global and local approaches provide substantial savings in the number of total function

evaluations.

 Reliability-Based Design Optimization Frameworks

 This section summarizes several popular RBDO frameworks. These frameworks

are based on the concepts of design sensitivity analyses, approximated limit state

function, approximated reliability constraints, and partial safety factor concept to convert

reliability constraints to approximately equivalent deterministic constraints, and RSA.

Double Loop Approach


 Initial Design
 deterministicc optimum)

 Probabilistic Analyses:
 FORM/SORM
 Inner Loop: iterative
 probabilistic analysesl
 SNo
 liability Cone e?
 yg................... Outer Loop: design
 Design Sensitivity Sp/8dd optimization
 from PA

 Approximate Reliability
 Constraints 0 at DP d

 Update Design
 using Optimizer

 No
 Design Converge?

 Yes
 Stop

Figure 2-1. Double loop approach: reliability analysis coupled inside design optimization

 The traditional approach of RBDO is to perform a double loop optimization: outer

loop for the design optimization (DO) and inner sub-optimization that performs reliability

analyses using methods such as FORM or SORM. This nested approach is rigorous and