please log in to view this image Eddie If you haven't already seen this one, I suggest you give it a try.
The towers were designed and built in the mid-1960s through the early 1970s. They represented a new approach to skyscrapers in that they were to be very lightweight and involved modular construction methods in order to accelerate the schedule and to reduce the costs. To a structural engineer, a skyscraper is modeled as a large cantilever vertical column. Each tower was 64m square, standing 411m above street level and 21m below. This produces a height-to-width ratio of 6.8. The total weight of the structure was roughly 500,000 t, but wind load, rather than the gravity load, dominated the design. The building is a huge sail that must resist a 225 km/h hurricane. It was designed to resist a wind load of 2 kPa, a total of lateral load of 5,000 t. In order to make each tower capable of withstanding this wind load, the architects selected a lightweight perimeter tube design consisting of 244 exterior columns of 36cm square steel box section on 100cm centers. This permitted windows more than one-half meter wide. Inside this outer tube there was a 27m à 40m core, which was designed to support the weight of the tower. It also housed the elevators, the stairwells, and the mechanical risers and utilities. Web joists 80cm tall connected the core to the perimeter at each story. Concrete slabs were poured over these joists to form the floors. Prior to the World Trade Center with its lightweight perimeter tube design, most tall buildings contained huge columns on 5m centers and contained massive amounts of masonry carrying some of the structural load. The WTC was primarily a lightweight steel structure; however, its 244 perimeter columns made it one of the most redundant and one of the most resilient skyscrapers. The early news reports noted how well the towers withstood the initial impact of the aircraft, however, 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. The fire is the most misunderstood part of the WTC collapse. It is argued that the jet fuel burns very hot, especially with so much fuel present which is not true. Part of the problem is that people often confuse temperature and heat. While they are related, they are not the same. Thermodynamically, the heat contained in a material is related to the temperature through the heat capacity and the density. Temperature is defined as an intensive property, meaning that it does not vary with the quantity of material, while the heat is an extensive property, which does vary with the amount of material. One way to distinguish the two is to note that if a second log is added to the fireplace, the temperature does not double; it stays roughly the same, but the size of the fire or the length of time the fire burns, or a combination of the two, doubles. The temperature of the fire at the WTC was not unusual, and it was most definitely not capable of melting steel. It is known that structural steel begins to soften around 425°C and loses about half of its strength at 650°C. But even a 50% loss of strength is still insufficient, by itself, to explain the WTC collapse. It is noted above that the wind load controlled the design allowables. 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. more to follow
But terrorists blasted the twin towers with their powerful Muslamic rayguns and softened the metal before the planes hit them. [video=youtube;AIPD8qHhtVU]http://www.youtube.com/watch?v=AIPD8qHhtVU[/video]
Al Qaeda, using powerful black magic, invoked the power of Mohammad (pbuh) to smite the towers. And lo, they were smoten.
I know. The Eiffel Tower is ****ing massive, but still a good 50m shorter. The tallest one I ever went up was the CN Tower in Toronto, 550m. Ridiculous really.
i spat off the top of the twin towers when I was up there in 99, if i had known how weak the structure was I might not have took the chance, the wind could have blown the spit against the buildings and we would all have been blown up floor by floor in a controlled manner one hour later
it's 550m to the top. the part you were on is only 445m. I say only, its still ****ing enormous. that one in dubai is 830m to the top, top floor 620m I went on the thrill rides on the stratosphere in vegas. It's a good 350m tall. It's scary as **** please log in to view this image please log in to view this image please log in to view this image
if they were so weak why didnt they topple when a commercial jet slammed into the side of it at 500mph?
