fbd-Ite problem

[z.gronti]

Dear khajehdehia,

It seems that the structure can't sustain the applied vertical load. Hence, you might need to decrease the gravity loading.

SeismoSoft srl

[dpucci]

Dear Seismosoft,
I am modeling a building of six storeys in reinforced concrete with infrm FB elements.I run an eigenvalue analysis and it works but when I run static analysis it ends with the message:
"fbd_Ite
Unable to apply the entire permanent load. Analysis terminated."
I changed the maximum iteration number to 1000,unchecked the option 'Do not allow element unbalanced forces in case of fbd_ite' and setted the convergence criteria on displacement/rotation based but it doesn't work.
How can I solve this problem?
Thanks

[z.gronti]

Dear dpucci,

Please try to increase the values for displacement and rotation tolerance from the Elements tab of the project settings. Another suggestion is to decrease the analysis load step. The following video might be helpful for you:
https://www.youtube.com/watch?v=p6tAyoofDog

Zoi Gronti
Seismosoft srl

[dpucci]

Thanks for your advice. I watched the video and I tried but it doesn't work. Is it possible that a big number of element classes causes this problem? Can I send you my model at support@seismosoft.com?
Thanks

[seismosoft]

Dear dpucci,
In addition to all the above, please check whether the static loads can be actually sustained by the structure, i.e. whether the loads are too large and cause a structural failure. This can be done by increasing gradually the loads anf checking if the analysis runs.
Further, note that more than 5-6 integration sections for the FB elements can cause significant convergence problems. Convergence problems might also arise if the length of the FB elements is relatively small.

SeismoSoft Support

[dpucci]

Dear Seismosoft,
the static loads can be sustained by the structure because I ran a static analysis before dividing infrm FB in six parts. Then I created new sections and new element classes to be assigned to bays and when I run analysis again it ends with error message. I have 4 integration sections so I think that the subdivision of columns and beams in 6 elements for a total of 3428 elements can cause the problem because the lenght of some elements is between 10 to 50 cm. Can I solve this problem using infrm DB elements?
Thanks.

[seismosoft]

Hi dpucci,

We had a look at your model and indeed the main problem seems to be the fact that you are using FB elements with 4 integration sections to model elements with length smaller than 0.70-0.80m. As you correctly pointed out, using DB elements will probably solve the proble.

Note also that end releases with inelastic frame elements can also cause some convergence difficulties (this is not very likely though in your case of just one element with end-releases).

SeismoSoft Support

[dpucci]

Hi,
thanks a lot to have taken a look at my model.
I tried with infrm DB elements but I have a Max_Tol error message and although I made settings adjustements I cannot solve. Modelling with infrm FB elements without subdivision of beams and columns in more elements and using 5-7 integration section is correct?In this way can I get accurate results?Because trying in this way it seems I can solve.
Thanks.

[ruipinho]

Dear dpucci,

The Help System/User Manual of SeismoStruct explicitely states that: "the suggested minimum number of integration points is 4, although 5-7 IPs are typically used (see figure below)".

Hence, why are you asking if "using 5-7 integration sections is correct"? Is there any particular reason for you to feel that the Manual of SeismoStruct could be suggesting something that is not correct?

Rui

[dpucci]

Hi Rui,
what I meant was if modelling with a single infrm FB element without subdivision into several elements is as accurate as modeling with subdivison. I never thought that Manual of SeismoStruct could be suggesting something that is not correct. I just want to be sure of what I'm doing.

Daniela