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ok, I found sensible reason. Total vertical load is 25 % of critical load (Euler's load), so stiffness is reduced by 25%, that's why the period changes.
The only question is - why this does not affect on eigenvectors?

Frank, do you mean 'system FullGeneral'? Then OpenSees print "invalid command name <<printA>>".

Approximatly axial force at 1 floor level is 17200/5=3440 kN in each column. As I wrote above I found that it is PDelta transformation that affects. To find this I erased BW from the model and there were near the same big difference in values. May be there is some command to show or write stiffness ...

My model is a 5-storey steel frame (h=3.5 m, total load ≈ 17200 kN). It consists of elastic beam-column elements joined with zerolength elements (using bouc-wen material) and equalDOF command. Notify in advance, that BW nonlinearity participates slightly in this effect, but it's input is not essenti...

Hello I found that PDelta transformation affects on eigen analysis result. When I apply only gravity loads, the first period is increasing by 16%! And if I use linear transformation than the period is nearly the same. The questions is: 1) Am I right and Pdelta can really affect that much on natural ...