Autodesk Robot Structural Analysis

[#1]

While reviewing steel code verification results after model modifications, I noticed the behavior that I do not understand and which is possibly a bug.

Below are the results for both models.

The first bracing point in both cases is at 4.27m (which is exactly where the calculation point is located, but it does not matter, I also checked the results for the point at 4.10m and observed the same behavior).

Forces and calculated coefficients are very similar with the exception of omega1.

Here is the relevant excerpt from the code:

Based on this:

A) for Buckling Z:
Shear force Fy is zero over the section considered, therefore clause 13.8.5(a) applies. Bending diagram Mz is in double curvature and the ratio of the moments is around 1, so omega1 should be 0.4 - as in the first model and not 1.0 as in the second model.

B) for Buckling Y

Shear force Fz varies linearly over the section considered (indicating distributed load between supports), therefore clause 13.8.5(b) applies and omega1 should be 1.0 - as in the second model and not 0.61 as in the first model.

[#2 · Accepted solution]

Patrick,

The calculations of omega1 is not fully automatic and it depends on the load scheme you selected. See the attached picture.

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.

[#3]

These settings were indeed different in both models. Thanks!