steel chevron braced frame

[smhzs]

I am really frustrated with the results of this modeling.

I have a single-bay 2-story steel frame with chevron (IV) braces. The beam to column connections are pinned. The braces do not participate in the results of the eigen-value analysis. I don not know why they are showing such a rigid behavior. I even checked with a simpler 1-story model.
I am suspicious of the brace to beam connection. Different possible modeling details and methods were tried though. None of them seems reasonable.
P-delta- Buckling in the columns are considered by initial imperfection at the midpoints.
Rigid diaphragm should be assigned.
Truss element and Iforced-based frame element (with hinges at the end points) were also tried for the braces.


I would appreciate it if you could help me.

Thanks.

[shahab_nab]

Dear SMHZS

I think, in your case,
you should consider imperfection in mid point of braces, not in columns. Because braces are expected to buckle before column's.

[smhzs]

Thanks for your reply. That should not be a problem. because I also tried with no imperfection at all.

[seismosoft]

Dear smhzs,

If you are suspicious about the manner in which the pinned connections of your braces are being modelled in v5.2.2 (i.e. with the use of link elements featuring zero rotational stiffness), you may perhaps want to try using the end-releases feature of SeismoStruct v6, which allow pinned connections to be modelled without the need for link elements to be introduced.

Seismosoft Support