Did Bin Laden expect the towers to fall?

Would OBL have expected the two towers to fall completely as a result of the airplane strikes? Or was that simply “icing on the cake” from his perspective?

I seem to recall that, on the tapes they found in Afghanistan of him discussing the operation, he said he had not expected the towers to collapse.

He claimed in videos that he didn’t.

Bin Laden didn’t expect New York towers to fall


According to a translated transcript issued by the Pentagon, bin Laden says the attacks on the World Trade Center did more damage than expected. “…we calculated in advance the number of casualties from the enemy, who would be killed based on the position of the tower,” he says, according to the transcript. “We calculated that the floors that would be hit would be three or four floors. I was the most optimistic of them all. (…Inaudible…) due to my experience in this field, I was thinking that the fire from the gas in the plane would melt the iron structure of the building and collapse the area where the plane hit and all the floors above it only. This is all that we had hoped for.”

Pentagon Releases Bin Laden Videotape, U.S. Officials say Tape Links Him to Sept. 11 Attacks

My understanding is that it was the unusual interior structure of the steel frame that contributed to the collapse of the two towers. Was this architectural feature not well known? Would a more traditional frame have been able to withstand the heat?

That’s my impression. Had they been built like the traditional lattice structure (like the Empire State Building), the building would have resisted fires longer and maybe even survived without collapsing. But that would have seriously reduced the building’s floor space, and that would have killed the economic viability of it (and they would have never been built in the first place–not enough return on investment). As it stands, when it first opened it took years for the buildings the vacancy rate to drop to a reasonable level.

I think the NIST report on the collapse of the towers included a calculation of a 707 hitting the towers and they would remain standing, but they were crude estimates plus nobody anticipated the fireproofing on the steel beams would be blown off by the crash. Jumbo jets were just beginning their rise to eminence (747, DC-10, L10-11) during construction, so my guess is that wasn’t on the architects calculations when the design was first set down on paper.

Others can correct me, but this is what I remember from the past decade.

If you’re a 9-11 Truther and argue otherwise, please don’t–this has been done to death in other threads.

Troofer crap notwithstanding…

The designers of the Twin Towers did some back-of-the-envelope calculations about the 707 hitting their buildings at approach speed, with the idea being that, like the crash into the Empire State Building, a plane might get lost in the fog on approach to a NYC airport. They didn’t take fuel/fire into account–just the impact’s kinetic energy and the ability of the building’s columns to redistribute the load. Their conclusion, which turned out to be correct, was that the buildings could take the impact and remain standing.

Given the speed with which the 767’s hit the buildings (400-500 MPH, IIRC) and the energy imparted, the towers did a pretty remarkable job of withstanding the impacts. Survivors have reported that they felt the building lean more than it ever had in the wind–and then revert back to standing up straight. The redundant nature of the perimeter columns, the core, and the link between them (especially with the hat truss up top) allowed the buildings’ loads to be redistributed to the intact columns.

The design, tube-within-a-tube, was indeed revolutionary at the time, and really a pretty brilliant solution to the problem of opening up more floor space in the building. Move those interior columns to the perimeter, link them to the core with the floor trusses and hat truss, and presto.

In hindsight, of course, it turned out to be one of the vulnerabilities on 9/11. It was easier for the hijackers to damage more columns since a great many were right there on the outside of the building. Also, the core columns were basically steel wrapped in drywall, rather than being concrete reinforced with steel, as in other buildings. The reinforced concrete core is a more robust design, which is likely why it was used in the new WTC7 (and maybe 1…I’m actually not sure, though if I were a betting man, I’d say they did it there, too.)

At any rate, UBL is on record as saying he didn’t expect the whole thing to fall. That, sadly, is more a reflection of just how strong those connections between the floor trusses and the perimeter columns were (in addition to the impacts blowing off the styrofoam-consistency fireproofing material.) The connections were so strong that, when the floor trusses either sagged or went into compression as the fires moved on and they cooled, actually pulled the perimeter columns inward–to the point of actually breaking them–which set the global collapse in motion. Once the “block” of undamaged floors above started moving downwards, the “block” of undamaged floors below simply couldn’t stop it. Too much kinetic energy. The buildings pancaked and unzipped.