@ moorea34

Comment se fait-il que l’explication concernant l’effondrement du WTC7 sur votre site qui repose sur la perte de résistance de l’acier sous l’effet de la chaleur ne correspond pas à celle du NIST, pour qui il s’agit essentiellement d’un effet de dilatation thermique (NIST NCSTAR 1A
page 21 & NIST NCSTAR 1-9 page 526) ?

NIST NCSTAR 1A
page 21
The initiating local failure that began the probable WTC 7 collapse sequence was the buckling of
Column 79. This buckling arose from a process that occurred at temperatures at or below approximately
400 °C (750 °F), which are well below the temperatures considered in current practice for determining
fire resistance ratings associated with significant loss of steel strength. When steel (or any other metal) is
heated, it expands. If thermal expansion in steel beams is resisted by columns or other steel members,
forces develop in the structural members that can result in buckling of beams or failures of connections.

Fire-induced thermal expansion of the floor system surrounding Column 79 led to the collapse of
Floor 13, which triggered a cascade of floor failures. In this case, the floor beams on the east side of the
building expanded enough that they pushed the girder spanning between Columns 79 and 44 to the west
on the 13th floor. (See Figure 1–5 for column numbering and the locations of girders and beams.) This
movement was enough for the girder to walk off of its support at Column 79

NIST NCSTAR 1-9
page 526
Walk off occurred when beams that framed into the girders from one side thermally expanded and the
resulting compressive forces in the beams pushed laterally on the girder from one side, sheared the bolts
at the seated connection, and then continued to push the girder laterally until it walked off the bearing
seat. A girder was considered to have lost vertical support when its web was no longer supported by the
bearing seat. The bearing seat at Column 79 was 11 in. wide. Thus, when the girder end at Column 79
had been pushed laterally at least 5.5 in., it was no longer supported by the bearing seat.