Wide Beam & Punching Shear Checks
Wide Beam & Punching Shear Checks
(OP)
To my understanding there are 4 main checks on concrete design.(Not including overturning,sliding, or anchorage)
1. Required steel for bending
2. Bearing/crushing strength
3. Wide Beam/one-way shear
4. Punching/ two-way shear
My confusion comes with the 1 & 2 way shear checks. I could see if you have an elevated slab supported by columns or a pile cap having 1&2 way shear failures, but if you have a slab on grade I just don't see how this shearing could happen. The way I see it is if a slab is sitting on compacted soil the only checks would be bending and crushing. The vertical load on the column will distribute through the slab and the soil will have reactions which would be a crushing failure. Just wondering what I am missing here? Greatly appreciate any direction on the issue. I have been assigned the task of checking a backlog of calculations and wondering if I am wasting my time checking the slabs on grade for shearing failures.
1. Required steel for bending
2. Bearing/crushing strength
3. Wide Beam/one-way shear
4. Punching/ two-way shear
My confusion comes with the 1 & 2 way shear checks. I could see if you have an elevated slab supported by columns or a pile cap having 1&2 way shear failures, but if you have a slab on grade I just don't see how this shearing could happen. The way I see it is if a slab is sitting on compacted soil the only checks would be bending and crushing. The vertical load on the column will distribute through the slab and the soil will have reactions which would be a crushing failure. Just wondering what I am missing here? Greatly appreciate any direction on the issue. I have been assigned the task of checking a backlog of calculations and wondering if I am wasting my time checking the slabs on grade for shearing failures.






RE: Wide Beam & Punching Shear Checks
Any concentrated load on a concrete section can cause punching shear. For the slab on grade, if your soil does not have adequate bearing capacity and is required to distribute out over an area of soil to achieve the required bearing capacity, then the soil reaction on the slab can punch through.
RE: Wide Beam & Punching Shear Checks
RE: Wide Beam & Punching Shear Checks
If the load in the pedestal gets too high, then it will tend to punch through in a classic two-way shear failure. This is definitely a non-ductile failure. Will it result in total collapse like for an elevated slab? Perhaps not....If you exceed the allowable soil pressures underneath the punching area, that soil partially supports the pedestal. That doesn't mean that you didn't experience a two-way failure... It just means that the consequences of the failure were slightly less severe than for an elevated slab.
I'm not aware of any published case studies or such that show this type of failure for slabs, but it has always been a major part of my design for these types of foundations.
RE: Wide Beam & Punching Shear Checks