they will replace the existing tie member with this plate installed. They'll have to replace the other adjacent tie too which they've drilled all the holes into. Maybe this is simply a splice to ensure the bridge stays up until they get the permanent fix figured out.

It seems that eventually they'll have to disassemble that node, at least in part. It wouldn't be possible if the bolts are covered by this temporary plate.

Brad Waybright

The more you know, the more you know you don't know.

I think LionelHutz and I were typing at the same time.

Brad Waybright

The more you know, the more you know you don't know.

That picture is quite fun.

I counted at least the same number of people leaning over the bridge rail as there are people doing something below.

Spot the ventilation tube going into the void space. Some pooor small and thin bastard is in there holding a spanner and fitting nuts to studs...

why not just cut out the damaged bit and weld in a new box section??

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

'Phase 1' complete, per TDOT:

https://www.tn.gov/content/dam/tn/tdot/region-4/i-...

Pictures released today are very low contrast, but looks like the inside 'mending plate' is much smaller in height. Seems like you can just make out the crack section near the chain fall on right hand side of picture:

I don't think there's a crack on the inboard side; previous photos show that there's a partial crack on the bottom, and full cracks on the outboard and top. It appears that they cut through the webbing of the vertical support near the crack to get the mending plate through to the other side, but they couldn't cut the horizontal strut attached at that point, which is why the inboard plate is only about half as tall as the outboard plate, which covers the full height of the box beam.


TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
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Somewhere on the Tennessee DOT page described the failure as a complete fracture of both sides and top, and 20% of the bottom.

Brad Waybright

The more you know, the more you know you don't know.

Correction-
https://www.tn.gov/content/dam/tn/tdot/region-4/i-...
No mention of any damage to the inboard plate. I would think it would have to be deformed and require some kind of repair.

Brad Waybright

The more you know, the more you know you don't know.

With the gap opened on the outboard side of the beam it is likely the inboard side is elastically twisted and bent. This is the natural result of tension loading an asymmetrical cross section.

<Speculation> the repair will require replacing the beam - drilled per the original dimensions. To install, the existing beam will be removed, and the load transferred to some sort of jig. </Speculation>

No small design problem.

TDOT announced the repair design today, in the interest of time, they are going to repair and reinforce the existing member rather than replace it:



https://www.tn.gov/content/dam/tn/tdot/region-4/i-...

I wonder how that's going to be different than what they have right now.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
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Wouldn't it have been easier, quicker, and just as effective to remove the bolts from one end of the plates joining the two tie beams, and install the repair plates from that point out past the crack? Those bolts aren't holding much now. Doing it that way would avoid compromising the strength of the good tie beam with all the new holes.

Extending the repair plates to the good tie beam didn't add anything. If the bolted joint at the end of the failed beam was good enough for the original build, it should be good enough for the repair. The spacer plates could have been much thinner since the nuts and bolts don't have to be cleared. It probably would have cut the added dead weight by more than half.

Except you can't expect the bolts on the ends of the damaged tie are not holding anything.

They probably felt it's best to do the least invasive thing rather than risk anything that might make the situation worse. I can see a lot of justification for that approach.

An imagined snippet of conversation;
"The fix will be as good as new."
"New wasn't that good. Can we try for better than new?"

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

A pic from 2016 .. Its been there for awhile.





https://www.mail.com/news/us/10803824-kayakers-pho...

Statements above are the result of works performed solely by my AI providers.
I take no responsibility for any damages or injuries of any kind that may result.

TDOT put up a photo gallery on Facebook with some more pictures:

https://www.facebook.com/media/set/?vanity=myTDOT1...

This one is interesting, it shows the hole they made to pass the 'inner' mending plate through:

Can you post some ,ore pics, Craig?
Some of us don't do facebook.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

This one shows exactly how the mending plate is offset from original plates. The crack is to the left, just off the edge of the image. Not clear that you have to log in to see the photos



TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
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I had a instinctively horrible feeling in my gut for a split second as my first glance had me thinking that cable was a crack.

My first thoughts were the same

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

1- The mending plates prevent access to the gusset/splice plate bolts so the repairs cannot involve any work to that area.
2- The long unsupported length of the mending plates should only be adequate to resist tension forces.
3- After the repair is complete, the hundreds of holes drilled in the member for connection of the mending plates will remain, or be welded shut, I think. I wonder how this affects the strength of the box member.

Brad Waybright

The more you know, the more you know you don't know.

The update from May 27 said something about "...removing a smaller section of the fractured piece...". Why do they have to remove it, and how would they remove it with the repair plates in place?

I'm having a hard time imagining how they can make further repairs without an extended shutdown and without removing the repair plates there now.

It's not making a lot of sense right now. The don't have much access to the crack or the splice plates to work on it. It doesn't make sense to be leaving all those bolt holes after the repair and cutting that big hole in the deck support beam that has to be repaired later doesn't seem to be a great idea either. It will be interesting to see how this proceeds.

I think that in order to have a complete metallurgical examination , then they would need to remove a piece and send it to a metallurgical lab, while protecting the fracture surface from damage during the removal process. After the surface is examined, the elemental analysis may offer a clue as to whether the failure was due to stress or due to a foundry error which may have introduced "poisons" into the steel , out of spec. Of course one relies on the lab to be perfectly honest in is presentation of results, but I am familiar with how some labs may shade their presentation of results to avoid implying liability onto a good client. One needs to read between the lines sometimes, or at least ask the correct questions.


"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick

How will several years of exposure and corrosion affect the metallurgical examination?

Quote:

or be welded shut, I think. I wonder how this affects the strength of the box member.

...in particular if the steel is not weldable... need coupons for that. Testing would have been the first thing that I would have looked at...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

Today's update - they are doing Ultrasonic testing of all the other similar welds while they wait for the repair parts:



More here:

https://www.tn.gov/content/dam/tn/tdot/region-4/i-...

A wide spread NDE effort is an appropriate response to the current situation.
<Opinion>If UT was not part of the original construction QC process, indications will be found. Interpretation of significance of indications which might have existed from the original construction can be challenging. </Opinion>

From ENR today (06/03/2021): Link



So I am assuming the PT is longitudinal (and temporary) over the 150 foot to apply preload, so that the 150ft long permanent steel plates can be installed, with 3,000 bolts.

8 each x 3" thick (I guess they mean dia?) rods - lets assume they are 3" dia @ 150 ksi PT bars, with 6.85 in² of net area each rod x 8 rods, so at to achieve 3,000,000 lbf that equates to a prestress of 55 ksi - so about 36% of MUTS, seems low but ballpark.

Not sure what the 20,000 ton refers!

Quote:

waross (Electrical)
21 May 21 14:50
Is it possible to develop enough force to close that gap with post tensioning strands and jacks to allow the beam to be replaced?

I guess the answer is yes.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

Here is TDOT's press release of what is to be done, maybe fills in some blanks in the ENR report:



LINK

Thanks Craig Neth.

20,000 lb makes more sense compared to 20,000 ton. Still, very 'beefy' PT brackets!!

In addition to repairing the failed piece, determining the root cause is of equal importance, and if it is due to overstress due to passage of overweight vehicles, the state will need to pretend that they will do a better job at ensuring the max permitted axle load is nhot exceeded. Perhaps a review of past permits that had allowed overweight vehicles to pass and a review of bypass routes that truckers can use to avoid the weigh scales is also prudent.

"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick

This ended up in my mail this morning and I don't know why... [Added] I suspect I know why... just my interest... did not know the poster, but responded that I would put the info on Eng-Tips.

https://www.aisc.org/globalassets/nsba/conference-...

https://docs.lib.purdue.edu/cgi/viewcontent.cgi?ar...


noted in FHWA Technical Advisory T5140.4 (1), “…the tied arch structure…is one of the most nonredundant structures, relying entirely on the capability of two tie girders to accommodate the total thrust imposed by the arch ribs.”

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

TDOT just posted a YouTube video (with really comical music) that explains the repair procedure:

https://www.youtube.com/watch?v=9QprIzj45n4



Link

The links which dik posted address lack of redundancy in tied arch bridges. But there is a distinction between the arch consisting of a single member vs. a truss. The bridge in this thread had substantial redundancy by truss action.

So the video posted by TDOT shows how the bridge will be temporarily supported to allow access for repairs. How the 'permanent strengthening repair plates' are to be employed remains a mystery.

Brad Waybright

The more you know, the more you know you don't know.

That's some funky music alright.

So it looks like they are adding extra steel plates in between all the existing bolted connections and then adding a further plate to bridge around the bolted sections.

Nothing about removing the damaged section or even sealing it.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

LittleInch is correct. It's easier to see the pieces if you step through the fast animation.

• https://files.engineering.com/getfile.aspx?folder=f7438c8a-f3dd-4f34-bdef-c

Still not much detail there. If that animation is to scale (probably not) it looks like the first set of plates actually overlaps part of the bolted node connection next to the failure. Then, the second set of plates overlap each end of the first. That would leave a gap between the new repair plates and the original steel and connections. That would certainly not lend itself to assisting with ongoing maintenance operations. Also, not able to determine if this stuff is bolted in place or welded. I'm not a civil, bridge, or structural guy, but it really looks like a patch job to me. I hope there's more detail to come out soon to change my mind.

Brad Waybright

The more you know, the more you know you don't know.

Three thousand bolts are required per June 04, 2021 release.

Quote (Retiredat46)

Three thousand bolts are required per June 04, 2021 release.

I'm guessing everything is bolted then.[bigglasses]

Brad Waybright

The more you know, the more you know you don't know.

Can anyone explain why they need to remove and then reinstall the "floor beam stiffeners"?

I think they are connected to the inside of that member where repairs are required

Brad Waybright

The more you know, the more you know you don't know.

Yep, you can see the end of one here.


Some slight mods will probably be required to reinstall them.

Are the permanent repair plates on both sides of the beam or only on the outboard side, as it appears in the video?
Do the repair plates compensate for the weakened top/bottom sides of the original beam? I can see where the top outboard joint is rusting, near the break.

TTFN (ta ta for now)
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So, the nuts on the ends of the 3" diameter PT rods are going to be like 6" across, How are they going to tighten them to get the tension needed? Is it like a 10' long box wrench?

TTFN (ta ta for now)
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IRstuff-
They have me wondering about all of that too. I'd like to see the repair plan.

Brad Waybright

The more you know, the more you know you don't know.

I presume hydraulically pull them and then double lock nut then take the load off?

Hydraulic jacks are non trivially big for something like 1000 ton, >20 diameter and about 3 ft tall https://www.alibaba.com/product-detail/10000-1000-...

So a couple of those and some sort of yoke for all 8 PT rods at the same time?

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
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I don't think they would want to depend on just one jack for such an important operation, and a yoke would rival the PT weldments in size/complexity.

Most likely the PT bars will be stressed with a multiple center-hole hydraulic rams.

Based upon info of 4 Jun 21 posts above, the 8 x 3" dia PT bars shall provide 3,000,000 lbf of preload, so that is only 365 kips per PT bar (about 54 ksi service stress for an ultimate tensile capacity of 150 ksi). So a 200 ton capacity ram would 'theoretically' work.

Elongation over 150 feet will be approx 3.5"

For scale, the following photo is a 200-ton center hole ram over vertical rock anchors (PT rods of 2-1/4" diameter). Stroke is 8" and weights approx 320 lb. 4" dia center hole.

Something like this, only bigger.

Thanks to Epoxybot for the original image.
There are other types but this illustrates the basic principle.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

Hydraulic Bolt Tensioning rams are likely going to be used, as they allow tightening the nuts with out interfering with the ram.
(NordLock)
These are often used on slew ring bolts, and other similar bolted connections where it is desirable to avoid twisting the bolt when applying tension.

waross - More accurately, thanks to Williams Form Engineering Corp.

Lots of updates today!

From Link:

Here's the latest on materials/fabrication:

• 3,000 bolts for the post-tensioning (PT) arrived Wednesday. Crews are replacing old with the new one by one.
• The PT weldments/anchors, fabricated by G&G Steel out of Russellville, AL, will be delivered this weekend.
• The PT rods are being fabricated. The first shipment is expected Monday, 6/14.
• Steel strengthening plates and splice plates for the permanent repair are also being fabricated. No timeline yet for delivery.

Construction work expected through the weekend:

• Hang additional rigging for Phase II work
• Finish miscellaneous steel removal for PT and Phase II work
• Attachment of PT anchors/weldments to the tie-beam
• Hang PT rod supports from floor beams in preparation for PT rod delivery on Monday
• Install Lower PT supports and protection on the platform
• Cut holes in floor beams for PT rods
• Remove and replace stiffeners at floor beams

First of the PT weldments installed:



More details: Here

It is interesting that with each 3" dia PT bar I was expecting each to pass through the bearing plate, however, based upon the photo they must be terminating the 3" dia PT bar before the bearing plate and transferring to a 6 bar/bolt yoke connection for preloading etc.

Grady Hillhouse did a nice summary of the bridge today on his Practical Engineering YouTube Channel:

https://www.youtube.com/watch?v=e8PodEM4Y8g

Tdot posted a picture on twitter today that shows the PT bars being installed, you can now see how they are transferring the load to the previously installed weldments.

TDOT posted some pictures of the hydraulic jacks this morning on Twitter:



Link

Update today, and a picture of the failure area:



Here's a slightly bigger view of the fracture area picture, scraped from the Word doc. Does the fellow inside have to run the plasma cutter???



Link

∧ Note the curved cut traced out for specimen "2B"; they must think there's still load flowing through that inboard plate, and so do I.

Based on the photos posted by IRstuff above on that weld seam split, and the photos of the rest of the crack, I'm thinking the tie never had its load significantly relieved. Methinks <15% was redistributed.

When the span expands and contracts due to temperature changes, does it push the piers back and forth slightly or will there be some type of sliding or rolling support to accommodate expansion/contraction cycles?
Could an issue with either the design or maintenance of that support led to the excess tension on the tie beam?

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

waross, the answer is probably both, and that's covered pretty well in the Structural Health Monitoring Paper (link above in post by 3DDave).

a pdf on the retrofit which shows some of the post-retrofit bearings:
https://cdn.trccompanies.com/legacy/images/121-Schamber.pdf

The original design would have had some form of rockers or sliders to accommodate the length variation. It would be interesting to see if the new bearings had a higher friction load as compared to the prior arrangement but I have not found details on the prior bearings to compare to.

Anyone know what the tie load would have been? The SHM paper leads me to think it's nominally around 6000kip per tie.

So then is the 3000kip post-tension load on the rods meant to take just half the load off the damaged member? I suppose that is a possibility.

TDOT just tweeted this:

Latest update:



And some images:




Source

From their FB page, this image of the fractured piece:

#ICYMI Monday in Memphis, the fractured piece of the I-40 Hernando DeSoto bridge was removed. On Tuesday, crews began installing new plates. Updates are posted on Monday and Friday each week. https://www.tn.gov/tdot/projects/region-4/i-40-her...
3 days ago

https://www.facebook.com/watch/?v=1732047853668574

Today's update from TDOT:



Bigger picture of some of the interior 'mending plates':



Link

I think that I have missed something important here.
I have no doubt that the repair work will ensure that that beam never breaks again.
BUT
Did I miss the reason why it broke?
Why is this important?
What about the three remaining identical tie beams?
If we don't know why the first one broke..........
Sorry if I have missed the answer.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

I think the answer is 'they don't know yet'. They only just removed the fractured piece on Friday, presumably it's gone back to a lab or testing facility for analysis and testing.

Thanks Craig.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

Update: The repairs to the fault are complete, but the ND testing identified 9 other areas that need plating:



Source

Latest update:



Seems like the ND testing found quite a few failed welds that needed repairs.

TDOT also published a picture of the 'phase 2' repairs with a fresh coat of paint:



Source

Interesting article about the fired bridge inspector:

"Plenty of blame to go around following Mississippi River Bridge closure". Link

According to him, the fault was not visible from the angle of the snooper truck because it could not go far enough outboard...

Definitely feels like a 'process' failure. I hope they are fixing the process rather than just making this fellow a scapegoat.

I don't buy this:

"According to him, the fault was not visible from the angle of the snooper truck because it could not go far enough outboard..."

The snooper bucket launches from the bridge deck and then articulates outboard on its way for inspectors to access structure under the deck. The bucket is absolutely outboard of the structure far enough to see the crack, even if there is some distance bridge length-wise.

The crack is very visible viewed from above, and from anywhere outboard. Not visible from directly below or inboard.

Heck, this crack was visible in photos taken by kayakers 100' below.

Something else must explain why it was missed... Repeatedly.

Quote:

The snooper bucket launches from the bridge deck and then articulates outboard

Do we know what model of snooper truck was used and if the truck had enough lateral reach to operate outboard?
All snooper trucks may not be equal.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

Two comments:
1. I had wondered why the beam had failed and if the failure was isolated to this member or could be more widespread.
I am glad to see that the consulting engineers had the same thought and tested and identified other problems.
2. Does this now look like an error in the original design? Are there any bridges of similar design and construction that should be rigorously inspected?

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

Here's picture of an Aspen-A75 truck on what looks like a reasonably similar bridge.

from https://www.bridgeriggers.com/on-road-equipment/a-...

Quote (Do we know what model of snooper truck was used and if the truck had enough lateral reach to operate outboard?
All snooper trucks may not be equal.)

According to the article, it is/was an Aspen-A75. Here's a bit of an excerpt from the article:

Quote (“When performing the inspection, we go down every 3(rd-?) cable,” he wrote. “This allows us to see both sides of the farthest floor beam away from us. Then we extend the boom to its full length and rotate under the structure, (once) we have rotated as far as we can go, we retract the aspen boom and rotate back the other way moving up and down getting close to the stringer and floor beam connections as far as the machine will allow.”

What Frazier was describing was the process of using an industrial bridge inspection unit called an Aspen A-75. Sometimes called a “snooper truck,” it’s a gigantic, 80,000-pound vehicle with a long, adjustable steel arm with multiple joints. At its tip is a basket that can hold 700 pounds.

To inspect the underside of a bridge, a team will park the Aspen on the deck of the bridge, climb into the basket and maneuver the arm down over the side of the bridge and horizontally underneath it. The arm includes a boom that can swing in a wide semicircle under the bridge, allowing the inspectors in the basket to hunt for potential damage.

Inspecting the entire length of the DeSoto Bridge required multiple stops — the team would park the Aspen A-75 and deploy its arm beneath the bridge 12 times each on the westbound and eastbound sides, according to an ArDOT document compiled from the inspectors’ statements. In addition to scanning the underside of the structure with the Aspen, teams would walk the length of the bridge to eyeball potential damage from the deck.)

Also, this:

Quote (“Mr. Frazier didn’t seem distressed and didn’t ask to see the crack,” Hill continued. “He kept saying that there was no way to see the crack because it was too dangerous to go past the underside of the tie girder. He said if you took the basket outside of the tie girder to move along the outside, the A-75 was unstable. He also said that he once moved it out there, and one of the tires lifted off the ground. He operated the A-75 in 2019 and 2020.”)

Since it sounds like the procedure always had the same start points and number of stops, it seems like you could potentially end up with consistent 'blind spots'.

Thanks for the information Craig.

Quote:

He said if you took the basket outside of the tie girder to move along the outside, the A-75 was unstable. He also said that he once moved it out there, and one of the tires lifted off the ground.

Sounds like possible inadequate training. Maybe a failure to properly use the axle locks.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

It definitely seems like there were more systematic failures here. One person should not be able to consistently screw up a process this important.

That’s a great article, Craig. Regarding the “one person” statement, it seems pretty clear that Frazier is a scapegoat. From the article:

Quote:

To clarify the reasons for Frazier’s firing, The Daily Memphian and Arkansas Nonprofit News Network relayed a series of questions to ArDOT’s public information officer, Dave Parker. In response to a specific question about Frazier’s termination, Parker responded that, “we have verified that Monty Frazier was the only inspector of the tie girder that was cracked between 2016 and 2020.” In a follow-up call on the evening of July 20, ArDOT’s Director, Lori Tudor, emphasized this point: “Monty Frazier was the only inspector who looked at that particular tie girder.”

This contention is contradicted by years of inspection reports provided to The Daily Memphian and ANNN. The ArDOT inspection reports include a description of each structural element of the bridge, identified by number. The tie girders on the DeSoto Bridge correspond to element #107, “Steel Open Girder/Beam.” At least five inspectors are listed as having inspected the bridge during that time. Monty Frazier is only one of them.

And

Quote:

Another photo shows the same crack in an image dated Oct. 24, 2014. The photo is from a French tourist, Philipe Suissa, who traveled to Memphis for two days in October 2014, during a road trip from New Orleans to Chicago. “We had a boat trip and I took the photo,” he said in an email to The Daily Memphian. Metadata analysis by The Daily Memphian confirmed the date of Suissa’s photo.

Frazier has been on staff at ArDOT since 2006, but didn’t participate in DeSoto inspections until 2016. DeSoto Bridge inspections have gone through multiple lead bridge inspectors — and dozens of inspectors — since 2014.

It's really difficult to believe none of the inspectors involved over the years raised a big red flag about not being able to do a proper inspection because the truck wasn't suitable for the job or it required too many stops along the bridge to see all of the tie beam.

However, looking at the pictures of the Aspen A-75, I can see why they might have to make stops pretty close together and do a backtrack/skip procedure to inspect all of the tie beam. If you divided the beam into sections A,B,C,D,E,F...., you'd park the truck at B to inspect A and C, then move to C to inspect B and D, then move to F to inspect E and G, etc. That's a bit confusing and time consuming, but doable. A good inspector would figure it out, and write a procedure to get the job done right.

Maybe they should have the inspectors draw a crack on the structure with a big sharpie or paint or whatever and then see if the next crew two years later actually find it.

Just kidding, sort of.

On a serious level, did anyone figure out what was going on on that beam to cause the fracture years ago, and then cause the fracture to deflect that much (a lot) and yet have the remaining part of the beam to NOT fail??

I've seen a lot of fractured steel (in machinery, mostly), but if loads are enough to break it half way through, you would think the remaining bit would fail soon after. Not be still hangin in there years later.

Edit: And man did they go big with the sistering plates!! That is a lot of steel added. CYA is strong here!!

With all of that extra weight from the repairs are they going to have to reduce the capacity of the bridge?

Quote (TugBoatEng)

With all of that extra weight from the repairs are they going to have to reduce the capacity of the bridge?

That's a valid point Tug.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

Craig Neth quoted that 16 plate repairs will be required. Maybe each repair is unique and won't require the same amount of plating? Then again, it sounds like the failures are systemic so they'll all require the same repair.

Now up to 17 additional repairs, from today's press release. These 'secondary' mending plates appear to be much smaller than the 'major' repair:



Source

From a post by ingenuity:

Not sure if that is 53 tones each or 53 tons total, but we are looking at hundreds of tons of added weight.If that is the weight of each plate plus the weight of the bolts they may be adding almost 1.7 thousand tons.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

Today's update:



Link

The posted a video on twitter of a truck driving across, apparently they are doing some load testing using the existing sensor network.

Work is wrapping up and the eastbound lanes are now open. Westbound lanes to open later this week.
https://www.tn.gov/content/dam/tn/tdot/region-4/i-...

Brad Waybright

The more you know, the more you know you don't know.

Does anyone have an estimate of how many tons were added to the bridge weight by the repairs?

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

Bill-
I saw it in one of the briefing documents here-Link

Brad Waybright

The more you know, the more you know you don't know.

"...150-ft long steel plates weighing 53 tons..."

Steel weighs about 40 pounds for a 1 foot square an inch thick.

If we assume each steel plate is 4 feet high and one inch thick, then each plate weighs 24,000 pounds--12 tons.

If there is a plate on either side of a beam, and there are two beams, it is looking like the 53 tons is the total for all four pieces.


I will guess the nuts and bolts will add another 3 tons.

spsalso