640 publications from this institution
In this paper, an important feature of time variant reliability problems is identified. The concept of barrier failure dominance (BFD) is introduced to characterize those problems where an out-crossing or overload failure is more likely to be caused by a very small realization of the barrier (resistance) than by an exceptionally large realization of the load process. This result arises from a study of the ensemble out-crossing rate approximation, reported in a previous paper and which is reviewed herein. It is shown how the notion of BFD can be used to understand the limits of application of the ensemble out-crossing rate approximation. It is also suggested that the acknowledgement of BFD can support the choice of the appropriate simplified solution method for particular problems. A three-dimensional load combination and a resistance degradation problem are studied as examples. The ensemble up-crossing rate approximation is compared with load process-based approximations, using the time-integrated approach, the load combination rule of Turkstra and the point-crossing formula.
The reliability analysis of offshore structures under wave and wind actions is considered using second order random wave theory. To represent non-Gaussian properties of the resulting wave kinematics, the Hermite moment transformation is used. Further, the so-called sample-specific linearization method developed already (to be used in conjunction with the directional simulation method and the linear wave theory) will be extended to take into account both (1) non-Gaussianity of wave/wind load due to nonlinear load processes and also (2) the non-Gaussianity of wave kinematics due to the nonlinear wave theory. This allows an out-crossing approach to be used to assess the structural probability of failure and the involving out-crossing rate (which is not generally available for non-Gaussian processes) is required to be estimated. Using the proposed procedure, simple structures are analyzed in one- and multi-dimensional cases and the results for structural probability of failure are compared with those obtained using simple linear wave theory. Outcomes show that the use of nonlinear wave theory may affect the results considerably.
