Buckling Factor for Simple Pinned Column

Aravind T — Wed, 27 Apr 2022 16:29:35 GMT

Hi,

I used the verification example for the buckling factors for determining the critical buckling loads for a simple column (pinned pinned).

However I get different results every time I run them. How do I ensure that the values I get are the same. (for ex, when I change the length say from 10 ft to 40 ft, the values are off for the 40 ft one). Similarly when I change to STAAD SPACE to find the minor axis buckling, it is off for slender column lengths.

For ex. the attached code is for a pinned-pinned W10x45 section with Ix = 248 in4 and Iy = 53.4 in4. A applied load of 160 kip in the Y dirn, length of 30 ft. The buckling factor should be 3.42 and 0.73 (for major and minor). Whereas I get 4.16 and 0.89.

Am I missing something, I checked the verification example and the code is the same.

Attached is the code.

UNIT FEET KIP
JOINT COORDINATES
1 0 0 0; 2 0 30 0;
MEMBER INCIDENCES
21 1 2;
DEFINE MATERIAL START
ISOTROPIC STEEL
E 4.176e+06
POISSON 0.3
DENSITY 0.489024
ALPHA 6.5e-06
DAMP 0.03
TYPE STEEL
STRENGTH RY 1.5 RT 1.2
ISOTROPIC STEEL_36_KSI
E 4.176e+06
POISSON 0.3
DENSITY 0.489024
ALPHA 6.5e-06
DAMP 0.03
TYPE STEEL
STRENGTH FY 5184 FU 8352 RY 1.5 RT 1.2
G 1.60615e+06
ISOTROPIC STEEL_50_KSI
E 4.176e+06
POISSON 0.3
DENSITY 0.489024
ALPHA 6.5e-06
DAMP 0.03
TYPE STEEL
STRENGTH FY 7200 FU 8928 RY 1.5 RT 1.2
END DEFINE MATERIAL
MEMBER PROPERTY AMERICAN
21 TABLE ST W10X45
CONSTANTS
MATERIAL STEEL_50_KSI ALL
SUPPORTS
1 PINNED
2 FIXED BUT FY MX MY MZ
LOAD 1 LOADTYPE None TITLE LOAD CASE 1
JOINT LOAD
2 FY -160
PERFORM BUCKLING ANALYSIS MAXSTEP 30

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Buckling Factor for Simple Pinned Column

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