The flying buttresses in large Gothic churches counterbalance the weight that the vault and the framework bring to bear on the walls by creating an equivalent pressure.
The flying buttresses of Notre Dame are the largest ever constructed during the Middle Ages. They provide a sense of balance and harmony to the cathedral. But in the absence of the roofs, all their weight came to bear on the walls.
To cancel out this pressure, the architects decided to relieve the flying buttresses of their own weight by placing arches under them, made of heavy wooden structures: they would have to remain in position until the vaults and the great attic of the cathedral were reconstructed.
Giants calculated to the nearest millimeter
Surveyors plotted 3D charts of each of the 28 flying buttresses, all of which are different. Thanks to these measurements, the engineering offices could then design each arch individually to correspond not only to the arch it was destined for but also to the available resting points for its future position. High-precision work!
Carpenters in Lorraine used larch wood to make these gigantic structures, each of which weighed more than 8 tons. The preassembled arches were transported to the Notre Dame site in two parts.
Spectacular installations
Positioning each arch was a new challenge: assembled definitively on the ground, the arch was fixed to a crosspiece designed to raise it while keeping it balanced. In fact, it had to be raised in a perfectly straight position and fitted smoothly into place without any knocks. There is a gap of only 6 meters between each arch, leaving no room for hesitation!
Once the arch was positioned on the concrete props set on the terraces of the cathedral to keep it straight and distribute the weight it would have to bear, rope workers attached to the flying buttress positioned the lagging (long wooden wedges) between the arch and the flying buttress: the flying buttress was thus neutralized and was no longer in danger of causing the vaults to collapse.
Form July 2 2019 to February 28 2020, 28 arches were thus installed under the flying buttresses of Notre Dame de Paris.
Main visual ©Patrick Zachmann – Magnum Photos / RNDP
