MCS given sample size, which is helpful in guiding the optimizer. In order to reduce the

computational cost of RBDO, especially problems with very low probability of failure, a

multi-fidelity based RBDO approach using probabilistic sufficiency factor was proposed,

which can find satisfactory design with low probability of failure by using a correction

factor to a response surface created by low-accuracy Monte Carlo Simulation. For

problem with low probability of failure, the sequential approach is computationally more

efficient than the multi-fidelity approach, but the design is more efficient in term of

obj ective function in the multi-fidelity approach.