Contents page 1 — “We can talk of luck that the overall structure is still” page 2 — “I guess, the reconstruction will be relatively quickly.” On a page

On Monday evening read broke out in the Cathedral of Notre-Dame in Paris a fire. The fire brought the middle of the Church tower to collapse and destroyed parts of the roof. “We will build this Cathedral together again,” said the President of France, Emmanuel Macron on the same evening. Wolfram Jäger, Professor for structural design at the Technical University of Dresden and as a structural engineer on the reconstruction of the Frauenkirche in Dresden involved, explains how this could go.

TIME ONLINE: Notre-Dame, in flames, clouds of smoke over Paris – the images were devastating. How bad is the damage really?

Wolfram Jäger: The entire wood roof structure is cross burned down, as well as the pointed tower over the crossing, so the area of the main and transept of the Cathedral. He crashed into the main ship and damaged the stone vault. In the process, burning the parts made it to the Church ship, the damage seems to be there but in limits. But for all the tragedy you have to hold on to: We can talk of luck that the overall structure of the building. The perimeter walls are stable and the buttresses that absorb the loads of the walls, the vaults and the roof, are probably largely intact. Just like the majority of the vault and most of the cross-ribs. The parts of the ceiling construction, therefore, the distribute the weight on the cob. You can say it this way: In the ceiling, a large hole is created. But the forces, the loads on the roof, walls and pillars, not in the Moment against each other so that the other vaults in the main vessel to collapse.

As the fire in Notre-Dame developed

“We can talk of luck that the overall structure is still”

© Zeit ONLINE

Zeit ONLINE: Still, some fear that the walls can withstand.

hunter: professionals on-the-spot will now have to assess where the dangers are. Then, one takes the supports, so that no further parts of the vault collapse. So the people who are involved in the structure, are not endangered, this has to be done from a safe Position. From the top of a scaffolding bridge, for example.

TIME ONLINE: And then the reconstruction begins?

hunter: It provides only an Overview of what damage there is and what needs to be added. Then one consults the historical documentation, makes drawings, and begins to renovate the damaged parts and to add the missing parts.

Wolfram Jäger is a civil engineer and Professor of structural design at the faculty of architecture of the Technical University of Dresden. Together with Fritz Wenzel, he led the structural design for the reconstruction of the Frauenkirche in Dresden. © Photo Atelier meißen, Radebeul

TIME ONLINE: The Cathedral was built from 1163 to 1345. To when back to the historical sources on the building?

hunter: the First sources from the period between 1225 and 1250, the tower floors were built, and the periods thereafter, in which more was built. The documentation can be supplemented with measurements and 3D Scans, which represent the whole building. To get centimeter-accurate figure of the cavity and the exact Geometry of the areas that build up again and need to connect, from scans to get to the Cathedral with a laser scanner from different positions. Then you get a centimeter-accurate illustration of the edges, which will close the vault again. So similar is the reconstruction of the Frauenkirche in Dresden. It burned down after the bomb attack on Dresden in the first place and then crashed, two days later, on 15. February 1945.

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