Keywords: computer aided design, transition curve, model, railway, AutoCAD®, GavranCivilModeller®.

The European Union has enacted various legislative measures aimed at achieving the opening up, integration and harmonization of national railways to form a European railway network. Harmonization of the national railway legislation with the aquis communitare on safety and interoperability is of a special importance for integration of the railway systems [1].

A modern approach in railway design implies the selection of the geometric form of transition curve and cant transition as a unique spatial element. Selection of the spatial form of cant transition is required by the type of superstructure or maintenance conditions of the track geometry during operation.

The use of transition curves with nonlinear changes of curvature is recommended for high speed rails laid on slab tracks, as a result of lower dynamic influences that these alignments cause. Also, in the case of slab tracks, engineers should consider the use of specific vertical alignment: one which includes the rising of the outer rail and the lowering of the inner rail. This type of vertical alignment also contributes to reducing of dynamic influences.

This paper describes the way to develop a three-dimensional model of a railway with transition curves with nonlinear changes of curvature, so that engineers can apply complex spatial geometry with ease.

The problem of three-dimensional model development in software based on computer aided design is solved regarding the construction works on sites. Hence, if the three-dimensional model is a curved surface, it will be made of linear segments. The length of these segments depends on the precision that is necessary to fulfil.

This paper provides information about the deviation that occurs in the three-dimensional model geometry regarding the designed geometry. Deviation in the horizontal plane occurs on the centre line along the transition curve. This is the first criterion for selection of the length of a linear segment. Deviation in a vertical plane occurs in nonlinear geometry of the cant transition. Since this geometry implies a small change of cant regarding the length of the transition curve, the amount of deviation will be les than adopted for a wide range of radii.

Deviation in the three-dimensional model occurs along the transition and circular curve on both, the outer and the inner model edge. In some cases, deviation of the inner edge can be significantly higher than the deviation of the centre line. Hence, this deviation is the only criterion for selection of the length of the linear segment for the three-dimensional model calculation. The length of 5m satisfies a large variety of radii and track widths.

1

Z. Popovic, "Interoperability and standardization of railway infrastructure - integration of Serbian railways", Railway Technical Review, 47, 6-9, Hamburg, Germany, 2007.

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