Probabilistic Design for Random Fatigue Loads

Abstract

Stationary random (or stochastic) processes have been used as a statistical model for loading due to earthquakes, wind, ocean wave forces, and vehicle environments and motions. Given that the dynamic forces on an element are a random process, the designer is required to specify the size of the element such that it will maintain its structural integrity with specified probability and at the same time provide a minimum-cost, minimum-weight component. An algorithm for the design of a single element (such as tensile member, rivet, bolt, weld, etc.) subjected to a stationary zero-mean random stress is presented. Fatigue was considered to be the mode of failure. A fatigue model is developed which includes the possibility that the stress process can be either narrow- or wide-band. The design algorithm considers variability in the material properties and the geometry of the element as well as uncertainty in the RMS level of the applied stress.