I have carried out eigen buckling analysis of cylindrical shell under axial compression under unit load using abaqus in model-1 and in model -2 i carried out riks analysis gave imperfection 0.2mm fotr shell thickness 2mm radius 0.25m,h=0.5 m after the 100 increment the the shell is subjected to load which is obtained from first buckling load in first mode here how to get the collapse load