Answer:
The message shown in Image 01 is displayed if you select the "Minimum distance between stiffeners: 30 ε t" check box in Details and the clear distance between the stiffeners is smaller than this minimum distance amin. The minimum distance is calculated as follows:
In this case, the distance of the stiffeners must be increased in Window "1.2 Stiffeners". For the buckling panel shown in Image 01, the clear distance between the stiffeners is:
Δz = z2 - z1 - (t1 + t2) / 2 = 890 - 600 - (10 + 10) / 2 = 280 mm
This distance is smaller than the minimum distance:
amin = 30 ⋅ ε ⋅ t = 30 ⋅ √(235 / 355) ⋅ 12 = 292.9 mm
Therefore, the position of Stiffener 2 should be entered at least
z2 = z1 + (t1 + t2) / 2 + amin = 600 + (10 + 10) / 2 + 292.9 ≈ 903 mm
specified.
This distance is also displayed as information in Window "1.2 Stiffeners" when placing the mouse pointer over Stiffener 2 (Image 02).
If the calculation should also be performed for a stiffener distance smaller than the minimum distance, the "Minimum distance between stiffeners: 30 ε t" check box must be deactivated (Image 03).
