Outcrossing Formulation for Redundant Structural Systems under Fatigue

Abstract

In many cases the resistance properties of structural systems as well as the loads acting on the structure depend on time. If the loads can be modelled by stationary processes and the resistances are time-invariant the determination of the time-dependent reliability essentially is a problem of load combination for which a number of solution procedures exists. The only method capable to handle nonstationary loading with some rigour appears to be the outcrossing approach [1] and the same appears to be true for cases where resistances deteriorate with time, e.g. due to load-induced fatigue, corrosion or aging. This is demonstrated in [2] and elsewhere for structural components. If, however, such deterioration occurs in a redundant structural system a reliability analysis meets serious complications. Structural failure, then, is most likely the result of a sequence of single or multiple componental failures at different random times each of which changing the stress regime in the structure. Furthermore, the load trajectory determines the specific failure sequences. Failure phenomena of this type will especially be found in certain types of railway bridges, aircraft structures and in maritime structures such as ships or offshore platforms. The quantification of the time-dependent reliability of those structures is not only the basis for a proper design of such structures but, probably more important, allows the selection of suitable inspection strategies and rational decisions about time and necessity of repairs.