non convergence analysis of special concen. br. frame

[cvatansever]

Dear All,

We are working on nonlinear analyses ( pushover and time history) of a split-X special concentrically braced frame with its bracing members susceptible to in-plane buckling. With two story split-X frame using the principals of SCBF model developed by Dr. Vesna, analysis converges depending on the behavior of rotational hinge based on Hsiao (2012). However, if we increased the number of the stories by 8 with the same principals as in two-story model the analysis does not converge. The followings are also provided.
HSS sections are used as bracing members
Initial imperfection of L / 500
Rotational hinges are employed to represent the connection of the bracing members
Bracing members, beams, columns are modeled using forcebeamcolumn element

Do you have any idea to figure out this problem ?

Thanks in advance.

[fmk]

have you tried doing stuff if the analysis fails to converge .. in large models braces that have buckled can cause a problem numerically (large disp with little force change) which makes convergence difficult .. some people remove the brace from the analysis after it has buckled a few times .. you might also look at using a norm on the unbalance if using the disp norm currently as something to try in the failure script.

[cvatansever]

Dear McKenna,

Thank you so much for your reply.
I definitely guessed that the numerical problem caused the convergence problem. Actually, I also overcame this problem (large model works properly) using hysteretic material model based on the FEMA 356 for the braces. But, I want to solve this convergence problem in the large model including braces represented by forcebeamcolumn (or nonlinearbeamcolumn) elements.

Do you have any example including the implementation that you talked about ?

Thanks a lot again.

Cuneyt,

[IsmBaha]

Hello Cuneyt,

Were you able to figure out the convergence problem of CBF model on taller buildings (based on Vesna's model)?

Selamlar,
Baha