Cylindrical Concrete Tank Horizontal Cracking 1

[JoelTXCive]

We have cylindrical concrete digester tank that sustained damage during Hurricane Harvey. The tank was constructed in the mid 1950s.

At this stage, we are trying to determine if it is worth pursuing a full forensic evaluation for the owner.

The tank has an inside diameter of 34.5 ft.
The overall height is 21 ft, but the tank is embedded 6 ft into the soil.
The tank sits on shallow foundations.
It is in the Houston area, so we can assume there is a high clay content in the supporting soils.

During Harvey, the tank was empty and the tank location was inundated with water.
I do not see a water line on the tank, but my understanding is the water depth was ~10ft plus outside the tank.

A large horizontal crack has appeared on one side of the tank. The crack does not go all the way around.

I'm not sure where to start looking first.......water pressure type failure? or maybe something with the ground?

1) Maybe the inundated soil expanded and contracted during the storm event?

2) Maybe the exterior vertical steel is really just temperature and shrinkage steel since it was never expected to be put in tension?
The tank walls are 12" thick so we are assuming there are 2 curtains of vertical steel.

Thoughts? I don't have a billing code yet, so I'm not sure how far we want to go down the rabbit hole.

Thanks!

 

[dik]

You may start with some geotech info about the soils to see if this is a problem. Examine the crack to see if it is fresh. I've often encountered 'fresh' cracks that were likely decades old. Then try to determine the cause of the cracking. Check with specialty product manufactures to see if the tank can be 'patched' or if epoxy or polyurethane injection can be used; the former can be used for limited structural repairs.

 

[LittleInch]

Is there any chance it got hit by anything during the flood or was that the direction of the highest wind?

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

 

[EdStainless]

Has anyone looked inside? Is there a crack also at ground level?

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[Archie264]

No water on the inside, 10' of water on the outside? Sounds like a possible stress-reversal situation to me. I would expect the cracks to appear on the inside but maybe they're there as well?

Edit: Hmmm, 'pon further reflection cracks on the outside might make sense. I was thinking in terms of stress-reversal in a pinned-pinned scenario but it's probably more of a cantilever situation. Vertically, that is. I know there's also hoop stress.

 

[epoxybot]

Is it just the photo lighting or is the more water staining below the crack than above the crack. Is the water staining from Harvey or long term deposits? Older stains that don't have continuity from one side of the crack to the other, might suggest the crack was existing and maybe the crack opened up due to pressure.

 

[dik]

Is that maybe a cold joint that no one noticed before?

Dik

 

[JoelTXCive]

Thank you all for the input. I'll see if I can find out further info and post.

I know the tank has a fixed concrete cap that is also supported by a center column.

I do not think the engineers that made a site visit were able to look inside the tank.

 

[oldestguy]

With 10 feet of water, I suspect it floated some. In the process there likely is a different support situation now as compared to before. Once inside can a topo survey be done to see if the bottom is warped possibly affecting wall support. There is a form mark visible in the photo. Perhaps an elevation survey on that form mark may tell something of distortion.

 

[JStephen]

Is it leaking? Can you just leave it as-is?

 

[TehMightyEngineer]

I'm going to go with flood wave horizontal pressure on the tank causing an ovaling and flexure of the wall in the vertical direction. The tank trying to float and any differential loss of supporting soil bearing capacity likely didn't help either. Maybe a combined shear and flexure failure of some sort. Either way, for a 70 year old tank I'd say this is far more trouble than it's worth. Demo and replace; specify the new tank be designed for flood loads and call it a day. But if the owner wants to pay for a repair rather than replace, then I'd not turn down the money. Going to be a difficult analysis to find anything conclusion I suspect.

Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

https://www.facebook.com/AmericanConcrete/