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

基础设施的恶化是许多国家普遍存在的问题。为了评估这类结构在未来继续服役的能力，需要开发简单实用的工具来评估结构的时变可靠性和性能。当一个结构受到多个时变荷载作用时，需要考虑参考期内组合的最大强度。本项目首次建立了组合最大强度的累积分布函数(CDF)的理论表达式。数值算例表明，无论荷载强度和随机过程的统计特性如何，CDF的理论表达式都能提供较好的估计。然后，引入构件退化阻力折减系数的概念，将时变可靠性问题近似为时变可靠性问题。有了该系数，时变电阻可等效为…本文提出了一种确定荷载和抗力系数的近似方法，数值算例表明，采用近似折减系数可以较准确地达到目标可靠性水平。定期的服役检查和适当的维修可以使退化的结构部件恢复到接近原始的状态。由于检查和维护成本高昂，因此需要在检查的范围和准确性、所需的可靠性水平和成本之间进行权衡。要设计一个最优的检测/维修策略，通常必须解决非线性优化问题。该近似方法可用于估计包括部件强度因恢复等原因而随时间不连续变化的情况的阻力减小系数。利用该方法，可以简化优化过程，避免了时变可靠性分析。较少

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