Zagadnienia niezawodności i bezpieczeństwa w mechanice materiałów i konstrukcji

Probabilistic methods are applied to mechanical reliability and safety problems on the macroscopic level, both to the loading and structural properties. First, some basic probability distributions have been taken under consideration, then a distribution-free analysis is attempted by means of the asymptotic distributions or by a ''second-order'' statistical analysis, where the exact form of the distribution remains undefined. Simple probabilistic theory of size-effect has been developed by Weibull for the brittle bodies. The extension of the theory to elastic-plastic structural systems is already accomplished in some cases. The design load depends on the anticipated service-life of the structure. This ''durability
effect'' has also been analysed by means of Gaussian stationary stochastic processes. Notions of reliability and safety are distinguished from the point of view of the effect of control. These notions correspond to the two extreme cases: no preliminary elimination of defective objects and the perfect elimination. If the control effect is taken into account, the specific fields of responsibility must be defined and delimited. The difference between safety and reliability is evident in the case of two or more safety parameters under control. The safety factor is easily decomposed into partial factors in these cases.