「Evaluation of structural integrity with partial safety factor method」
We are making study of applying the partial safety factor (PSF) method that enables the rational and quantitative evaluation based on probability of failure to structural integrity evaluation. It is the purpose of our research to determine simply and rationally whether the detected defects in plants in service are acceptable or unacceptable by using partial safety factor method.
While the traditional method insure the safety of structures by multiplying the strength term by the sole safety factor, partial safety factor method multiplies both strength and load terms by multiple safety factors.
Partial safety factors are not determined
uniquely for an objective reliability and depend on the variance of parameters.
For this reason, we have to use appropriate factors for their variances. We
focus on a crack like flaw, which is one of the most dangerous defects in
plants, and analyze sensitivity of the variances of the stress, yield stress
and fracture toughness to partial safety factors. Fig.1 shows the definition
of the limit state function based on R-6 method, which is widely used for
the assessment of crack like flaws. Fig.2 shows the calculation result. When
evaluating the clack like flaw in the plastic collapse dominant region, different
partial safety factors in accordance with the variance of the yield stress
must be used.
u Y. Mogami，S. Sakai，T. Sasaki，”Evaluation of Structural Integrity with Partial Safety Factor Method”，JSME M&M2008，（2008）
Fig1. Definition of limit state function based on R-6 method
(a) PSF for the stress and the crack length (b) PSF for the fracture toughness and the yield stress
Fig2 Partial safety factors calculated for each variance of the yield stress