@FF Tja liebe FF, stell dir vor, das weiß ich alles...leider bist du es, die wenig Ahnung von der eigentlichen NIST Untersuchung hat - sonst würdest du sowas nicht behaupten - gerne kann ich es dir bei Bedarf erklären. Aber dir steht natürlich frei -so als ehemalige Metallbauerin
;) gern eine Einschätzung dazu abzugeben:
Um den Bogen zu bekommen:
So und das Ganze sollte man jetzt mal in Zusammenhang setzen mit der von NIST angenommenen Erhitzung des Stahls von ungefähr 10 - 15min mit bis zu 1100 F an der Einschlagstelle durch Kerosin und später dann die Bürobrände, die laut NIST, den Stahl nur um die rund 250 Grad erhitzten, was nach Aussage von Nist nicht reichte um den Stahl zu schwächen:
NIST NCSTAR 1 Seite 90
There was no evidence to indicate that the joining method, weld materials, or welding procedures were inadequate. Fractures of the columns in areas away from a welded joint were the result of stretching and thinning. Perimeter columns hit by the plane tended to
fracture along heat-affected zones adjacent to welds.
The failure mode of spandrel connections varied. At or above the impact zone, bolt hole tear-out was more common. Below the impact zone, it was more common for the spandrels to be ripped from the panels. There was no evidence that fire exposure changed these failure
modes
Observations of paint cracking due to thermal expansion. Of the more than 170 areas examined on 16 perimeter column panels, only three columns had evidence that the steel reached temperatures above 250 °C: east face, floor 98, inner web; east face, floor 92, inner web; and north face, floor 98, floor truss connector. Only two core column specimens had sufficient paint remaining to make such an analysis, and their temperatures did not reach 250 °C. NIST did not generalize these results, since the examined columns represented only 3 percent of the perimeter columns and 1 percent of the core columns from the fire floors.
Observations of the microstructure of the steel. High temperature excursions, such as due to a fire, can alter the basic structure of the steel and its mechanical properties. Using metallographic analysis, NIST determined that
there was no evidence that any of the samples had reached temperatures above 600 ºC.
NIST NCSTAR 1-3c Seite 235
"The majority of areas examined using the paint cracking technique had “negative” results,
indicating that temperatures of the elements did not exceed 250 °C, even though photographic
evidence indicated that several locations experienced severe fire exposure, up to 15 min of direct flaming, prior to collapse. "
...
"From the limited number of recovered structural steel elements, no conclusive evidence was
found to indicate that pre-collapse fires were severe enough to have a significant effect on the
microstructure that would have resulted in weakening of the steel structure."
NIST schiebt alles auf das Versagen von Schraubverbindungen, die gerissen sind - wenn der Stahl aber nicht, heiss genug gewesen ist um seine Festigkeit zu verlieren - wie konnte dennoch alles nachgeben?
Da hier "Experten" am Werk sind - können die sicher eine Einschätzung geben
dh_awake schrieb:Welchen Sinn sollte es machen, all die anderen Metalle zum Vergleich heranzuziehen?
kannnichsein schrieb:Stahl ist ein Metall
