Load Combinations

Abstract

The modelling of load variables is treated briefly in section 3.5. It is stressed there that load variables and other actions are typically time-varying quantities which are best modelled as stochastic processes. In section 3.5, it is also shown that when dealing with a single time-varying load in connection with barrier crossing problems (see section 9.4) the detailed time variation is not of relevance. This is due to the fact that in such cases the distribution of the maximum value of the loading process in a given reference periode can be derived from the arbitrary-point-in-time distribution (see figure 3.13 on page 57). When the loading process is continuous then the probability distribution of the maximum value (largest extreme) is likely to be very closely approximated by one of the asymptotic extreme value distributions, treated in section 3.3. In this way instead of modelling a single load variable as a stochastic process {X(t)} it is modelled by a stochastic variable, say Y (see also section 9.5). Therefore, in reliability analysis, single load variables imply no special difficulties. A number of examples in chapters 5 and 6 of analysis and design of simple structures loaded by single loads illustrate this fact.