Abstract

In this work the results of investigations into how to optimise a network arch for the special demands of railway traffic are presented. Network arch bridges have inclined hangers that cross each other at least twice. The beneficial structural behaviour leads to slender bridge members mainly subjected to axial forces. Structural parts above the bridge deck are therefore more likely to be tolerated. Furthermore, the high stiffness and therefore small deflections favour the application of network arches for railway bridges. Stress ranges caused by the load character of railway bridges require special considerations for the design. Adequate solutions are elaborated considering as an example a double track railway bridge spanning 100 meters. The arrangement of the hangers has considerable influence on the structural behaviour. It decides on the forces and force variations within the network arch depending on many parameters, as for example span, rise, number of hangers, loading or arch curvature. A new introduced type of hanger arrangement is involved in an optimisation process with regard to the mentioned parameters. This improved hanger arrangement provides a simple method of designing network arches with small hanger forces and small bending moments in the chords. The hanger connection details call for special attention to fatigue strains. The fatigue design check is decisive for the hanger cross section. Various designs of hanger connection details for circular hangers are tested by numeric analysis. A hanger connection detail is derived from the results satisfying the special demands of slender arches as they are found in network arches. The structural behaviour of a network arch favours a lower chord consisting of a concrete slab. Its vertical deflections are limited to ensure passenger comfort and track stability. Alternatives with and without transverse prestressing are compared considering the deformation behaviour and economic differences. Several other construction details such as arch root point, bearings or drainage are elaborated on and the solutions are presented. An erection method using a temporary lower chord is assessed and described in detail. The investigations confirm the suitability of network arches for railway bridges. Economic advantages due to significant savings of steel compared to other arch bridges contribute to the overall convincing performance.