After the first [ Max. Cycle ] number of iterations, the current calculated eigenvalue is multiplied by [ Factor ], and used as an estimated eigenvalue for the next [ Max. Cycle ] number of iterations.  This continues until either the convergence criteria is satisfied or when [ Max. Shift ] * [ Max. Cycle ] iterations are completed.  There is no general rule for an optimum [ Max. Shift ], [ Max. Cycle ], and [ Factor ] combination, but experience has shown that [ Max. Shift ] = 3, [ Max. Cycle ] = 10,  [ FAC ] = 0.8 is a fairly good set of values to use.
 
 
 
 

1. [ Torsional Geometric Stiffness ] - if you are not interested in considering elastic local flange buckling, then leave the option blank.
2. [ Approximate Shear Distortion ] - the option basically considers vertical stresses in the web.  This option is needed if you want to consider such effects as local web crippling at concentrated loads and sideway web buckling

 

 
 
 
 

1. Checking [ UnSym. ] optionsets the initial buckled shape to be unit out-of-plane displacement for the left one third of the nodes, and one half out-of-displacement in opposite direction for the remaining two thirds of the nodes.
2. Checking [ Sym. ] option sets the initial buckled shape to be unit out-of-plane displacement for all nodes.