26. The Interactive Method—Reliable and Reproducible S-N-Curves for Materials

Based on a new developed research method—the Interactive Procedure—the characteristic fatigue strength curve (e.g. 5%-quantile obtained at a level of confidence of 90%) was determined directly by test results. As an example new experimental investigations on reinforcing steel were conducted on pure single bars as well as on bars embedded in concrete. The lower stress level was kept constant according to the usual design situation. Another example with a shear loaded fastener system—steel element in concrete—shows that the load bearing capacity increases, if the concrete strength increases. A third example shows the differences between prestressing steel tested without embedment and casted in concrete. For the development of a complete whole S-N-curve for steel 3–5 static and 20–25 cyclic tests are necessary.