Answer:
In the "c/t-Parts and Effective Cross-Section" tab of the "Calculation Parameters" dialog box, you can define the settings for the automatic creation of c/t-parts.It is also possible to specify an angle from which a support should be created between two elements. If elements are connected at a smaller angle, they are regarded as a connected c/t-part. Stiffeners (longitudinal ribs, slopes [lips], bulges, and so on) are not recognized by the program during the automatic generation of the c/t-parts. The c/t-parts have to be adjusted manually. You can make the changes in Table "1.7 Notional Flat Widths | EN 1993‑1‑3" or in the "Edit Notional Flat Width" dialog box.
The input field for Element is "significant" controls whether a curved element is taken into account as a c/t-part. If the length of the arc is larger than the diameter entered here, it cannot be neglected.
A corresponding error message appears before the calculation.
The option Element is "straight" refers to curved elements. The arcs are usually excluded from the determination of the effective widths because the standards do not provide clear specifications. A curved element is assumed to be straight if the ratio of the connecting line (start/end node) to the element length is higher than the specified value.
EN 1993-1-3 
to DIN 18800-2 
.jpg?mw=350&hash=91f398b559b26a6ac36fd7ecdf5e395e7b9b856d)
.png?mw=600&hash=49b6a289915d28aa461360f7308b092631b1446e)
