Why Notre Dame Cathedral has not fallen – 18/04/2019

Those who followed the fire of Notre Dame on Monday they were afraid to see something similar to the sinking of the New York Twin Towers, September 11, 2001, also broadcast live on television.

The 96-meter needle drop which crowned the roof of Notre-Dame made fear that immediately after, the vault collapses on the central nave, the flames propagate inside and the devastation was total. Until this century, there have not been two television shows of urban disasters the most spectacular.

After the announcement by firefighters of the fire control, an initial list of damages was made public: the flames had devoured the gabled roof and the wooden structure more than one thousand square meters of surface that supported it; they also spilled the needle and indirectly caused three holes in the stone vault, the biggest at the height of the cruise. But the walls, buttresses, flying buttresses and the two towers of the characteristic façade of Notre-Dame they were still standing. This has been confirmed by official sources that the limestone structure has resisted. It is therefore possible, but unlikely, that the structural damage to the temple exceeds what we already know.

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Why are some buildings subject to terrible fires, earthquakes or terrorist attacks flowing? Why others not?

Each case presents its particularities. In the book Why buildings fall, Matthys Levy and Mario Salvadori, describe factors of security of a the structure, from his theory and his calculation to the quotation, going through the materials and its badembly, or by external agents.

In the case of twin towers Manhattan, the impact of the two Boeing 767s (who charged Weighed more than 150 tons each and flew between 700 and 800 kilometers at the hour) Did not give them the coup de grace, despite its brutality and despite the damage it caused to the perimeter pillars. The skyscrapers designed by Minoru Yamasaki fell because of post-impact fires, fueled by the 36,000 liters of fuel transported by the two aircraft, caused temperatures of nearly 1000 degrees, which weakened the metal structure of the building and caused its collapse, between one and two hours after the attack.

In the case of Notre Dame, there was no impact of extraneous elements to the cathedral, but there was a huge supply of fuel that burned so fiercely: the wooden structure ten meters high, a hundred long and thirteen wide in the nave (forty on the transept), known as the forest 1200 oak trunks that made it. This structure, located above the vaults, supported the roof of the cathedral, which was in turn lead sheets. They were trunks in many cases already members of the original structure of the thirteenth century, some from trees felled with four hundred years of life. Since Notre Dame's age is about 850 years old, we can say that some oaks in its structure were 1200 years old.

This wooden construction, like the one located inside the needle (five hundred tons of weight) Burned almost completely. The stony structure of the vault, on the other hand, resisted. Except in its transept section, in the central part of the Latin cross floor of the building. Probably because the fall of the needle through the burning forest had an impact on the vault at that time and caused its partial collapse. The photos available from inside the temple after the crash show there a big hole in the vault, in addition to two other minors. It is obvious that the fire can be completed in a little over an hour, as in Paris, with a complex and secular wooden structure. But the robustness of the Gothic construction made of large blocks of stone, walls of remarkable thickness and a vault operated by compression prevent its collapse.

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The Minister of Culture, Franck Riester, said that "the main structure of the temple (stone) was saved, but the situation is still precarious ". Perhaps because, as the engineer Javier Fernández points out, "this structure has already resisted nearly a thousand years. Not to mention that the medieval computing systems were approximate and generated by isostatic structures, in which the charges rest on one point and not on another, and where an incident such as that which has been suffered can destabilize the whole ".

Llátzer Moix – The Vanguardia.

GML