[/b]Still nothing from your about WTC7 which just caught fire and fell down, was never hit by a plane. It's obvious you want to keep the subject on the towerss where there are many more factors to blow smoke around, plane hits, jet fuel, etc. That's how deniers buffalo you.
I will gladly talk abou the WTC7, but I stick to the towers in this post.
The towers were designed to withstand multiple hits from jetliners,
Nowhere in my research did I find that it was designed to withstand multiple hits from jetliners. It was designed to withstand a hit from a 707.
the way all New York City skyscrapers were after 1945 when a B-25 bomber lost in fog hit the Empire State Building (google b-25 empire state 911research).
Agreed.
Deniers say "but those were 707 hits, not 767s! Good grief you Truthers are so dumb!) But here are the design specs of both:
The maximum takeoff weight for a Boeing 707-320B is 336,000 pounds.
The maximum takeoff weight for a Boeing 767-200ER is 395,000 pounds.
The wingspan of a Boeing 707 is 146 feet.
The wingspan of a Boeing 767 is 156 feet.
The length of a Boeing 707 is 153 feet.
The length of a Boeing 767 is 159 feet.
The Boeing 707 could carry 23,000 gallons of fuel.
The Boeing 767 could carry 23,980 gallons of fuel.
In other words, they are basically the same size with a fully loaded 707 actually heavier than a half-fueled 767 (which they were for the short flight to California for these long-haul jets.)
Funny that you are using the latest Boeing 707, the 707-320B. The 707 models before where shorter, had a smaller wingspand, and had a maxuim takeoff weight 80,000 pounds less. However, it is consevable that they where designing for the 320B since it came out in the early 60's when they where starting to design the towers.
[quote[Once again, the kinetic energy of the plane hits would have been like a gnat bite to 40,000 tons of 4-foot wide steel beams and cross-bracing in core structure, since planes are light, mostly hollow aluminum tubes with heavy landing gear and engines. If you scale down the 96,000 tons of steel in the frame to 100 lbs. (think of two of those 45-lb plates in the gym) and melt it into rebar to build a scale model of the steel frame, the weight of the plane would equal one empty aluminum beer can with an ounce of kerosene in it. The steel columns are anchored in 10 feet deep of concrete which is in turn bolted into bedrock. The structure was built to remain standing even with up to half of the core columns cut, with the load transferred to the remaining columns. [/quote]
When one recognizes that the buildings had more than 1,000 times the mass of the aircraft and had been designed to resist steady wind loads of 30 times the weight of the aircraft, this ability to withstand the initial impact is hardly surprising. Furthermore, since there was no significant wind on September 11, the outer perimeter columns were only stressed before the impact to around 1/3 of their 200 MPa design allowable.
The only individual metal component of the aircraft that is comparable in strength to the box perimeter columns of the WTC is the keel beam at the bottom of the aircraft fuselage. While the aircraft impact undoubtedly destroyed several columns in the WTC perimeter wall, the number of columns lost on the initial impact was not large and the loads were shifted to remaining columns in this highly redundant structure.
So it did withstand the impact of the planes. Not questioning that.
Why did the official NIST report lie when it said:
But the chief WTC engineer John Skilling said the exact opposite, saying:
Why did the Associated Press lie about the size of the 707? A report said:
"Many believed the towers were built to withstand the impact of a Boeing 707 - the largest aircraft at the time, but much smaller than the jets that crashed into the buildings." "WTC surveillance tapes feared missing," AP, 12/10/2002
Skilling also said "live loads on these [perimeter] columns can be increased more than 2000% before failure occurs." (Engineering News Record, 4/2/1964)
Poor reporting. It happens.
Adiabatic flame temperature of kerosene is still 980C, not 2000C like you said. All adiabatic means is with no heat loss during transfer. Using a big word doesn't change the properties. The NIST and FEMA reports concluded the fires never exceeded 600C or so. Again, if the fires had been even 1000C the people wouldn't have been seen standing in the windows so near them, they would have been shriveled. Firefighters and survivors report what you'd expect of normal office fires and kerosene: flames lick it walls and partitions but petering out. One could see part of a wing burning, which means if she could stand close enough to see it, it wasn't blast furnace temperature in there. She wouldn't have lived. The black smoke we saw is evidence of cool burning, oxygen-starved fires.
It is known that structural steel begins to soften around 425°C and loses about half of its strength at 650°C. This is why steel is stress relieved in this temperature range. But even a 50% loss of strength is still insufficient, by itself, to explain the WTC collapse. The WTC, on this low-wind day, was likely not stressed more than a third of the design allowable, which is roughly one-fifth of the yield strength of the steel. Even with its strength halved, the steel could still support two to three times the stresses imposed by a 650°C fire.
It was the distortion of the steel in the fire. The temperature of the fire was not uniform everywhere, and the temperature on the outside of the box columns was clearly lower than on the side facing the fire. The temperature along the 18 m long joists was certainly not uniform. Given the thermal expansion of steel, a 150°C temperature difference from one location to another will produce yield-level residual stresses. This produced distortions in the slender structural steel, which resulted in buckling failures. Thus, the failure of the steel was due to two factors: loss of strength due to the temperature of the fire, and loss of structural integrity due to distortion of the steel from the non-uniform temperatures in the fire.
So the steel didn't even have to melt to fail. And given how long the towers stood is credit to its designers.