Abstract
Elastic instability of simply supported spherical shells subjected to the quasi-static exernal pressure under both immovable and movable boundary conditions (including the relaxation of edge constraint) has been studied. Numerical calculation has been performed by means of new basic equations expressed in terms of deflections u, v, w, and two independent shell parameters a/h, β, which take account of the follwer force. Results obtained here have been compared with previous results and the effect of the relaxation to the instability of shells have been expressed. Finally, both snap-through and bifurcation buckling pressure were lowerd by the effects of the relaxation of edge constraint, especially decreasing of the snap-through buckling pressure is remarkable. So, it can be said that the instbility of simply supported spherical shells not always arise the bifurcation buckling in the region 0.22<β(5<α).
