Concrete overlay of movable steel orthotropic bridge decks

The deck plate of steel orthotropic bridges is loaded in fatigue by traffic. Increases in both the traffic intensity and the magnitude of the wheel loads have caused premature fatigue cracking of steel bridges in the Netherlands, mostly on very busy motorways. Overlaying the steel orthotropic bridges with 50 mm of heavily reinforced concrete has proved to be a suitable way of reducing the steel stresses at critical locations in the steel deck plate of fixed bridges. This repair method adds no weight to the bridge because the asphalt is simply replaced by a concrete layer.
The self-weight of the overlay has to meet strict demands in the case of movable bridges because the wearing surface is only a few millimetres thick. Reducing the depth of the overlay might be effective provided the reinforcement is not susceptible to corrosion. Suitable types of reinforcement were researched in an earlier study in which the bending stiffness of the composite structure, the strength of the steel-concrete interface layer and the bond between the reinforcement and the concrete were investigated in static experiments. The study of the fatigue behaviour of the composite section (concrete layer + steel deck plate) will be discussed in this article.