With rectangular, round and polygon columns, the punching perimeter at the curtain ends is automatically calculated in accordance with TS 500 , taking into account the floor gaps .
A z = Punching area
d = Slab useful height
u p = Punching circumference
As stated in TS500 Section 8.3.1 ;
Gaps "5d" or closer at the edge of the loaded area are taken into account when calculating the punch circumference. The reduction to be made in the perimeter of the punching because of the gaps, u p , should be performed by not taking into account the circumference remaining within the radial lines to be drawn tangent to the slab edge from the center of gravity of the loaded area, Figure 8.4a.
In cases where the ratio of loaded area dimensions is more than 3.0, the perimeter to
be calculated with the assumption h = 3b should be used, Figure 8.4b. This situation is also taken into account in curtain or group curtain ends.
In cases where the perimeter of the loading area is concave (in polygon columns), the perimeter obtained after eliminating the concave with the tangents should be used as the punching perimeter in the calculations, Figure 8.4c.
If there is more than one critical section (for example, if there is a table at the head of the column), each critical section should be evaluated separately and the most unfavorable section should be considered.