The Finite Element Method is nowadays widely used in structural design, both for the Servicebility Limit State (SLS) and also for the Ultimate Limit State (ULS). Especially the ULS design rules are based on the idea of ensuring sufficient structural reliability, which is usually expressed in a maximum admissible failure probability. This is commonly achieved by prescribing design rules and establishing partial safety factors. These load and resistance factors are calibrated for a wide range of typical cases with typical dimensions. For more extraordinary cases it could be that the application of these concepts leads to extremely conservative or possibly also to unconservative designs. The presented approach enables us to use the optimization potential for these case. Furthermore, the determination of failure probabilities is a substantial and indispensable element in modern risk-based design strategies.
In this article we present a way of determining the structural reliability respectively the failure probability by means of probabilisitic calculations directly. To this end Plaxis is coupled with the generic probabilistic toolbox ‘ProBox’, developed by TNO Built Environment and Geosciences. ProBox enables us to carry out a reliability analysis using Plaxis in a fully automatized manner. We will also show that, in contrast to common prejudices, probabilistic analysis does not necessarily require thousands or millions of calculations as e.g. the Monte Carlo method, if we use more advanced and more efficient reliability techniques.