Another Sewage Treatment Wall Collapsing
Another Sewage Treatment Wall Collapsing
(OP)
Even though this seems to be a poorly constructed project, I've got to believe that there is a design aspect to this.
Note that the Gatlinburg Wall Collapse looked very similar to this one.
Note that the Gatlinburg Wall Collapse looked very similar to this one.






RE: Another Sewage Treatment Wall Collapsing
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Another Sewage Treatment Wall Collapsing
RE: Another Sewage Treatment Wall Collapsing
... but there's not a hint that they were checked for the increased effective hydrostatic pressure exerted by a load of Imported Norwegian Magic Rock.
Mike Halloran
Pembroke Pines, FL, USA
RE: Another Sewage Treatment Wall Collapsing
RE: Another Sewage Treatment Wall Collapsing
From skim reading the structural section of the report, seems like enough red flags were raised that the owner should have perhaps taken more drastic action. I know it is very expensive and they may not have many alternatives to shutting down sections of WWT plant, but look at their options NOW.
And this was just built @ 5 years ago! Not to overstate the obvious, but this should not be happening, especially in the US on municipal projects where public health and safety are paramount.
RE: Another Sewage Treatment Wall Collapsing
Of course there's almost never one single cause for a disaster like this. Several things had to go wrong.
RE: Another Sewage Treatment Wall Collapsing
The extra reinforcement in 350 would of course add to the capacity of the walls, etc., but if designed correctly, under 318, there shouldn't have been a collapse.
RE: Another Sewage Treatment Wall Collapsing
That's what I'm wondering about. It's unlikely to be something marginal because I doubt most engineers would raise a concern on a 5% or 10% difference.
RE: Another Sewage Treatment Wall Collapsing
RE: Another Sewage Treatment Wall Collapsing
RE: Another Sewage Treatment Wall Collapsing
RE: Another Sewage Treatment Wall Collapsing
RE: Another Sewage Treatment Wall Collapsing
RE: Another Sewage Treatment Wall Collapsing
Agree Hokie, I remember the other W VA failure was similar, where the front walls met the side walls. There was a "pull-away" failure of the front wall apparently from inadequate development of the horizontal reinforcement. But that W VA wall was fairly tall, this one seems like it is more in the 10-12' range judging from the video.
The pic from the main article- look at the walls in the background, there are horiz rebar stubs visible extending out from the side walls. So from this limited info I would speculate, if I must,that there were no hooks and the wall simply pulled away from the side wall (I can't imagine them detailing it like this!), or they did provide hooked bars at that connection and they failed in tension.
WWTP tanks are not my area of expertise, but square box tank structures with uniform pressures don't seem THAT complicated... Any other theories from some tank designers? If there were that many leaks as the peer review report indicated, could that be from rapid corrosion?
RE: Another Sewage Treatment Wall Collapsing
RE: Another Sewage Treatment Wall Collapsing
What is the gradation of those special rocks? I bet they're pretty granular - lots of surface area for microbes. If its like a coarse poorly graded filter sand or pea gravel I can imagine some really significant lateral loads developing there at saturation.
RE: Another Sewage Treatment Wall Collapsing
RE: Another Sewage Treatment Wall Collapsing
Compare that to a water or wastewater tank. The pressure is 62.4 pcf times the depth of the liquid. It can't be less than that. This pressure is likely to be there for a long period, maybe years at a time.
There are some companies, big and small, that design for these loadings all the time. We have procedures in place to assure a good design product. Even we make mistakes. We learn something from every project. But on occasion, companies dabble in this work. They're the local favorites, they know somebody, they're owed the job, whatever. If they don't respect what they're doing, mistakes are made. I'm not going to say that they can't do a good job. It's just a different mindset.
When hokie66 says "1.4, 1.7 whatever?", he might be right, as long as everything else is done perfect. It's a dirty little secret, but a lot of the load factors, phi factors, cracking calculations, etc., are there to protect from normal mess-ups in construction, design and operation.
Enough of my soap box ranting. Just remember, next time you see a tank full of poop, thank people like me. And if it's running down the creek, thank someone else.
RE: Another Sewage Treatment Wall Collapsing
Instead of single hooked bars, I like U-shaped bars at corners and Tees, along with vertical bars at all inside corners.
In addition to that, we always use corner bars (45 degrees in plan) to address the reduced concrete shear capacity due to the aggravating additional net tension.
As much as I dislike tort lawyers and "expert witness" engineers that usually seem to just feed on their own, they do serve a purpose in these unfortunate events. Bottom feeder engineers will steal jobs away from the experienced engineers in the short term, but also get purged from the system from time to time.
RE: Another Sewage Treatment Wall Collapsing
True for clear water.
Where do you factor in the additional weight of slurries and such?
Mike Halloran
Pembroke Pines, FL, USA
RE: Another Sewage Treatment Wall Collapsing
RE: Another Sewage Treatment Wall Collapsing
But those fancy rocks would add to the pressure, wouldn't they?
RE: Another Sewage Treatment Wall Collapsing
I'll have to check around.
RE: Another Sewage Treatment Wall Collapsing
So Jed, ATSE, others, what about my original question about the failure mechanism in these tanks, looking at the pictures of horizontal rebar stubs extending out from the inside walls. Any guesses?
RE: Another Sewage Treatment Wall Collapsing
Stub rebar at wall ends as shown in the photo make no sense to me either - it appears like bar ends. Very improbable that the bars all fractured uniformly in tension with the same stickout. Guessing that horiz bar lap was lacking.
Just guessing again, but possibly due to creep and lack of tension capacity at the T-intersection, the perimeter wall started to separate from the perpendicular web walls, with the wall behavior changed from 2-way action to 1-way action, and base moment demand increased 4x, immediately hinging at the base.
RE: Another Sewage Treatment Wall Collapsing
A surprisingly clean failure though. Thanks for your 2 cents.
RE: Another Sewage Treatment Wall Collapsing
thread507-296127: Tank Collapses and Kills Two
That one looked like there were ferrules in the ends of the cross walls, and the end walls were cast later, and the screwed in bars failed. Would seem impossible to install hooked bars into ferrules...maybe that's what they proved. Could have been the same in this one, but they didn't even try to hook the bars.
RE: Another Sewage Treatment Wall Collapsing
RE: Another Sewage Treatment Wall Collapsing
Another consideration that needs to be included in the size of the horizontal reinforcing in rectangular tanks is the direct tension forces that the walls experience from counteracting the fluid pressure on the end walls.
RE: Another Sewage Treatment Wall Collapsing
RE: Another Sewage Treatment Wall Collapsing
RE: Another Sewage Treatment Wall Collapsing
RE: Another Sewage Treatment Wall Collapsing
My bet is that when the reports come out, they will indicate that there was either an error in the design calculations, or the wrong reinforcing was called out on the drawings, or the shop drawing had the wrong reinforcing and it wasn't caught during the review.
RE: Another Sewage Treatment Wall Collapsing
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RE: Another Sewage Treatment Wall Collapsing
Any time a client complains about our invoices, I think I'll attach those photos.
RE: Another Sewage Treatment Wall Collapsing
RE: Another Sewage Treatment Wall Collapsing
Being a cynic, I can't help but think that lawyers do this to help their colleagues by generating billable work for other lawyers. Think of it as a professional courtesy. Meanwhile engineer's tend to be like prostitutes fighting over a customer.
It's a shame that we as engineers can't be like lawyers and find ways to create work. Look at how many TV commercials there are by lawyers suing for everything and anything.
RE: Another Sewage Treatment Wall Collapsing
It's a classic case of the blind leading the blind.
RE: Another Sewage Treatment Wall Collapsing
The forensic report repeats the 62.4 psf number, as if the tanks were filled with just water. One look at photo 7 of the forensic report suggests otherwise. Anybody know the specific gravity of the magic special imported particulates in that tank?
Mike Halloran
Pembroke Pines, FL, USA
RE: Another Sewage Treatment Wall Collapsing
They dwell on reinforcing lap lengths. But to prove that they had something to do with a failure needs a study of the stresses in the reinforcing at the lap location. After all, development lengths are allowed to be reduced if the analysis shows the bars aren't fully loaded.
This sloppy report, with its multiple offenders, will result in a muddying of liability, and no one being held accountable.
RE: Another Sewage Treatment Wall Collapsing
All those leaking cracks prior to the collapse, and in walls that haven't collapsed, shows the lack of adequate horizontal reinforcement. And the little stubs of bars sticking out of the interior walls answers the question we had from the original photos.
RE: Another Sewage Treatment Wall Collapsing
RE: Another Sewage Treatment Wall Collapsing
The wall was clearly deficient in both vertical and horizontal reinforcement (only about .0038 Ag horizontal in a water retaining wall).
The wall wasn't cantilevered off the base slab, but according to the drawings was supposed to be pinned to the base slab as a propped cantilever. The photos show very short lengths of bar protruding from the base slab, rather than the hooked bars which should have been there, similar to the internal wall. The whole cantilever was dependent on passive resistance of the earth, which would have been fill material. When the ground finally moved enough, down she came.
The failure of the report to investigate the actual mechanism of collapse is inexplicable.
RE: Another Sewage Treatment Wall Collapsing
RE: Another Sewage Treatment Wall Collapsing
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"We shape our buildings; thereafter they shape us." -WSC
RE: Another Sewage Treatment Wall Collapsing
It is a very poor report. It seems that the investigators had never designed a water holding structure.
It will be interesting to see the SGH report and its findings.
RE: Another Sewage Treatment Wall Collapsing
I think it's also very possible that one-way (vertical) bending was the planned design, it was done poorly, the wall went into two way action, and the inadequate horizontal steel and lack of support from the side walls (planned or unplanned) was the end of the story.
The calculations would be a big help (hopefully they haven't "disappeared"), but more complete drawing information would go a long way.
RE: Another Sewage Treatment Wall Collapsing
Gumpmaster has identified the same major deficiency I saw, but which not mentioned in the report by the insurance company's engineer. Granted, the wall vertical reinforcement was inadequate, but that is not why it fell. Neither was the woefully inadequate horizontal reinforcement. It collapsed because of the connection between the wall and the tank base slab.
RE: Another Sewage Treatment Wall Collapsing
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RE: Another Sewage Treatment Wall Collapsing
RE: Another Sewage Treatment Wall Collapsing
A contractor is currently asking our firm on a water treatment plant to use mechanical splices for the intersecting walls in a water tank. Currently, we have designed and detailed corner bars with lap splices in both directions.
I have used these mechanical splices before, but never in a liquid retaining structure. In light of this, has anyone used these in the past on tank structure, and would you continue to use them in light of the failure? I realize that mechanical bar splices may not have been the cause of the failure, but it has me questioning their use.
Thoughts??
RE: Another Sewage Treatment Wall Collapsing
When you think about how little of the ultimate capacity is utilized if these bars are designed correctly, you appreciate how only a cascading series of errors can cause a catastrophe like this.
RE: Another Sewage Treatment Wall Collapsing
We had a job were we specified the couplers shown in the link below. During the inspection, we noticed that not one of the coupler screws were tightened properly (the tops torque off when properly tightened).
The Contractor commented, "Huh, I never saw those twist off before!" Which is a little unsettling.
So keep an eye out for this. It's clear in the manufacturer installation instructions that the screwheads torque when properly installed, but sometimes that information doesn't always make it to the site.
http://www
"We shape our buildings, thereafter they shape us." -WSC
RE: Another Sewage Treatment Wall Collapsing
RE: Another Sewage Treatment Wall Collapsing
RE: Another Sewage Treatment Wall Collapsing
See the attached link for more information:
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RE: Another Sewage Treatment Wall Collapsing
I would usually avoid a lap splice at this location but by my interpretation of ACI 318, the lap splice length meets the code.
RE: Another Sewage Treatment Wall Collapsing
This kind of report has lawyers licking their chops.
RE: Another Sewage Treatment Wall Collapsing
RE: Another Sewage Treatment Wall Collapsing
RE: Another Sewage Treatment Wall Collapsing
"We shape our buildings, thereafter they shape us." -WSC
RE: Another Sewage Treatment Wall Collapsing
Unfortunately, the pattern for these problems is that the people who know the technical details aren't talking. Just like the Gatlinburg, Tennessee wall failure, I'd sure like to look a the design drawings. They blamed that on a corrosion affect at the tie in walls, which I still don't completely believe.
RE: Another Sewage Treatment Wall Collapsing
Mike Halloran
Pembroke Pines, FL, USA
RE: Another Sewage Treatment Wall Collapsing
RE: Another Sewage Treatment Wall Collapsing
"We shape our buildings, thereafter they shape us." -WSC
RE: Another Sewage Treatment Wall Collapsing
RE: Another Sewage Treatment Wall Collapsing
http://www.pressconnects.com/article/20110516/NEWS...