The expected life of a shared-load system can be extended if the adjustment of loads is allowed. In this paper, this goal is achieved by keeping the system's reliability always in the maximum situation during its service. A design example of a two-column supporting system is used to demonstrate this idea. Two kinds of materials, 316-SS and Cr-Mo, are considered. The thermal environments of the columns are different, one is 568 degrees C and the other 501 degrees C. Material creep phenomenon dominates the strength decay which follows the Manson-Haferd model. The results show that the expected life of the optimal load-adjusting case is approximately four times that of the averaging-load case. The numerical example also investigates the variations of one-nit survival probabilities and it shows that the columns fail almost at the same time for different loading situations, but it is still at a very low level when the optimal-load adjustment is made. This indicates that the optimal loading situation gets inside the spirit of the design principle, even at the operation time beyond the system's expected life. (C) 1998 Elsevier Science Limited.
