Protective roof for the tram

What does not sound spectacular at first glance turned out to be a real challenge for a structural engineer: For a civil engineering project, the undisturbed operation of traffic has to be maintained at Rathenauplatz in Dresden. The reason for the unusual task is that, due to limited space, the components have to be lifted over the busy tramway track, as they cannot be transported directly from their storage area to the intended installation site on the construction site. It is therefore necessary to secure the tracks with a protective roof structure.

An engineering firm was commissioned to prepare the structural analysis for such a steel structure. In the initial calculations, however, it became clear that the classical static equivalent load assumptions for taking into account an impact caused by falling loads led to stresses that were clearly too high. Therefore, realistic equivalent loads had to be determined. The static equivalent load is generally derived from the elastic response of the stressed area of the structure. By energetic comparison, loads proportional to the deformability of the structure are obtained for a known drop height and with the appropriate dimensions.

Another task was to develop and realize a suitable structure that could damp the forces generated by falling components by providing the longest possible deceleration path. The starting point was a multi-layer trapezoidal sheet metal structure that can absorb the input energy by plastic deformation. In a first step, numerical calculations of the exemplary supporting structure were carried out, from which the experimental drop tests could be derived. After the successfully performed tests, further calculations were carried out to estimate the real load-bearing behavior of such a protective structure and to transfer the obtained knowledge to the real structure.

The result of the investigations is that the numerical representation of the test showed a very good agreement with the performed experiments and could be well validated with the help of these. The subsequent purely numerical dimensioning resulted in a structure that absorbs a mass of approx. 1000 kg impacting the structure from a drop height of 4 m to such an extent that there is no danger to the streetcar traffic moving underneath.