An observation platform is supported by 12 steel cables. Cross-sectional area of each cable can be treated as a normal random variable with a mean value of 160 mm2 and a coefficient of variation (COV) of 0.05. The yield strength of the cables' steel can also be treated as a normal random variable with a mean value of 380 MPa and a COV of 0.08. It can be assumed that the cross-sectional areas of individual cables are independent random variables while the yield strength of steel is fully correlated across all cables.

The weight of the platform can be modelled as a normal random variable with a mean value of 400 kN and COV of 0.10. The maximum capacity of the platform is 100 people. The weight of a person can be modelled as a normal random variable with a mean value of 650 N and COV of 0.20.

Find by the FOSM method the safety index and the probability of failure of the platform due to yielding of the supporting cables when the platform operates at its maximum capacity. It can be assumed that at failure the cable behaviour is ductile and the cables represent a parallel system