Keywords: تجزیه و تحلیل خطی دو طرفه; Buckling; Robust design; Knockdown factor; Imperfection; Truncated cone; Threshold knockdown factor; Vega launcher; CC; Clamped boundary conditions; Exp.; Experiment; F; Axial force; GNA; Geometrically nonlinear analysis; H; Height of a truncated cone; h;