Reliability-Based Structural Optimization

During the design of any structure, the engineer is faced with a series of decisions which are mandated by the needs of the users of the stracture (e.g. non-collapse, functionality). However, the latter do not uniquely define the final design. Usually there are multiple alternatives that satisfy the aforementioned constraints, amongst which the engineer has to choose. Structural optimization provides a rational framework for assessing the various options and making a decision in an optimum manner based an the performance criteria that must be satisfied . It is widely accepted that the performance of a structure during its lifetime exhibits substantial random variability compared to the predictions made during the design phase. This is due to the inherent uncertainties in a number of parameters that come into play and which can be external to the structure (such as loads, environmental effects) or intemal (as in the material properties, construction defects). Naturally, the randomness observed carries over to the design criteria and performance constraints that must be satisfied by the structural system. The field of probability and statistics provides the mathematical vehicle for dealing with those uncertainties. In this context, a performance constraint (i.e. non-collapse) is satisfied with a certain probability and the design criteria (i.e. the cost) become random variables. In order to provide a realistic and rational framework of structural optimization which accounts for those uneertainties, the field of Reliability-Based structural Optimization (RBO) has arisen. The latter is an interdisciplinary engineering task. The goal of the present project is to extend structural optimization beyond the well-established and well-studied problem of weight minimization, to problems of practical engineering interest. These involve the optimization of structures with regard to minimizing costs while maintaining a target level of safety or reliability, and also include inspection procedures both at the beginning of the structural life as well as after certain periods to assure the target reliability during the entire design life. In addition, the optimization procedures could include (computational) fracture und fatigue analysis in order to derive an appropriate quality assurance program, where maintenance and repair play an important role.