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Punching shear in beam

Punching shear in beam

Punching shear in beam

Can punching shear be a problem in beam if the flexural shear capacity is satisfied? (ie. providing beam ligatures)

RE: Punching shear in beam


Yes, if the beam is wide enough compared to the support width for there to be a critical shear plane transverse to the beam direction.
This must be checked for Band beams which are normally wide and shallow.

RE: Punching shear in beam

Thanks, RAPT
If punching shear has to be checked, would you treat it as punching shear in a flat plate? Would you consider the effect of flexural shear reinforcement in the check? If yes, how does the code include the shear reinforcement?

RE: Punching shear in beam

In my experience, if you are supporting the beams directly onto a pile, then the loads will be reasonably small. In this case, due to the depth of the beam being, generally, thicker than a slab or base for the given load then punching shear should not be much of a problem. A check is required, of course!

If the reactions from the beam grillage are high enough to cause a punching shear problem then you would be better of with a pile cap.

RE: Punching shear in beam


Yes, the check would be the same as for a Flat Plate or a Flat Slab but based on the overall depth.

If punching reinforcement is needed, I would think you could include the flexural shear reinforcement on the faces where it is required for the extent of the punching perimeter in your calculation of the area of punching reinforcement to add. Your flexural shear reinforcement will be full width of the beam but you should only consider that which is in the punching zone.

Another solution, if the concrete shape is not fixed, would be to add a Drop panel to the soffit of the beam at the support (as you would do for a Flat Slab but only for the width of the beam, not L/3). This would have several effects for you, reducing flexural reinforcement, increasing flexural and punching shear capacity and reducing deflections. THis would be preferrable as detailing punching shear reinforcement will not be easy.

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