julien99 a écrit :Je veux savoir où c'est indiqué et de quelle manière c'est démontré. C'est pourtant pas compliqué ce que je vous demande.
Les simulations vous montre les poutres de support en train de courber et de plier sous le poids et les planchers se désintégrer.
Mais si vous voulez des citations précises, je vais vous aider:
http://www.nist.gov/customcf/get_pdf.cfm?pub_id=861610
the entire building above the buckled-column region moved downward as a single unit, resulting in the global collapse of WTC 7
Donc la section en mouvement, celle qui tombe, agissait pratiquement en une seule unité.
The slope of the velocity curve is approximately constant between about 1.75 s and 4.0 s, and a good straight line fit to the points in this range (open-circles in Figure 3-15) allowed estimation of a constant downward acceleration during this time interval. This acceleration was 32.2 ft/s2 (9.81 m/s2), equivalent to the acceleration of gravity g.
Donc pendant que la section tombait, elle tombait en un seul bloc, à la vitesse de l'accélération gravitationelle (chute libre).
For discussion purposes, three stages were defined, as denoted in Figure 3-15:
In Stage 1, the descent was slow and the acceleration was less than that of gravity. This stage corresponds to the initial buckling of the exterior co
lumns in the lower stories of the north face. By 1.75 s, the north face had descended approximately 2.2 m (7 ft).
In Stage 2, the north face descended at gravitational acceleration, as the buckled columns provided negligible support to the upper portion of the north face. This free fall drop continued for approximately 8 stories or 32.0 m (105 ft), the distance traveled between times t= 1.75 s and t= 4.0 s.
In Stage 3, the acceleration decreased somewhat as the upper portion of the north face encountered increased resistance from the collapsed structure and the debris pile below. Between 4.0 s and 5.4 s, the north face corner fell an additional 39.6 m (130 ft).
As noted above, the collapse time was approximately 40 percent longer than that of free fall for the first 18 stories of descent. The detailed analysis shows that this increase in time is due primarily to Stage 1. The three stages of collapse progression described above are consistent with the results of the global collapse analyses discussed in Chapter 12 of NIST NCSTAR 1-9
Donc pour résumer, pendant l'initiation de la chute (étape 1) le building a commencé à tomber lentement, puisque quand les structures de support ont commencé à courber, elles offraient encore quelque peu de résistance (on parle de milisecondes). Ensuite, pendant l'étape 2, ses structures n'offraient pratiquement plus de support, puisqu'elles se désintégraient et la charge de support était déplacée, donc aucune résistance à la chute de la masse. Ensuite, pendant l'étape 3, les débris et les restes du building qui s'amassaient ont fait ralentir la chute du building.
C'est pendant l'étape 2 qu'on peut dire que le building est tombé presqu'en chute libre.
"To say that you won't respect the results of the election is a direct threat to our Democracy. The peaceful transfer of power is one of the things that makes America, America!…Look, some people are just sore losers.”" Hillary Clinton
qui me re-re-re-resort la "chute libre", je le mords.
A
