Fatigue Reliability of Structures Sujected to Earthquake Loading

许多工程结构的设计都要考虑材料的疲劳破坏。例如，海上结构必须承受连续振荡的风和波浪荷载。在极端条件下，载荷可能在短时间内显著波动。大量的损坏和大多数故障都是由这些短时间负载引起的。现有的评估疲劳失效概率的方法假设加载过程是平稳的（即加载特性不随时间变化），这可能不适用于极端加载条件。本研究建立了一个适应非平稳加载过程的疲劳失效可靠性模型。该模型将结构对非平稳荷载的响应描述为一个随机过程。计算该响应过程的交叉统计量，以确定期望的负荷反转次数；利用断裂力学的方法确定由这些载荷反转引起的累积损伤。最后，将估计的损伤与一个极限准则进行比较，从而计算出失效的概率。这种方法改进了现有的设计程序，用于在非平稳载荷下容易疲劳破坏的结构，例如由地震引起的结构。这些信息还可以用于为许多类型的结构指定合理的设计、检查、维护和修理方案。

The design of many engineered structures is governed by considerations of material fatigue failure. For example, offshore structures must withstand continuous oscillatory wind and wave loads. Under extreme conditions, the loading may fluctuate significantly over short time periods. Substantial damage, and most failures, are caused by these short-time loads. Existing methodologies for evaluating the probability of fatigue failure assume that the loading process is stationary (that is, the loading characteristics do not change with time), which may not be appropriate for extreme loading conditions. This study develops a reliability model for fatigue failure that accommodates nonstationary loading processes. The model describes the response of the structure to nonstationary loads as a random process. The crossing statistics of this response process are calculated in order to determine the expected number of load reversals; the accumulated damage resulting from these load reversals is determined using the methods of fracture mechanics. Finally, the estimated damage can be compared to a limiting criteria so as to calculate the probability of failure. This methodology improves upon existing procedures for the design of structures prone to fatigue failure under nonstationary loads, such as those caused by an earthquake. This information can also be used to specify rational design, inspection, maintenance, and repair schemes for many types of structures.