There are even photographs of it somewhere. While it's true the building was damaged, does that cause a symmetrical collapse? It seems highly unlikely.
I have a lifelong friend that is an architect. We spoke on the phone about this for about 45 minutes. (yes I realize that is not long) but he made some interesting points. He says that he would consider at least 4 factors.
1) Seismic impact from two 110 story buildings collapsing within 600 feet of it. He says that there is a difference in designing a building to withstand seismic tremors located miles underground and one happening at your doorstep. The distribution of such a force is different.
2) Debris. His estimates were 20-25% depth to 60% of the facing facade was ripped out. He says it is impossible to calculate what kind of damage that can have on a structure. But added that it wasn't good and that the remaining structural elements would have to absorb the shifting weight of the building, the impact, vibration, and structural weakening. Things like cracked concrete and beams that were pulled, bent, and ripped out of the structure. He says that calculating the impact that wrenching effect had on the remaining structural elements is nearly impossible.
3) Most buildings get their strength from the core of the building where things like the elevator shafts and stair wells are also located. The likelyhood of this core being damaged along even a 40% portion (a rough estimate given his earlier estimate of 60% of the facing facade being damaged) of the facing side is pretty high. Couple this with the fact that the main weight of the building was concentrated in 3 large trusses located in the bottom 20% of the building. Apparently, he says that there was 2 trusses running parallel to the facing facade and one running perpendicular.
4) Catastrophic failure of the truss as a cascading effect. He says it is likely that the closest portion of the perpendicular truss was weakened in the aftermath of the debris impacts, seismic force, ripping and pulling forces, vibrations, and rapid weight redistribution. When this truss failed, he says that the first thing to go would be the core portion of the building on that side. This is why you see a drop in the Penthouse first. Then the core of the building would systematically fail and redistribute weight and force to the other two trusses. He says this would most likely be a very rapid progression.
He also think that the fires were most likely inconsequential and just hindered an accurate assessment of the condition of the building more than actually contributing to its demise. However, he did say that firemen were watching the building and were commenting on how it was leaning towards the gouged section of the building.
I asked about the 8 floor free fall and he says that in reality it probably wasn't an actual free fall. More likely it was a further progression of the collapse pushing from one end of the building (where the perpendicular truss was located) to the other (where the parallel trusses were located) he says that the image might look like a free fall but in reality was a continuous wave like collapse. Combine that with the probable lateral movement (lateral to the gouged facade) and it would probably give the visual effect of a smooth free fall.
As I have already stated before any ire/insults are flung his/my way. It was about a 45 minute conversation. He looked into this several years ago with a couple other architect and engineers and this was their rough finding. Anyway, I thought that it might be pertinent to the conversation so after some deliberation here it is.
