Lsn6 - 440 mph, assume stopped in 1sec F = ma = 9000000 lbs...

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1 ME4123/6123 – Lesson 6 Case Study: WTC “Twin Towers”
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2 Time Line 8.45 AM Boeing 767 hits floors 94-99 tower 1 9.03 AM Boeing 767 hits floors 78-84 tower 2 9.50 AM Tower 2 collapses 10.29 AM tower 1 collapses
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3 Background 1362 ft 110 floors 207 ft Square base Glass, Al, Concrete, Steel The Aircraft Boeing 767 375 passengers 23,980 gallons of fuel 63,300 lbs of thrust x 2 @ 35000 ft 530 mph cruise speed Weight 450000 lbs The Towers Service core 87 x 137
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4 Some Numbers Max TOGW of 767: 412,000 pounds Kinetic energy, both planes: 9 x 10 9 Joules ~ 2 tons TNT Height of the Towers: 1365 feet Weight of the Towers: 1.25 million tons Collapse Energy: 2 x 10 12 Joules ~ 500 tons TNT Energy/gallon of JP-4: 135,000 BTU 767 fuel capacity: 24,000 gallons Approx fuel detonated at impact: 3,000 gallons Burning energy, fuel: 5 x 10 12 Joules ~ 1200 tons TNT ! Source: Scientific American, Nov 2001, p. 15
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5 Stress @ Impact
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Unformatted text preview: 440 mph, assume stopped in 1sec F = ma = 9000000 lbs Moment at base M = 6320000000 ft-lbs psi I Mc 36 = = Very Low 207 ft Square base core 87 x 137 6 WTC Structure & Collapse Weak zone Melting T steel = 1570 C Flame T of Kerosene = 1727 C 7 24.5 25 25.5 26 26.5 27 27.5 28 28.5 200 400 600 800 Temp (deg F) Elastic modulus (Msi ) Source: Metals Handbook, Vol 1 Burn temp of JP-4: 2000 deg F Steel Modulus vs. Temp 8 Failure Theory Impact energy of B767 severed ~half of vertical supports (but towers didnt fall) Burning residual fuel cooked remaining structural elements at 2000 o F for 45 to 110 minutes Pyrophoric Al from airframe melts, burns at 3270 o F Remaining steel beams: Melt? Yield? Buckle? Summarizing: What happened? How did it happen? Implications? Recommendations?...
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This note was uploaded on 09/08/2011 for the course MECHANICAL 4123 taught by Professor Horstemeyer during the Fall '10 term at Mississippi State.

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Lsn6 - 440 mph, assume stopped in 1sec F = ma = 9000000 lbs...

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