punching shear check in presence of drop beams
punching shear check in presence of drop beams
(OP)
Hi guys,
How do u treat a punching shear check when the slab - column being checked versus punching has a beam framing from one side into the column ?
Personally, what I do is that I subtract from the column reaction the shear carried by the beam (Vu) and perform the usual checking after I subtract again the beam width from the bo (critical perimeter) ??
I think this is a conservative method. How about subtracting from the carried column reaction the nominal shear Vn instead of vu ?
thanks for the help
How do u treat a punching shear check when the slab - column being checked versus punching has a beam framing from one side into the column ?
Personally, what I do is that I subtract from the column reaction the shear carried by the beam (Vu) and perform the usual checking after I subtract again the beam width from the bo (critical perimeter) ??
I think this is a conservative method. How about subtracting from the carried column reaction the nominal shear Vn instead of vu ?
thanks for the help






RE: punching shear check in presence of drop beams
RE: punching shear check in presence of drop beams
Shear links are so inexpensive that the cost is negligible and the extra safety factor assures peace of mind.
You can never be too safe when it comes to punching shear.
RE: punching shear check in presence of drop beams
HermanLJ, by "shear links" I presume you mean stirrups, which are not generally used in slabs, unless the slab is quite thick.
RE: punching shear check in presence of drop beams
RE: punching shear check in presence of drop beams
as said before, subtracting Vu is a conservative method. I think a punching failure will happen if the surrounding beam will also fail in shear (correct me please). In this case, I think that we should subtract from the column reaction the nominal shear that can be resisted by the beam. for example, if the beam stirrups has 4 legs of 12mm diameter , then we should subtract from column reaction the ultimate shear that can be resisted by these 4 legs.
I think it will greatly depend of the mode of failure. I think, for the time being, I will deduct the Vu unless I have some good reference talking about this problem.
RE: punching shear check in presence of drop beams
RE: punching shear check in presence of drop beams
RE: punching shear check in presence of drop beams
RE: punching shear check in presence of drop beams
RE: punching shear check in presence of drop beams
therefore, the depth of the beam (beam section) and stirrups will be contributing to the punching shear resistance of the slab, and ignoring that will be "playing it extra safe", but is it necessary to thicken the slab if the punching shear ratio is not ok but on the limit?
RE: punching shear check in presence of drop beams
RE: punching shear check in presence of drop beams
RE: punching shear check in presence of drop beams
RE: punching shear check in presence of drop beams
RE: punching shear check in presence of drop beams
You should think in terms of shear stress instead of shear force. The beam on one end of the column will not affect the shear stress in the slab on the other end. A punching shear failure would be an 'unzipping' type failure. The beam might in fact arrest that unzipping to prevent collapse, but failure would still have occurred.
Yes, with a continuous beam, punching shear failure is much less of a concern.
RE: punching shear check in presence of drop beams
to compute the punching shear force (manually if you suspect punching shear failure, since safe does not calculate punching shear in this situation )you must use the tributary area method in the pdf file I attached (critical loading surface area), calculate the punching shear force and moment acting on the column and then divide by the Area of concrete resisting p.shear (perimeter of critical shear failure zone* effective depth of slab ) you will get the stresses then you can compare with the capacity of concrete to see if links are required use ACI 318M-11 ... 11.11.7.2.
RE: punching shear check in presence of drop beams
RE: punching shear check in presence of drop beams