Slab Thickened Under Wall Loads

[JohnnnyBoy]

It seems like in construction and a few buildings that I have been apart of that under partition wall in commercial buildings that a slab thickening is added under the partition walls. In the scenario I am speaking of we are taking over the design from another engineering firm for construction and they have specified there to be a thickening under a 18'-0" partition wall (approximately 180 lbs/linear foot). Using the subgrade modulus and a spring stiffness of the soil it seems like a thickening is over designed and not necessary. In talking with some senior engineer I was told to leave it there and that through general practice it does benefit the slab.

Now obviously there is some benefit to it and it may reduce cracking in the long run assuming possible settlement of the soil or many other factors although is it completely necessary. Just to clarity this would not be load bearing.

Thanks in Advance.

 

[txeng91]

I agree, thickening the slab seems unnecessary. 180 plf is pretty much nothing and even the thinnest slabs (4" or so) should be able to support that. In fact your soil bearing should be high enough that youe slab shouldn't be doing anything besides putting the load directly into the subgrade through compression.

 

[kmart30]

Erosion! A thickened edge will protect this edge from washing out and preventing your k value from dropping to zero. Did they compact and prepare the soil on the outside of the wall(surrounding grades) the same they did within the footprint of the building and beneath the partition wall areas? If they did then from a structural standpoint you should be ok with a 4 inch slab but if not then your k-value right on the edge of your wall will be drastically less. Regardless, erosion would be the main reason why I always specify a thickened edge. Yes you can have gutters and grade everything perfectly but water always seems to find these areas.

 

[JohnnnyBoy]

The building would be compacted and have a 6" granular subbase. As for the exterior of the building it will be a pile and grade beam foundations so I would hope that there should not be any erosion at the interior of the building assuming proper compacted and grading for rainwater although as kmart30 had said there will always be more risk and most likely some settlement or erosion. Since the weight of the wall itself is very small though in comparison to the strength of the slab would having the wall even cause slab cracking if there is settlement (or cause more cracking then what would already occur.

 

[Nor Cal SE]

I agree that you shouldn't need any thickened slab under an interior non-bearing partition wall. Based on kmart30's post, I believe he has a mistaken understanding of your impression, thinking the walls in question are exterior walls.