Problems of convergence. Soft stoy or not?

04-Unexpected behaviour/errors
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QuerenSuriano
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Joined: 28 Apr 2018, 17:58

Problems of convergence. Soft stoy or not?

Post by QuerenSuriano » 13 Sep 2018, 18:06

I'm modeling a 4-level steel frame building in Seismostruct for a pushover analysis. I am having problems of convergence and I have followed the recommendations that the program gives me, the message that appears to me when stopping the analysis is this: "The structural model can not withstand the defined loading" ... I have verified loads and structural properties of the elements , as well as the connection of the elements through an analysis of eigenvalues.
What I have managed to verify in the analysis log is that all the columns of the first level 1 come to meet the criteria of yield in only ONE of its extremes, the extreme (A). This criteria performance of yield has been defined by the user based on chord rotation. I can also mention that the last result that the program shows me is the failure of two columns of the first level (the failure criterion was also defined by user)

I understand that to define a failure mechanism for soft story is necessary that BOTH ends of the columns of the first level are in yielding. That is why it is my doubt, whether the building has really collapsed or not and that is why it is not possible to continue the analysis, because in my case only ONE extreme of the the columns reached yielding

Note: to define the performance criteria I used ASCE 41-13


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z.gronti
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Joined: 16 Oct 2013, 08:14

Re: Problems of convergence. Soft stoy or not?

Post by z.gronti » 14 Sep 2018, 14:57

Dear QuerenSuriano,

I took a quick look at your model and realised that you have assigned performance criteria with Residual Strength. Please note that the assignment of a small percentage for residual strength might cause difficulty in the convergence of the analysis. This does not have to do with the failure mechanism of your structure. I ran the analysis with Keep Strength in all performance criteria and the analysis was completed successfully. Hence, you should either check the percentages you have assigned in the Residual Strength or make further modifications to the Project Settings.
Are the rigid diaphragms of the upper floor correctly inserted? If they are, I think that the 4-V88 and 4-V89 should be one element.
Zoi Gronti
Seismosoft Srl.

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seismosoft
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Re: Problems of convergence. Soft stoy or not?

Post by seismosoft » 14 Sep 2018, 19:02

QuerenSuriano, the fact that the model cannot converge after the members' failure probably means that you simply have structural failure, i.e the failed members cannot withstand the vertical loads.
Seismosoft Support

QuerenSuriano
Posts: 9
Joined: 28 Apr 2018, 17:58

Re: Problems of convergence. Soft stoy or not?

Post by QuerenSuriano » 15 Sep 2018, 23:49

Thanks for the help. I did the test to increase the columns of the first level W14X90 the% RS to 60 and the chord rotation in the criterion of failure I changed it from the value I had from 4θy (chord rotation yield) to 6θy and it was completed with a target displacement the 0.35 m

But my question is: I have verified that in the ASCE 41-13 the non-linear properties of the W14X90 column are% RS = 20% and θc = 4θy. Then I did the test to decrease the target displacement to 0.141 m and the analysis was completed. So, which analysis would be valid?
What I am trying to do with the analysis is to set damage thresholds according to the ASCE 41-13

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seismosoft
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Re: Problems of convergence. Soft stoy or not?

Post by seismosoft » 16 Sep 2018, 14:58

All these are issues that are probably better discussed with your supervisor.
In any case, do not confuse the the target displacement according to the pushover methodologies (as calculated in the Target Displacement module of the post-processor) with the maximum displacement to which we push the building (as set by in the pre-processor in the Loading Phases module).
Seismosoft Support

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