Probabilistic Design Method On Cylinder Shells Under External Pressure

Buckling of cylinder shells under external pressure is very complicated. The imperfections in geometry, material and geometric nonlinearity often make it difficult to solve the buckling problem by theoretical or analytical solution. With the development of numerical analyses, many scholars using it to research the buckling of cylinders subjected to external pressure, and it also begin to introduced in many standards. From now on, the design method are all determined, don’t consider the effect of variation of geometric dimensioning and imperfection. This paper study on the effect of geometric imperfection on the buckling of cylinder shells under external pressure, with probabilistic method.Compare to any other standards, like GB150, ASME Ⅷ-2and EN13445, EN1993-1-6gives more clear rules for numerical analyses in design. With the numerical analyses of10real cases in "consistent imperfect buckling analysis method", it is illustrated that EN1993-1-6has advantages over GB150, and is equal to ASME Ⅷ-2, EN13445. The design approaches defined in EN1993-1-6, ASME Ⅷ-2and EN13445are advanced.The geometric imperfection used in "consistent imperfect buckling analysis method" is quite different form the geometric imperfection in reality, and the numerical results always less than the test values. To get more accurate value, this paper use the simplified double Fourier series to represent the geometric imperfection based on measuring data, and take material and geometric nonlinearity into consideration in the later. Compare to "consistent imperfect buckling analysis method", the values got in this way is much more close to test values.According to ASME Ⅷ’s rules for geometric imperfection, this paper analyze the maximum geometric imperfection of a cylinder that the buckling pressure will not be less than80%of the perfect cylinder. The results show that:when the LIDo is small, with the LIDo value increases, the geometric imperfection value that cylinder can withstand decreases. In the case of a larger L/Do value, with L/Do value increases, the geometric imperfection value that cylinder can withstand increases. The geometric imperfection value e in numerical analyses always greater than that in ASME Ⅷ-2.At last, this paper use the method in PDS, come up with a probabilistic design method on cylinder shells under external pressure. In this method, the geometric imperfection is represented by simplified double Fourier series, and consider the effect of geometric dimensioning, geometric imperfection, material yield stress and so on. Using this method can get the distribution of critical buckling value, and the test values are in the area that2times of standard deviations to mean values. At the same time, the critical buckling values are greater than other standard when reach the99.999%degree of reliability.