Residential Slab-on-grade point and line loads

[XR250]

I design alot of houses where the Arch. wants a colored, radiant slab, but it also has to carry point and line loads in some locations.
I have been simply showing thickened areas at these locations but, consequently, the control joints don't do their job due to the thickness. The slab is also less likely to slide as needed due to shrinkage and thermal effects.
On the current one, I am considering calling out isolated footings in these locations poured up to the level of the bottom of the slab and screeded smoothly. Then adding a slip sheet of some sort on top.
I could also do the same thing except leave them 4" low and let the gravel transfer the loads to the footings.

I'd love to hear other's thoughts and experiences with this issue.

 

[KootK]

I've been doing the 4" low business for a long time and it seems to work well. Interesting to hear of thickened slabs having gone wrong as I do that too.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[XR250]

Interesting to hear of thickened slabs having gone wrong as I do that too.

I have seen on a number of occasions a crack bypassing the control joint at thickened locations. Might have happened regardless so who knows.
I have to install some interior shearwall anchor rods thru the slab into the footing. Seems the gravel would makes things messy for that. Maybe I will pop the footing up to B.O.S. level in those locations.

 

[Contraflexure74]

Where ever I have block walls I always install individual footings with isolation joints in the slab.

 

[XR250]

Where ever I have block walls I always install individual footings with isolation joints in the slab.

I do the same

 

[EngineeringEric]

Is your control joint in the center of the thickened slab?

When i do a thickened slab supporting a timber bearing wall, i still try to locate CJ beyond the thickened part to one side. This means there is a joint in the slab not under a wall which may be a problem for some tiled floors... but depending on the system i believe it can be addressed above the slab.

 

[XR250]

EE,


I try to do that as well, but the Arch's generally push for it to be under the wall.

 

[EngineeringEric]

And when Arch push for the joint location you get a 1.5" SJ in a 12" slab next to a 4" SOG I've been this position before!

If the arch cares that much, you can present them with where the SJ is going or tell them that you will need to provide an isolated spread footing below the wall, then vertical dowels into a 8" tall stem wall for the wall to sit on. plus the bond breaker. plus the hardboard. plus the multiple concrete placements. and extra everything else. I like keeping the slab isolated from a structural view but i don't to save everyone else money.

I hate how we all get put in the same position so often

 

[KootK]

Where ever I have block walls I always install individual footings with isolation joints in the slab.

Ate you guys doing this for non-bearing block walls as well?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[XR250]

Ate you guys doing this for non-bearing block walls as well?

I don't run into this very often, but i believe I have done it both ways in the past.
Seems it might be easier to have a separate footing for construction sequencing reasons (build the walls before the slab gets placed)

 

[jayrod12]

Ate you guys doing this for non-bearing block walls as well?

Depends on the height of the non-bearing wall to me.