1-Way shear check for post load on slab-on-grade

[north_man]

Hi, I'm a bit confused on how to determine the shear force at the critical section for 1-way/beam action shear for a post load in a slab on-grade.

I understand he concept of the critical section but if the slab-on-grade is theoretically infinite relative to the extents of the post, wouldn't V_f be infinite at the critical section? See sketch attached.

 

[EngDM]

I believe for slab on grades you need the subgrade reaction modulus and treat the slab as continuously supported by springs. This will determine what length of b you can use for your shear calculations. I'm not sure if there are perhaps approximate methods for when you don't have the subgrade reaction modulus.

Of course you could check it as a pad footing almost, but the larger you take b as, the larger your moment arm is for checking the moment in the slab. This does not account for the continuity of the slab.

Give the attached article a read.

Article

 

[north_man]

Yeah, that was my impulse to check it as a pad footing and that there would be some kind of critical section for which to take moments and shear about but wasn't sure what that would be relative to the face of my post or post base.

 

[EngDM]

I'm not sure I would be focusing on one way shear for this application anyways, two way shear seems more applicable since you are "infinite" in the one way shear direcion, the crack would have to either terminate at both ends of the slab (yea right) or punch out a chunk.

Here's another resource:

ACI 360R-06

 

[north_man]

Yeah that makes sense!

Awesome. Thanks.