The fact that the WTC can stand in a hurricane is why the plane does not push it over, a simple calculation of what the plane has vs the 200 mph hurricane. Thus the design resists being pushed down. Kind of free that a big plane impact can't push it over. The lateral strength of the WTC is what keeps high speed aircraft impacts from pushing it over; but it can't stop the plane from entering if over the design impact speed; you don't want the plane inside the WTC killing occupants like ESB tiny impact from a small plane.
Robertson designed the shell to stop a plane going 180 mph.
The design solution to meet the vision of the architect was to move the columns to the outside, which had to be strong enough to hold up the WTC, half of it, and strong enough to be the lateral support. The steel was also "stronger", various grades to meet the lateral support design.
If you take the WTC ability to stand in a hurricane with massive lateral forces, you could calculate what it takes to push the WTC over, and a plane going 600 mph will not push the WTC over; instead the plane will enter the WTC until the KE is done. The WTC towers could survive the big hole in the side because the shell redistributes the load. The floor at still hanging on the remaining core and shell.
How did Robertson design the building to stop a plane? He knows the strength of the steel and his design. Why can't he design to stop a plane; it is called math and physics; not big talk, not googled up BS, and not just plain BS.
Robertson calculated it - you could do it today if you take the time.
Why did Robertson pick 180 mph? Only an idiot pilot would hit the WTC, one who is low on fuel and has no option when lost in the fog but to try land in the NYC area. If the pilot had fuel he would fly out of the fog, stop being lost and go to a suitable airfield. The speed limit below 10,000 feet is 250 knots; in the other post some engineers calculated the WTC would stop a 767 at 250 knots, a speed higher than Robertson.
An aircraft at 1000 feet should be configured to land, at or below 200 knots. What would you design for in an aircraft impact.
The ESB would not stop a tiny bomber, the WTC would. Different designs. The ESB stops the planes inside, the WTC stops the planes outside up to 250 knots. Too bad the terrorists pilots broke the "law", speeding below 10,000 feet like military pilots do sometimes.
Make the steel thicker, more than 20mm.
ftp://ftp.ecn.purdue.edu/ayhan/Korucu/Karim and Fatt_(ASCE)0733-9399(2005)131_10(1066).pdf
Check their work...
Robertson had to design for the lateral strength to survive a hurricane; it is not the same as stopping a plane at the shell. Robertson was interested in avoiding people being killed from an impact, like the ESB.
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