Rack Loads on Slab on Grade

[SperlingPE]

I did a search here and found good information for rack column loads on slabs on grade for isolated columns.

What to do for back to back columns?
The Shentu research notes a radius of influence. In my situation the columns are within each other's radius of influence. How does this affet the capacity of the slab. The cited references do not go into this.

I am looking for Westergaard, Ringo, anderson infomration for this situation as well

 

[csd72]

Treat the back to back columns as a single point load.

 

[BAretired]

Could you tie the columns together and treat them as a single column?

BA

 

[SperlingPE]

If I treat as a single point load without tying them together on a single base plate, there would still be tension at the top of the slab. No?

My first thought was to combine the columns together on a single base plate and treat as a single point load.

 

[csd72]

Where is the tension coming from? The bearing spreads through the thickness of the slab and it will effectively see it as one load if they are close enough together.

Maybe you need to give us a bit more info on your exact situation.

 

[BAretired]

If the columns are close together, I think there will be tension on the bottom of the slab and compression on top.

BA

 

[SperlingPE]

back to back i smeant to mean the racks are back to back
the columns themselves are inboard a little bit and are 11" apart center to center.

I see this as two discrete loads

 

[BAretired]

If the slab dishes down between the columns, which I believe it will with 11" clear, it will have compression on top.

BA

 

[SperlingPE]

BAretired
Any numbers or support for positive bending?
I could see that as well as negative bending.
I just need something to hang my hat on.

the concrete slab is existing.
the racks are ordered
the pallet loads are known
the only loading variable that I can control is the size of the base plate

 

[BAretired]

The only dimension we know is 11" c/c columns. Maybe if you provide a sketch showing column spacing, someone could help you with the analysis.

BA

 

[csd72]

Yes, still more information required to give an accurate comment.

AperlingPE, to get an idea of what sort of shape the slab will take, turn it upside down and treat the posts as columns and the ground reaction as a udl. Not accurate for analysis but it gives you a good idea on how it will tend to behave.