Hi. I am a student and recently I started my first project on Etabs to model a steel structure. I had faced some problems therefore I seek for your valuable advice. The problems are:
1) When I have done the analysis, there was a warning-“ Eigenvalue 3 was found out of sequence.” popped out.
2) Also when I started steel frame design, I found out that the axial force in the column is in negative value and some of them showing red colour.
May I know what exactly the problem is and how to resolve it? The Etabs file is attached below. I hope that someone can help me to clear my doubt. Thank you.
RUNNING ANALYSIS AS A SEPARATE PROCESS
USING THE STANDARD SOLVER (PROVIDES COMPLETE INSTABILITY INFORMATION)
NUMBER OF JOINTS = 1610
WITH RESTRAINTS = 225
WITH MASS = 1604
NUMBER OF FRAME/TENDON ELEMENTS = 1435
NUMBER OF SHELL ELEMENTS = 1132
NUMBER OF CONSTRAINTS/WELDS = 3
NUMBER OF LOAD PATTERNS = 7
NUMBER OF ACCELERATION LOADS = 9
NUMBER OF LOAD CASES = 8
NUMBER OF MASS SOURCES = 2
ADDRESSABLE PHYSICAL MEMORY (RAM) = 7.672 GB
PARALLELIZATION OF ANALYSIS OPERATIONS:
(Env. variable SAPFIRE_NUM_THREADS = 0)
NUMBER OF THREADS: STATE (AUTOMATIC) = 2
NUMBER OF THREADS: STIFFNESS (AUTOMATIC) = 2
NUMBER OF THREADS: EVENT (AUTOMATIC) = 2
NUMBER OF THREADS: MOVE (AUTOMATIC) = 2
NUMBER OF THREADS: RESPONSE (AUTOMATIC) = 2
NUMBER OF THREADS: SOLVE (AUTOMATIC) = 2
NUMBER OF THREADS: FORM (AUTOMATIC) = 2
E L E M E N T F O R M A T I O N 12:32:51
NUMBER OF COUPLED CONSTRAINT EQUATIONS = 0
L I N E A R E Q U A T I O N S O L U T I O N 12:32:51
FORMING STIFFNESS AT ZERO (UNSTRESSED) INITIAL CONDITIONS
USING MASS SOURCE: MsSrc1
TOTAL NUMBER OF EQUILIBRIUM EQUATIONS = 8976
APPROXIMATE "EFFECTIVE" BAND WIDTH = 128
NUMBER OF EQUATION STORAGE BLOCKS = 1
MAXIMUM BLOCK SIZE (8-BYTE TERMS) = 1147837
SIZE OF STIFFNESS FILE(S) = 8.792 MB
NUMBER OF EQUATIONS TO SOLVE = 8976
---------------------------------
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 = 0, OK.
---------------------------------
L I N E A R S T A T I C C A S E S 12:32:52
USING STIFFNESS AT ZERO (UNSTRESSED) INITIAL CONDITIONS
TOTAL NUMBER OF CASES TO SOLVE = 7
NUMBER OF CASES TO SOLVE PER BLOCK = 7
LINEAR STATIC CASES TO BE SOLVED:
CASE: DEAD
CASE: LIVE
CASE: WINDX
CASE: WINDY
CASE: MANSORY
CASE: FINISHES
CASE: ~LLRF
E I G E N M O D A L A N A L Y S I S 12:32:52
CASE: MODAL1
USING STIFFNESS AT ZERO (UNSTRESSED) INITIAL CONDITIONS
USING MASS SOURCE: MsSrc1
NUMBER OF STIFFNESS DEGREES OF FREEDOM = 8976
NUMBER OF MASS DEGREES OF FREEDOM = 2782
MAXIMUM NUMBER OF EIGEN MODES SOUGHT = 12
MINIMUM NUMBER OF EIGEN MODES SOUGHT = 1
NUMBER OF RESIDUAL-MASS MODES SOUGHT = 0
NUMBER OF SUBSPACE VECTORS USED = 24
RELATIVE CONVERGENCE TOLERANCE = 1.00E-09
FREQUENCY SHIFT (CENTER) (CYC/TIME) = .000000
FREQUENCY CUTOFF (RADIUS) (CYC/TIME) = -INFINITY-
ALLOW AUTOMATIC FREQUENCY SHIFTING = YES
Original stiffness at shift : EV= 0.0000000E+00, f= .000000, T= -INFINITY-
Number of eigenvalues below shift = 0
Forming stiffness, new shift: EV= 1.0000000E-03, f= 0.005033, T= 198.691765
Number of eigenvalues below shift = 251
Forming stiffness, new shift: EV= 5.0000000E-04, f= 0.003559, T= 280.992589
Number of eigenvalues below shift = 146
Forming stiffness, new shift: EV= 2.5000000E-04, f= 0.002516, T= 397.383531
Number of eigenvalues below shift = 83
Forming stiffness, new shift: EV= 1.2500000E-04, f= 0.001779, T= 561.985178
Number of eigenvalues below shift = 47
Found mode 1 of 12: EV= 1.2519803E-04, f= 0.001781, T= 561.540539
Found mode 2 of 12: EV= 1.2519803E-04, f= 0.001781, T= 561.540539
Forming stiffness, new shift: EV= 6.2500000E-05, f= 0.001258, T= 794.767061
Number of eigenvalues below shift = 27
Forming stiffness, new shift: EV= 3.1250000E-05, f= 0.000890, T= 1123.970
Number of eigenvalues below shift = 14
Forming stiffness, new shift: EV= 1.5625000E-05, f= 0.000629, T= 1589.534
Number of eigenvalues below shift = 2
Forming stiffness, new shift: EV= 7.8125000E-06, f= 0.000445, T= 2247.941
Number of eigenvalues below shift = 0
Found mode 3 of 12: EV= 1.2916113E-05, f= 0.000572, T= 1748.292
* * * W A R N I N G * * *
EIGENVALUE 3 WAS FOUND OUT OF SEQUENCE
Found mode 4 of 12: EV= 1.2916113E-05, f= 0.000572, T= 1748.292
Found mode 5 of 12: EV= 2.3206534E-05, f= 0.000767, T= 1304.292
Found mode 6 of 12: EV= 2.3206534E-05, f= 0.000767, T= 1304.292
Found mode 7 of 12: EV= 2.3217637E-05, f= 0.000767, T= 1303.980
Found mode 8 of 12: EV= 2.3217637E-05, f= 0.000767, T= 1303.980
Found mode 9 of 12: EV= 2.3992956E-05, f= 0.000780, T= 1282.738
Found mode 10 of 12: EV= 2.3992956E-05, f= 0.000780, T= 1282.738
Found mode 11 of 12: EV= 2.9689614E-05, f= 0.000867, T= 1153.128
Found mode 12 of 12: EV= 2.9689614E-05, f= 0.000867, T= 1153.128
NUMBER OF EIGEN MODES FOUND = 12
NUMBER OF ITERATIONS PERFORMED = 48
NUMBER OF STIFFNESS SHIFTS = 8
Etabs problem file.EDB Column report.pdf
