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# Civil Engineering/Etabs - Structure is Unstable -

Question
QUESTION: Dear Sir
i m working on a 3B + G + 11 storey structure, Dynamic analysis has been done , without pdelta

Building is modelled at Certain angle (40 deg) as per site

From 6th floor to terrace in a particular Panel near CG

(Warnings are there)

* * * W A R N I N G * * *
THE SOLUTION LOST 10.1 DIGITS OF ACCURACY FOR DOF U2 OF CONSTRAINT       1
LOCATED AT X =   28.546041, Y =   23.660107, Z =   61.050000,
STIFFNESS MATRIX DIAGONAL VALUE =  1.4281E+17

* * * W A R N I N G * * *
THE SOLUTION LOST 12.0 DIGITS OF ACCURACY FOR DOF R3 OF CONSTRAINT       1
LOCATED AT X =   28.546041, Y =   23.660107, Z =   61.050000,
STIFFNESS MATRIX DIAGONAL VALUE =  8.7241E+19

* * * W A R N I N G * * *
EXCESSIVE LOSS OF ACCURACY WAS DETECTED DURING THE SOLUTION OF EQUATIONS
NUMBER OF DIGITS LOST EXCEEDED 11.0

* * * W A R N I N G * * *
THE STRUCTURE IS UNSTABLE OR ILL-CONDITIONED !!
CHECK THE STRUCTURE CAREFULLY FOR:
- ONE OR MORE INTERNAL MECHANISMS, OR
- ZERO OR NEGATIVE STIFFNESS PROPERTIES, OR
- EXTREMELY LARGE STIFFNESS PROPERTIES, OR
- BUCKLING UNDER P-DELTA LOADS (IF ANY), OR
- AN EIGEN SHIFT (IF ANY) ONTO A NATURAL FREQUENCY

i tried few options

1. By manually meshing that panel , then analysed the model

2. Beam Slab system is there ( Making that Particular panel as shell and Auto mesh was done), then analysed the model

3. I removed those panels (from 6th to terrace) ,then analysed the model

still unable to solve that, nearly same warnings are coming

what could be the reason ?

(I have checked my model by seeing the deformed shape by  increasing the Scale of animation, to see any members  deformormation is more than expected, model is ok there are no such members)

( i also tried by exporting the model as e2k text and then importing it back to run.)

still unable to solve that

First of all you need to perform a static analysis. Please let me know the result.

Regards
BEH

---------- FOLLOW-UP ----------

QUESTION: Thanks for the reply sir

I have performed static analysis

same kind of warnings are coming

* * * W A R N I N G * * *
THE SOLUTION LOST 10.1 DIGITS OF ACCURACY FOR DOF U2 OF CONSTRAINT       1
LOCATED AT X =   28.546041, Y =   23.660107, Z =   61.050000,
STIFFNESS MATRIX DIAGONAL VALUE =  1.4281E+17

* * * W A R N I N G * * *
THE SOLUTION LOST 12.0 DIGITS OF ACCURACY FOR DOF R3 OF CONSTRAINT       1
LOCATED AT X =   28.546041, Y =   23.660107, Z =   61.050000,
STIFFNESS MATRIX DIAGONAL VALUE =  8.7241E+19

* * * W A R N I N G * * *
EXCESSIVE LOSS OF ACCURACY WAS DETECTED DURING THE SOLUTION OF EQUATIONS
NUMBER OF DIGITS LOST EXCEEDED 11.0

* * * W A R N I N G * * *
THE STRUCTURE IS UNSTABLE OR ILL-CONDITIONED !!
CHECK THE STRUCTURE CAREFULLY FOR:
- ONE OR MORE INTERNAL MECHANISMS, OR
- ZERO OR NEGATIVE STIFFNESS PROPERTIES, OR
- EXTREMELY LARGE STIFFNESS PROPERTIES, OR
- BUCKLING UNDER P-DELTA LOADS (IF ANY), OR
- AN EIGEN SHIFT (IF ANY) ONTO A NATURAL FREQUENCY

Is this the issue with Diaphragm ?
i have assigned to slabs as rigid Diaphragm

2. one more Query im having sir
In warning messages
THE SOLUTION LOST 10.1 -
what does this 10.1 stands for

Dear azhar

the location of instability is given to you in the warning. Check the node and the connections in it. You know that you dont have to release all degrees of freedom in a node . For instace if you have 2 beam interconnected in a joint with hinge you have to define one beam with moment release and the other with no release. You canthave a dregree of freedom with no constraint and at least one constraint must exist. For instance if you define a joint without any member crossing it , the stiffness matrix gets odd and no solution will be available.

Regards
BEH

Civil Engineering

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