The traditional engineering approaches are to design
safety margins, or safety factors, into the equipment. The
safety factor (SF) is defined as the ratio of the capability
of the system to the force placed on the system. The
safety margin (SM) is the difference between the system
capability and the force. Failure will occur if the safety
factor is less than 1 or the safety margin becomes negative.
This is often a deterministic approach that ignores
the variability present in both the forces placed on a system
and the system’s ability to react the force [1].
By the late 1930s both forces and strengths were being
commonly expressed as statistical distributions. The
probability and statistics theories were employed into
engineering design [2]. It is difficult to implement the
probabilistic design in engineering for the sake of the
determination of forces and strengths distributions. It has
been shown that the distribution of material resistance
(such as yield strength, tensile strength, etc.) generally
follows a normal distribution; However the distribution
of applied forces acting on the element is difficult to be