Concrete Slab Thickness and Your Large Tank Size

[Dustin1300]

Some of you might be following along on my build but I'm working on a 600 gallon DT in my basement. While getting some help on the design of my steel stand someone brought up how thick my slab is. I had not even considered the slab thickness but if my 4" slab is not enough and it requires 1 foot, I might feel a bit defeated on this one. :headwallblue::headwalls::headwallblue::headwalls::headwallblue:

What is everyone else's experience on this topic?

 

[SPotter]

when my contractor prepped my basement floor for the stand he framed out the area that stand was going to be and poured some kind of quick crete thats about 1/4" thick. I can't remember which quick crete it was but he said it would double the strength of the floor. I will call him tomorrow and find out what it was called.

 

[thelizardkin]

you shouldn't need to worry 600 gallons will be fine on concrete

 

[TheFishTeen]

Ya, I wouldn't be worried. Im not the one throwing out the big cash for a large tank (yet), but If it were me I would not be worried at all with concrete. Especially with your dimensions, 96X48X30 is nicely distributed by the 48" depth.

 

[Rploaded]

Concrete has a working psi rating of around 3600 psi. Your 4" slab is more then sufficient.

 

[Rploaded]

when my contractor prepped my basement floor for the stand he framed out the area that stand was going to be and poured some kind of quick crete thats about 1/4" thick. I can't remember which quick crete it was but he said it would double the strength of the floor. I will call him tomorrow and find out what it was called.

Your contractor laid out a leveling cement at that thickness. Doubling the strength is a bit far out there. Unless the 2 surfaces became bonded at the molecular level all you have is two separate layers of concrete; each with a working strength of around 3600 psi.

 

[Dustin1300]

Sorry, but I failed to subscribe to my own thread! :headwalls:

I've been doing lots of head wallies this weekend...

I'm glad to hear positive feedback on my concrete. Because of the concern that was brought up, I'm going to pick up a 1/4" masonry bit tonight to drill a few samples to see how thick the slap is in that area. Since the wall I'm putting tank against is an interior wall, it's not load bearing so I'm not expecting it to be a footer and is likely 4 inches thick like under the place I looked.

Tanks end will be against the wall where the ladder is in picture below. This was taken a couple months back of my 'fish room'.

Steve, did you have the floor poured just for tank? Did they use rebar to tap into existing footer/slab?

 

[SPotter]

ok so after speaking with my contractor today he told me the reason he did this was because my floor wasn't 100% level and didn't want to take any chances so he created a form and poured the quick crete to create a level the surface under the stand. He said it was either do that or use metal shims under the metal stand and after talking to some masons and the guy that built the stand they all felt it would be better to just level out that area of the floor.

 

[Dustin1300]

I just picked up a 1/4" masonry bit on way home and did a sample of where the tank will be and it is just a little more than 4" deep. One of the other sites they ask me to measure the time it took....Took about 50 seconds to drill 4 inches with a new bit and with a Dewault hammer drill.

Steve, you know how thick your floor is?

 

[BigOldReef]

You have to account for how much of the stand is in contact with the floor. If you think your tank/stand/system fully loaded is 8000lbs, then if it was all balanced on one leg that was an inch by an inch then you have and exerted weight on the floor of 8000lbs/sq Inch....

Now when you take that stand and split it up into only coming in contact at the 4 corners, that drops to 2000lbs /sq inch.

Now, even if your stand was built out of 4 4x4's - That's 16" of contacting surface area per leg, add 4 legs thats 64 sq inches. Divide the 8000lb tank weight by 64 and the pressure exerted on the concrete is now only 125lbs /sq inch.

Now let's assume your stand is built out of 2x2 steel legs that run the perimeter of the tank 96x48... You should have approximately 568 square inches of contact with the floor (perimeter only - no center bracing) and now your exerted weight is 8000/568 or 14lbs/sq in.

Especially on a basement floor, the concrete doesn't have to be that thick to support the dispersed weight.

 

[Dustin1300]

You have to account for how much of the stand is in contact with the floor. If you think your tank/stand/system fully loaded is 8000lbs, then if it was all balanced on one leg that was an inch by an inch then you have and exerted weight on the floor of 8000lbs/sq Inch....

Now when you take that stand and split it up into only coming in contact at the 4 corners, that drops to 2000lbs /sq inch.

Now, even if your stand was built out of 4 4x4's - That's 16" of contacting surface area per leg, add 4 legs thats 64 sq inches. Divide the 8000lb tank weight by 64 and the pressure exerted on the concrete is now only 125lbs /sq inch.

Now let's assume your stand is built out of 2x2 steel legs that run the perimeter of the tank 96x48... You should have approximately 568 square inches of contact with the floor (perimeter only - no center bracing) and now your exerted weight is 8000/568 or 14lbs/sq in.

Especially on a basement floor, the concrete doesn't have to be that thick to support the dispersed weight.

That is how I broke it down on our local club forum after starting to stress after some others said no way they would put this tank on 4" of slab of concrete.:furious:

To give even more even distribution I'm also going to put the stand on 2X6 or 2X8 treated timbers to add some additional weight distribution! I'm feeling a lot better about things now but just wanted to make sure others agreed. I've not yet heard back from any of the 'experts' with credentials I sent everything off to. (Not saying anyone does not have the credentials:spin3

 

[BigOldReef]

Well, I am not an engineer. But this theory/explanation comes directly from 'Expert Witness' testimony in a trial I did, used to explain why Giant Bulldozers (64,000lbs) don't crush underground pipes when they roll over the top of them.

I also happen to have a General Contractor's License, so while I can't engineer the house, or design it, in Cali I am allowed to build it

 

[BigOldReef]

Well, I am not an engineer. But this theory/explanation comes directly from 'Expert Witness' testimony in a trial I did, used to explain why Giant Bulldozers (64,000lbs) don't crush underground pipes when they roll over the top of them.

I also happen to have a General Contractor's License, so while I can't engineer the house, or design it, in Cali I am allowed to build it

 

[iced98lx]

Dustin-
when you got to fill your hole, be sure to get a sealant and seal it post-filling or if you ever have a wet gravel bed (god forbid) you could see water seeping it's way up the hole, I wish I would have gotten here faster, I would have urged you to believe the others in this thread and NOT drill any hole you don't HAVE to if you have a remotely wet gravel bed (sump pump? ever ran?) etc.

I'm sure you'll be fine, but do watch it to make sure if you have a sump pump and it runs.

 

[Dustin1300]

Well, I am not an engineer. But this theory/explanation comes directly from 'Expert Witness' testimony in a trial I did, used to explain why Giant Bulldozers (64,000lbs) don't crush underground pipes when they roll over the top of them.

I also happen to have a General Contractor's License, so while I can't engineer the house, or design it, in Cali I am allowed to build it

Understood and I'll post something here shortly on what I'm trying to do to better distribute the load.

 

[Dustin1300]

Dustin-
when you got to fill your hole, be sure to get a sealant and seal it post-filling or if you ever have a wet gravel bed (god forbid) you could see water seeping it's way up the hole, I wish I would have gotten here faster, I would have urged you to believe the others in this thread and NOT drill any hole you don't HAVE to if you have a remotely wet gravel bed (sump pump? ever ran?) etc.

I'm sure you'll be fine, but do watch it to make sure if you have a sump pump and it runs.

Basement has redundant sump pumps and battery backups, ground has been very dry lately so no worries. I was planning on filling the small holes with hydraulic concrete tonight so no big worries

 

[Dustin1300]

One of the things I've consistently got feedback on is that this is a lot of weight displaced on a small area. To feat this, I'm going to use a platform (2X4s and 2X8s) to build the stand upon which will help distribute the weight better. Below are some of the details

Steel Stand:
2(96X2) + 2(44X2) = 560 square inches

With Treated Lumber:
2(96X7.25) + 3(32X7.25) + 4(33.5X3.5) + 6(9.625X3.5) = 2,759.125 square inches

 

[BigOldReef]

You're close on the theory, but the wood in the middle of the stand won't really have the weight transferring to it.

However running the 2x8 around the perimeter will help with what you want to do.

 

[Dustin1300]

You're close on the theory, but the wood in the middle of the stand won't really have the weight transferring to it.

However running the 2x8 around the perimeter will help with what you want to do.

I also questioned using that center bottom steel. It's another few pounds and few dollars I may take out. :dance:

 

[BigOldReef]

Dustin, Sorry I didn't answer completely. The center steel bracing is good. It helps distribute the weight, but all the wood, that doesn't have the steel stand sitting upon it, is not doing anything to disperse the weight.