punching shear with only top reinforcement 1

[Bammer25]

Maybe a dumb question for some, but I am checking punching shear in a slab on grade. I intend to only have top reinforcing, so am I restricted to only using the depth down to rebar for punching shear check? that is going to seriously constrain me. I have 25Kip wheel loads and a 6" slab.

I know i can lower the rebar down to where i need it for punching shear, but id like to keep it up near the top for moment.

 

[KootK]

Good on you for identifying the rebar placement issue. I'd switch to the plain concrete punching provisions. The stuff below is taken from ACI 318-19

 

[Bammer25]

thanks. i did not think to do that. odd thing is i got a higher capacity than i would have with the rebar at the bottom of the section...

 

[RPMG]

With this section, I think you're supposed to subtract 2" from the "footing" depth because it's cast against soil, not that this code applies.

ACI 318-14 1.4.7
This Code does not apply to design and construction of slabs-on-ground...

 

[KootK]

Now that the SOG is probably a spread footing, I'd be tempted to say that code does apply.

 

[JLNJ]

If it is a 25 kip wheel load, then your 6" slab might not be appropriate. 25,000# is pushing it. Check with some of the pavement design references. The slab near the joints/edges will be a problem if you have a load which can be located anywhere.

If this is a post load with a defined location, then you might be able to add a thick base plate and some grout to activate more of the slab perimeter (and design it per ACI 318).

 

[Bammer25]

Bending is not an issue and punching is fine. It’s in a contaminated area so we cant dig at all. Backfill with crushed stone, compact, pour.

 

[Bammer25]

Since we are on the subject, how do you guys normally check your structural slabs? I usually just model it in STAAD and take comservative moments with 12x12” plate elements.

 

[KootK]

I feel that TR34 is the state of the art for this nowadays.

The method in this article is quick but some question its validity: Link