Leong Shi Ming

Hi, Mr. Umar. Thanks for your reply to clear my doubt. May I know is there any quick way to locate the part causing the eigenvalue instability problem?

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