Answer:
The very time-consuming design in STEEL EC3 and ALUMINUM may be caused by cross-sections of the "General" type.
These can be seen in Window 1.3 Cross-Sections. For these cross-sections, it is necessary to calculate the stresses for the cross-section classification with SHAPE‑THIN in the background. The result combination (RC) for the design may contain a lot of load combinations (CO), which is why the SHAPE‑THIN calculation is performed very often and takes a very long time. However, there is a workaround. With the option shown in the second image, the enveloping internal forces of the RC are used, and not every CO contained in the RC is calculated. Although this may be more conservative, it is faster because not every CO requires a SHAPE‑THIN calculation; only the envelope does.
