Diamonds cannot verify the punching shear automatically in (foundation) slabs. You need to start the calculation manually:
- Go to the reinforcements results
. - Choose the punching shear reinforcement
. - First select the point where the concentrated load is applied. While keeping the SHIFT-key pressed in, select the surrounding slab(s).
- Click once with the right mouse button. This dialogue appears:
- Upper part
Diamonds shows a schematic drawing of the selected slab and the point where the punching shear should be verified. - Punching verification around point with rectangle
With the dimensions Lx’ and Lz’ and the position of the point (α, ex’ and ez’), you impose the size of the red rectangle in the upper part.
All mesh triangles that are completely or partially withing the red rectangle, are colored in yellow.
Within this area, all the potential contours in which punching shear can occur, will be verified.
You specifically need to impose this area, because it will determine which mesh triangles will be colored once this calculation is completed. Since Diamonds cannot recognize overlapping contours, you want the mesh triangles with results never to overlap. - Imposed parameters
Diamonds uses default values for the parameters below, but you can easily adjust their values. This allows you to optimise your design without having to repeat the elastic analysis and reinforcement calculations over and over again. You just play with the parameters below until you have the desired design. Then you go to the geometry configuration and make the relevant changes (if there are any).- The contact surface corresponds to the area subject to the concentrated load.
- If the punching is caused by a column, the shape and dimensions of the zone subject to the concentrated load are known.
- If the punching is caused by a point load or support, Diamonds uses a circle with a diameter of 20 cm.
- Thickness and concrete cover of the slab.
When several slabs of different thickness are considered, Diamonds takes only the lowest thickness into consideration. - Main reinforcement
The punching shear resistance is calculated using the maximum value of the theoretical tensile reinforcement calculated by Diamonds and the practical reinforcement defined by you in the point where the verification is carried out. When tensile reinforcement is present in the two orthogonal directions (
and 
), Diamonds will use the weighted average 
.
Depending on the orientation of the punching shear cone, it will either be the top or bottom reinforcement.
However, the default main reinforcement used by Diamonds is often a peak value! Because points are sensitive to peaks. It is advised to define the practical reinforcement or enter the practical reinforcement amount after “Main reinforcement”.
If you are in doubt between top or bottom reinforcement, you can always check what Diamonds has taken.
When Diamonds was unable to calculate the longitudonal reinforcement, it will use the minimum reinforcement.
- The contact surface corresponds to the area subject to the concentrated load.
Notes:
- For a slab, the contours to be verified must lay within a distance 2d from the edge of the column (EN 1992-1-1 §6.4.4(2)).
For a foundation slab, the contours to be verified must lay within a distance between d and 2d from the edge of the column (EN 1992-1-1 §6.4.2 (2)). - If punching shear reinforcement is required, Diamonds will increase the contour with a distance +0.5d until there is no longer need for punching shear reinforcement.
The reinforcement calculated this way for a reference contour should, theoretically, be applied between the edge of the column and the contour itself. This is why the quantities of punching shear reinforcements are always expressed in mm²/m². - The concentrated load is not necessarily centered in the red rectangle, therefor a coefficient β is introduced in the calculations. Diamonds uses the default values for β given in EN 1992-1-2 Figure 6.21N. It is not possible to make Diamonds take a different β coefficient into account.
- β = 1,15 for a center column
- β = 1,5 for a corner column
- β = 1,4 for an edge column
- In the case of a honeycomb slab, Diamonds takes the minimum thickness for the entire surface into account.
- Diamonds will take no specific measures when and opening is within the contours. Therefor Diamonds cannot handle openings close to elements subjected to punching shear.
In this article we described how Diamonds can verify the shear force in one point. However, Diamonds does not automatically verify the shear force in all the other points of the plate. Essentially, you would need to check if VEd < Vc.Rd in each mesh node. But because the shear force is less accurate (it is the second derivative of the deformations in an EEM calculation) and very peak-sensitive, this is not implemented in Diamonds.
