Stresses in asphaltic wearing courses on renovated steel bridge decks

Fatigue damage is a common problem in a lot of bridges with orthotropic steel decks. Frequent maintenance is required to prevent aggravation of the problems, which gives a lot of nuisance for the traffic using the bridge. This comes especially into play at large (river) crossings where not many alternatives are available. Therefore, methods are investigated for strengthening of those bridges in such a way that the magnitude and frequency of maintenance works can be reduced. In 2012, research work which focussed on the strengthening of bridges with movable steel decks (where usually a surface treatment is applied instead of an asphaltic surfacing) was finished, which showed very promising results. FEM modelling, laboratory tests and the application on a bridge deck in use all showed significant stress reductions. This thesis investigates the applicability of the above described renovation method for fixed bridges where an asphaltic wearing course should be taken into account. This does result in extra dead load on the renovated deck. Furthermore, the occurring stresses in the surfacing should now be taken into account. To investigate this structure, a characteristic part of the bridge deck (the deck plate between two stiffener webs) is simplified to a simply supported beam. The proposed renovation method is based on the addition of an extra steel plate with a polyurethane core between the original deck and this additional plate. A thicker core means more mass, but it also increases the bending stiffness of the whole structure. The extra mass from the reinforcement has to be compensated so that the dead load on the main girders and foundation is not increased. This demands special properties of the surface layer. For the wearing course, Brugflex is selected. This asphalt mix developed by Heijmans is stiff in vertical direction, but flexible in horizontal direction so that a good resistance against both rutting and fatigue cracking is obtained. For the membrane between the steel and asphalt, Parafor Ponts is selected. This bituminous membrane from the Icopal Group provides a good cohesion between the wearing course and the deck plate and has excellent waterproofing properties. It was chosen to use a finite element analysis approach to investigate the behaviour of the renovated structure, when subjected to a moving load. First, a lot of tests had to be executed to identify the membrane shear and tension properties at different temperatures and deformation rates. Finally those test results were combined to predict the properties for any arbitrary temperature and deformation rate. For the other materials, those characteristic properties were already defined. Finally, the renovated structure was modelled as a simple supported beam. Besides a reference model, similar to the surfacing on the Van Brienenoordbrug, five different geometries with varying asphalt thicknesses were constructed. It was tried to give all those renovated geometries a similar mass as the reference model, which was achieved by varying the core thickness between the two steel plates. The finite element analysis showed some promising results. With respect to the reference model, the bending stresses in the steel and asphalt were significantly reduced. Especially the decreased tension stress in the asphalt is important regarding fatigue cracks. Also the shear stresses in the membrane were considerably lower than in the reference model. Overall, the proposed renovation method showed encouraging results, which recommend further research. In the future, this renovation method might probably be a good option when an existing orthotropic bridge deck suffering fatigue has to be strengthened.

Subject

Asphalt
Steel
Bridge
Deck
Abaqus
FEM
Prony

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master thesis

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