To analyze the influences of distributed axisymmetrical imperfection parameters on thin wall cylindrical shell buckling reliability,the authors derived an equivalent safety margin for thin walled cylindrical shells with an initial distributed axisymmetrical imperfection,using Budiansky\'s critical solution and advanced first order second moment(AFOSM).

We established the safety margins contained basic variable with the distinct concept,and gave the calculating formulae of the reduced member stiffness matrix and the opposite sign of the equivalent nodal force with failure occurred at beam-member or plate-member.

The safety margin of every slice is assumed to be normal distribution and the safety margin of two next slices is bivariate normal distribution.

In the paper the reliabilty analysis of structural systems with member cross-sectional area,length and loads,being random variables,adopting stochastic finite element method to give safety margins of failure modes.

Hence how to identify the dominant failure paths and how to generate the structural safety margins are also the matters that should be solved.

Various the models for the fatigue reliability evaluation are classified into threetypes according to the status equations, that is, cumulative damage model, residual strength modeland fatigUe life model.