The paper reviews the present BS 5500 code for regulations for design of externally pressurised axi-symmetric ring stiffened cylinders and in conjunction with the available experimental data and finite element non-linear analysis results, quantities the model uncertainty factor associated with various failure modes and carries out reliability analysis. The reliability analysis includes Advanced First Order Second Moment method (AFOSM) and also checks are made with other methods such as Second Order Reliability Method (SORM), Directional Simulation and Monte Carlo Simulation to confirm the accuracy. It is found that the difference between these methods are so small that the values obtained from AFOSM are acceptable in practice. Various submarine type structures are designed according to BS 5500 having various diameters and different diving depths. Sensitivity analysis confirms the important design variables so that these variables may only be considered when establishing a design code format. The model uncertainty factor is very sensitive and its effect on various modes of failure are established. Out-of-roundness of the frame is the important control identified for careful shape measurement and analysis during construction. The effect of this parameter is established in terms of reliability index.
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