we call here the Birger's safety factor that is more closely related to the target reliability.
A Birger's safety factor of 1.0 implies that the reliability is equal to the target reliability;
a Birger's safety factor larger than 1.0 means that the reliability exceeds the target
reliability; and Birger's safety factor less than 1.0 means that the system is not as safe as
we wish.
Design potential approach
Tu et al. (2000) used the probabilistic performance measure, which is closely
related to Birger's safety factor, for RBDO using FORM. Figure 2-2 summarizes the
design potential approach.
Initial design
(deterministicoptmm
Probabilistic Analyses:
FORM/SORM
Inner Loop: iterative
probabilistic analyses
SNo
liability Cone e?
y g .................... .. Outer Loop: design
Design Sensitivity Sp/8dd optimization
from PA
Approximate Reliability
[constraints p at DPP dk )
Update Design
Using Optimizer
No
Design Converge?,
Yes
Stop
Figure 2-2. Design potential approach: reliability constraints approximated at design
potential point dpk; reliability analyses still coupled inside design
optimization
They showed that the search for the optimum design converged faster by driving
the probabilistic performance measure to zero than by driving the probability of failure to