According to DIN EN 1992‑1‑1, the sum of the soil pressures within the punching cone may be assumed as having an unloading effect of 100% if the critical perimeter in the punching shear design of the foundation slab is determined iteratively. If, to simplify the calculation, the constant control perimeter is taken at a distance of 1.0 d, 50% of the sum of the soil pressures within the constant control perimeter may be assumed as having an unloading effect.
In the "Details" section, this is taken into account by the factor kred. If you select the "Iterated calculation of the control perimeter" option, the value for kred is taken as 1.00. If the "Definition of Distance ..." is selected, the value for kred is set to 0.50. You can, however, also specify a user‑defined value. You can also, for example, select the iterative calculation and specify 0.5 for kred.
In the design details for the punching design, you get the value for delta VEd, which was determined under consideration of the factor kred.
