Need for Grade Beams?

[Structures33]

I am trying to avoid using grade beams in an industrial renovation. It is essentially a new building being constructed inside of an existing shell.

I will have concrete piles spaced approx 8-10 feet in each direction with pile caps. Some will have two piles to a cap. The piles will be embedded in the caps enough that they're considered fixed. The floor slab will be 12" thick and will be tied to the pile caps.

I see no need for grade beams except in a few locations where I need some lateral distribution. I'm looking for any experience, thoughts, input, suggestions you may have regarding this layout. Thanks.

 

[msquared48]

So, with no grade beams, are you just going to put extra steel in the slab over the pile to mimic the grade beams?

Mike McCann
MMC Engineering

 

[Structures33]

Yes, I have modeled the slab and the piles with all the building loads. So I will pull the moment and shear values from the FEM and they will be used to design the slab.

 

[briancpotter]

What's the loading on the floor, and what's your concern about using grade beams? Cost? Depending on the loading, it might be cheaper to use grade beams with a thinner slab.

Brian C Potter, PE

http://simplesupports.wordpress.com

 

[msquared48]

If that is the case, then I would consider locally dropping the bottom of the slab in the area of the grade beams to lock the pile into place so they will not move laterally in a seismic revent, if your location is subject to such action, but this could also be done with reinforcing bent into the slab I guess, same was with grade beam anchorage to the pile.
























Mike McCann
MMC Engineering

 

[Structures33]

briancpotter - There will be a 250psf LL and heavy equipment loads at various locations on the floor slab. We will need to have the thicker slab regardless, which is one of the main reasons I was hoping to eliminate the grade beams. They are laborious and expensive. It seems that with the close spacing of the piles and caps that a 12" slab would provide the necessary rigidity and load transfer.


msquared48 - If possible, I'm trying to elminate the need for forming up the grade beams - added time, labor and expense. Dropping the slab won't accomplish that. It is not a high seismic zone but the soil is not good, hence the piles.

 

[msquared48]

Sorry, I meant to say in the area of the pile, not the grade beams, but with little seismic force, it's a moot point anyway...

Mike McCann
MMC Engineering

 

[BAretired]

If grade beams do not provide anything useful, I would agree that omitting them makes sense.

BA

 

[briancpotter]

I don't see any reason omitting them would be a problem, assuming load/deflection requirements are met.

Brian C Potter, PE

http://simplesupports.wordpress.com

 

[slickdeals]

What is the relationship between the top of pile cap and bottom of 12" slab? In cases where you only have a single pile, is it directly connecting to the 12" slab or do you still have a pile cap?

 

[Structures33]

Even with a single pile, we will still have pile caps and the pile caps will be tied to the 12" slab.

 

[DST148]

@structures33 : Agree with the posts above: for 12" thick two way-slab spanning about 10 feet the grade beams may be omitted.
Since bottom reinforcing needs to be placed on top of the piles, how much is the embedment of the piles into the slab?

 

[Structures33]

Embedment will be 16" into pile cap. There will be another 16" above that for the rest of the pile cap and then the 12" slab.

 

[hokie66]

Structures33,
There is nothing wrong with your concept. I am not sure why grade beams would be of benefit, and they would certainly complicate construction.