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Help me identify this water tank failure?

Help me identify this water tank failure?

Help me identify this water tank failure?

(OP)
Can anyone offer any ideas as to how this failure has occurred in a water tank in the attached photos?
The tank construction consists of a GRP wall, with steel framing around the outside, presumably to provide lateral restraint to the tank. The framing sits on RC beams which are on a raft footing.
One of the steel columns has completely sheared through the RC beam and pulled away from the tank, bending the horizontal ring beam in the process. It is clear that the baseplate anchors where installed outside the beam reinforcement, significantly reducing the shear capacity.
On first appearance it looks like the horizontal pressure from the tanks has caused the failure, however the tank wall itself is still intact with no apparent evidence of stress in the seem connection. The client is certain that vehicle impact has not occurred, however I have my doubts. There is no evidence of impact on the steel column however.
does anyone have any thoughts?
Thanks in advance

RE: Help me identify this water tank failure?

Are you sure the ring beam hasn't buckled or been subject to some sort of axial force buckling it and finding the weak spot as the connection from the column. How long / what is the end connection of the buckled beam.

Has that been hit?

Can't see how the tank can affect that support.

A few more pictures would help.

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

RE: Help me identify this water tank failure?

just one col failure.....which one?....why just this one particular col?...how is this col different than the others in construction and loading?...these are some of the questions that would come immediately to mind....one immediate cause may be the lateral pressure on the col and it"s resulting shear @ the base but then the question arises why no sign of distress @ the other cols?...

RE: Help me identify this water tank failure?

I would bet that the concrete got hit somehow. The level of rust on the bolts suggests that it's been like that for a long time. This is further indicated by the lack of debris from the footing.

Seems more likely that the footing failed or was hit, and the column, without its foot, pulled the ring out.

TTFN (ta ta for now)
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RE: Help me identify this water tank failure?

A wedge shaped chunk of concrete below and left of the column has a different color and texture from the rest of the beam. It appears to have been poured afterwards for some unknown reason. The concrete which has been removed appears to have failed in a vertical line following a vertical bar which is visible in the photo.

It looks like a tensile failure caused by water pressure, although impact is a possibility too. It was not adequately tied to the beam to resist any significant horizontal force.

BA

RE: Help me identify this water tank failure?

A drawing of the tank would help. Is the I beam supposed to be connected to the tank wall? Your first photo shows two open vertical holes? As BA pointed out the concrete beam appears to have been two pours, which suggests a repair subsequent to the original construction. The anchor rods look fairly short as well; the rebar doesn't look properly detailed. I'm leaning towards BA's opinion that it's a tensile failure. Is this a pre-engineered tank? If so, call the manufacturer, although they might say they're not responsible for designing and detailing the concrete beams.

RE: Help me identify this water tank failure?

Have you looked at temperature caused expansion of the horizontal steel member, as from sun heating? Could that have moved out the column taking with it the horizontal member?

RE: Help me identify this water tank failure?

Quote (oldestuguy)

Have you looked at temperature caused expansion of the horizontal steel member, as from sun heating? Could that have moved out the column taking with it the horizontal member?

You beat me to it on that one!

RE: Help me identify this water tank failure?

Are the anchors connecting the steel to the beam expansion type anchors? Is there sufficient width to the beam for the expansion anchors to work?

Dik

RE: Help me identify this water tank failure?

Interesting mystery, I gotta say that aside from thermal effects I don't see a conclusive explanation for this damage if you assume a vehicle impact is not the cause. Very curious if you do find any more clues.

Professional and Structural Engineer (ME, NH, MA)
American Concrete Industries
www.americanconcrete.com

RE: Help me identify this water tank failure?

I assume a GRP tank is pretty flexible. Say that the tank is empty, wind loading causes the tank wall to flex (deflect). Reaction to the wall deflection is that the weakest column base fails in shear (pops outward). BAretired may have spotted why one particular column was susceptible to failure.



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RE: Help me identify this water tank failure?

Are those anchors post installed wedge anchors?

RE: Help me identify this water tank failure?

Many of the concrete anchorage failures that I've encountered have been the result of thermal forces. Any cause to suspect thermal expansion here?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Help me identify this water tank failure?

I don't know why it wanted to move that way, maybe expansion of the steel. But there was very little holding it, and this is not the first time it has happened. As pointed out above, the concrete where the anchors were was a sloppy repair. The structural steel appears to be galvanized, but the anchors are not. They look to be expansion anchors, Trubolts or the like, and not corrosion resistant. The corrosion of the anchors could have contributed to the spalling. And there was no reinforcement which was effective in restraining the anchors.

All in all, destined to fail.

RE: Help me identify this water tank failure?

Is that column connected to the tank higher up? If so, how did those connections fare?

RE: Help me identify this water tank failure?

The larger view seems to show that the columns are fixed across the top of the tank to create a ring around the tank.

The column that failed seems to be on the outside.

It is feasible that the tank did expand when filled as the column seems to be in close contact with a vertical seam. Given that examination of the first photo seems to show a repair line then this column and foundation appear to be more prone than the others to failure of the concrete and column being pushed out than the others

I don't really understand why those columns are there, but maybe to support a platform on top of the tank? If so why place it so close to the tank.

If you look at the tank to the left, it seems to be a similar size, but has a much meatier connection of the columns to a slab, not a set of supports.

Was the tank actually installed 90 degrees wrong? i.e. those columns should sit on the much bigger beams on the left and right?? or were the beams cast 90 degrees out?? Stranger things have happened and then everyone just goes - Sod it put it on the bases, no one will know and nothing will happen???

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

RE: Help me identify this water tank failure?

LittleInch,
I don't understand the system either, but it looks like these "columns" are on all four sides.

RE: Help me identify this water tank failure?

You look as though you're right - Damn - I thought I had a good reason there for a few minutes...

I think BA retired has it best - these columns appear to be an afterthought and were poured after the main supports

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

RE: Help me identify this water tank failure?

(OP)
Thanks for all the replies. Some interesting theories there.

Hokie66 - at the top of the columns there is a series of horizontal ties connecting the columns together. all the other connections are fine, it is just that one column at the base that has failed.
I doubt that thermal expansion is a factor as there are a number of water tanks there in the vicinity (exact same construction) and only this one has the problem.a few of them do have some cracks at the end of the RC beams though indicating that the problem with the anchors is consistent.
I'm still at a loss though as to why the column would push out that far and how the horizontal beam has deformed the way it has.

RE: Help me identify this water tank failure?

Those 'columns' are not really columns, but vertical beams: they resist water pressure, the GRP walls with metal corners cannot of course withstand the pressure as flat plates in bending. So I guess that simply one of the beams simply failed at the base (due to inadequate design and manufacture, possibly aided by an impact). There must have been a pretty large deflection of the wall, but this could have been elastic, so it is no more visible.
One condition for this to be true is that the tank was not empty at the time of the failure, and that, when clarke1973 visited the tank, it had been already emptied.
Now of course many questions will arise, for clarke1973, on the acceptability of the other beam supports and perhaps other bad details of this and other similar tanks.

prex
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RE: Help me identify this water tank failure?

I agree with prex. The tank has more in common with a cofferdam than a "tank". The bottom of the tank keeps the tank wall from failing, but does not prevent the center of the wall from bulging:

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RE: Help me identify this water tank failure?

If you look at pictures of others then it seems this is the case.

The only thing to maybe check is to see if that horizontal beam which is deflected was actually or was supposed to be bolted to a beam running under the tank. Connection details on other tanks seem to show you build the beams like a complete box.

If you look closely there seems to be room for four bolts holding the beam/column to the base, but only two have been used.

you can just see in the first photo there is a horizontal beam under the tanks along the line of the concrete beam, but not clear how / if it was attached to the bent channel.

Lots to investigate!

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

RE: Help me identify this water tank failure?


It appears to me that the concrete beam that the column was attached to had been repaired in some fashion, judging by the difference in color each side of the diagonal crack visible in the first picture. I see no evidence of reinforcing steel emerging from the intact concrete. Perhaps a patch/repair was done after the original concrete was placed and was not properly tied to the original concrete and quite possibly was done with lesser quality concrete.

Ralph
Structures Consulting
Northeast USA

RE: Help me identify this water tank failure?

Now this one should be labeled a "typical Rube Goldbereg tank design." What a bunch of beams and columns with no apparent experts doing the "design". Going in and replacing or "repairing" those concrete "beams" will surely be a job. Looking back, perhaps a series of many more photos would have shown the problem right away. Good luck fixing this mess. Full replacement may be cheaper.

RE: Help me identify this water tank failure?

Those 'inward' sets of wedge anchors appear to be bent as well. I'm on board with SRE's latest sketch.

I wouldn't trust any of the anchorage at the bottom anymore. Seems an 'easy' fix might be take shear out of the anchors by adding tension struts or rods across the bottom to opposing vertical beams just like they did at the top. Doesn't seem like it'd be that hard to retrofit.

RE: Help me identify this water tank failure?

There should be X bracing on each of the 4 sides to resist lateral force and prevent bending of any column. If a column bends out of alignment is center of gravity will act to create a moment at the base causing the concrete base to spall and the bottom of the column pulled out the bottom beam of the tank.

RE: Help me identify this water tank failure?

Maybe someone put a sling around the column and yarded some equipment around?

Looks to me like the horizontal beam was originally under the lip of the tank.

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