Help me. Warning message after runnning model , not analysing - ETABS 17

[HoangHuynh]

Hello everyone , I need help. After running the Model , I checked the log and it showed that :
* * * W A R N I N G * * *
THE STRUCTURE IS UNSTABLE OR ILL-CONDITIONED !!
CHECK THE STRUCTURE CAREFULLY FOR:
- INADEQUATE SUPPORT CONDITIONS, OR
- ONE OR MORE INTERNAL MECHANISMS, OR
- ZERO OR NEGATIVE STIFFNESS PROPERTIES, OR
- EXTREMELY LARGE STIFFNESS PROPERTIES, OR
- BUCKLING DUE TO P-DELTA OR GEOMETRIC NONLINEARITY, OR
- A FREQUENCY SHIFT (IF ANY) ONTO A NATURAL FREQUENCY

TO OBTAIN FURTHER INFORMATION:
- USE THE STANDARD SOLVER, OR
- RUN AN EIGEN ANALYSIS USING AUTO FREQUENCY SHIFTING (WITH
ADDITIONAL MASS IF NEEDED) AND INVESTIGATE THE MODE SHAPES


---------------------------------
BASIC STABILITY CHECK FOR LINEAR LOAD CASES:
NUMBER OF NEGATIVE STIFFNESS EIGENVALUES SHOULD BE ZERO FOR STABILITY.
(NOTE: FURTHER CHECKS SHOULD BE CONSIDERED AS DEEMED NECESSARY,
SUCH AS REVIEWING EIGEN MODES FOR MECHANISMS AND RIGID-BODY MOTION)

NUMBER OF NEGATIVE EIGENVALUES = 4981
Certainly it didn't analyse. I 've already checked model , assigned restraints.
Please help me . I'm doing graduated thesis

 

[Blackstar123]

Rerun the model using standard solver. Software will identify the coordinates at which warnings are originating. Then you maybe able to determine the reason for a particular warnings.

 

[HoangHuynh]

I did it but it took a lot of time . I used standard solver , and waited for 45min but it 's still not run.
I made the model again carefully but I still received this message again .
Do you know the main cause ? or your friend know?

 

[Blackstar123]

45 min is quite a lot of time. Either your system is very slow or your model is very heavy. Did you use very small size of mesh for the area elements? What version of ETABS are you using?

Do you know the main cause? or your friend know?

Not I or anyone else could guess the reason for a particular warning unless we know what's the warning is about.

Nevertheless, most newbies make a muddle of area meshing which results in excessive warnings. So I'll hazard a guess and say area meshing is most probably the culprit.

 

[HoangHuynh]

oh thank you , but maybe it'snot the cause , my meshing 's good .
My model has a Transfer beam (0.8x1.8). are there any problem about restraint between Column , Transfer beamm, and Wall system above ??

 

[Blackstar123]

Well as I said earlier, I couldn't guess unless I know the nature of warning.

To reduce the analysis running time, what you could do is, make separate models for each story (delete everything else but the story under consideration). The idea behind this is to reduce the number of dof's so that running time could be reduced. This will also help you in identifying and eliminating the warnings floor by floor.

After identifying the warnings, you can then make changes in your main model accordingly.

 

[Blackstar123]

My model has a Transfer beam (0.8x1.8). are there any problem about restraint between Column , Transfer beamm, and Wall system above ??

It might help if you provide views of those parts of your model which think are the cause of the warning.

 

[HoangHuynh]

hello , I did cut off 31 stories above . after running , the negative eigenvalues reduced , only 230 instead of 4981 .
This is the first story above the transfer beam . What happening with that walls ?? . Is it the reaseon ? The picture and the file afte I cut off the stories below . Can you have a look ?

 

[HoangHuynh]

I used the Standard solver and the message :
L I N E A R E Q U A T I O N S O L U T I O N 19:27:08

FORMING STIFFNESS AT ZERO (UNSTRESSED) INITIAL CONDITIONS

TOTAL NUMBER OF EQUILIBRIUM EQUATIONS = 99426
APPROXIMATE "EFFECTIVE" BAND WIDTH = 2728

NUMBER OF EQUATION STORAGE BLOCKS = 5
MAXIMUM BLOCK SIZE (8-BYTE TERMS) = 66610304
SIZE OF STIFFNESS FILE(S) = 2.482 GB

NUMBER OF EQUATIONS TO SOLVE = 99426

* * * W A R N I N G * * *
NUMERICAL PROBLEMS ENCOUNTERED DURING EQUATION ASSEMBLY:

TYPE LABEL DOF X-COORD Y-COORD Z-COORD PROBLEM VALUE
----- ------- -- ----------- ----------- ----------- ------------- -----------
Cnstr 2 U1 42875.000 19000.000 123200.000 Diag = 0 --> 1.00E-10
Cnstr 2 U2 42875.000 19000.000 123200.000 Diag = 0 --> 1.00E-10
Cnstr 3 U1 42875.000 19000.000 119900.000 Diag = 0 --> 1.00E-10
Cnstr 3 U2 42875.000 19000.000 119900.000 Diag = 0 --> 1.00E-10
......(a lot of)
Solving 5 equation blocks

Block 1 by block 1

* * * W A R N I N G * * *
NUMERICAL PROBLEMS ENCOUNTERED DURING EQUATION SOLUTION:

TYPE LABEL DOF X-COORD Y-COORD Z-COORD PROBLEM VALUE
----- ------- -- ----------- ----------- ----------- ------------- -----------
Joint ~2341 UY 72620.000 21675.000 11100.000 Lost accuracy 13.1 digits
Joint ~2341 UY 72620.000 21675.000 11100.000 Diagonal < 0 -2.95E-07
.....
Block 3 by block 2
Block 3 by block 3
DO you know the meanings of these ? I 've already assigned restraints .
I made many models by the same way , but this is the first time I 've faced this problem
please help me

 

[JoshPlumSE]

Yes, look at those locations for your instabilities.

x=42875
y=19000
z=119900

x=72620
y=21675
z=11100

The program is telling you that the model is essentially unrestrained / unstable at these locations. I don't know why. Maybe a connectivity problem, maybe a problem with the meshing, or boundary conditions.

 

[HoangHuynh]

oh I see it , most of these joints are located on the wall . These joints 're at the position which I meshed .
I used Auto mesh option to mesh( Mesh size is 1m for floor and wall , I also add restraint on edge for wall ) .
I made another model before and It's find . But this model has this problem , I even made it two times.
Why did these joints lose accuracy? How to resolve it ?
Can anyone give me a suggestion ?

 

[JoshPlumSE]

Try adding in a "Dummy member" at those locations. Something that will help connect those joints to the walls that they're supposed to connect to.

My tendency would be to use a member made of the same material as the wall that is square and of the same thickness of the wall. Just so that any load going to those joints will then reasonably transfer to the other joints connected to the member along that line.

 

[Blackstar123]

What did you define in your area type? "shell-thin" or "membrane"?

 

[Blackstar123]

Also, are these dots near upper grids unsupported joints/points?

Just curious, what exactly are these red walls? Are there any columns at this story? Are these walls only between some floors or are they running from the base to the roof?

 

[Blackstar123]

I also add restraint on edge for wall

I don't think adding edge constraint is necessary, since you're using auto mesh.
As far as I know, edge constraint is usually added between the area elements with different mesh sizes.

 

[HoangHuynh]

I choose Shell-thick for slab and wall.
My model has column system run from the second Base to the Story 3 . And I have the Transfer beam at this Story ( to transmit loads from walls to columns). From the story 3 to the Roof is Wall system . besides, I also reduced the hardness of Wall every 10 story . I also have 2 Wall Core system run from Base to Roof.

 

[Blackstar123]

If I were you, I would delete all these red walls and provide columns here just to check if the rest of the model is working fine and the walls are the only elements that causing problems. This way I can focus all my energy in finding out why walls are behaving in this odd fashion.

From your warnings, I agree with JoshPlumSE that,

The program is telling you that the model is essentially unrestrained / unstable at these locations.

 

[HoangHuynh]

yes , I did cut off the story has red walls. there are only 3 stories which have columns , beams, and Wall core.
I checked and these joints appeared on the Wall Core , at the position I meshed . That are faded joints , how can I choose and fix it ?
I deleted Wall Core and drawed it again , assign restraints at the base , auto mesh . But the problem still happened .
I ran another model but it was still ok . dont know why the problem appear . Feeling no way to fix

 

[HoangHuynh]

I did post 2 files above.

the first file is the original version
the second file is after I cut of stories to run Standard solver .
I really need help (

 

[Blackstar123]

Don't you have a supervisor to guide you?