A monopile is made of a thin-walled hollow steel tube of circular cross-section with the diameter of 0.6 m; the coefficient of variation (COV) of the diameter can be neglected. The mean modulus of elasticity of the steel is 200 GN/m and its COV is 0.04. The mean height of the monopile is 12 m and its COV is 0.03. The mean thickness of the tube wall is 14 mm and its COV is 0.05. The monopile is loaded at the top by a load W with mean of 1.5 MN and COV of 0.16. Assume that the monopile can be modelled as a slender column fixed at its base and free at the top end, i.e., its critical buckling load is PEI/(4L), where L is the monopole height and for a thin walled tubular section Frt (r- the tube radius and t- thickness of the tube wall). It can also be assumed that all random variables are normally distributed and statistically independent. (a) Calculate the safety index and the probability of failure of the monopile due to buckling using the FOSM method. (b) Calculate the safety index and the probability of failure of the monopile due to buckling using the AFOSM method. (c) Compare the results obtained in (a) and (b) and comment on their differences and possible reasons for that.