The Earthquake Engineering Online Archive

Measures of structural safety under imperfect states of knowledge

Der Kiureghian, Armen

UCB/SEMM-1988/06, Dept. of Civil Engineering, University of California, Berkeley, 1988-03, 35 pages (500/C23/88/06)

A reliability index defined under conditions of uncertainty due to estimation and modeling errors is a point estimator of safety. A set of fundamental requirements on the point-estimator reliability index are formulated, motivated by needs in structural code development. Existing reliability indexes are examined in light of these requirements and are found to be lacking with regard to one or more of the requirements. Based on concepts in Bayesian statistical decision theory, a new index is introduced which is shown to satisfy all the stipulated requirements. Methods are developed for quantifying the uncertainty in the measure of safety arising from the imperfect state of knowledge. It is shown that existing reliability methods can be used to compute the probability distribution or variance of the safety measure. A simple example shows the uncertainty in the reliability index as a function of the sample size.

Available online: http://nisee.berkeley.edu/documents/SEMM/SEMM-88-06.pdf (21 MB)