Using ground floor slab for horizontal forces

[DAVE9999]

Can you use a ground floor slab to take horizontal forces from columns? Instead of relying on spread footers to resist sliding.

Typically I have not because the slab is placed with expansion joints around the columns but I was curious what others do

 

[driftLimiter]

We drag shear into SOG pretty regularly. When we do this we detail joints to have continuous reinforcement in some region nearby. There are basically two actions the slab can do to take the shears. You can push and pull on the slab and resist the load by friction or you can use the floor slab like a diaphragm.

 

[DAVE9999]

Thanks, I'll stick to what I normally do and use grade beams if necessary to share the load to other footings

 

[EcoGen]

We have specified this in the past but you will need a way for the horizontal shear to get into the slab from the column. You can do this by specifying "hairpin" tie bars that wrap around the concrete pier base below the column and each leg of the hairpin extends at 45 degrees into the SOG. What happens to the sliding load after it enters the SOG however is another story and is not entirely clear to me. But in some ways you can justify it since the amount of SOG area in contact with the soil provides a LOT of sliding resistance for the whole building. If you can rely on the entire SOG contact area that is.

EcoGen Consultants LLC
Structural Engineers
ecogenconsultants.com

 

[Trippelsewe]

> Can you use a ground floor slab to take horizontal forces from columns

I do this alot though I do sometimes worry about it. Slabs on grade are often seen as non-structural items and people have no issue ripping them up or trenching them.

 

[OldDawgNewTricks]

Can you use a ground floor slab to take horizontal forces from columns

I do this alot though I do sometimes worry about it. Slabs on grade are often seen as non-structural items and people have no issue ripping them up or trenching them.

Yep, that's why ACI 318 says "A slab-on-ground may be designed to act as a structural diaphragm or to provide required ties between foundations. The construction documents should clearly identify any slab on ground that is a structural diaphragm, and state that saw cutting or joints are prohibited unless approved by the licensed design professional. Joints can affect the integrity of the slab and its ability to act as a structural diaphragm, unless structural repairs are made." But I doubt whether the guy with the saw looks at the drawings before starting to cut the slab.