| Product(s): | SACS |
| Version(s): | ALL |
| Area: | Collapse Module |
Query:
Hello Bentley
Could someone please help to clarify how out‑of‑straightness is handled in SACS Collapse analysis? The manual mentions that the imperfection needs to be specified using a harmonic function, and I would appreciate a bit more detail on how this should be defined in the Collapse Advanced input. Any guidance or examples on the correct method for specifying out‑of‑straightness would be very helpful.
Answer:
This factor is linked with the Tolerances for alignment and straightness set in many codes depending on which one you are using. As you could see in the samples in the collapse manual, we make mention of factors like 1/1000, or 1/666 of L; these ones depend on the elements for which you want to emphasize your review. for example: Beams, columns, Stiffened plane plates, etc, etc.
SACS doesn’t take into account the effects of straightness by default, and as you can see in the description card, this is considered by default as 0
But depending on the importance of the element you want to check, you can consider this effect setting the correct factor according to the code used. As an example, you can refer to the DNV-C401 code. on this standard you can find an entire chapter that talks about this tolerance and factor that you can use.
Currently what SACS do, is to apply this factor to all elements in the model performing a more realistic result taking into account the real Fabrication tolerances
it's important to highlight that If the model already has some dead load or weight as the first load case in the load sequence, that load case will be enough to model most of the out-of-straightness and its effect on member buckling. Saying that users can always add this out-of-straightness in addition of the weight/dead load.
for more information about the straightness function see this post