A series of tests were performed on steel cylindrical shells subjected to internal pressure, bending and shearing forces. Conclusions are summarized below. (1) The lower limit of buckling load can be described as follows. When σ_h/σ_γ≦0.3, _bσ_m=_bσ_o+(0.56 _0σ_<cγ>-_bσ_m)(σ_h/σ_γ)/0.3…(10.1) When σ_h/σ_γ>0.3,_bσ_m=0.8 _0σ_<cγ>(1-σ_h/σ_γ)…(10.2) where _bσ_m: the maximun extreme fibre stress at the bottom of shell σ_h: hoop stress due to internal pressure σ_γ: the yield point stress _bσ_<mo>: the lower limit of buckling stress without internal pressure _0σ_<cγ>: compressive buckling stress without internal pressure in the axisymmetric mode (2) The _bσ-θ curve under the monotonic horizontal loading is simply identified to be a skelton curve as shown Fig. 3, where ba is the extreme fibre stress at the bottom of the shell and θ is the overall inclination of the shell. The stationary value termed by _bσ_<0.02> in the range of large deformation can be calculated by using equation (6). _bσ_<0.02>=50 σ_γ/(γ/t)…(6) where _bσ_<0.02>: _bσ at the point of θ=0.02 γ: external radius t: wall thickness (3) Under repeated loading, the relation between _bσ and θ is easily costructed from the skelton curve on the basis of the same hysteresis rule as is applied to the case without internal pressure.