Evolutive Cross Section with Design Elements

SOFiSTiK Teddy
1

I just had a look at the youtube video “Composite Bridges: Design Combinations” (see link below) and I have a question. When dealing with evolutive cross-sections, for example a composite or post-tensioned bridge, maxima shall not be used to combine the CSM results with the variable loads as these forces act on different cross sections.

However, in the youtube example, maxima is directly used on an evolutive cross section, which is not correct for beam elements. I understand that this is why the example uses “design elements” rather than “beam elements”.

My understanding is that:

  1. The stresses of the beam elements for the ULS / SLS combiantion will not be correct.
  2. The stresses of the design elements for the ULS / SLS combiantion are correct.

Could you please clarify the above? Could you please clarify the pros / cons of using “design elements” rather than AQB?

Thanks a lot in advance!

2

Had similar question regarding this tutorial. This is the answer from sofistik. Hope it helps.

What Jürgen Bellmann explains is still correct: For designs with AQB with existing construction history, the final superposition must be carried out
in AQB. This is the only way for AQB to know which load cases from construction history act on which partial cross-section.
However, in our tutorial of a composite bridge our relatively new module COMPSITE is used.
In version 2025 COMPOSITE can classify the cross-sections and perform elastic-elastic or elastic-plastic design depending on this. And
COMPOSITE is able to realize that there are load cases from construction history within the MAXiMA-results and on which cross section they act.
All other designs after using COMPOSITE are carried out with AQB and the familiar rules apply.