Need advice on footing under possible 5000g+ tank in Basement

[Kentrob11]

Hello all...I've posted about this proposed tank before but I think I have had a change in plans and want to go bigger. I have a picture of the footing that was poured beneath the area where the tank was to be but it does not extend all the way to the footing for the basement walls. I want the tank to go all the way to the walls on both the back and one side so my question is, am I OK with having that gap without footing under it? The footing is about 12" thick...

 

[Kentrob11]

 

[David R]

How tall is the tank? That will determine the weight on the floor and how strong your floor needs to be. You could certainly build a tank all the way to the walls, but may be limited in how tall it is if you go off the extra-thick area. How thick is the floor on top of the footing?

 

[jsodwi]

Where is the tank going? Where the big rectangular footing is? Dimensions of tank would be helpful as well as stand design. When I was putting my big tank in I did some research and if I remember correctly. Concrete had a crush threshold of 10000 lb per square inch that's with a 4" thick concrete floor

 

[Student of Architecture]

Standard concrete has a bearing capacity of 5000 psi. With a 3.5" slab that is standard to residential construction this comes to around 17500 psi. This can be increased with rebard however the wire mesh normally used is only for crack control and will not do what rebar will. Cracks will always form in concrete regardless of load. What you need is the soil bearing capacity because you are sitting the tank on the slab which is equivalent to sitting the tank directly on the compacted soil. If you do not have a soils report from a civil engineer then you should assume 1000 psi bearing capacity. Normal settlement in a residential structures is up to 2 in., but more is differential settlement that can destroy your house. If the soil cannot support the tank you should downsize it. Otherwise you are going to have many more problems.

 

[Kentrob11]

The tank would go right into that corner where the large footing is. The footing is 12" thick, 7' wide and about 14' long and the concrete floor is supposed to be average 3.5-4" thick. The soil underneath is ridiculously compact clay...After the basement wall is in place, I think the wall footing extends another 8" or so past the inside wall surface all the way around. The tank dimensions will be roughly 16' long by 6' wide by 5' tall. Does this help?

 

[Student of Architecture]

The footing is irrelevant. It merely takes the bearing area from the slab and moves it 12" deeper. Footings serve different functions in different applications, but in this case it doesn't add anything to your project. Footings are for where a load is carried from above to the ground to prevent punchthrough or crushing of the slab. Rediculously compact by your standards may not mean by soils analysis standards. This is what is necessary to be safe using anything more than 1000 psi.

 

[Student of Architecture]

I think you should be alright with what you plan, but without giving it more consideration and calculations (more specific) I cannot be sure.

 

[sashimimaster]

Its all comes down to lbs per sq inch. If your tank is spread out the the psi is less. If it's tall and concentrated it's another story.

 

[Student of Architecture]

I did a quick calculation and it seems that you would only be around 2.5 psi +/- to do the size above. This is not a guarantee, but is a pretty good estimate.