I just got done looking up the construction of the WTC. They used carbon steel In the construction, and A light weight 1,200 psi concrete flooring
The yield strength assigned to any grade of steel is the point at which it will bend and not regain its original shape. So A36 steel -- a mix of carbon and iron, like all steels -- can handle 36,000 pounds per square inch (36 kilopounds) of pressure before it begins to deform, and 52,000 psi of compression before deformation.
( Source: ASTM.org)
In the external walls of towers one and two of the World Trade Center, the steel also varied by thickness to allow for different pressure loads at different levels. In the lower levels, the thickness was most frequently around 4 inches (10 centimeters), while at higher floors, it could be as thin as 0.25 inch (0.64 centimeter).
(source:
FEMA)
In the construction of the floors themselves, a mix of A36 and ASTM A 242 steel was used. it's load strength is 46,000 psi. ASTM A 242 is what is known as a high-strength, low-alloy (HSLA) steel, which means that it was extra-strong, allowing less of it to be used which makes for a lighter building. Also this would mean the upper floors were allot lighter than the lower floors, and contained less mass than the lower floors.The WTC used high-strength, load-bearing perimeter steel columns called
Vierendeel trusses that were spaced closely together to form a strong, rigid wall structure, supporting virtually all lateral loads such as wind loads, and sharing the gravity load with the core columns. The perimeter structure containing 59 columns per side was constructed with extensive use of prefabricated modular pieces each consisting of three columns, three stories tall, connected by
spandrel plates.
(Source:Wikipedia)
I have seen figures stating that 1,500,000 tons of materials went into the building of the twin towers. So that would be 750,000 tons, or 1,500,000,000 lbs per tower. If we completely disregard the fact that 2/3 of the towers weight was in their base, and lower levels, we come up with each floor weighing 6,818 tons, or 13,636,000 Lbs. Each tower had 3,800,000 square feet of office space. That would be 34,545 Sq ft pr floor. 1 square foot = 144 square inches, so that equals 4,974,480 Sq inches pr floor. That would come to a wopping 2.74 Psi load pr floor being carried by 36,000 to 52,000 psi rated beams. At ground level with all the floors pressing upon them, the beams at the base would be carrying around 301.40 psi. That's allot of weight.
If I'm wrong, explain to me, show me, teach me, Yelling, name calling, and pointing out my spelling accomplishes nothing.