Reliability Analysis Method for Degrading Structures Taking Combination of Load Processes into Account

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The deterioration of infrastructures is a widespread problem in many countries. In order to assess such structures for continued future service, simple and practical tools need to be developed for evaluating the time-dependent reliability and performance of the structures.When more than one time-varying load act on a structure, the maximum intensity of the combination during the reference period needs to be considered. This project first developed the theoretical expressions of the cumulative distribution function (cdf) of the maximum intensity of the combination. Numerical examples show that the theoretical expression of the cdf provides fairly good estimate regardless of the statistical characteristics of the load intensity and stochastic processes.Then the concept of a resistance reduction factor due to degradation of a component is introduced to approximate a time-dependent reliability problem as a time-independent one. With the factor the time-varying resistance can be equivalentl … More y replaced with a time-invariant resistance, and load and resistance factors can be determined for the assessment applying simple AFOSM.An approximation method to determine the factor is proposed, and numerical example shows that the target reliability level can be achieved fairly accurately using an approximate reduction factor.Periodic in-service inspection followed by suitable maintenance may restore a degraded structural component to near-original condition. Since inspection and maintenance are costly, there are tradeoffs between the extent and accuracy of inspection, required level of reliability, and cost. To design an optimum inspection/maintenance strategy, generally non-linear optimization problem must be solved. The approximation method can be applied to estimate a resistance reduction factor including the cases when the strength of a component changes discontinuously in time due to, such as, restoration. Using the proposed method, the optimization can be simplified avoiding time-dependent reliability analysis. Less