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The possibility of omitting rail expansion devices from the track configuration, when continuously welded rail is continued over temporary bridge decks, is investigated in detail. More specifically, the related rail track to temporary bridge interaction phenomena are analysed using finite element modelling. A first parametric analysis assesses the additional rail stresses due to moving trainloads and temperature variations, based on stipulations provided in the unit identification code 774-3R. In addition the model is expanded to a more complex structure that is able to simulate the buckling behaviour of the rail track using non-linear methods. Using this model, a second parametric study is performed in which only thermal loading is considered. This allows for determining the parameters, which are predominant in determining the critical buckling temperature of the rails, and for assessing the magnitude of the safety margin necessary, when it comes to thermal buckling of the rails and the temporary bridges. It can be concluded that, depending on the magnitude of two main factors, the lateral ballast resistance and the amplitude of the initial track misalignment, a considerable reduction of the track stability might arise. Therefore, a minimal characteristic lateral ballast resistance of 4 kN is recommended along with a maximal allowable misalignment amplitude of 7 mm has to be prescribed when thermal track buckling has to be considered in the design.

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<p>Determining for the structural behaviour of steel tied arch bridges is the introduction of a large compressive force in the arch section. As a consequence, slender steel arches are highly sensitive to not only in-plane but especially out-of-plane buckling. At present, no specific buckling curves for out-of-plane buckling exist for non-linear or curved elements in international codes and calculation methods. Hence, the buckling curves for straight columns, as determined by ECCS, are used, which can leads to some inaccuracy in the assessment of the critical buckling load for arch bridges, resulting in heavier cross sections.</p><p>This manuscript presents two practical calculation methods to design for the buckling behaviour of slender steel tied arch bridges. The first one follows the empirical calculation method as proposed in the Eurocodes. However, an alternative definition of the buckling factor is necessary. This allows for a better representation of the out-of-plane stiffness of the arch cross section and of the influence of the wind bracings between both arches.</p><p>In addition, a second calculation method is proposed, based on the use of simplified finite element models to determine the relative slenderness of the bridge structure. Both methods are validated using results from much more detailed three dimensional finite element models of several tied arch bridges. These models include variations of the bridge length, dimensions of the arch cross-section, boundary condition, load type, etc.</p><p>Comparing the results of both methods with realistic simulation, it becomes quite clear that a higher buckling curve can be used than proposed by the Eurocode, thus resulting in a more economic and aesthetic bridge design.</p>

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