On the assessment of robustness

Authors

Jack W. Baker, Matthias Schubert and Michael H. Faber

Abstract

A framework for assessing robustness is proposed, taking basis in decision analysis theory. Robustness is assessed by
computing both direct risk, which is associated with the direct consequences of potential damages to the system, and indirect
risk, which corresponds to the increased risk of a damaged system. Indirect risk can be interpreted as risk from consequences
disproportionate to the cause of the damage, and so the robustness of a system is indicated by the contribution
of these indirect risks to total risk. A framework is presented for measuring robustness in this way, and implications for
system modelling and acceptable levels of robustness are discussed. Numerical studies of idealized structural systems are
performed using this framework, to demonstrate the use of the proposed robustness index and provide insight into system
properties affecting robustness. Considered exposures include the design live load and an extraordinary exposure representing
a fire or explosion that causes the loss of one or more system components. The results indicate that properties affecting
system reliability, such as number of components or the stochastic properties of the load, also affect robustness. Perhaps
more interestingly, it is seen that properties such as failure consequences and time to repair a damaged system also affect
this measure of robustness. The assessment framework is applied here to study damage tolerance, but the procedure can be
applied as well to other aspects of robustness such as tolerance to human error in design or construction.

Published in/by

Journal of Structural Safety, in press