In the twentieth century in Belgium, continuous railway bridges were strongly discouraged because of this track-bridge interaction phenomenon. The publication of the codes EN 1991-2 and UIC 774-3 offered design criteria regarding the track-bridge interaction, so continuous bridges could be calculated according these codes and result in a, hopefully, more slender design. The influence of these design criteria on the substructure of railway infrastructure is investigated based on two case studies.

A first case study concerns a new viaduct with a succession of simply supported decks next to a track in service. Retaining structures were avoided, and piers or foundations consisting of a single bored pile were chosen as the substructure during the preliminary design. During detailed design, the design criteria as given in the different codes were checked. The structure satisfied all criteria but one, the relative longitudinal displacement between the end of a deck and the adjacent abutment or the relative longitudinal displacement between two consecutive decks. The problem was in the stiffness of the consecutive abutment and piers. One side of the viaduct posed no problem, given the gradual reduction of the stiffness. In order to satisfy the requirement at the other side, steel beams functioning as springs were integrated in the design, increasing the stiffness of the first two piers after the abutment.

A second case study concerns the preliminary design of a new railway viaduct, with a succession of continuous decks (four spans of 20m). A slender design was demanded by the representatives of the Flemish Government Architect and the city of Mechelen, translated in minimal, round piers as a substructure. A comparison was made for different pier-deck connections, given a minimal diameter (1.2m) for the piers satisfying the strength criteria. Subsequently, the minimal diameters were checked regarding the design criteria for the use of continuous track. Negative results were achieved for the displacement criterion, and the diameter had to be increased to 1.6m. The slender design demand could not be achieved, and the option of a viaduct was excluded.

To conclude, the design criteria for the track-bridge interaction should be taken into account during preliminary design, and are an obstacle for a slender design of railway infrastructure substructures. One may pose questions as to whether the design criteria are not too strict.

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