Seismosoft | Earthquake Engineering Solutions

hello seismosoft

according to your notice i searched buckling for concentric braced frame in forum and i found some user suggest using initial imperfection for this reason, now how can i model initial imperfection for bracing members in compression? and it is a question for me that can this method work better than st-mn and st-mp nonlinear material(for considering buckling)or not? and which of them is best method?

thank you

Dear mohamad reza,

As we have noted already, you need to read the bibliography on the topic, where answers to your repeated questions can be readily found. In our previous response to you, we have suggested two publications already, and herewith suggest an additional one:

Uriz P., Filipou F.C., Mahin S.A. (2008) "Model for Cyclic Inelastic Buckling of Steel Braces," ASCE Journal of Structural Engineering, vol. 134, no. 4.

In addition to reading scientific/technical publications, you can also carry out a Google search on "Modeling braced frames using beam-column elements", which will provide with concrete guidance on the topic.

If you follow our suggestions, you will quickly realise that, with regards to your questions:
- at least two beam-columns elements should be used, so that you can introduce an imperfection midway through
- if you are interested in detailed modelling of the buckling, however, you may want to use up to 10 beam-column elements
- typical imperfections are of 0.05-0.1% of the free brace length
- the 'stl_mp' model, rather than the 'stl_mn' one, should be employed

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