Fuzzy reliability assessment of bridge piers in presence of scouring

The design of bridge piers placed in riverbeds has to deal with variable hydraulic forces acting on structures with foundations which may be prone to scour effects. The conventional design of drag forces, scour depths and foundation bearing capacity is carried out by means of equations which involve a certain number of uncertainties regarding flow, sediments, structural and geotechnical parameters. A sound reliability assessment of bridges piers against scouring risks must take into account the uncertainties inherent in these parameters. Due to the phenomenological nature of these uncertainties, a fuzzy approach seems to be the most adequate to deal with to this kind of problems. In the first part of this study, the role of the uncertain parameters is assessed by considering separately their effects on the drag forces and on the general and local scour evaluation. In the second part, the previously obtained responses regarding the drag forces and the scouring depths are used as input data for a fuzzy analysis of the pier foundation reliability. Different design contexts are studied: embedded foundations and foundations with exposed piles; effects of clear water and live bed scour conditions; different ratios between vertical superimposed and lateral hydraulic loads. A sensitivity analysis allows to estimate the influence of the various uncertain variables on the partial and on the global responses.