Concrete overlay of movable steel orthotropic bridges: The repair method for movable steel bridges

In 1997 cracks were found in the relatively new movable part of the Van Brienenoord bridge, a repair method for steel orthotropic bridges has searched for ever since. For fixed bridges a solution was found: the steel deck plate is overlayed with a concrete layer with a thickness varying between 50mm and 120mm and on top of the repair layer a new wearing surface is created. The concrete layer is either connected by studs or by an epoxy layer. Movable bridges have a thin wearing surface. Due to weight restrictions, it is not possible to apply a relatively thick concrete layer on top of the steel deck plate. So, different solutions have been researched and the best option seems to be to overlay the steel deck plate with a thin heavily reinforced concrete layer. This method has already been analysed under static loads, but also the fatigue resistance should be guaranteed. This master thesis project aims at designing a 20mm concrete layer in order to increase the lifespan of an orthotropic steel deck of a movable bridge by replacing the wearing surface of this deck by this concrete layer. The main topic dealt with is to determine the fatigue life of the repaired structure. It is assumed that the governing position in the structure is the connection between the trough web and the steel deck plate above the crossbeam. At this position the largest hogging moment exists. Three different alternatives are defined to come up with the most effective solution, all with the same composition, dimensions and material properties except the type of reinforcement. The repair method consists of a 17mm thick high strength fibreless concrete layer, on top of an epoxy layer sprinkled in with calcinated bauxite. The different types of reinforcement are: epoxy coated and sprinkled in with sand Carbon Fibre Reinforced Polymer (CFRP), stainless steel and epoxy coated “ordinary” steel reinforcement, all with a bar diameter of 6mm. The centre to centre distance of the rebars is 12mm and the concrete cover on the rebars is 6mm thick. The stresses occurring due to the fatigue loading based on the Eurocode (load model 3) are calculated and the fatigue lifetime of each material is defined. Since uncertainties exist about the fatigue behaviour of the interaction between materials, an experimental research has been started. Test specimens were created and dynamically loaded by a hogging moment in a four point bending test. In the experimental research it became clear that the steel reinforced alternatives fail by reinforcing bar failure, whereas the CFRP alternative fails by debonding of the rebars. Besides these failure modes, concrete cracks occurred in the anchorage zone of the reinforcement. These cracks have been further researched, because they might become critical in practice. It is concluded that the concrete is only governing in case of relatively high moments.