Composite structure with braces problem with seismic analysis error no 5000

[Anonymous]

Hello , This error didn't show before introducing the tension only braces with releases.

Also I checked reactions and it's putting not available on seismic load cases only , but without the braces the calculations would go just fine .My load combinations are exact.

I ticked matrix update after subdivision , and turned BFGS to 0 , the tolerance to .001 and max iteration number to 200 and they didn't help.

I changed structural analysis from automatic to sparse , the calculations are taking forever , the superimposed dead load case would take more than an hour so I stopped the calculations.

[Artur.Kosakowski · Accepted solution]

Hi @Anonymous

Do you mean response spectra analysis for the equivalent lateral force analysis for seismic? Mind that use of the nonlinear elements for the prior is doubtful.

How to approach seismic analysis for nonlinear model in Robot Structural Analysis

If I managed to answer your question(s) press the Accept as Solution button please. This will help other users to find solution(s) much faster. Thank you.

[Anonymous]

Hello Artur thanks 

1-    well I made some modifications before for the braces and It worked

but now I noticed a huge problem regarding the beams , where they are taking very low bending moment , of course it's because of the offsets since I have rigid links for composite action ; I've read solutions for this problem but they all include removing offsets and modifying moment of inertia which is an option only found for rc sections , not steel sections 

I even tried just removing the offset and changing the slab to cladding but still results not realistic and way too low bending on beams 

2-   I also remarked that some people said in the forum that offset would also give bad results for the slab, so why would someone put the rigid links and the offset for then ?!why was it recommended in the forum before?and also without the rigid links and the offset it's impossible to design the slab

what shall I do ?

[Artur.Kosakowski · Accepted solution]

Hi @Anonymous

but now I noticed a huge problem regarding the beams , where they are taking very low bending moment , of course it's because of the offsets since I have rigid links for composite action ; I've read solutions for this problem but they all include removing offsets and modifying moment of inertia which is an option only found for rc sections , not steel sections 

I have already asked for this option being available for steel sections too. Let's hope will be heard 

As a temporary solution you may adopt what I suggested in the Post 2 from https://forums.autodesk.com/t5/robot-structural-analysis-forum/change-the-moment-of-inertia-of-a-standard-steel-section/m-p/4442633

If I managed to answer your question(s) press the Accept as Solution button please. This will help other users to find solution(s) much faster. Thank you.

[Anonymous · Accepted solution]

Thanks again Artur

Hope it'll get better , anw everything worked out fine in the end 

and I've done my hand calculations and seen that offsets with rigid links  have given incorrect results and it was better to remove them , So I don't know why it was recommended in some of these topics in this forum

So I'll mark your 2 posts as solutions since they are helping , and I'll mark this post as a solution to help other users to know that offsetting with rigid links is such a waste of time .

[Artur.Kosakowski]

Hi @Anonymous

Offsets are fine if you don't need to look at the results in beams therefore they can be fine to be used in some situations  such as e.g. floor deflections of vibrations.