An initial bow imperfection for curved members (a chain of straight segments along a faceted curve).
When designing bridges made out of two trusses linked by a deck with rigid joints at the bottom and unrestrained laterally at the top requires a buckling check of the top chords (effective length). There are two options how to do it:
1) initial imperfection as a buckling mode deformation + P-Delta to amplify the effect - there is a problem with a meshed floor as it takes ages to find a mode relevant to top chords, meshed deck to flimsy;
2) initial imperfection as a geometrical bow + P-Delta to amplify the effect (e.g. as per EC3 already in Robot but only for straight members)
For option one, as it is at the moment I have spent so much time analyzing 500-1000 modes to find the right one. If there was a feature to skip modes for shells or if there was a chance to bring buckling mode from a different phase (a model without the deck shell and buckling developed for SW+Dead), then life would be easier.
Also, Hollow Sections joints design taking into account out of plane moment.
With those feature described above, RSA is sufficient to design any steel U-Frame bridge (in the UK) out of the box.
