Development of Minimum Life-Cycle cost Design Criteria

9510243环境负荷下民用基础设施系统的设计程序已逐步从主要基于判断/经验、半概率性向概率性转变。然而，基于长期风险和收益优化的程序还没有开发出来。对于危害暴露时间较短但故障仍可能造成严重后果的现有设施的评估和维修/改造，尤其需要这样的程序。该国的大量民用基础设施系统正在老化，许多系统需要更换。维修/翻新问题将变得更加尖锐。合理的基于全寿命周期费用的设计准则需要考虑载荷和抗力不确定性、危险暴露时间、故障后果费用和运行维护费用以及费用/损失随时间折现的影响。该项目的目标是：(L)制定根据生命周期确定设计标准的方法；(2)将其应用于常规规则和标准未涵盖的新设施和翻新设施。该问题被描述为关于设计变量的期望总寿命周期费用最小化的问题，即设施的设计载荷和阻力或相应的LRFD格式的载荷和阻力系数。需要研究的任务是：(1)将荷载和阻力中的不确定性(包括随机荷载发生时间、强度和相关性、失效后果的代价以及随时间折算成本/损失)描述为约束最小化问题；(2)开发求解的优化算法；(3)研究荷载和阻力不确定性以及阻力随时间恶化的影响；(4)建立成本函数模型并检查设计的灵敏度；(5)确定设计荷载。这项研究将影响新的设计概念和方法的发展，这些概念和方法对下一代规范和标准具有重要影响。结果还将在制定维修/翻新准则方面产生更直接的好处。***

9510243 Wen Design procedures for civil infrastructure systems under environmental loadings have gradually changed from largely judgments/experience-based, semi- probabilistic, to probabilistic. Procedures based on optimization of long-term risk and benefit, however, have not been developed. Such a procedure is specially needed in evaluation and repair/retrofit of existing facilities whose hazard exposure time is short but whose failure may still cause serious consequences. A large number of the nation's civil infrastructure systems are aging and many are in need of replacement. The repair/retrofit problem will become more acute. Rational life-cycle cost based design criteria are needed in which effects of loading and resistance uncertainty, hazard exposure time, costs of consequence of failure and operation and maintenance, and discount of cost/loss over time are all taken into consideration. The objectives of this project are: (l) development of methodology for determination of design criteria based on life-cycle and (2) application to new and retrofitted facilities not covered by regular codes an standards. The problem is formulated as that of minimization of expected total life-cycle cost with respect to the design variables, i.e., design loads and resistance of the facility or corresponding load and resistance factors in a LRFD format. The required research tasks are to: (1) formulate the design as a constrained minimization problem considering uncertainties in the load and resistance including random load occurrence time, intensity, and correlation, costs of failure consequences, and discounting cost/loss over time; (2) develop of optimization algorithm for solution; (3) study the effect of load and resistance uncertainty and resistance deterioration over time; (4) model cost functions and examine sensitivity of design and (5) determine the design loads. The research will impact the development of new concepts and metho dologies of design that have important implications in the next generation codes and standards. The results will also have more immediate benefit in development of guidelines for repair/retrofit. ***