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On January 19, 2017, the 17-storey steel-framed Plasco in Tehran collapsed after a large fire broke out, seemingly putting to rest the question of whether a steel-framed building could collapse entirely due to fire.

But the well-known group 'Architects and Engineers for 9/11 Truth' believes it has found evidence that this was a controlled demolition.

Do they have a case?

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    The claim that the building in Tehran was destroyed in a controlled demolition is only notable because it is used by AE911 Truth, "an American non-profit organization promoting the conspiracy theory that the World Trade Center was destroyed in a controlled demolition" (Wikipedia), to promote their cause. Instead of removing these connections to 9/11 from the question they should be brought out more clearly.
    – Schmuddi
    Oct 1, 2021 at 13:06
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    We require questions on this site to be about widely-believed ("notable") claims. Some users confuse that with claims coming from sources that they consider reliable. The source of this question's claim might not be considered reliable, but they are widely read. I have deleted comments that insist on reliable sources for this question. (Answers, of course, should use reliable sources.)
    – Oddthinking
    Oct 2, 2021 at 2:41

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The "truthers" own report claims that collapse due to fire was "improbable" because according to their estimation it would have required simultaneous heating of all support columns.

However, according to experts' report(s) (i.e. Preliminary modelling of Plasco Tower collapse) (2018) what happened was that the reinforced concrete floors buckled under the heat and internally fell one on top of the other. And this caused the columns to then collapse inwards. As far as I can tell the "truthers" report didn't take this possibility into account, while other works evaluated it fairly thoroughly through simulations etc.

There's also more recent (2020) paper (by different authors) but having the same general conclusion of how the collapse proceeded (i.e. floors first). This analysis also found that connection failure between beams (supporting the floors) and the columns could have occurred due to the heat (of the fire):

An important observation in debris was the out-of-plane bending of the beam-to-column gusset plates. Based on the results of numerical analysis, this phenomenon has occurred because the filler plate of the top and bottom chords in the main trusses was present only on one side of the gusset plate. This arrangement creates an initial imperfection and consequently an eccentricity in axial force of chords, which develops an additional out-of-plane bending in gusset plate under gravity loads. As the deflection of the beam gets larger at elevated temperatures, this out-of-plane moment becomes more significant, which may eventually lead to connection failure. As indicated in Figure 19, initially, von Mises stress of diagonal bars and welds of the end angles reach to maximum tensile stress, and then von Mises stress of other members exceeds the yield stress of steel material. Debris observation in Figure 19 also shows this failure well.

More generally, somewhat subtle design flaws in joints (that e.g. only become an issue when seriously heated) were probalby fairly hard to analyze in the 1960s when that building was designed. There are e.g. some examples of US truss bridges (built in the same decade) collapsing due to connection design flaws (and no heating was required, but there was extra load and some rusting involved).

Nowadays truss systems (for use in buildings rather than bridges) are more serious scrutinized how they behave under fire conditions, at least in the US. (Wood-to-metal truss systems in particular can collapse in mere minutes due to differential heating of the materials and charring around the gusset plates.) Even for full steel truss systems, US standards of the 1980s only required they withstand the fire for 2-3 hours, which suggests that it's probably difficult to economically engineer them for more. It was also noted at the time that practical fire tests were difficult due to the need of large furnaces (presumably computer simulations were still rather impractical/expensive) so only joint sub-assemblies were tested in this concrete way. Issues like the effects of whole beam elongation would probably not have been accounted for except by calculation (p. 8).

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    I might be misremembering things, but wasn't the "floors lost structural integrity, fell on each other and caused a domino effect that took down the entire building" roughly the reason why the WTC collapsed?
    – Nzall
    Oct 2, 2021 at 21:34
  • @Nzall kind of. In the Twin Towers, the columns failed, and the top floors fell through the flimsy beams below. In WTC7, 14th floor downward pancaked, leaving columns unbraced.....
    – Abdullah
    Oct 4, 2021 at 6:27
  • It would be nice if you could address their claims of reports of "explosive material" and molten metal.
    – Abdullah
    Oct 4, 2021 at 6:51
  • @Nzall yup, and was also completely ignored by the 9/11 "truthers" for the obvious reason that it'd utterly invalidate their "arguments".
    – jwenting
    Oct 4, 2021 at 8:00

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