In the thick shell theory based on first-order shear deformation theory, the 1/(1 + ζ/Ri) term of strain-displacement relations is treated approximately. When the terms of strain-displacement relations and stress resultants are treated exactly, equilibrium of the moment about the normal to mid-surface is satisfied without using modified strain-displacement relations. The error of the displacement, stress and frequency caused by first- and second-approximation is investigated.
