Problem with seismic analysis results

[Anonymous]

Hi everyone,

I have the following problem: when I carry out seismic analysis with the parameters of the attached pic1, including live loads for Mass Conversion, I get the following awkward result (pic2) in the reaction table. When I exclude live loads from Mass Conversion, results seem normal. Has anyone meet the same problem?

[Rafal.Gaweda]

File please.

[Anonymous]

Dear Rafal,

the file can be downloaded from the following link:

http://www.4shared.com/rar/qC2bkTCcba/Structure_-_v85p.html

during analysis you will see that a node has instability type 3. I have tried to solve the instability problem several times but always another node with instability is obtained. Is the instability problem relevant to the above prescribed problem? As you can see in the model are several user defined columns. Are columns-beams-slab properly connected in order to have rigid connections?

Thank you in advance.

[Rafal.Gaweda]

Workaround:
either do not use eccentricities in Modal or delete case 14 from Loads to Mass Conversion list

[Anonymous]

Dear Rafal thank for your answer but it seems that excluding lc 14 from load conversion list hasn't solved the problem (I get exactly the same picture in reaction table - use of Robot 2015). Additionally, ec8 asks for eccentricities to be taken into account, so I think it is right to perform four seismic analysis. Is there another way to achieve solution to the problem ?

Thank you in advance

Ioannis Verroios

[Rafal.Gaweda]

File with results (no case 14 converted) : http://we.tl/sGWfU1vaYA

[Anonymous]

Hi Rafal,

sorry for my late response. I saw the file you have sent me. I suppose that the problem was the solver because I tried to include lc14 and it seems to work. So, thanks a lot for your vital help. I have another question for the same file. Why the the total masses in the three directions UX-UY-UZ are not the same (see attached pic)?

[Rafal.Gaweda · Accepted solution]

The difference is ~0,15% so I think it is not worth to worry about it