*HEADING                                                                      
LATERAL EIGENVALUE BUCKLING: B31OS, *BEAM SECTION, SECTION=I
*** Small perturbation of flange dimension (around value of 3.0)
*** are introduced to insure stable results for QC procedure.
*NODE
 1,0.0,0.0,0.0
 21,12.0,0.0,0.0
*NGEN,NSET=ALL
 1,21
*ELEMENT,TYPE=B31OS
 1,1,2
*ELGEN,ELSET=BEAM
 1,20,1,1
*BEAM SECTION,SECTION=I,ELSET=BEAM,MATERIAL=MAT
 0.345,0.69, 0.3001,0.2999, 0.027,0.027, 0.0145
 0.0,-1.0,0.0
*MATERIAL,NAME=MAT
*ELASTIC
 2.1E11,0.3125
*BOUNDARY
 1,1,4
 21,2,4
*STEP
*BUCKLE
10,,14,50
*NODE PRINT
U, 
RF  , 
*NODE FILE, FREQUENCY=1, LAST MODE=3
U,RF  
COORD, 
*DLOAD
BEAM, PZ, -1.
*EL PRINT,FREQUENCY=0
*MODAL FILE
*END STEP