How to calculate punching shear reinforcement

What is punching

Punching is the failure of a plate submitted to a concentrated load. The element causing the load is punched through the plate. The failure surface is conical: punching cone.

How to calculate the punching shear reinforcement

In case of a footing

• The punching shear reinforcement is automaticaly calculated in the general reinforcement design .

In all other cases

• Calculate the reinforcement  or F2.
• Go to the reinforcement results and activate the button for the punching reinforcement .
• First select the point, then select all surrounding plates.
  If you select the surrounding plates first, it becomes hard to see if the point is selected or not.
• Click once with the right mouse button. The dialog below opens. Here you:
  

  (click on the image to enlarge)

  Define the zone in which punching should be verified Dimensions Lx’ & Lz’ Orientation Eccentricity Make sure the zone is larger than the punching cone. Rather too big than too small. If the zone is too small, the first punching, you might get the false impression no punching reinforcement is needed! Define the contact surface If the punching is caused by a column, you’ll see the section dimensions here. If the punching is caused by a point load or support, you’ll see a default contact surface (0,028m²). The user must modify this to the correct value. In both cases, the adaptability of the contact value can be used to verify the effect of a thicker column/support, without having to reanalyse the whole model. Define the plate thickness By default you see the plate thickness from the geomety. The user can modify the value to verify the effect of a local thickening, without having to reanalyse the whole model. See the main reinforcement Diamonds uses the maximum of the calculated reinforcement and the practical reinforcement. The user can modify the value to verify the effect of more practical reinforcement.

  • Click OK to start the calculations.
  • The result is a reinforcement amount in mm² per m² plate surface. The amount can be destributed over a circular or an rectangular pattern. Ask a detailed view  to hoover over the results and see the distances to were the punching shear reinforcement should be placed.
    

Notes:

• Be cautious when the columns/ point loads causing punching are close to each other. Diamonds will not take any overlap of the punching cones into account.
• When you modify a value and you’re satisfied with the punching reinforcement, don’t forget to actually implement that change in the model.