ETABS MODEL Instability: How to Locate and Fix?

[@spyfromsparta]

I had an error while running analysis. The error was NEGATIVE EIGEN VALUES. After struggling for a bit, I searched the internet where your video suggested me to run standard solver. After running that I got the coordinates as 3,7.5,15. When I checked the model I found that I had replicated the vertical bracings from Grid 1 to Grid 2. As both are of different heights due to sloped roof, some joints were disconnected. After I redrew the bracings I ran the analysis again, this time without errors. So thanks for your service.

[@minmichmin]

Thanks a lot! This video help me solve the unstable problem suddenly.

[@salimmwami7745]

Great video, very helpful. I have a problem though, apart from joints being the errors, there is also another error type named Cnstr, what is this error? if i try to locate it it takes me to a point that is within the model yes, but not part of any element of the model whatsoever, not even art of joint on model so i fail to solve it, and this error has more than 11 digits loss of accuracy. really need help on this.

[@TheStructuralWorld]

I think that is a loose joint or flying nodes. Locate that joint/nodes and delete it. That will solve your problem. If you cant delete try assinining none property and delete.

[@salimmwami7745]

@@TheStructuralWorld Should i locate it the same way? i've tried that but still the warning keeps on coming.

[@TheStructuralWorld]

@@salimmwami7745 yes you must find away to delete that node. Then it will be ok.

[@canerozek6088]

i have a problem about period , may u help for the period should be around 2 sc. but it is so much low (0.1sc.)

[@Paigham72]

Sometimes Etabs shows huge reinforcement at station Loc 0.0 in columns what is the solution and reason of this issue?

[@christellee6417]

Hello, Thank you for the video, I am getting lost of accuracy value superior to 11, but when I check the joints unique name it start with ~, for instance ~12354 and such joint doesn't exist and I don't know what wrong and how to fix it. The eigenvalues below shift = 2. Do you have any advice?

[@TheStructuralWorld]

To fix it, you have to locate first the joint. Try to check the location of that joint using the x and y coordinates exactly as shown in this video. It may be a loose frame or joint that causes instability.

[@alinaveed590]

Export your model to e2k file and then reimport that e2k file.

[@tnsman83]

I just happened to see this question. The ~ before a joint is an internally meshed joint. Turn on the analytical mesh and you will see a node of a FEM joint from a shell element. These usually happen when there are two internal joints close together but they do not actually touch, so they are on the edge of the adjacent meshed element, rather than at a joint so ETABS rigidly constrains the node so there is a solution and this can result in "lost digits of accuracy". I have found these to not really affect the results. You can try and fix them by manually meshing local areas that are affected or just splitting some of the larger shells up into smaller shells, say at column lines.

[@christellee6417]

@@tnsman83 oh thanx, i will try that

[@jayshah6293]

I do pushover analysis but error

[@mehdiazizi3831]

I had 3 instability warnings but after set the p-delta on NONE, i got no warning.!?? how can i fix it?

[@TheStructuralWorld]

what exactly is the warning?

[@loloezzat9254]

thank you sir

[@shoebrahman8484]

Unable to fix this warning

[@CherryyBombs]

Thank you!!!!

[@mahmoudal-samawi4718]

Thanks

[@abeedshaikh2036]

In model you assign fix support to all joints include all storeys joint ?why

[@TheStructuralWorld]

All joints are not assigned as fixed support. I just turned on the visibility of the joints.

[@Nataq1945]

I could identify the joint ant tried to solve it but, could not. Anyway, thanks for your video.

[@TheStructuralWorld]

You're welcome!

[@meerannair5861]

Thanku sir

[@ajazsayyed8487]

Sir how to do static seismic analysis? In etab

[@TheStructuralWorld]

In ETABS, you just need to input the seismic parameters and the program will do the analysis. All you have to do is to check the analysis results according to the code limitations.

[@ajazsayyed8487]

@@TheStructuralWorld Thank you sir.