Fatigue Reliability and Design

At present, the fatigue provision in most design specifications in this country is based upon test data presented in the form of modified Goodman diagrams. The recent AISC specification is based upon a constant-range criterion. In any event, neither the randomness of fatigue lives nor that of applied loads is being considered. In this paper, a simple and reliability-based procedure is presented for the fatigue design of structures. The probability distribution for repeated loads can be obtained from dynamic analysis or field measurements. In addition, the stress-life-probability relations are available from single-stress-level laboratory tests. With an initial configuration of the structure, the distribution of repeated stresses can be computed. Then, the life of the structure can be predicted using a cumulative-damage criterion and an acceptable probability of failure. The computed life is compared with the design life, and the design can be modified in an iterative manner.