Probabilistic analysis of the structural behaviour of a bridge prestressed concrete beam

The VIPP are simple span viaducts made of precast concrete girders prestressed by post-tension. This type of construction was largely developed after the second world war, thanks to its girders launching system which allowed the crossing of non classical obstacles with reasonable height. The many design and execution mistakes, and the absence of corrective maintenance actions to restore the defective waterproofing of these bridges, have led to several structural problems. The detailed description of these problems shows how much the diagnosis of these structures is essential to conclude a relevant revaluation of their performance. It is in this context that a prestressed girder was preserved from the Merlebach's bridge demolition to test several assessment experimental techniques and models to apprehend its mechanical behavior. In this context, deterministic and probabilistic analyses have been applied. For this purpose, a structural model have been developed and coupled with the LCPC reliability toolbox. The structural reliability has been studied by response surfaces methods and by support vector machines, providing probability functions of the sag at mid-span for various loadings. The mean and median model response, as well as confidence intervals, are calculated thanks to mechanical properties obtained from testing. The probabilistic structural response is then compared to the experimental response, showing that the mean model describes correctly the real structural behavior and that the experimental 90% confidence intervals belong to the numerical 90% confidence interval