Characteristic Service Stresses

Abstract

A prerequisite for a reliable load assumption is an understanding of the essential and characteristic operational states of engineering constructions. Measurements or theoretical derivations of service stresses, for instance, with the application of numerical simulation models, constitute an essential instrument for this purpose. The service stresses are considered in the time and frequency ranges. The evaluation in the time range provides a means of controlling the measurements under operational conditions and is also useful for obtaining information on the effect of specific operational conditions and states on the value and variation of the stresses with time. From a visual standpoint, this is possible only for a limited period of time. The frequency distribution of amplitudes (load spectrum or load matrix) constitutes the basis for the fatigue-life estimate for structural components and thus also for the analytical and experimental proof of fatigue life. The frequency analysis, which is discussed only for one example, can provide important information on the cause of high stress amplitudes and thus is often useful for explaining cases of damage. A frequency analysis, for example the power density spectrum, cannot contribute directly to the fatigue-life estimate, because the number of cycles of the oscillations is lost in the process [Sons89].