Analysis of variability of the long-term deflection of a new kind of composite bridge deck

Nearly 400 composite railway bridge decks of a new kind with U shaped cross section have been constructed in Belgium over the last ten years. The construction of this new kind of bridge deck is rather complex with preflexion of steel girders, prestressing of a concrete slab and two-phases concreting. They seem to perform according to expectations, but some variability has been observed between the measured camber at prestressing and the camber computed by a classical computation method using a pseudo-elastic analysis with modular ratios. Thanks to a statistical analysis performed on a set of 36 decks, the most significant variables that explain the variability of the camber at prestressing have been determined. For the same sample, the long-term camber under permanent loading have been computed by two methods and have been compared with measurements taken one or two years after the construction of the bridge decks. At long-term, the camber computed by the step-by-step method shows a very good agreement with the measured camber.