2nd order analysis

I need to check steel structures using 2nd order analysis to Design according to global stability and i need also to include Siesmic effect in combinations. how can i do that ?

you need perform dynamic analysis with th2 together. you can do it in ase module, check the command step. however the task is not easy, at first shot perform the modal analysis and rsa to obtain initial ground acceleratorion property. the another way is command sfix linearize th2 stiffnes and then perform rsa. it should be good apx., as long as ground acc. do not increase axial forces in element significantly.